GOLDEN STAR RESOURCES
NI 43-101 Technical Report on the Wassa Gold Mine
Mineral Resource & Mineral Reserve Update and
Preliminary Economic Assessment of the Southern Extension Zone
Western Region, Ghana
QUALIFIED PERSONS
Matthew Varvari, FAusIMM
- Mitchel Wasel, MAusIMM CP(Geo)
Philipa Varris, MAusIMM CP(Env)
Report Date:
1 March 2021
Effective Date: 31 December 2020NI 43-101 Technical Report (March 2021) Wassa Gold Mine
CONTENTS
1 EXECUTIVE SUMMARY_______________________________________________________________ 16
1.1 Terms of Reference ________________________________________________________________ 16
1.2 Location and Setting _______________________________________________________________ 16
1.3 Mineral Tenure, Permits, Royalties and Agreements ______________________________________ 16
1.4 History __________________________________________________________________________ 17
1.5 Geology and Mineralization _________________________________________________________ 17
1.6 Drilling and Sampling_______________________________________________________________ 18
1.7 Data Verification __________________________________________________________________ 18
1.8 Metallurgical Test Work ____________________________________________________________ 19
1.9 Mineral Resource Estimate __________________________________________________________ 19
1.10 Mineral Reserve Estimate __________________________________________________________ 21
1.11 Mining Methods _________________________________________________________________ 21
1.12 Recovery Methods________________________________________________________________ 24
1.13 Infrastructure ___________________________________________________________________ 26
1.14 Environmental Studies, Permitting and Social or Community Impact ________________________ 27
1.15 Capital and Operating Costs ________________________________________________________ 28
1.16 Economic Analysis ________________________________________________________________ 29
1.17 Preliminary Economic Assessment of the Southern Extension Zone _________________________ 30
1.18 Conclusions and Interpretations _____________________________________________________ 32
1.19 Recommendations________________________________________________________________ 36
2 INTRODUCTION ____________________________________________________________________ 38
2.1 Terms of Reference ________________________________________________________________ 38
2.2 Wassa Gold Mine__________________________________________________________________ 38
2.3 Principal Sources of Information______________________________________________________ 39
2.4 Qualified Persons__________________________________________________________________ 39
2.5 Effective Dates____________________________________________________________________ 39
2.6 Previous Technical Report___________________________________________________________ 40
3 RELIANCE ON OTHER EXPERTS ________________________________________________________ 41
4 PROPERTY DESCRIPTION AND LOCATION________________________________________________ 42
4.1 Location of Mineral Concessions______________________________________________________ 42
4.2 Mineral Rights ____________________________________________________________________ 45
4.3 Royalties and Other Payments; Encumbrances __________________________________________ 46
4.4 Historic Environmental Liability and Indemnity __________________________________________ 46
4.5 Permits and Authorization __________________________________________________________ 47
5 ACCESSIBILITY, CLIMATE, LOCAL RESOURCES, INFRASTRUCTURE AND PHYSIOGRAPHY ___________ 49
5.1 Accessibility ______________________________________________________________________ 49
5.2 Physiography and Vegetation ________________________________________________________ 49
5.3 Land Use and Proximity to Local Population Centres ______________________________________ 49
5.4 Local Resources and Infrastructure____________________________________________________ 50
5.5 Climate and Length of Operating Season _______________________________________________ 50
6 HISTORY __________________________________________________________________________ 52
6.1 Wassa __________________________________________________________________________ 52
6.2 Hwini Butre, Benso and Chichiwelli____________________________________________________ 52
6.3 Production History, Previously Declared Resources and Reserves____________________________ 53
7 GEOLOGICAL SETTING AND MINERALIZATION ____________________________________________ 55
Page 2NI 43-101 Technical Report (March 2021) Wassa Gold Mine
7.1 Regional Geology__________________________________________________________________ 55
7.2 Local Geology and Mineralization _____________________________________________________ 57
8 DEPOSIT TYPES_____________________________________________________________________ 71
8.1 Wassa __________________________________________________________________________ 71
8.2 Hwini Butre ______________________________________________________________________ 72
8.3 Hwini Butre ______________________________________________________________________ 74
8.4 Chichiwelli _______________________________________________________________________ 75
9 EXPLORATION _____________________________________________________________________ 76
9.1 Wassa __________________________________________________________________________ 76
9.2 Hwini Butre ______________________________________________________________________ 78
9.3 Benso and Chichiwelli ______________________________________________________________ 79
10 DRILLING__________________________________________________________________________ 80
10.1 Surface Drilling __________________________________________________________________ 80
10.2 Underground Drilling______________________________________________________________ 81
10.3 Sampling _______________________________________________________________________ 81
11 SAMPLE PREPARATION, ANALYSES AND SECURITY ________________________________________ 84
11.1 Sample Preparation_______________________________________________________________ 84
11.2 Sample Dispatch and Security _______________________________________________________ 84
11.3 Laboratory Procedures ____________________________________________________________ 84
11.4 Quality Control and Quality Assurance ________________________________________________ 87
11.5 Specific Gravity Data _____________________________________________________________ 104
12 DATA VERIFICATION _______________________________________________________________ 106
12.1 Drilling Database ________________________________________________________________ 106
12.2 Other Verifications by the Qualified Person ___________________________________________ 106
13 MINERAL PROCESSING AND METALLURGICAL TESTING ___________________________________ 107
13.1 Early Metallurgical Test Work ______________________________________________________ 107
13.2 2015 Test Work Program__________________________________________________________ 107
13.3 Test Work Findings ______________________________________________________________ 109
14 MINERAL RESOURCES ______________________________________________________________ 119
14.1 Introduction____________________________________________________________________ 119
14.2 Mineral Resource Estimation Procedures _____________________________________________ 120
14.3 Mineral Resource Database _______________________________________________________ 121
14.4 Grade Shell Modelling ____________________________________________________________ 123
14.5 Statistical Analysis and Variography _________________________________________________ 132
14.6 Block Model and Grade Estimation__________________________________________________ 151
14.7 Model Validation and Sensitivity____________________________________________________ 156
14.8 Mineral Resource Classification ____________________________________________________ 165
14.9 Mineral Resource Statement_______________________________________________________ 171
14.10 Mineral Resource Risks __________________________________________________________ 173
15 MINERAL RESERVES ________________________________________________________________ 174
15.1 Cut-off Grade___________________________________________________________________ 174
15.2 Modifying Factors _______________________________________________________________ 175
15.3 Mineral Reserve Statement________________________________________________________ 175
15.4 Mineral Reserve Risks ____________________________________________________________ 176
Page 3NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16 MINING METHODS_________________________________________________________________ 177
16.1 Mineral Resources Considered in Mining Plan _________________________________________ 177
16.2 Mining Locations ________________________________________________________________ 178
16.3 Current and Upper Mining Zones (Panels 1-3) _________________________________________ 180
17 RECOVERY METHODS ______________________________________________________________ 207
17.1 Processing History _______________________________________________________________ 207
17.2 Flow Sheet Description ___________________________________________________________ 207
17.3 Processing Schedule _____________________________________________________________ 210
18 INFRASTRUCTURE _________________________________________________________________ 213
18.1 Electrical Infrastructure___________________________________________________________ 215
18.2 Surface Water Management _______________________________________________________ 217
18.3 Workshops and Other Site Buildings_________________________________________________ 218
18.4 Site Accommodation _____________________________________________________________ 218
18.5 Waste Rock Storage______________________________________________________________ 219
18.6 Tailings Storage _________________________________________________________________ 221
19 MARKET STUDIES AND CONTRACTS ___________________________________________________ 227
19.1 Market Studies _________________________________________________________________ 227
19.2 Contracts ______________________________________________________________________ 227
20 ENVIRONMENTAL STUDIES, PERMITTING AND SOCIAL OR COMMUNITY IMPACT ______________ 228
20.1 Relevant Legislation and Required Approvals__________________________________________ 228
20.2 International Requirements _______________________________________________________ 232
20.3 Environmental and Social Setting ___________________________________________________ 233
20.4 Environmental and Social Management ______________________________________________ 246
20.5 Environmental and Social Issues ____________________________________________________ 249
20.6 Closure Planning ________________________________________________________________ 252
21 CAPITAL AND OPERATING COSTS _____________________________________________________ 254
21.1 Introduction____________________________________________________________________ 254
21.2 Capital Costs ___________________________________________________________________ 254
21.3 Operating Costs _________________________________________________________________ 257
21.4 Closure Costs ___________________________________________________________________ 259
22 ECONOMIC ANALYSIS ______________________________________________________________ 260
22.1 Assumptions ___________________________________________________________________ 260
22.2 Stream, Taxes and Royalty ________________________________________________________ 261
22.3 Economic Results, Base Case_______________________________________________________ 261
22.4 Economic Results, Consensus Case __________________________________________________ 263
22.5 Sensitivity _____________________________________________________________________ 265
23 ADJACENT PROPERTIES _____________________________________________________________ 267
24 OTHER RELEVANT DATA AND INFORMATION ___________________________________________ 268
24.1 Southern Extension PEA Introduction________________________________________________ 268
24.2 Mineral Resources used in the PEA__________________________________________________ 270
24.3 Mining Methods ________________________________________________________________ 271
24.4 Metallurgical Testing _____________________________________________________________ 302
24.5 Recovery Methods_______________________________________________________________ 309
24.6 Infrastructure __________________________________________________________________ 311
24.7 Environmental, Permitting and Social and Community Impact ____________________________ 311
Page 4NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 5
24.8 Closure Planning ________________________________________________________________ 312
24.9 Capital and Operating Costs _______________________________________________________ 312
24.10 Economic Analysis ______________________________________________________________ 317
24.11 Conclusions and Interpretations ___________________________________________________ 323
25 CONCLUSIONS AND INTERPRETATIONS ________________________________________________ 328
25.1 Conclusions ____________________________________________________________________ 328
25.2 Risks__________________________________________________________________________ 332
25.3 Opportunities __________________________________________________________________ 334
26 RECOMMENDATIONS ______________________________________________________________ 336
26.1 Current Operations ______________________________________________________________ 336
26.2 Southern Extension Zone _________________________________________________________ 337
27 REFERENCES ______________________________________________________________________ 341
28 DATE AND SIGNATURES_____________________________________________________________ 345NI 43-101 Technical Report (March 2021) Wassa Gold Mine
LIST OF FIGURES
Figure 1-1 Underground Production History and Mineral Reserve plan ……………………………………………………………….. 24
Figure 1-2 Processing Production History and Mineral Reserve plan……………………………………………………………………. 25
Figure 1-3 Gold Production History and Mineral Reserve plan ……………………………………………………………………………. 26
Figure 1-4 Processing schedule for Southern Extension PEA ………………………………………………………………………………. 31
Figure 1-5 Gold Production Schedule for Southern Extension PEA ………………………………………………………………………. 31
Figure 1-6 Project Execution Plan, Southern Extension Panels 4 and 5 ………………………………………………………………… 37
Figure 4-1 Wassa Mine Location in Ghana, West Africa (United Nations, 2018) ……………………………………………………. 42
Figure 4-2 Wassa Mine Location in Ghana, West Africa (GSR, 2021) ……………………………………………………………………. 43
Figure 4-3 Location of operations and infrastructure and concession boundaries (GSR, 2021) ……………………………….. 44
Figure 7-1 Location of Wassa on the Ashanti Belt (Perrouty et al 2012)……………………………………………………………….. 56
Figure 7-2 Total magnetic intensity reduced to pole, of the Ashanti Belt (modified from Perrouty et al, 2012)…………. 58
Figure 7-3 Compilation of geochronology dating from the Ashanti Belt (Perrouty et al, 2012)………………………………… 59
Figure 7-4 Regional geology of the Ashanti belt, showing Wassa, GSR tenure and major deposits (GSR, 2020)…………. 61
Figure 7-5 Wassa mine-scale geology (modified from Bourassa, 2003 and Perrouty et al, 2013) …………………………….. 62
Figure 7-6 Vertical section through Nose of deposit-scale F4 fold, Wassa Main deposit…………………………………………. 63
Figure 7-7 Eburnean folds and foliations from Wassa mine, Starter pit ……………………………………………………………….. 64
Figure 7-8 Eburnean folds and foliations from Wassa mine, B-Shoot pit………………………………………………………………. 65
Figure 7-9 Wassa section through 19,650 mN showing high-grade zones, F3 closures, parasitic folding ………………….. 66
Figure 7-10 Wassa section through 19,925 mN showing interpretation with tight-spaced drilling…………………………… 67
Figure 7-11 Wassa section through 18,900 mN showing interpretation and wide spaced (surface) drilling………………. 67
Figure 7-12 Hwini Butre section through 33,100 mN…………………………………………………………………………………………. 69
Figure 8-1 Syn-Eoeburnean veins from B-Shoot, 242 and South-east zones (modified from Perrouty et al, 2013) …….. 72
Figure 8-2 Mineralization exposure in Father Brown pit, smoky quartz vein…………………………………………………………. 73
Figure 8-3 Mineralization exposure in Adoikrom pit, potassic alteration ……………………………………………………………… 73
Figure 8-4 Mineralization exposure in Subriso West pit, sheared volcanics ………………………………………………………….. 74
Figure 8-5 Mineralization exposure in Subriso East pit, fine grained pyrite…………………………………………………………… 74
Figure 8-6 Mineralization at Chichiwelli East, hydrothermal veins ………………………………………………………………………. 75
Figure 8-7 Mineralization at Chichiwelli West, shear hosted ………………………………………………………………………………. 75
Figure 9-1 Wassa soil geochemistry and anomalies (GSR, 2018) …………………………………………………………………………. 76
Figure 9-2 Wassa airborne magnetic coverage (GSR, 2004)………………………………………………………………………………… 77
Figure 11-1 Transworld Laboratories sample processing flow sheet ……………………………………………………………………. 85
Figure 11-2 Intertek sample processing flow sheet……………………………………………………………………………………………. 86
Figure 11-3 HARD plot comparing fire assay and BLEG for field duplicates…………………………………………………………… 88
Figure 11-4 HARD plot of all coarse rejects (2011) from SGS ………………………………………………………………………………. 89
Figure 11-5 HARD plot of all coarse rejects (2012) from SGS ………………………………………………………………………………. 89
Figure 11-6 HARD plot of all coarse rejects (2013) from SGS ………………………………………………………………………………. 90
Figure 11-7 HARD plot of all Surface Drilling coarse rejects (2014) from SGS………………………………………………………… 91
Figure 11-8 HARD plot of all Surface Drilling coarse rejects (2015) from SGS………………………………………………………… 92
Figure 11-9 HARD plot of all Surface Drilling coarse rejects (2016) from SGS………………………………………………………… 92
Figure 11-10 HARD plot of all Surface Drilling coarse rejects (2017) from SGS and Intertek ……………………………………. 93
Figure 11-11 HARD plot of all Surface Drilling coarse rejects (2018) from Intertek ………………………………………………… 93
Figure 11-12 HARD plot of all Surface Drilling coarse rejects (2019) from Intertek ………………………………………………… 94
Figure 11-13 HARD plot of all Surface Drilling coarse rejects (2020 Jan-Aug) from Intertek ……………………………………. 94
Figure 11-14 HARD plot of all Surface Drilling coarse rejects for 2018-19 for Father Brown & Adoikrom, from Intertek95
Figure 11-15 HARD plot of 2018 Wassa duplicate analysis (Intertek vs SGS)………………………………………………………..103
Figure 11-16 Wassa duplicates correlation plot (Intertek vs SGS)……………………………………………………………………….103
Figure 13-1 West view of metallurgical sample locations (GSR, 2015) ………………………………………………………………..108
Figure 13-2 Comparative indicated deportment of gold from diagnostic leach results………………………………………….112
Figure 13-3 Variation of UCS and CWi results with depth (mRL)…………………………………………………………………………113
Figure 13-4 2015 Ball Mill Bond Work Index against sample depth (mRL)……………………………………………………………114
Figure 13-5 2015 Abrasion Index against sample depth (mRL) …………………………………………………………………………..114
Figure 13-6 Leach recovery kinetic curves……………………………………………………………………………………………………….116
Figure 14-1 Wassa long-range (grey) and short-range (cyan) Mineral Resource estimation model limits ………………..119
Page 6NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-2 Wassa LR model structural ‘Form’ surfaces (oblique view looking N up plunge), surfaces show deposit scale
F4 fold as well as rolling over of mineralization at depth …………………………………………………………………………..124
Figure 14-3 North-facing cross sections showing structural form (18950 mN and 19170 mN) ……………………………….125
Figure 14-4 Structural form surfaces used in the SR model ……………………………………………………………………………….125
Figure 14-5 Images showing the structural control surfaces on sections 19,750 mN and 19,635 mN. The images show
the longer, LR model defined control surfaces and the shorter, mine geology defined control surfaces………….126
Figure 14-6 Short-range isoshell modelling parameters (SRK, 2020) …………………………………………………………………..127
Figure 14-7 SE Isometric view of final LR model Leapfrog Isoshells (blue = >0.4 g/t, red = >1.5 g/t)………………………..128
Figure 14-8 Long section looking East showing the mineralized and halo domain shells on 39,940E (top image). Section
on 39,940E (lower image) displaying the same data, cut by that section line, and the assay data used to create
the domain shells. RED = mineralized domain; BLUE = halo domain…………………………………………………………..129
Figure 14-9 Model section at U=-28.0 in transformed space generated with 2.0 tolerance in V direction ……………….130
Figure 14-10 Mineral Resource wireframes and drill hole locations for the Benso deposits (GSR, 2010) …………………131
Figure 14-11 Mineral Resource wireframes and drillhole locations for Chichiwelli (GSR, 2008) ……………………………..132
Figure 14-12 Probability Plot for LG (left) and HG (right) Domains North of 19400N (top row) and South of 19400N
(bottom row) (SRK, 2020) ……………………………………………………………………………………………………………………..133
Figure 14-13 Histogram showing the uncapped 2m Au composite grade distribution for the mineralized domain …..134
Figure 14-14 Histogram showing the uncapped 2m composite grade distribution for the halo domain ………………….135
Figure 14-15 HG Variogram from anchor point 1 (SRK, 2020)…………………………………………………………………………….137
Figure 14-16 LG Variogram from anchor point 14 (SRK, 2020)……………………………………………………………………………137
Figure 14-17 Variogram for the short-range HG & LG mineralized domains (SRK, 2020) ……………………………………….138
Figure 14-18 Gold grade probability plot with outliers and far out thresholds highlighted (RMS, 2020) ………………….139
Figure 14-19 Inferred nugget effect for gold grade in each vein unit for FBZ deposit (RMS, 2020)………………………….140
Figure 14-20 Fitted experimental variogram points for gold grade in FW for FBZ deposit (RMS, 2020) …………………..141
Figure 14-21 Fitted experimental variogram points for gold grade in HG for FBZ deposit (RMS, 2020)……………………142
Figure 14-22 Fitted experimental variogram points for gold grade in HW for FBZ deposit (RMS, 2020)…………………..143
Figure 14-23 Inferred nugget effect for gold grade in each vein unit for ADK deposit (RMS, 2020)…………………………144
Figure 14-24 Fitted experimental variogram points for gold grade in FW for ADK deposit (RMS, 2020) ………………….145
Figure 14-25 Fitted experimental variogram points for gold grade in HG for ADK deposit (RMS, 2020)…………………..146
Figure 14-26 Fitted experimental variogram points for gold grade in HW for ADK deposit (RMS, 2020)………………….147
Figure 14-27 South-North Swath Plot Comparing Estimated Grades and Informing Capped Composites (SRK, 2020).157
Figure 14-28 Quantile-Quantile Comparison of Block Model Grades to Declustered Change-of-Support Corrected Gold
Distributions for LG (left) and HG (right) domains (SRK, 2020)……………………………………………………………………158
Figure 14-29 SWATH plot in the E-W direction X dimension. Blue line represents Block model Estimated grades and
Red is 2m drill hole composites grades (SRK, 2020) ………………………………………………………………………………….159
Figure 14-30 SWATH plot in the N-S direction Y dimension. Blue line represents Block model Estimated grades and
Red is 2m drill hole composites grades (SRK, 2020) ………………………………………………………………………………….159
Figure 14-31 SWATH plot in the elevation direction Z dimension. Blue line represents Block model Estimated grades
and Red is 2m drill hole composites grades (SRK, 2020) ……………………………………………………………………………160
Figure 14-32 Measured and estimated gold grades at data locations (RMS, 2020)……………………………………………….161
Figure 14-33 Swath plot comparison of composites, nearest neighbor estimates and kriging estimates for uncapped
and capped grades in HG for FBZ deposit (RMS, 2020) ……………………………………………………………………………..162
Figure 14-34 Swath plot comparison of composites, nearest neighbor estimates and kriging estimates for uncapped
and capped grades in HG for ADK deposit (RMS, 2020) …………………………………………………………………………….162
Figure 14-35 Wassa LR model Indicated Mineral Resource classification surface and solids. All blocks above surface
and within solid mesh were classified as Indicated Mineral Resources (GSR, 2021)………………………………………166
Figure 14-36 Estimation metrics associated to Indicated (top) and Inferred (bottom) classified Resources (SRK, 2020)
………………………………………………………………………………………………………………………………………………………….167
Figure 14-37 645m RL section showing resource classification, boundary solid and drill holes (GSR, 2020) …………….169
Figure 14-38 Father Brown and Adoikrom Indicated Mineral Resource surface and Inferred Mineral Resource solids.
All material above Magenta surface was classified as Indicated Mineral Resources all material below surface and
within cyan (ADK) and red (FBZ) 3D meshes was classified as Inferred Mineral Resource ……………………………..170
Figure 15-1 Wassa UG cut-off optimization……………………………………………………………………………………………………..174
Figure 16-1 Mineral Resources considered in Mineral Reserve and models applied……………………………………………..177
Figure 16-2 Schematic of Wassa location descriptors……………………………………………………………………………………….178
Figure 16-3 Wassa mine design and asbuilt, plan view (GSR, 2021) ……………………………………………………………………179
Page 7NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 16-4 Wassa mine design and asbuilt, longitudinal view…………………………………………………………………………..180
Figure 16-5 Wassa underground production history…………………………………………………………………………………………180
Figure 16-6 Stope cycle for Panel 2 primary stopes ………………………………………………………………………………………….182
Figure 16-7 Panel 2 primary/secondary stope extraction sequence, transverse stopes…………………………………………182
Figure 16-8 Stope cycle for Panel 2 secondary stopes ………………………………………………………………………………………183
Figure 16-9 Oblique view of Wassa Panels 1-3, asbuilt and planned development……………………………………………….184
Figure 16-10 Typical level layout, Panels 1-2 570 mRL ………………………………………………………………………………………185
Figure 16-11 Oblique view of Panels 3 242 Area, planned development and stopes…………………………………………….185
Figure 16-12 Oblique view of Panels 3 B-Shoot Area, planned development and stopes ………………………………………186
Figure 16-13 Stereonet plant of Wassa joint set database…………………………………………………………………………………187
Figure 16-14 Principal stress measurement Magnitude vs Depth……………………………………………………………………….189
Figure 16-15 Support, Barton’s Q-Index chart (Barton and Grimstad, 1993)………………………………………………………..190
Figure 16-16 Stope axes measurements………………………………………………………………………………………………………….192
Figure 16-17 Matthews Stability Graph, transverse stopes (Mathews et al, 1981) ……………………………………………….193
Figure 16-18 Matthews Stability Graph, longitudinal stopes (Mathews et al, 1981) ……………………………………………..193
Figure 16-19 B-Shoot Pillars, modelled factors of safety from Phase 2 software, (GSR, 2018)………………………………..194
Figure 16-20 Wassa paste plant Dec-2020, thickener and storage tank in foreground ………………………………………….196
Figure 16-21 Paste fill distribution modelling…………………………………………………………………………………………………..197
Figure 16-22 Wassa Panels 1 and 2 ventilation circuit to end of life……………………………………………………………………199
Figure 16-23 Wassa Panel 3, B-Shoot Upper ventilation circuit………………………………………………………………………….199
Figure 16-24 Wassa Panel 3, 242 ventilation circuit………………………………………………………………………………………….200
Figure 16-25 Underground dewatering longitudinal view………………………………………………………………………………….201
Figure 16-26 620 mRL main pump station……………………………………………………………………………………………………….202
Figure 16-27 Lateral development schedule for Mineral Reserve……………………………………………………………………….204
Figure 16-28 Ore mining schedule for Mineral Reserve …………………………………………………………………………………….204
Figure 16-29 Underground Production History and Mineral Reserve plan …………………………………………………………..205
Figure 17-1 Wassa processing plant flow sheet ……………………………………………………………………………………………….209
Figure 17-2 Processing schedule for Mineral Reserve plan………………………………………………………………………………..211
Figure 17-3 Gold Production schedule for Mineral Reserve plan………………………………………………………………………..211
Figure 17-4 Processing Production History and Mineral Reserve Plan…………………………………………………………………212
Figure 17-5 Gold Production History and Mineral Reserve plan …………………………………………………………………………212
Figure 18-1 Wassa key infrastructure (GSR, 2018) ……………………………………………………………………………………………213
Figure 18-2 Wassa site layout (GSR, 2021) ………………………………………………………………………………………………………214
Figure 18-3 Wassa site layout and underground workings (GSR, 2021)……………………………………………………………….215
Figure 18-4 Site electrical distribution…………………………………………………………………………………………………………….216
Figure 18-5 Wassa Main pit catchments …………………………………………………………………………………………………………217
Figure 18-6 Tara Camp………………………………………………………………………………………………………………………………….219
Figure 18-7 Waste dump locations (Golder, 2016)……………………………………………………………………………………………220
Figure 18-8 Section through nominal waste dump design …………………………………………………………………………………220
Figure 18-9 Wassa TSF 1 and TSF 2 aerial view (August 2020) ……………………………………………………………………………221
Figure 18-10 View from north of TSF 1 looking southeast (November 2020) ……………………………………………………….222
Figure 18-11 TSF 1 and TSF 2 layout (Geosystems, 2018) ………………………………………………………………………………….224
Figure 20-1 Pra River basin and location of Wassa……………………………………………………………………………………………234
Figure 20-2 Wassa topography and drainage with sub-catchments ……………………………………………………………………235
Figure 20-3 Conceptual underground water flow path model (Golder, 2016)………………………………………………………236
Figure 20-4 Conceptual groundwater model (Golder, 2016) ……………………………………………………………………………..237
Figure 20-5 Groundwater contours and flow (Golder, 2016)……………………………………………………………………………..238
Figure 20-6 Conceptual geo-environmental model, E-W section (Golder, 2016)…………………………………………………..239
Figure 20-7 Paste pH vs NPR for Open Pit ……………………………………………………………………………………………………….241
Figure 20-8 Paste pH vs NPR for Waste …………………………………………………………………………………………………………..241
Figure 20-9 Paste pH vs NPR for Underground…………………………………………………………………………………………………241
Figure 20-10 Paste pH vs NPR for South Inferred……………………………………………………………………………………………..241
Figure 20-11 NPR vs S% for Open Pit………………………………………………………………………………………………………………241
Figure 20-12 NPR vs S% for Waste………………………………………………………………………………………………………………….241
Figure 20-13 NPR vs S% for Underground ……………………………………………………………………………………………………….242
Page 8NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 20-14 NPR vs S% for South Inferred………………………………………………………………………………………………………242
Figure 20-15 GSOPP oil palm plantation on TSF 1 …………………………………………………………………………………………….247
Figure 22-1 Cash Flows by Year for Mineral Reserve – Base case ……………………………………………………………………….261
Figure 22-2 Cash Flows by Year for Mineral Reserve – Consensus case……………………………………………………………….263
Figure 22-3 Sensitivity analysis of the Mineral Reserve base case ($1,300 /oz)…………………………………………………….265
Figure 22-4 Sensitivity analysis of the Mineral Reserve consensus case (av. $1,751 /oz)………………………………………266
Figure 24-1 Illustration of Wassa location descriptors………………………………………………………………………………………270
Figure 24-2 Mineral Resources considered in Southern Extension PEA (LR model only)………………………………………..270
Figure 24-3 Longitudinal Section looking east, showing the Southern Extension Panels………………………………………..271
Figure 24-4 Cross sectional view, Southern Extension, highlighting the width and complexity across the deposit ……272
Figure 24-5 Oblique view of the Southern Extension showing twin decline layout (looking northeast) …………………..273
Figure 24-6 Schematic of a 4-lift primary transverse stope (illustration not to scale) ……………………………………………274
Figure 24-7 Generic downhole stope activity sequence…………………………………………………………………………………….275
Figure 24-8 Primary/secondary stope extraction sequence, transverse stopes ……………………………………………………276
Figure 24-9 Pillarless retreat stope extraction sequence, transverse stopes………………………………………………………..277
Figure 24-10 Generic wide-width mining (illustration not to scale)…………………………………………………………………….278
Figure 24-11 East decline, oblique looking north-west ……………………………………………………………………………………..280
Figure 24-12 West decline, oblique view looking north-east……………………………………………………………………………..281
Figure 24-13 Generic production block layout with primary/2ndary sequence and vent flows, longitudinal view…….283
Figure 24-14 Level layout (295 mRL) showing deposit width and twin decline arrangement, plan view ………………….284
Figure 24-15 Haulage level arrangement, 470 mRL…………………………………………………………………………………………..285
Figure 24-16 Oblique view, approximate Resource development and infill drilling horizons, looking north west……..286
Figure 24-17 Geotechnical drill hole data in Southern Extension, plan (left) and longitudinal (right) views
(OreTeck, 2020)……………………………………………………………………………………………………………………………………288
Figure 24-18 Wassa preliminary principal stress gradient with reference mines and regions (OreTeck, 2020) …………289
Figure 24-19 Geotechnical rock mass model in Southern Extension, showing Q-prime in plan (left) and cross-section
(OreTeck, 2020)……………………………………………………………………………………………………………………………………290
Figure 24-20 Unsupported stable stope spans for expected rock mass conditions and current design hydraulic radii
(Mathews, 1981; Potvin, 1988)………………………………………………………………………………………………………………292
Figure 24-21 Unsupported hanging-wall stable hydraulic radii for Southern Extension, longitudinal view
(OreTeck, 2020)……………………………………………………………………………………………………………………………………293
Figure 24-22 Wassa Panels 4-8, ventilation stages, oblique view ……………………………………………………………………….295
Figure 24-23 Panels 4-8, production block ventilation flows ……………………………………………………………………………..296
Figure 24-24 Primary fan applied pressure (air density 1.1 kg/m3 ) and motor power (75% efficiency) ……………………297
Figure 24-25 Heat loads and cooling summary for Y12 (SRK, 2021)…………………………………………………………………….297
Figure 24-26 Estimated refrigeration capacity over mine life (SRK, 2021)……………………………………………………………298
Figure 24-27 Lateral development schedule for Southern Extension PEA ……………………………………………………………300
Figure 24-28 ROM material mining schedule for Southern Extension PEA …………………………………………………………..300
Figure 24-29 Electrical distribution with Phase 2 expansion required to support Southern Extension …………………….302
Figure 24-30 Metallurgical Sample Drillhole Location……………………………………………………………………………………….304
Figure 24-31 Ball Mill Bond Work Index against sample depth (mRL) ………………………………………………………………305
Figure 24-32 Direct Leach – Grind Sensitivity Summary…………………………………………………………………………………….306
Figure 24-33 Preg-robbing Characterization Summary ……………………………………………………………………………………..307
Figure 24-34 Processing schedule for Southern Extension PEA ………………………………………………………………………….309
Figure 24-35 Gold Production schedule for Southern Extension PEA ………………………………………………………………….311
Figure 24-36 Cash Flows by Year for Southern Extension – Base Case…………………………………………………………………318
Figure 24-37 Cash Flows by Year for Southern Extension – Consensus Case ………………………………………………………..320
Figure 24-38 Sensitivity analysis of the Southern Extension PEA base case ($1,300 /oz) ……………………………………….322
Figure 24-39 Sensitivity analysis of the Southern Extension PEA consensus case ($1,585 /oz) ……………………………….323
Figure 26-1 Project Execution Plan, Southern Extension Panels 4 and 5 ……………………………………………………………..340
Page 9NI 43-101 Technical Report (March 2021) Wassa Gold Mine
LIST OF TABLES
Table 1-1 RGLD stream payment structure ………………………………………………………………………………………………………. 17
Table 1-2 Wassa Measured and Indicated Mineral Resource, as at 31 December 2020 …………………………………………. 20
Table 1-3 Wassa Inferred Mineral Resource, as at 31 December 2020…………………………………………………………………. 20
Table 1-4 Wassa Mineral Reserve, as at 31 December 2020……………………………………………………………………………….. 21
Table 1-5 Wassa, mine design quantities for Mineral Reserve plan……………………………………………………………………… 22
Table 1-6 Stable stope dimensions for Mineral Reserve plan ……………………………………………………………………………… 22
Table 1-7 Mining schedule quantities for Mineral Reserve plan ………………………………………………………………………….. 23
Table 1-8 Mobile fleet purchase schedule for Mineral Reserve plan ……………………………………………………………………. 24
Table 1-9 Processing schedule quantities for Mineral Reserve plan …………………………………………………………………….. 25
Table 1-10 Capital Cost Summary for Mineral Reserve plan ……………………………………………………………………………….. 28
Table 1-11 Cost Estimate, Operating for Mineral Reserve plan …………………………………………………………………………… 29
Table 1-12 Operating Cost Summary for Mineral Reserve plan …………………………………………………………………………… 29
Table 1-13 Conversion of Inferred Mineral Resource to PEA inventory………………………………………………………………… 31
Table 2-1 Qualified persons and site visits ……………………………………………………………………………………………………….. 39
Table 4-1 Mineral rights held by GSWL ……………………………………………………………………………………………………………. 45
Table 5-1 Communities neighbouring Wassa Mine……………………………………………………………………………………………. 50
Table 6-1 Recent Production History, Wassa…………………………………………………………………………………………………….. 54
Table 7-1 Deformational history of the Ashanti Belt (Perrouty et al, 2012)…………………………………………………………… 60
Table 10-1 Exploration data used for Mineral Resource models………………………………………………………………………….. 81
Table 11-1 Summary of analytical quality control data from 2014 to early 2017 …………………………………………………… 90
Table 11-2 CRM for 2003-2007 (TWL) ……………………………………………………………………………………………………………… 96
Table 11-3 Geostats CRM for 2008-2012 (SGS) …………………………………………………………………………………………………. 96
Table 11-4 Gannet CRM for 2008-2012 (SGS)……………………………………………………………………………………………………. 97
Table 11-5 Gannet CRM for 2013 (SGS)……………………………………………………………………………………………………………. 97
Table 11-6 Gannet CRM for 2014-2017 (SGS)……………………………………………………………………………………………………. 98
Table 11-7 Gannet CRM for 2014 to 2017 (Wassa Site Lab)………………………………………………………………………………… 98
Table 11-8 Gannet CRM for 2018 (Intertek) ……………………………………………………………………………………………………… 98
Table 11-9 Gannet CRM for 2019 Wassa UG (Intertek)………………………………………………………………………………………. 99
Table 11-10 Gannet CRM for 2020 Jan-Oct, Wassa UG (Intertek)………………………………………………………………………… 99
Table 11-11 Gannet CRM for 2019 Wassa surface drilling (Intertek) ……………………………………………………………………. 99
Table 11-12 Gannet CRM for 2018-2019 Father Brown/Adoikrom surface drilling (Intertek)………………………………….. 99
Table 11-13 Blank sample summary statistics 2011 to Oct-2020………………………………………………………………………..100
Table 11-14 Blank sample summary statistics 2019, Wassa surface drilling (Intertek)…………………………………………..100
Table 11-15 Blank sample summary statistics 2018-2019 Father Brown/Adoikrom surface drilling (Intertek)………….100
Table 11-16 Gannet CRM for quarter core sample analysis (Intertek)…………………………………………………………………101
Table 11-17 Summary HARD plot results for quarter core sample analysis………………………………………………………….101
Table 11-18 Summary HARD plot results for 2013 round robin program …………………………………………………………….101
Table 11-19 Round-robin descriptive statistics 2012 ………………………………………………………………………………………..102
Table 11-20 Round-robin descriptive statistics 2017 ………………………………………………………………………………………..102
Table 11-21 Summary HARD plot results for 2017 round robin program …………………………………………………………….102
Table 11-22 Summary HARD plot results for 2018 round robin program …………………………………………………………….103
Table 11-23 Specific gravity test results, open pit…………………………………………………………………………………………….104
Table 11-24 Specific gravity test results, underground drilling 2017 …………………………………………………………………..104
Table 11-25 Specific gravity test results, underground drilling 2018 …………………………………………………………………..105
Table 11-26 Specific gravity test results, surface drilling 2018……………………………………………………………………………105
Table 11-27 Specific gravity test results, surface drilling 2020……………………………………………………………………………105
Table 13-1 Ore zones represented by the variability samples ……………………………………………………………………………107
Table 13-2 Summary and location of test work samples……………………………………………………………………………………108
Table 13-3 Screened head assay results………………………………………………………………………………………………………….109
Table 13-4 Elemental and chemical analysis results………………………………………………………………………………………….110
Table 13-5 Summary of diagnostic leach results………………………………………………………………………………………………111
Table 13-6 Results of Crushability Tests: UCS and CWi ……………………………………………………………………………………..112
Table 13-7 Results of 2015 BWi and Ai Tests……………………………………………………………………………………………………113
Page 10NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Table 13-8 Gravity Gold Recovery Test Results ………………………………………………………………………………………………..115
Table 13-9 Whole Ore Leach and CIL test results……………………………………………………………………………………………..115
Table 13-10 Leach test results and reagent consumptions………………………………………………………………………………..116
Table 13-11 Overall gravity leach recoveries……………………………………………………………………………………………………117
Table 13-12 Reconciliation of assay and back-calculated head grades from test work ………………………………………….117
Table 13-13 Comparative settling test results………………………………………………………………………………………………….118
Table 14-1 Wassa LR model drill hole database as at February, 2020 …………………………………………………………………121
Table 14-2 Wassa Underground short-range drill hole database as of December 1, 2020……………………………………..122
Table 14-3 Father Brown/Adoikrom drill hole database as of December 2020 …………………………………………………….122
Table 14-4 Benso drill hole database as of December 2012……………………………………………………………………………….122
Table 14-5 Chichiwelli drill hole database as of 2012………………………………………………………………………………………..122
Table 14-6 Leapfrog trend inputs for creation of 1.5 g/t and 0.4 g/t LR model grade Isoshells……………………………….124
Table 14-7 Leapfrog trend inputs for creation of 1.5 g/t and 0.4 g/t SR model grade Isoshells……………………………….126
Table 14-8 LR modelling extents…………………………………………………………………………………………………………………….126
Table 14-9 LR Isoshell modelling parameters…………………………………………………………………………………………………..126
Table 14-10 SR block model extents……………………………………………………………………………………………………………….127
Table 14-11 Summary Gold Statistics of Assays and Composites ……………………………………………………………………….132
Table 14-12 Comparison of Uncapped and Capped Gold Composite Grades – LR model ………………………………………133
Table 14-13 Comparison of uncapped and capped gold composite grades – SR model…………………………………………134
Table 14-14 Local variogram orientations and anchor point locations………………………………………………………………..136
Table 14-15 Local variogram models by domain ………………………………………………………………………………………………136
Table 14-16 Descriptive statistics for Hwini Butre modelled domains (uncapped & capped) …………………………………139
Table 14-17 Capping values selected from analysis of the probability plot ………………………………………………………….140
Table 14-18 Fitted variogram parameters for gold grade in FW for FBZ deposit…………………………………………………..144
Table 14-19 Fitted variogram parameters for gold grade in HG for FBZ deposit …………………………………………………..144
Table 14-20 Fitted variogram parameters for gold grade in HW for FBZ deposit ………………………………………………….144
Table 14-21 Fitted variogram parameters for gold grade in FW for ADK deposit………………………………………………….148
Table 14-22 Fitted variogram parameters for gold grade in HG for ADK deposit ………………………………………………….148
Table 14-23 Fitted variogram parameters for gold grade in HW for ADK deposit …………………………………………………148
Table 14-24 Fitted major variogram directions in original space ………………………………………………………………………..148
Table 14-25 Descriptive statistics for Benso modelled domains (capped)……………………………………………………………149
Table 14-26 Descriptive statistics for simplified Benso modelled domains (capped) …………………………………………….149
Table 14-27 Variogram parameters for the Benso zones…………………………………………………………………………………..150
Table 14-28 Descriptive statistics for Chichiwelli modelled domains (capped) …………………………………………………….150
Table 14-29 Chichiwelli high grade capping …………………………………………………………………………………………………….150
Table 14-30 Variogram parameters for Chichiwelli zones………………………………………………………………………………….151
Table 14-31 Wassa LR model definitions, upper left hand corner coordinates …………………………………………………….151
Table 14-32 Average Bulk Density used for LR model ……………………………………………………………………………………….151
Table 14-33 Wassa SR model definitions…………………………………………………………………………………………………………152
Table 14-34 LR model Estimation Parameters …………………………………………………………………………………………………153
Table 14-35 SR model estimation parameters …………………………………………………………………………………………………153
Table 14-36 Kriging search parameters for each vein unit in each deposit ………………………………………………………….153
Table 14-37 Father Brown block model parameters…………………………………………………………………………………………154
Table 14-38 Adoikrom Zone block model parameters ………………………………………………………………………………………154
Table 14-39 Hwini Butre rock density……………………………………………………………………………………………………………..154
Table 14-40 Benso block model parameters……………………………………………………………………………………………………154
Table 14-41 Benso ellipsoid search neighbourhood parameters………………………………………………………………………..155
Table 14-42 Benso rock density……………………………………………………………………………………………………………………..155
Table 14-43 Chichiwelli block model parameters……………………………………………………………………………………………..155
Table 14-44 Chichiwelli ellipsoid search neighbourhood parameters………………………………………………………………….156
Table 14-45 Chichiwelli rock density ………………………………………………………………………………………………………………156
Table 14-46 Global mean comparison between nearest neighbor and kriged thickness models for FBZ. ………………..160
Table 14-47 Global mean comparison between nearest neighbor and kriged thickness models for ADK. Variable ….160
Table 14-48 List of least reliable estimates FBZ………………………………………………………………………………………………..161
Table 14-49 List of least reliable estimates ADK……………………………………………………………………………………………….161
Page 11NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Table 14-50 Global mean comparison between nearest neighbor and kriged Gold models for FBZ ………………………..162
Table 14-51 Global mean comparison between nearest neighbor and kriged Gold models for ADK……………………….163
Table 14-52 Global mean comparison between nearest neighbor and kriged Gold models for FBZ within the densely
sampled area……………………………………………………………………………………………………………………………………….163
Table 14-53 Global mean comparison between nearest neighbor and kriged Gold models for ADK within the densely
sampled area……………………………………………………………………………………………………………………………………….163
Table 14-54 Global mean comparison between nearest neighbor and kriged Gold models for FBZ within the sparsely
sampled area……………………………………………………………………………………………………………………………………….164
Table 14-55 Global mean comparison between nearest neighbor and kriged Gold models for ADK within the sparsely
sampled area……………………………………………………………………………………………………………………………………….164
Table 14-56 Composition of Classified Blocks for Open Pit Extraction Above a Cut-Off Grade of 0.4 g/t Gold ………….167
Table 14-57 Composition of Classified Blocks for Underground Extraction Above a Cut-Off Grade of 2.1 g/t Gold ….168
Table 14-58 Wassa Measured and Indicated Mineral Resource, as at 31 December 2020 …………………………………….172
Table 14-59 Wassa Inferred Mineral Resource, as at 31 December 2020…………………………………………………………….172
Table 15-1 Wassa UG cut-off grade calculation………………………………………………………………………………………………..174
Table 15-2 Wassa Mineral Reserve, as at 31 December 2020…………………………………………………………………………….175
Table 16-1 Upper mine inventory change, OP to UG ………………………………………………………………………………………..181
Table 16-2 Wassa Panels 1-3, design quantities for Mineral Reserve ………………………………………………………………….186
Table 16-3 Joint sets used for stope design……………………………………………………………………………………………………..188
Table 16-4 570 decline stress measurement……………………………………………………………………………………………………188
Table 16-5 Wassa rock mass characterization parameters (Barton et al, 1974) ……………………………………………………189
Table 16-6 Modified Stability Number (N’) for Panels 1-3, transverse stopes (Potvin, 1988)………………………………….191
Table 16-7 Modified Stability Number (N’) for Panels 1-3, longitudinal stopes (Potvin, 1988) ……………………………….191
Table 16-8 Stable stope dimensions, Panels 1-3 ………………………………………………………………………………………………192
Table 16-9 Wassa ventilation model calibration, Dec-2020 ……………………………………………………………………………….198
Table 16-10 Wassa mining schedule quantities for Mineral Reserve plan……………………………………………………………203
Table 16-11 Mobile fleet productivity assumption……………………………………………………………………………………………206
Table 16-12 Mobile fleet schedule for Mineral Reserve plan……………………………………………………………………………..206
Table 17-1 Historic plant production, grades and recoveries……………………………………………………………………………..207
Table 17-2 Key plant design and operating parameters…………………………………………………………………………………….208
Table 17-3 Processing schedule quantities for Mineral Reserve plan ………………………………………………………………….210
Table 18-1 TSF 2 stage design details ……………………………………………………………………………………………………………..226
Table 20-1 Primary environmental approvals for mines in Ghana ………………………………………………………………………229
Table 20-2 Environmental approvals obtained for Wassa mine………………………………………………………………………….231
Table 20-3 Communities around Wassa………………………………………………………………………………………………………….245
Table 20-4 Closure cost estimates, at Dec-2020……………………………………………………………………………………………….253
Table 21-1 Cost estimate, Major Projects for Mineral Reserve plan ……………………………………………………………………254
Table 21-2 Mine development capital allocation for Mineral Reserve plan………………………………………………………….255
Table 21-3 Cost estimate, Minor Projects for Mineral Reserve plan……………………………………………………………………255
Table 21-4 Mobile Fleet, categories ……………………………………………………………………………………………………………….256
Table 21-5 Cost estimate, Mobile Fleet replacement schedule for Mineral Reserve plan………………………………………256
Table 21-6 Capital cost summary for Mineral Reserve plan……………………………………………………………………………….257
Table 21-7 Cost estimate, Operating for Mineral Reserve plan ………………………………………………………………………….258
Table 21-8 Operating cost summary for Mineral Reserve plan…………………………………………………………………………..259
Table 21-9 Closure cost summary for Mineral Reserve plan ………………………………………………………………………………259
Table 22-1 Key life of mine inputs and assumptions used in the economic model for Mineral Reserve…………………..260
Table 22-2 Cash flows, Mineral Reserve economic analysis – Base case ……………………………………………………………..261
Table 22-3 Mineral Reserve economic analysis – Base case ………………………………………………………………………………262
Table 22-4 Cash flows, Mineral Reserve economic analysis – Consensus case……………………………………………………..263
Table 22-5 Mineral Reserve economic analysis – Consensus case………………………………………………………………………264
Table 22-6 Sensitivity results for the Mineral Reserve at different gold prices and discount rates………………………….265
Table 22-7 Sensitivity results of the Mineral Reserve base case ($1,300 /oz)……………………………………………………….265
Table 22-8 Sensitivity results of the Mineral Reserve consensus case (av. $1,751 /oz)…………………………………………266
Table 24-1 Stope Modifying Factors contained in the MSO settings……………………………………………………………………279
Table 24-2 Conversion of Inferred Mineral Resource to PEA inventory……………………………………………………………….279
Page 12NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 13
Table 24-3 Proposed Resource diamond drilling quantities relative to stope timing by Panel………………………………..286
Table 24-4 Wassa Panels 4-8 mine design quantities………………………………………………………………………………………..287
Table 24-5 Modified Stability Number (N’) for Panels 4 and 5, transverse stopes (after Potvin, 1988) ……………………291
Table 24-6 Modified Stability Number (N’) for Panels 4 and 5, longitudinal stopes (after Potvin, 1988) ………………….291
Table 24-7 Stable stope dimensions, Panels 4 and 5…………………………………………………………………………………………292
Table 24-8 Wassa mining schedule quantities, Southern Extension PEA ……………………………………………………………..299
Table 24-9 Mobile fleet schedule, Southern Extension PEA……………………………………………………………………………….301
Table 24-10 Metallurgical Composite Sample Location …………………………………………………………………………………….303
Table 24-11 Metallurgical Composite Head Assay ……………………………………………………………………………………………304
Table 24-12 Bond Ball Work Index Results………………………………………………………………………………………………………305
Table 24-13 Gravity Recovery Gold – Summary ………………………………………………………………………………………………..306
Table 24-14 Reagent Consumption Summary ………………………………………………………………………………………………….307
Table 24-15 Diagnostic Leach Summary ………………………………………………………………………………………………………….308
Table 24-16 Processing Schedule, Southern Extension PEA……………………………………………………………………………….310
Table 24-17 Cost estimate, Major Projects for Southern Extension PEA ……………………………………………………………..312
Table 24-18 Mine development capital allocation for Southern Extension PEA ……………………………………………………312
Table 24-19 Cost estimate, Minor Projects for Southern Extension PEA ……………………………………………………………..313
Table 24-20 Cost estimate, Mobile Fleet addition/replacement schedule for Southern Extension PEA …………………..313
Table 24-21 Capital cost summary for Southern Extension PEA …………………………………………………………………………314
Table 24-22 Cost estimate, Operating for Southern Extension PEA…………………………………………………………………….315
Table 24-23 Operating cost summary for Southern Extension PEA …………………………………………………………………….315
Table 24-24 Closure cost summary for Southern Extension PEA ………………………………………………………………………..316
Table 24-25 Key life of mine inputs and assumptions used in the economic model, PEA ………………………………………317
Table 24-26 Cash flows, PEA economic analysis – Base Case……………………………………………………………………………..318
Table 24-27 Economic Analysis – Base Case……………………………………………………………………………………………………319
Table 24-28 Cash flows, PEA economic analysis – Consensus Case …………………………………………………………………….320
Table 24-29 PEA Economic Analysis – Consensus Case …………………………………………………………………………………….321
Table 24-30 Sensitivity results for the Southern Extension PEA at different gold prices and discount rates …………….322
Table 24-31 Sensitivity results of the Southern Extension PEA base case ($1,300 /oz) ………………………………………….322
Table 24-32 Sensitivity results of the Southern Extension PEA consensus case ($1,585 /oz) ………………………………….323
Table 24-33 Geology, Mining and Processing risks for Southern Extension………………………………………………………….325
Table 24-34 Economic risks for Southern Extension………………………………………………………………………………………….326
Table 24-35 Geological Drilling opportunities for Southern Extension ………………………………………………………………..326
Table 24-36 Mine design and productivity opportunities for Southern Extension ………………………………………………..327
Table 25-1 Geology, Mining and Processing risks for the Mineral Reserve…………………………………………………………..332
Table 25-2 Infrastructure risks for the Mineral Reserve…………………………………………………………………………………….332
Table 25-3 Capital and Operating Cost risks for the Mineral Reserve………………………………………………………………….333
Table 25-4 Environmental and Social Risks ……………………………………………………………………………………………………..333
Table 25-5 Mineral Resource Opportunities…………………………………………………………………………………………………….334
Table 25-6 Mine design and productivity opportunities for the Mineral Reserve …………………………………………………334
Table 25-7 Sustainability Opportunities ………………………………………………………………………………………………………….335
Table 26-1 Cost estimate for 2021 – 2022 Resource definition drilling and technical studies…………………………………339NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 14
LIST OF ABBREVIATIONS
2020 PEA
Preliminary Economic Assessment of potential expansion of the underground mine
to extract the Inferred Mineral Resource in the Southern Extension zone
AAS
Atomic adsorption spectroscopy (sampling)
AC
Air-core (drilling)
ADK
Adoikrom (deposit)
Ai
Bond abrasion index (metallurgical testing)
ALS
ALS Minerals
ARD
Acid rock drainage
ARO
Asset retirement obligations (closure planning)
BDG
BD Goldfields (company)
BLEG
Bulk leach extractable gold (assaying)
BWi
Bond ball mill work index (metallurgical testing)
CIL
Carbon in leach (processing method)
CIM
Canadian Institute of Mining, Metallurgy and Petroleum
CMCC
Community Mine Consultative Committee
CRM
Certified reference material (sampling QA/QC)
CSL
Compacted soil liner (civil construction)
CWi
Bond low impact crushing work index (metallurgical testing)
CYAP
Community Youth Apprenticeship Program
DD
Diamond core (drilling)
EIA
Environmental Impact Assessment
EIS
Environmental Impact Statement
EMP
Environmental Management Plan
EMS
Environmental and social management system
EPA
Environmental Protection Agency (Ghana)
ESR
Excavation support ratio (geotechnical)
FBZ
Father Brown (deposit)
FOS
Factor of safety
FS
Feasibility study
HW
Footwall
G&A
General and administration
GAI
Geochemical abundance index (geochemistry)
GC
Grade control
GSI
Geological strength index (geotechnical)
GSOPP
Golden Star Oil Palm Plantation
GSR
Golden Star Resources
GSSTEP
Golden Star Skills Training and Employability Program
GSWL
Golden Star Wassa Limited
HARD
Half absolute relative difference (statistics)
HBB
Hwini Butre Benso (deposit group)
HBM
Hwini Butre Minerals (company)
HG
High grade
LG
Low grade
HL
Heap leach (processing method)
HW
Hanging-wallNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 15
ICOLD
International Committee on Large Dams
ILR
In-line reactor (processing method)
IP
Induced polarization
Jn
Joint number (geotechnical)
Jr
Joint roughness (geotechnical)
Jw
Joint alteration (geotechnical)
L.I.
Legal Instrument
LG
Low grade
LHOS
Long hole open stoping (mining method)
LR (model)
Long-range model (geological modelling)
LVA
Locally variable anisotropy (geological modelling)
MOU
Memoranda of Understanding
MSG
Modified Stability Graph (geotechnical)
MSO
Mineable Stope Optimiser (mine planning)
NAG
Not acid generating (geochemistry)
NPV
Net present value
OK
Ordinary kriging (geological modelling)
PCP
Practical closure plan (closure planning)
PVC
Poly-vinyl chloride
QA/QC
Quality assurance, quality control
QP
Qualified person
RAB
Rotary air blast (drilling)
RC
Reverse circulation (drilling)
RGI
Ryal Gold Inc (company)
RGLD
RGLD Gold AG (company)
RL
Relative level
RMR
Rock mass rating (geotechnical)
RMS
Resource Modelling solutions (company)
ROM
Run of mine
RPEEE
Reasonable prospects for economic extraction
RQD
Rock quality description (geotechnical)
SGL
Satellite Goldfields Limited (company)
SJR
Saint Jude Resources (company)
SR (model)
Short-range model (geological modelling)
TSF
Tailings storage facility
UCS
Unconfined compressive strength
US$
United States dollar/s
VRA
Volta River Authority (Ghana)
WSL
Wassa site laboratory (assaying)
WUC
Western University College, Tarkwa (Ghana)
WUG
Wassa underground mine
XRD
X-ray diffraction
XRF
X-ray fluorescenceNI 43-101 Technical Report (March 2021) Wassa Gold Mine
1 EXECUTIVE SUMMARY
1.1 Terms of Reference
This Technical Report has been prepared to meet the requirements defined by Form 43-101F1, by and for
Golden Star Resources, describing the Wassa gold mine in Ghana. GSR owns a 90% interest in and manages
Golden Star Wassa Limited, who’s primary asset is the Wassa gold mine, with the Government of Ghana
owning the remaining 10%.
The report provides updated information on the currently operating Wassa Gold Mine:
- Updated Mineral Resource and Mineral Reserve estimates, as at 31 December 2020; and
- Summary of a Preliminary Economic Assessment of potential expansion of the underground mine
to extract the Inferred Mineral Resource in the Southern Extension zone (2020 PEA).
The 2020 PEA has no impact on the Mineral Reserves, nor on the key assumptions and parameters
supporting the Mineral Reserves, which are current, valid and do not rely on any assumptions in the PEA.
The PEA is a scoping level study which is conceptual in nature and there is no certainty that production and
financial outcomes will be realized. It has been prepared within the following framework:
- Production schedules to appropriately consider conversion risk of the Inferred Mineral Resource;
- Methodologies and design quantities based on proven, currently available technologies;
- Mine production constrained within current processing capacity (2.7 Mtpa);
- Costs to reflect current operational experience; and
- Minimise capital demand needed to establish full production.
The intent of the framework is to present a deliverable PEA plan which can be executed with GSR’s current
operational and financing capacity. Potential enhancements outside this framework are presented as
opportunities outside of the PEA outcomes and can be investigated as part of the forward work plan.
Mineral Resources and Mineral Reserves have been prepared in accordance with the 2014 CIM Definition
Standards and 2019 Best Practice Guideline.
Units in the report are metric and monetary units are United States dollars (US$) unless otherwise stated.
1.2 Location and Setting
The Wassa Mine is located in a rural setting near the village of Akyempim in the Wassa East District, in
Ghana’s Western Region, 80 km north of Cape Coast and 150 km west of the capital Accra.
The climate is classified as wet semi-equatorial with a dry season from November to February. The wettest
month is June with an average 241 ± 85 mm and annual average rainfall is 1,996 ± 293 mm.
1.3 Mineral Tenure, Permits, Royalties and Agreements
GSWL holds three mining leases (Wassa, Hwini Butre, Benso) and several prospecting leases in the region
and full details are presented in Table 4-1.
EIA studies have been undertaken to support permitting and there is considerable background
environmental data.
The Wassa Mining Lease stipulates a 5% royalty on gross revenue, paid quarterly to the Government of
Ghana and the government holds a 10% free-carried interest, which entitles a pro-rata share of dividends.
GSR is party to a gold purchase and sale agreement with Royal Gold, Inc. through its wholly owned
subsidiary RGLD Gold AG (RGLD) which was amended and restated on 30 September 2020. The stream
covers all gold produced within GSWL’s mineral concessions. The stream payment structure is outlined in
Table 1-1. The stream payments are treated as a revenue adjustment.
Page 16NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 17
Table 1-1 RGLD stream payment structure
Stream Tier
Attributable Ounces
% of spot paid
Application
Tier 1
10.5%, until 240,000 oz reached
20%
119,997 oz sold to end-December 2020
Tier 2
5.5%
30%
All production after Tier 1 completed
1.4 History
Golden Star acquired the 90% share in Wassa in September 2002 from Standard Bank after the foreclosure
of Glencar Mining’s share of Satellite Gold Limited. At the time Wassa was an open pit operation treating
3.0 Mtpa through heap leach, with gold recovery of 55-60%.
The carbon in leach plant was commissioned in 2005 and upgraded in 2013 to treat 2.7 Mtpa of fresh rock
feed only. Ore has been mined mostly by open pit, with underground development commencing in 2015
and forming the majority of the ore supply since 2018. Gold production has varied from 184 koz in 2009 to
104 koz in 2016 and has averaged 157 koz/yr for the past three years (2018-2020).
1.5 Geology and Mineralization
1.5.1 Wassa
The Wassa property lies within the southern portion of the Ashanti Greenstone Belt along the eastern
margin and within a volcano-sedimentary assemblage located close to the Tarkwaian basin contact.
Wassa lithology is characterized by lithologies of the Sefwi Group, consisting of intercalated meta-mafic
volcanic and meta-diorite dykes with altered meta-mafic volcanic and meta-sediments which are locally
characterized as magnetite rich, banded iron formation like horizons (Bourassa, 2003). The sequence is
characterized by the presence of multiple ankerite-quartz veins, sub-parallel to the main penetrative
foliation and Eoeburnean felsic porphyry intrusions on the south-eastern flank of the Wassa mine fold.
Wassa mineralization is subdivided into a number of domains: F Shoot, B Shoot, 242, South East, Starter,
419, Mid East, and Dead Man’s Hill. Each of these represents discontinuous segments of the main
mineralized system. The South- Akyempim deposits are located 2 km southwest of the Wassa Main deposit
on the northern end of a mineralized trend parallel to the Wassa Main trend.
Mineralization is hosted in highly altered multi-phased greenstone-hosted quartz-carbonate veins
interlaced with sedimentary pelitic units. It is structurally controlled and related to vein densities and
sulphide contents.
Wassa mineralization is quite old and has been affected by several phases of deformation since
emplacement. Two major folding events were likely emplaced early in the deposit’s deformational history,
with Gold mineralization later remobilized into the hinges of a tight folding event and finally, the deposit
scale fold which influences the open pit configuration.
Remobilized gold in the hinges of the tight folding event are the primary underground mining targets and B
Shoot and F-Shoot are the two main zones. These zones plunge to the south at approximately 20 degrees
with Mineral Resource now defined more than 800 m south of the current underground Mineral Reserve.
1.5.2 Regional Deposits
The Hwini Butre concession is underlain by three deposits: Adoikrom, Dabokrom and Father Brown, which
are all characterized by different styles of mineralization within the Mpohor mafic complex, which consists
mainly of gabbroic and gabbro-dioritic intrusive horizons.
At Father Brown and Dabokrom, mineralization is associated with quartz vein systems that are locally
surrounded by extensive, lower grade, disseminated quartz stockwork bodies, especially at Dabokrom. At
Adoikrom, the mineralization is shear hosted and characterized by the absence of quartz veins; gold is
associated with fine grained pyrite and intense potassic alteration. NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The Benso concession is underlain by four main deposits: Subriso East, Subriso West, G Zone and I Zone
which all have a similar style of mineralization.
The Benso deposits are hosted in two dominant rock types, Subriso West and I Zone are hosted within
Intermediate feldspar porphyry intrusives and meta-volcanics, whereas Subriso East occurs along the
contact between carbonaceous phyllites and meta volcanics. Mineralization at Benso is associated with
late deformational stages of the Eburnean orogeny and deposits are shear hosted along subsidiary
structures.
The Chichiwelli deposit consists of two sub-parallel mineralized trends hosting two distinct types of
mineralization. The Chichiwelli West trend is a shear zone hosted deposit with a quartz, carbonate, sericite
and potassic alteration assemblage, the mineralization is associated with pyrite. The Chichiwelli East trend
is a quartz vein associated deposit with an ankerite and sericite alteration assemblage. Mineralization is
also associated with pyrite along vein selvages and in the wall rocks.
1.6 Drilling and Sampling
Drilling is carried out by diamond core (DD), reverse circulation (RC) and RAB/air-core techniques. Surveys
are conducted on drill hole collars (by total station) and downhole (by either multi-shot downhole camera,
or gyro instrument for deeper holes).
A standardized approach to drilling and sampling is applied where typically, sampling is carried out along
the entire mineralized drilled length. Sampled spacing is 1.0 m for RC and for DD samples according to
mineralization, alteration or lithology. Core is split into equal parts along a median to the foliation plane to
ensure representative samples for assaying. The remaining half core is retained for reference and
additional sampling if required.
Sample preparation on site is restricted to core logging and cutting, or RC and RAB sample splitting.
Facilities consist of enclosed core and coarse reject storage facilities, covered logging sheds and areas for
the splitting of RC and RAB samples (with Jones riffle splitter).
From site, samples are transported by road to the primary laboratory in Tarkwa for sample preparation and
chemical analysis. Sample security involves:
- Chain of custody of samples to prevent inadvertent contamination or mixing of samples; and
- Rendering active tampering of samples to be as difficult as practicable.
As the samples are loaded, they are checked and the sample numbers are validated. The sample dispatch
forms are signed off by the transport driver (dispatched by the laboratory) and a GSR representative.
Sample dispatch dates are recorded in the sample database as well as the date when results are received.
Sample assays are performed at either the Wassa Site Lab, SGS or Intertek (formerly TWL), with both
independent labs located in Tarkwa. GSR submits quality control samples to each lab for testing purposes.
Both SGS and Intertek laboratories are independent of GSR and are accredited for international
certification for testing and analysis.
1.7 Data Verification
Core logging and sampling procedures adopted by GSR are consistent with industry standards and validated
by external consultants checking logging against the remaining half-core with no major errors identified.
Procedures are in place with several steps to verify the collection of drill hole data and minimize potential
for data entry errors. Data entry and database management involves logging of holes directly into an SQL
Acquire database via laptop computers linked to the main database, with built-in validation tools designed
to eliminate erroneous data entry.
Analytical data is checked for consistency by GSR personnel:
- Upon receipt of digital assay certificates; the assay results, along with the control sample values,
are extracted from the certificates and imported into the Acquire database;
Page 18NI 43-101 Technical Report (March 2021) Wassa Gold Mine
- Failures and potential failures are examined and depending on the nature of the failure,
re-assaying is requested from the primary laboratory; and
- Analysis of quality control data is documented, along with relevant comments or actions
undertaken to either investigate or mitigate problematic control samples.
GSR relies on the laboratory operators’ QA/QC processes for assaying, as well as GSR’s own independent
QA/QC program. The GSR program includes inserting blanks, certified reference materials (aka: standards)
and pulp or coarse reject duplicates into sample batches before sample lab submission. QA/QC procedures
required >=10 % of the samples submitted to the independent laboratories are check samples.
1.8 Metallurgical Test Work
Metallurgical test work for underground ore was completed as part of the 2015 underground feasibility
study. The test work program showed general consistency with ores previously treated from the open pits.
This has subsequently been confirmed by actual processing results where, since 2015, overall plant
recoveries between 94-96% have been achieved.
1.9 Mineral Resource Estimate
The MRE has been updated for the on the basis of RC and DD drilling at four properties – Wassa, Hwini
Butre, Benso and Chichwelli. At Wassa, 30,067 drill holes for 1,353,740 m used to estimate a Long-Range
Model and 2,875 drill holes for 544,233 to estimate a short-range model (SR model), limited to the mine
area. The Father Brown/Adoikrom MRE has been updated with 3,736 drill holes for 154,589 m. The Benso
MRE was updated using 3,162 drill holes for 130,506 m and Chichiwelli used 506 drill holes for 33,494 m.
Data was validated prior to use in estimation and is considered fit for the purposes of Mineral Resource
estimation by the Qualified Person (QP).
Mineralization was modelled via grade shells at Wassa. The long-range (LR) model used indicator
methodology and the SR model used the raw assay data to interpolate grade shells. The halo domain was
interpreted at 0.4 g/t Au and the high grade/mineralization domain was interpreted at 1.5 g/t Au. Both cut
offs were determined by visual inspection and separated different grade populations in the data. Structural
trend surfaces informed the mineralization interpolation and orientation of search ellipses for both models.
At Father Brown and Adoikrom, GSR and Resource Modelling Solutions (RMS) used a vein modelling
technique, where the vein unit is modelled by estimating the position of the vein and thickness, hanging
wall, high grade and footwall. At Benso, mineralization and oxidation wireframes were created by GSR.
The mineralization zones of Benso are structurally controlled with gold emplacement related to the density
of quartz veining and sulphide content. At Chichiwelli, mineralization wireframes were interpreted at a
nominal 0.5 g/t Au cut off. Mineralization is structurally controlled with gold emplacement related to the
density of quartz veining and sulphide content. The mineralization hosting structures generally trend
north-south and dip moderate-steeply to the east at 60°.
Assay data was composited (3 m for Wassa LR model, 2 m for Wassa SR model, 2 m for Benso and
Chichiwelli), top cut based on review of population disintegration via probability plots. Variograms were
modelled where possible, to characterize the grade continuity in grade estimation.
Grades were estimated using ordinary kriging into parent cells for all deposits. At Wassa (long-range and
short-range) using locally oriented search ellipses, based on structural trends. Three search passes with
successively larger search ranges were used to estimate grades into blocks. The LR model had a block size
of 10 x 10 x 5 m and the SR model had a block size of 1 x 2.5 x 2.5 m. In situ dry bulk density has been
estimated to be 2.80 t/m3 based on measurements by GSR and Intertek in 2017 and 2018.
Block sizes at Father Brown and Adiokrom models were 1 x 2 x 2 m (X x Y x Z) chosen to reflect the
geometry of the deposit. A density of 2.70 t/m3 was assigned. At Benso, the block size chosen was 12.5 x
25 x 10 m (X x Y x Z) to reflect the average spacing of drill fences along strike. Grade was estimated into
mineralization domains with soft boundaries between oxidation units, using four search passes. A density
of 1.80 t/m3 for oxide and 2.70 t/m3 for fresh was assigned. A block size of 12.5 x 25 x 8 m (X x Y x Z) was
Page 19NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 20
chosen for Chichiwelli, grades were estimated in four search passes and a density of 1.80 t/m3 was assigned
to oxide and 2.68 t/m3 to fresh.
Validation was completed via inspection of swath plots, cross sections, mean grade comparisons between
composites and blocks.
The basis of the Mineral Resource classification included confidence in the geological continuity of the
mineralized structures, the quality and quantity of the exploration data supporting the estimates,
confidence in the density measurements and the geostatistical confidence in the tonnage and grade
estimates. Reasonable prospects for eventual economic extraction (RPEEE) was informed via pit shell
optimization for open pit Mineral Resources (Benso, Chichiwelli, HBB Other) and cut off grade estimation
for underground mineral resources (Wassa, Father Brown, Adoikrom). A gold price of US$1500 /oz and
costs from the operations were used in pit shell optimization and cut off grade estimation.
- The Mineral Resource estimate complies with the requirements of National Instrument 43-101 and
has been prepared and classified in accordance with the 2014 CIM Definition Standards and 2019
Best Practice Guidelines.
- Measured and Indicated Mineral Resources are reported inclusive of Mineral Reserves;
- Underground deposits within the Mineral Resource are reported at a cut-off grade of 1.4 g/t;
- Open pit deposits within the Mineral Resource are reported at a cut-off grade of 0.55 g/t, within
optimized pit shells calculated at a $1,500 /oz gold selling price;
- The Mineral Resource models have been depleted using appropriate topographic surveys;
- Regional OP includes deposits at Benso, Chichiwelli and HBB Others;
- Mineral Resources are reported in-situ without modifying factors;
- No open pit resource has been reported for the Wassa deposit, as engineering studies have
determined Wassa will be mined by underground methods only; and
- All figures are rounded to reflect the relative accuracy of the estimate.
Table 1-2 Wassa Measured and Indicated Mineral Resource, as at 31 December 2020
Table 1-3 Wassa Inferred Mineral Resource, as at 31 December 2020
Measured & Indicated Mineral Resource, at 31 December 2020
Meas. & Ind.
Mineral Resource
at 31 December 2019
Measured Resource
Indicated Resource
Meas. & Ind.
Mineral Resource
Mt
Au g/t
koz
Mt
Au g/t
koz
Mt
Au g/t
koz
Mt
Au g/t
koz
Wassa OP
–
–
–
–
–
–
–
–
–
29.18
1.29
1,206
Wassa UG
5.90
4.45
843
18.96
3.55
2,162 24.85
3.76
3,005 16.20
3.89
2,027
Father Brown
/Adoikrom UG
–
–
–
1.31
7.96
335
1.31
7.96
335
0.91
8.67
254
Regional OP
–
–
–
3.10
1.98
197
3.10
1.98
197
2.51
2.32
187
TOTAL
5.90
4.45
843
23.37
3.59
2,694 29.26
3.76
3,537 48.81
2.34
3,675
Inferred Mineral Resource
at 31 December 2020
Inferred Mineral Resource
at 31 December 2019
Mt
Au g/t
koz
Mt
Au g/t
koz
Wassa OP
–
–
–
0.62
1.31
26
Wassa UG
70.50
3.39
7,689
58.82
3.75
7,097
Father Brown
/Adoikrom UG
2.66
5.30
453
1.88
6.07
367
Regional OP
0.87
1.47
41
0.42
2.14
29
TOTAL
74.02
3.44
8,183
61.74
3.79
7,518NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 21
1.10 Mineral Reserve Estimate
The Mineral Reserve has been calculated with a cut-off grade of 1.9 g/t, which is below 2.4 g/t applied
previously. The change has been driven by lower operating costs, achieved through increasing
underground mining rates that have been sustained through 2019 and 2020 and validated by an
assessment during 2020 which showed the optimal NPV for the Mineral Reserve will be achieved at a
cut-off of 1.9 g/t and ore mining rate of 5,000 t/d (1.8 Mtpa).
Modifying factors are applied to stopes at 5.0% diluton and 96.1% recovery and 0.0% diluton and 100.0%
recovery for development, which are based on actual performance to end-November 2020.
The Mineral Reserves have been prepared in accordance with the 2014 CIM Definition Standards and 2019
Best Practice Guidelines.
Material is included in the Mineral Reserve as follows:
- The Mineral Reserve estimate complies with the requirements of National Instrument 43-101 and
has been prepared and classified in accordance with the 2014 CIM Definition Standards and 2019
Best Practice Guideline.
- The Mineral Reserve is reported at a cut-off grade of 1.9 g/t, calculated at a $1,300 /oz gold selling
price;
- Modifying factors are applied as 5.0% dilution and 96.1% recovery for stopes;
- Material based on Measured Mineral Resources are reported as Proven Mineral Reserves;
- Material based on Indicated Mineral Resources are reported as Probable Mineral Reserves;
- Material based on Inferred Mineral Resources are excluded from Mineral Reserve;
- Economic analysis of the Mineral Reserve demonstrates economic viability at $1,300 /oz gold price;
and
- All figures are rounded to reflect the relative accuracy of the estimate.
Table 1-4 Wassa Mineral Reserve, as at 31 December 2020
1.11 Mining Methods
1.11.1 Mine Design
Mining is by underground with trackless access by decline (1:7 gradient), operated by GSWL personnel. The
method is long hole open stoping (LHOS), mostly with transverse uphole stopes, in 25 m lifts, mined top
down, in primary/secondary sequence. Stable unsupported stope heights are up to 100 m and stopes are
mined to full orebody width.
The mine is divided into Panels, which reflect progressive stages of capital development. The Mineral
Reserve includes Panels 1, 2 and 3, which lie between 150-650 m depth.
The December 2019 Mineral Reserve proposed to extract material below the B-Main and 242 pits by open
pit methods. This has changed to underground extraction (Panel 3) based on trade off studies during 2020
which concluded underground extraction provided improved selectivity and reduced capital demand.
Mineral Reserve, at 31 December 2020
Mineral Reserve
at 31 December 2019
Proven Reserve
Probable Reserve
Mineral Reserve
Mt
Au g/t
koz
Mt
Au g/t
koz
Mt
Au g/t
koz
Mt
Au g/t
koz
UG, Panels 1 & 2
4.28
3.28
451
4.48
2.99
430
8.75
3.13
881
7.42
3.72
889
UG, Panel 3
–
–
–
2.06
2.94
195
2.06
2.94
195
–
–
–
Open Pit
–
–
–
–
–
–
–
–
–
9.92
1.57
500
Stockpiles
0.69
0.58
13
–
–
–
0.69
0.58
13
1.06
0.62
21
TOTAL
4.97
2.91
464
6.54
2.97
625
11.50
2.94
1,089 18.41
2.38
1,410NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 22
Panels 1 and 2 contain Proven and Probable Mineral Reserve. Panel 3 contains only Probable Mineral
Reserve, plus Inferred Mineral Resource which is excluded from the plan informing the Mineral Reserve.
Panels 1 and 3 leave 6-10 m intact rock pillars between stopes, with ad-hoc waste rock fill to enable pillar
recovery or for simple waste disposal.
Panel 2 is planned for paste backfill. Primary stopes have been extracted, with voids awaiting
commissioning of the paste fill plant in early 2021. Once primary stopes are filled, secondary stope
extraction will commence. Stopes are up to 100 m high and are separated vertically by sill pillars which will
be recovered after stopes above and below are extracted and filled.
Table 1-5 Wassa, mine design quantities for Mineral Reserve plan
1.11.2 Geotechnical
Geotechnical assessments have been completed and the rock mass quality is classified Very Good, using
Barton’s (Barton et al, 1974) classification and Geological Strength Index (GSI) rating systems.
In-situ stress measurements have been taken and mining induced seismicity is not expected to have an
impact until mining approaches 1,000 m depth (Mineral Reserve is down to 650 m depth).
Geotechnical design for development has been done using Barton’s Q support classification and
development excavations lie within Category 1, “No Support Required”, although and minimum standard
pattern is applied, consisting of friction bolts and mesh to the back and upper walls of all headings.
Geotechnical design for stopes has been done using the Stability Graph method to determine the stable
stope design geometry and stope geometries contained in Table 1-6.
Table 1-6 Stable stope dimensions for Mineral Reserve plan
Panels 1-2
B-Shoot
Panel 3
B/F-Shoot
Panel 3
242
Ore Mined, by Panel
‘000 t
8,755
1,245
818
g/t
3.13
2.71
3.30
‘000 oz
881
109
87
Ore Mined, Total
‘000 t
10,818
g/t
3.09
‘000 oz
1,076
Development, Total
m
44,173
Dev’t Capital
m
20,392
Dev’t Operating
m
23,781
Vertical Development
m
2,776
Mined to Waste
‘000 t
2,469
Paste Backfill
‘000 m3
2,967
Stope Dimension
Transverse Stope
Longitudinal Stope
MIN
MAX
Design (m)
MIN
MAX
Design (m)
Height
m
25
100
100
<15
25
25
Strike Length
m
25
25
25
<60
70
70
Width across Strike
m
15
30
25
<15
15
15
Dip, end/side-walls
65°
65°
65°
65°
65°
65°NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 23
1.11.3 Ventilation
The ventilation network for Panels 1 and 2 is planned to provide 50 m3 /s per working area for up to 9
working areas with total airflow of 590 m3 /s.
Total airflow is currently 440 m3 /s and will be increased to the design flows with addition of two new
5.5-6.0 m diameter shafts (one each for intake and exhaust) which are budgeted in 2021 and 2022. Both
shafts will be located at the southern end of Panel 2.
The Panel 3 B-Shoot area will connect to the Panel 1 -2 network and will enable increase airflow with an
additional exhaust raise planned to be collared in the saddle between the Main and South-east pits.
The Panel 3 242 area will be ventilated with an independent network incorporating an exhaust drive mined
from the Main pit connecting to the 242 ramp which will have a portal in the 242 pit. Up to 190 m3 /s will
flow through the 242 ramp with fans placed in the exhaust adit portal.
1.11.4 Mining Schedule
Table 1-7 Mining schedule quantities for Mineral Reserve plan
CY21
CY22
CY23
CY24
CY25
CY26
Definition Drilling
Resource Dev’t & Infill
‘000 dd.m
36.0
5.0
15.0
5.0
–
–
Grade Control
‘000 dd.m
13.5
12.3
13.1
12.2
6.5
–
Total Dev’t
‘000 dd.m
49.5
17.3
28.1
17.2
6.5
–
Development
Capital
m.adv
2,582
5,943
6,756
5,111
–
–
Operating
m.adv
7,272
4,996
5,289
5,926
296
–
Total Dev’t
m.adv
9,855
10,939
12,045
11,037
296
–
Vertical Development
v m
977
891
464
443
–
–
Backfill
‘000 fill.m3
546
597
592
621
445
166
Material Movement
Waste, tonnes
‘000 t
463
657
737
609
3
–
ROM, tonnes
‘000 t
1,784
1,826
1,804
1,939
2,020
1,445
ROM, Au grade
g/t
3.08
3.11
3.29
3.07
2.94
3.10
ROM, cont.Au
‘000 oz
176.7
182.5
190.6
191.3
191.0
144.1
Total Movement
‘000 t
2,247
2,483
2,541
2,549
2,023
1,445
Haulage
Tonnes x Kilometres
Mtkm
6.8
8.0
8.7
9.3
6.7
4.8
Avg. Distance
km
3.01
3.22
3.43
3.64
3.33
3.33
1,076.3
13,287
44.3
3.33
20,392
23,781
44,173
2,776
2,967
2,469
10,818
3.09
Total/avg
118.6
61.0
57.6NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 24
Figure 1-1 Underground Production History and Mineral Reserve plan
1.11.5 Mobile Equipment
The current mobile equipment fleet will continue to be used and progressively move toward standardized
machine types:
- Development Jumbos: continue current twin-boom machine, nominally Sandvik DD421;
- Production Drills: continue current 89-115 mm top-hammer, nominally Sandvik DL421;
- UG Loaders: current mixed fleet of 18 t units, progress toward 21 t, nominally Sandvik LH621; and
- UG Trucks: current fleet of 40 t units, progress toward 60 t machines, nominally Volvo A60H.
Table 1-8 Mobile fleet purchase schedule for Mineral Reserve plan
1.12 Recovery Methods
The Wassa processing plant is a conventional CIL plant with a four stage crushing circuit (p80 <8 mm)
feeding two independent ball mills of 3 MW each (p80 <75 μm).
The grinding circuit includes gravity recovery by Knelson concentrators and intensive leach in an Acacia
reactor. Cyclone underflow has cyanide and oxygen added prior to pumping to leach circuit via the in-line
reactor pipeline. The CIL circuit consists of six stages of agitated leach with an residence time of 18-20 h at
full capacity.
Loaded carbon is acid washed and stripped and gold is electrowon onto steel mesh prior to smelting to
produce doré bars.
Development Jumbo
4
5
5
5
1
–
Production Drill
2
2
2
3
3
2
UG Loader
6
5
4
4
3
3
UG Truck
8
9
7
8
6
4
ROM & Ancillary
9
1 0
1 0
1 0
8
6
CY26
Machine Type
CY21
CY22
CY23
CY24
CY25NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 25
Table 1-9 Processing schedule quantities for Mineral Reserve plan
Figure 1-2 Processing Production History and Mineral Reserve plan
CY21
CY22
CY23
CY24
CY25
CY26
Feed, from Underground
Tonnes
‘000 t
1,711
1,893
1,996
2,228
2,001
338
Au grade
g/t
3.14
3.01
2.95
2.95
2.89
3.03
cont.Au in Feed
‘000 oz
173
183
190
211
186
3 3
Feed, from LG Stockpile
Tonnes
‘000 t
361
100
–
–
–
225
Au grade
g/t
0.62
0.61
–
–
–
0.61
cont.Au in Feed
‘000 oz
7
2
–
–
–
4
Total Processed
Tonnes
‘000 t
2,072
1,993
1,996
2,228
2,001
563
Au grade
g/t
2.70
2.89
2.95
2.95
2.89
2.06
cont.Au in Feed
‘000 oz
180
185
190
211
186
3 7
Recovery
g/t
94.4%
94.3%
94.1%
93.9%
93.6%
90.8%
Au Produced
‘000 oz
170
175
178
199
174
3 4
Total/avg
10,167
2.99
976
686
0.62
1 4
10,852
2.84
990
93.9%
930NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 1-3 Gold Production History and Mineral Reserve plan
1.13 Infrastructure
Surface infrastructure to support the mining and processing operations is in place and includes:
- Access roads;
- Electrical power supply – access to grid, on-site generation and site distribution;
- Waste storage areas and open pit water storage areas, including water diversion structures;
- Main exhaust fans for underground ventilation;
- Processing facilities for processing up to 2.7 Mtpa;
- 4,000 tpd paste plant, recently completed;
- 2 Tailings Storage Facilities (TSF) – TSF 1 is being revegetated and TSF 2 is active;
- Maintenance workshops and site electrical distribution infrastructure;
- Site administration buildings; and
- Accommodation camp.
The mining and processing of the Mineral Reserve does not require any major upgrades to the site surface
infrastructure, other than for the ventilation outlined in Section 0.
TSF design capacity exceeds requirements for the Mineral Reserve plan, without accounting for tails which
will be used for paste backfill.
The design of TSF 2 meets the requirements of the Minerals and Mining (Health, Safety and Technical)
Regulations, 2012 (L.I. 2182) and takes due consideration of the recommendations of the International
Committee on Large Dams (ICOLD), the Australian Committee on Large Dams (1999) and the Canadian Dam
Association guidelines (2007).
The minimum Factor of Safety (FOS) values calculated for all conditions on both the downstream and
upstream slopes which were found to meet, and in some conditions exceed, the Minerals and Mining
(Health, Safety and Technical) Regulations, 2012 (L.I. 2182) requirements for factors of safety.
Page 26NI 43-101 Technical Report (March 2021) Wassa Gold Mine
1.14 Environmental Studies, Permitting and Social or Community Impact
There is a successful history of permitting, environmental and social risk management at Wassa
1.14.1 Sustainability
GSR supports, is subject to and / or incorporates enhanced disclosure on a range of international
requirements including:
- Human Rights, via the UN Sustainable Development Goals
- Anti-Corruption, through Ghana’s designation as Extractive Industries Transparency Initiative
compliant
- Voluntary codes, including International Cyanide Management Code certification; Responsible Gold
Standard and the Responsible Gold Mining Principles
- Resettlement, land acquisition and compensation, through conforming to the International Finance
Corporations’ Performance Standard 5 on Land Acquisition and Involuntary Resettlement.
There are corporate assurance processes in place, including independent reviews, audit and/or validation
to ensure conformance with the codes and standards.
1.14.2 Environmental Considerations
The first Environmental Certificate for Wassa (and all other managed concessions) was received in
September 2006 and is maintained in good standing with submission of and Environmental Management
Plan (EMP) every three years, with the most recent Environmental Certificate issued in 2020.
The EMP is supported by:
- Surface water management, with an emphasis on diversion to minimize contact water.
- Hydrogeology, which concluded in 2016 and 2019 that expected drawdown will not have significant
impact on community ground water boreholes.
- Geochemistry: analysis has consistently shown ore and waste lithologies, are generally not acid
generating (NAG) which is validated by over two decades of mining.
- Water Quality:
o Surface water in vicinity of the open pits, conforms to the EPA Effluent Quality Guidelines;
o Underground drainage studies indicate that water quality guidelines be met with
discharges predicted to be generally neutral to alkaline with low concentrations of TDS,
sulphate and metals. This is validated by routine sampling results.
- Air Quality is routinely monitored and an array of dust suppression mitigations are employed
during dry season conditions.
- Noise is routinely monitored at neighbouring villages and results show noise emanations are not the
result of Wassa activity.
- Vibration has been modelled and results conform to regulatory limits, which has been validated by
monitoring results.
- Biodiversity surveys have been conducted for baseline establishment and measuring impacts.
o Flora: Species of conservation significance are actively propagated for revegetation use and
areas identified to host quality unprotected remnant forest are specifically avoided;
o Fauna: A 1996 study found no species of small mammal, bats, birds, herpetofauna, or
amphibians of outstanding conservation merit. Several species of large mammal with
conservation significance were located but observation required traversing over 10 km into
a Forest Reserve to observe, likely due to high hunting pressures and impacts of logging.
Page 27NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 28
1.14.3 Social Considerations
The main areas of focus for socio-economic improvement are: health, education, electricity and water
supply, and livelihood opportunities. Social investment initiatives include:
- Golden Star Development Foundation: GSR’s main partnership vehicle to implement a variety of
community development projects and programs.
- Golden Star Oil Palm Plantation: GSOPP is a community-based oil palm plantation company
established in 2006 as a non-profit subsidiary of GSR.
- Capacity Building and Livelihood Enhancement: The Golden Star Skills Training and Employability
Program (GSSTEP) provides skills training in non-mining sectors, increasing economic diversity.
- Local Procurement: The GSWL MOU on Local Employment and Contracts builds on the history of
building local procurement capacity around Wassa.
Unauthorized small-scale mining (galamsey) occurs on and around the Wassa leases. In addition to the
initiatives above, GSWL conducts engagement programs and collaborates with the Minerals Commission,
legal small-scale mining associations and community organizations to cede areas of concessions to facilitate
legal small-scale mining, along with appropriate security around active mining areas. With this approach,
GSR has the opinion that galamsey around Wassa has little potential to impact current or future operations.
1.14.4 Closure Planning
Closure concepts and provisional plans are required for permitting and updated three-yearly in the EMP.
The Asset Retirement Obligation estimate is $19.83 M and Practical Closure is estimated at $14.31 M.
1.15 Capital and Operating Costs
Capital and operating cost estimates apply the following bases:
- All costs are in US$ for both historic actuals and forward looking expenditures. Majority of costs
(including local Ghana) are aligned to US$, negating the effect of exchange rates.
- Expenditures aligned to physical schedules over the life of the project.
- Forward estimates calibrated to 2020 actual spend (Jan-Dec 2020).
1.15.1 Capital Costs
Capital costs have been classified into growth (to expand or increase capacity of the operation from the
current established base) and sustaining (sustain the established base) capital.
Table 1-10 Capital Cost Summary for Mineral Reserve plan
Mine Development
$M
Mining UG
$M
Definition Drilling
$M
Processing
$M
Site G&A
$M
TSF
$M
Mobile Fleet
$M
Projects, Ventilation
$M
Projects, Other
$M
Total
$M
Unit Cost per Proc.t
$/t
Unit Cost per rec.oz
$/oz
Sustaining Capital
51.7
33.2
–
5.5
18.3
9.8
18.2
–
–
136.5
75.69
757
Growth Capital
26.6
–
8.6
–
–
–
–
7.5
5.0
47.7
24.53
281
7.5
5.0
184.3
16.02
180
Total/avg
78.3
33.2
8.6
5.5
18.3
9.8
18.2NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 29
1.15.2 Operating Costs
Operating costs have been estimated as follows:
- Analysis of 2020 actual spend;
- Analysis of share of fixed and variable cost for each activity, at the cost element level (eg: fuel,
labour, consumables);
- Calculation of periodic spend, driven by scheduled units of a physical activity; and
- Review of step change fixed costs where higher physical rates are planned.
Table 1-11 Cost Estimate, Operating for Mineral Reserve plan
Table 1-12 Operating Cost Summary for Mineral Reserve plan
1.16 Economic Analysis
The Mineral Reserve has been valued using discounted cash flows to determine NPV, as at 31 December
- It shows positive cash flow at the $1300 /oz reserve selling price and supports declaration of a
Mineral Reserve.
For the Mineral Reserve:
- Growth Capital:
$47.7 M;
- Development Duration: nil (in production);
- Production Phase Life: 6 years (2021-2026);
- Production Phase Rate: 171 koz/yr;
- All-in Sustaining Cost: $881 /oz; and
- After-tax NPV5%:
o Base Case ($1,300 /oz):
$121.2 M (100% basis)
o Consensus Case (av $1,751 /oz):$335.6 M (100% basis)
(Consensus of 27 banks and financial institutions, as at the end of January 2021)
UofM
Mining, Development
m.adv
Mining, Production
stope.t
Mining, Backfill
fill.m3
Mining, Surface Haulage
ROM.t
Mining, Overheads
ug.all.t
Mining, Geology
ug.ddm.op
Processing
mill.t
G&A
mill.t
Refining
rec.oz
1.27
9,665
Description
Lateral Development
Stope Material
Paste Backfill
ROM Material
Driving Quantity
Resultant Rate
$/ROM.t mined
7.05
18.24
4.87
220,378
Tonnes Processed
20.37
99,942
Tonnes Processed
9.24
Grade Control Drilling, UG
13,767
0.89
24,399
Total Material Mined, UG
2.26
197,269
52,640
Expenditure
$ ‘000
76,247
4,610
Au Produced
0.43
CY21
CY22
CY23
CY24
CY25
CY26
Total Operating
Mining
$M
70.1
65.5
66.4
70.5
60.8
40.7
Processing
$M
37.1
39.6
35.2
37.0
38.1
33.4
Site G&A
$M
17.5
17.9
17.2
17.5
17.7
16.7
Total Operating
$M
124.7
123.1
118.8
125.1
116.6
90.7
Unit Cost per Proc.t
$/t
64.11
57.89
65.85
64.48
57.74
54.32
Unit Cost per rec.oz
$/oz
733
696
658
694
652
657
Total/avg
220.4
104.6
699.0
60.76
682
374.0NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 30
1.17 Preliminary Economic Assessment of the Southern Extension Zone
The PEA is entirely based on an Inferred Mineral Resource and there is no certainty that further geological
drilling will result in the determination of higher Mineral Resource classification, nor that production and
financial outcomes will be realized. Mineral Resources that are not Mineral Reserves do not have
demonstrated economic viability.
The PEA of the Southern Extension zone has been completed with the following limits and scope:
- Inferred Mineral Resource south of 19,240 mN;
- Scoping level mining study:
o Mining method selection and methodology;
o Stope optimization;
o Mine design to determine development quantities which inform cost estimate;
o Ventilation design and modelling;
o Simulation of truck haulage to validate production rate;
o Definition drilling strategy;
o Preliminary scheduling;
- Review of metallurgical test work and processing capacity;
- Review of permitting requirements;
- Estimation of capital and operating cost; and
- Economic analysis.
The PEA shows the Southern Extension project is potentially economically viable with an after-tax NPV at
5% discount rate, of $ 783.5M (100% Basis).
- Growth Capital:
$228.8 M;
- Development Duration: 6 years (Y1-Y6);
- Production Phase Life: 11 years (Y7-Y17);
- Production Phase Rate: 294 koz/yr;
- All-in Sustaining Cost: $778 /oz; and
- After-tax NPV5%:
o Base Case ($1,300 /oz):
$452.2 M (100% basis)
o Consensus Case ($1,585 /oz): $783.5 M (100% basis)
Conversion risk of the Inferred Mineral Resource has been addressed through application of cut-off grades
and modifying factors in the different mining panels. 54% of metal is included in the PEA inventory for
Panels 4 and 5 where there is more definition drilling and the inclusion factor decreases to 48% for the
deeper panels 7 and 8 where definition drilling is more widely spaced. NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 31
Table 1-13 Conversion of Inferred Mineral Resource to PEA inventory
Units
Panel 4
Panel 5
Panel 6
Panel 7
Panel 8
Total
Inferred Mineral
Resource,
in-situ
Mt
7.8
11.5
8.6
19.6
18.6
66
Au g/t
3.0
3.1
2.7
4.0
3.6
3.4
Moz
0.76
1.14
0.74
2.52
2.14
7.3
PEA Inventory
Mt
4.1
5.5
3.1
9.4
7.8
30
Au g/t
3.3
3.5
3.7
4.3
3.8
3.8
Moz
0.42
0.61
0.37
1.31
0.94
3.6
Conversion to PEA
Inventory
%Moz
54%
49%
48%
50%
Cut-off Grade
Au g/t
2.3 g/t
2.9 g/t
–
Modifying Factors,
Stopes
7.5% Dilution
95.0% Recovery
13.0% Dilution
75.0% Recovery
–
Figure 1-4 Processing schedule for Southern Extension PEA
Figure 1-5 Gold Production Schedule for Southern Extension PEANI 43-101 Technical Report (March 2021) Wassa Gold Mine
Realization of the production schedule from the PEA carries a number of risks in addition to those defined
in Section 1.18.2.
- Geology:
The primary risk is that the PEA is based on an Inferred Mineral Resource. As further definition
drilling is completed, current interpretations and estimates of geological continuity, gold grade, and
mineralization volumes may not be realized.
- Mining:
The PEA is based on a scoping level study and assumes increased productivity rates which are
planned but not yet achieved. The main risks to achieving the PEA outcomes are that geotechnical
conditions result in slower production and if operations are unable to achieve development
advance and stope turnover rates.
- Processing:
Limited metallurgical test work has been completed for the PEA mining area. Results generally
suggest processing will be consistent with current operations, but there is minor variability and
further test work may identify that planned recoveries and throughput rates may not be achieved.
- Capital and Operating Costs:
The PEA is based on a scoping level study and with further studies, capital and operating costs,
which are based on current costs and increased productivity, may increase.
There are a number of opportunities specific to the PEA plan as studies progress.
- Geology:
The Inferred Mineral Resource which informs the PEA is open to the north, south and up and down
dip. Should further drilling increase the defined mineralization, project life and production rates
may be increased. Further drilling may also confirm the materially higher grades and
mineralization continuity in the deeper Panels 7-8 so that less conservative modifying factors can
be applied.
- Mining:
Stope size and level intervals are consistent with current operations and may be increased as
studies progress, which would reduce development quantities and cost. Haulage optimization
studies and emerging electrification technology may confirm an alternative to the planned diesel
truck system which would result in reduced costs (mostly ventilation) and emissions.
1.18 Conclusions and Interpretations
1.18.1 Conclusions
The following interpretations and conclusions are made by the Qualified Persons in their respective areas of
expertise, based on the review of data contained in this Technical Report.
- Mineral Titles and Agreements, Surface Rights, Royalties and Encumberances:
The required mineral titles, surface and access rights, permits and approvals exist and are in good
standing required to support ongoing operations.
There is a 5% royalty on gross revenue payable to the Government of Ghana.
There is a two-tier gold stream to Royal Gold Inc. and royalty payments and tax to government are
payable prior to the stream payments.
- Exploration, Driling and Data Collection:
The following are appropriate to support estimation of Mineral Resources and Mineral Reserves:
o Understanding of the geological setting, lithologies and structural and alteration controls
on the mineralization;
o Exploration programs completed to date;
Page 32NI 43-101 Technical Report (March 2021) Wassa Gold Mine
o Sampling methods used to collect raw data;
o Sample preparation, analysis and security;
o Quantity and quality of the lithological, structural, collar and down-hole survey data
collected during drilling programs; and
o QA/QC programs to address issues of precision and accuracy.
- Metallurgical Test Work
Test work programs have been completed which are reflective of processing plant performance
and used samples which reasonably represent the plant feed scheduled in the Mineral Reserve
plan.
No significant metallurgical issues were identified and this has been validated by actual plant
performance.
- Mineral Resource Estimates
Mineral Resources are estimated as:
o Measured and Indicated Mineral Resource: 29.3 Mt at 3.76 g/t, containing 3.54 Moz; and
o Inferred Mineral Resource: 74.0 Mt at 3.44 g/t, containing 8.18 Moz.
The Mineral Resources have been prepared in accordance with the 2014 CIM Definition Standards
and 2019 Best Practice Guideline. Mining is assumed by underground methods at Wassa and
Hwini Butre, and open pit methods at all other locations.
Mineral Resources have a reasonable chances for of eventual economic extraction, with estimates
constrained as follows, assuming $1,500 /oz gold selling price:
o Open Pit: constrained by open pit optimization shell based on a $1,500 /oz gold selling
price and cut-off grade (0.55 g/t); and
o Underground: constrained by cut-off grade (1.4 g/t).
- Mineral Reserve Estimate
Proven and Probable Mineral Reserves are estimated as 11.5 Mt at 2.94 g/t, containing 1.09 Moz.
The Mineral Reserves have been prepared in accordance with the 2014 CIM Definition Standards
and 2019 Best Practice Guidelines. Mining will be by underground long hole open stoping. The
former open pit component of the Mineral Reserve has been replaced by underground extraction.
Mineral Reserves are supported by a positive economic test assuming $1,300 /oz gold selling price.
- Mining Methods
The mine plan and schedule use:
o Conventional underground mining practices and equipment to carry out long hole open
stoping, consistent with currently employed techniques;
o Demonstrated mining rates based on recent development and stoping performance;
The mine plan includes appropriate consideration of:
o Geotechnical conditions;
o Stope modifying factors;
o Mine ventilation;
o Mine dewatering;
o Scheduling interactions and rates; and
o Mobile fleet capacities.
The introduction of paste fill will require integrating into the stope cycle sequence to enable
secondary stoping to commence.
Page 33NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 34
- Recovery Methods
Recovery methods in the processing plant and forward recovery assumptions (average 94.1%) are
supported by test work and plant history.
The processing plant capacity exceeds mine production in all years for the Mineral Reserve plan.
- Environmental, Permitting and Social Considerations
All required environmental and social regulatory requirements to support ongoing operations are
in place and maintained in good standing.
GSR complies with international requirements on environmental and conservation, human rights,
and anti-corruption. It has adopted voluntary international codes on corporate responsibility in the
areas of cyanide management, TSF design, responsible gold mining and resettlement.
GSWL has posted and periodically updates its reclamation bond ($13.7 M at end of 2020).
For environmental impacts, appropriate studies and surveys have been completed, design features
and management practices are established and monitoring programmes are in place for:
o Water quality;
o Air quality;
o Noise and vibration; and
o Biodiversity.
GSR supports a number of community and social initiatives:
o Golden Star Development Foundation (community and social development projects);
o Golden Star Oil Palm Plantation (agribusiness sponsored by GSR which aims to become self
supporting); and
o Capacity building and livelihood enhancement (skills training, local procurement)
These initiatives proactively aim to build capacity and diversify the economy of local communities
as well as reduce uptake of small-scale illegal mining.
- Capital and Operating Costs
Capital and operating costs have been estimated based on actual 2020 activity costs and 2021
budget costs, projected through the mine plan.
o The growth capital cost for the life of mine is $47.7 M; and
o The sustaining capital cost for the life of mine is $136.5 M.
Unit production costs estimated for the Mineral Reserve are:
o Direct operating cost: $669 /oz;
o All-in sustaining cost: $902 /oz; and
o All-in cost: $964 /oz.
- Economic Analysis of the Mineral Reserve
An economic analysis to support the declared Mineral Reserve was prepared. Using the
assumptions outlined in this Technical Report, the operations show a positive cash flow at the
$1300 /oz reserve selling price and support the declaration of a Mineral Reserve.
o Growth Capital:
$47.7 M;
o Development Duration: nil (in production);
o Production Phase:
6 years, averaging 171 koz/yr;
o All-in Sustaining Cost: $941 /oz; and
o After-tax NPV5%:
▪ Base Case ($1,300 /oz):
$117.3 M (100% basis)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
▪ Consensus Case (av $1,751 /oz):$331.7 M (100% basis)
1.18.2 Risks
Realization of the production schedule from the Mineral Reserve carries a number of risks.
- Geology:
Tightly spaced definition drilling is required which, if not completed sufficiently ahead of
production could cause production delays or unexpected grade outcomes and negatively impact
production and cash flow.
- Mining:
Delivery of the Mineral Reserve plan requires maintaining current productivity for development
and stoping activities. Geotechnical conditions are currently very good, but ongoing review and
management is required to ensure adverse geotechnical results do not adversely impact
production and cash flow.
- Processing:
No material processing risks were identified for the Mineral Reserve.
- Infrastructure:
Delays to commissioning and/or achieving design capacity of the paste backfill plant and mining
system will adversely impact production. The intake and return ventilation shafts are not yet
geotechnically assessed and adverse findings may add cost and/or time to complete the upgrade,
impacting production rates and cash flow.
- Capital and Operating Costs:
Capital and operating costs may significantly increase, particularly if productivity assumptions are
not met or there are adverse movements of major cost components (eg: labour, energy).
- Environmental and Social:
Delivery of the Mineral Reserve plan requires access to personnel outside the local communities
and this may be impacted by both regional (competition, security) and global (pandemic, transport)
factors. Additionally, modernization of practices and technology may reduce reliance on
un/semi-skilled labour, limiting accessibility to jobs for local community members, which may
adversely impact community support and/or increase artisanal mining around Wassa with
commensurate negative outcomes for closure costs and reputation.
1.18.3 Opportunities
A number of opportunities have been identified with potential to add value to the Mineral Reserve plan.
- Mineral Resource:
Upside potential exists for the Mineral Resource from definition drilling to upgrade the large
Inferred Mineral Resource which is the Southern Extension zone and various targets to grow the
defined mineralisation which are not yet tested.
- Productivity and Mine Design:
Mining practices could deliver improved cost and productivity outcomes through application of
technology, geotechnical design optimization and improvements to the paste backfill system after
it reaches steady-state operation.
- Sustainability:
Identified opportunities exist for emissions reduction (electrification, haulage optimization and
application of renewables), water (efficiency and quality preservation) and energy efficiency
(comminution optimization).
Page 35NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 36
1.19 Recommendations
Based on the positive results of the technical and economic analysis of the Mineral Reserve of the Wassa
gold mine, the following actions are recommended:
- Continue definition drilling to support production in Panels 1 and 2 and increase geological
confidence in Panel 3;
- Complete drilling programs with potential to increase the defined mineralization (main Wassa
orebody, local soil sampling anomalies and regional including Father Brown/Adoikrom UG).
- Continue extraction of the Mineral Reserve by underground methods, at the optimized cut-off
grade of 1.9 g/t and transition the upper areas previously planned for open pit mining, to more
selective underground extraction to improve margins and bring forward production;
- Continue delivery of major capital projects (paste backfill plant and system, ventilation upgrade
with two new shafts to surface, development of Panel 3 underground);
- Continue processing using CIL treatment in the Wassa processing plant;
- Continue current governance practices to ensure ongoing statutory compliance and license to
operate is maintained, including management systems, social investment programs and corporate
responsibility programs; and
- Investigate potential to expedite stoping from the Panel 3 (242 and B-Shoot).
For the Inferred Mineral Resource in the Southern Extension Zone, based on the positive results of the
preliminary economic assessment, the risks and opportunities identified, and conclusions made, the
following actions are recommended to progress the project:
- Continue definition drilling to increase geological confidence to enable upgrading classification of
the Inferred Mineral Resource for Panels 4 and 5;
- Commence technical studies to feasibility study level for the disciplines of metallurgy, geotechnics,
ventilation and mine design;
- Complete option and trade-off studies to optimize the project plan, including assessment of
alternative haulage options (eg: shaft, conveyor), equipment selection (eg: semi/full automation,
battery electric) and mine design (level interval);
- Conduct trials in the current operation to validate the proposed stoping methodology in Panels 4-8;
- Investigate electrification and renewable energy options to reduce emissions;
- Complete site water balance model and assess opportunities to improve water efficiency and
reduce discharged contaminants; and
- Review crushing and grinding circuit to optimize comminution efficiency.
The progressive development plan proposed for the Southern Extension zone has the project being
developed in three major phases of definition drilling and capital investment.
- Panels 4 and 5: Resource development drilling in progress and studies planned to inform and
investment decision at the end of project year 2 (Y2).
- Panels 6 and 7: Resource development drilling in Y6-7, decline development starting Y6 and stope
production in Y8.
- Panel 8: Resource development drilling in Y10, decline development starting Y10 and stope
production in Y12.
The project execution plan for progressing to production from the Southern Extension zone outlines the
activities for only the first phase (Panels 4 and 5) to reach an investment decision with a feasibility level
study and the potential timeframe to production. The estimated cost to deliver the feasibility study is
$14.0 M, which is mostly for definition drilling ($13.2 M).NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 1-6 Project Execution Plan, Southern Extension Panels 4 and 5
Page 37NI 43-101 Technical Report (March 2021) Wassa Gold Mine
2 INTRODUCTION
2.1 Terms of Reference
This Technical Report has been prepared to meet the requirements defined by Form 43-101F1, by and for
Golden Star Resources, describing the Wassa gold mine in Ghana. The report provides updated information
on the currently operating mine, including an updated Mineral Resource and Mineral Reserve estimate.
The Report also contains the summary of a Preliminary Economic Assessment (PEA) completed in support
of the potential expansion of the underground mine to extract the Inferred Mineral Resource in the
Southern Extension zone (2020 PEA).
The PEA has been prepared within the following framework:
- Underground mining rate increased to fully utilise the installed processing capacity (2.7 Mtpa);
- Production schedules to appropriately consider conversion risk of the Inferred Mineral Resource;
- Methodologies and design quantities based on proven, currently available technologies;
- Costs to reflect current operational experience; and
- Minimise capital demand needed to establish full production.
The intent of the framework is to present a deliverable PEA plan which can be executed with GSR’s current
operational and financing capacity. Potential enhancements outside this framework are presented as
opportunities outside of the PEA outcomes and can be investigated as part of the forward work plan.
The 2020 PEA has no impact on the Mineral Reserves, nor on the key assumptions and parameters
supporting the Mineral Reserves. The Mineral Reserves are current, valid and do not rely on any of the
assumptions made in the 2020 PEA.
The 2020 PEA is conceptual and outlines a mining inventory which is entirely based on an Inferred Mineral
Resource. Inferred is the lowest level of confidence for a Mineral Resource and there is no certainty that
further geological drilling will result in the determination of higher Mineral Resource classification, nor that
production and financial outcomes will be realized. Mineral Resources that are not Mineral Reserves do
not have demonstrated economic viability.
The Mineral Resources and Mineral Reserves have been prepared in accordance with CIM Definition
Standards for Mineral Resources and Mineral Reserves, adopted by the CIM Council on May 10, 2014, and
the CIM Estimation of Mineral Resources and Mineral Reserves Best Practice Guidelines, adopted by CIM
Council on November 29, 2019.
References within this report to “GSR” include Golden Star Resources (GSR) and Golden Star Wassa Limited
(GWSL) as the context requires.
Golden Star is a Canadian federally-incorporated international gold mining and exploration company,
producing gold in Ghana, West Africa. This report has been prepared to satisfy GSR’s obligations as a
reporting issuer in Canada.
Units used in the report are metric units unless otherwise stated. Monetary units are in United States
dollars (US$) unless otherwise stated.
2.2 Wassa Gold Mine
The Wassa Gold Mine is located near the village of Akyempim in the Wassa East District, in the Western
Region of Ghana. It is 80 km north of Cape Coast and 150 km west of the capital Accra. The property lies
between latitudes 5°25’ and 5°30’ north and between longitudes 1°42’ and 1°46’ east. GSWL owns the
rights to mine the Wassa, Benso and Hwini Butre concessions. GSR owns a 90% interest in and manages
GSWL with the Government of Ghana owning the remaining 10%.
Page 38NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 39
2.3 Principal Sources of Information
This Technical Report was prepared by GSR. Information for the report was based on published material, as
well as data, professional opinions, and unpublished material from work completed by GSR. It includes
information provided by and discussions with third party contractors and consultants engaged by GSR.
Section 27 contains the list of reports and documents used in preparation of this report.
Major contributions by contractors and consultants have been reviewed and approved by QP’s as follows:
- Environmental impact assessment studies undertaken by Golder Associates (Ghana and South
Africa);
- Geological modelling:
o Long-range model resource estimate prepared by SRK (Toronto);
o Short-range model wireframe and resource estimate prepared by SRK (Moscow).
- Geotechnical assessment prepared by OreTeck Mining Solutions (Australia);
- Metallurgy and Processing assessment prepared by MineScope Services (Australia);
- Mine Ventilation assessment prepared by SRK (US);
- Tailings storage facility design and geotechnical assessments by Knight Piésold Ghana (the engineer
of record); and
- Paste backfill studies carried out by Outotec (Canada) Ltd.
2.4 Qualified Persons
Matt Varvari (not independent) is the Qualified Person (QP) responsible for overall project management of
the Technical Report and specifically, Sections 1-3, 6, 13, 15-19 and 21-27 of this report. They are a Fellow
of the Australasian Institute of Mining and Metallurgy and have the required qualifications and experience
to act as a QP. Matt is based in London, UK and is employed full-time by GSR as Vice President Technical
Services.
- Mitchel Wasel (not independent) is the QP responsible for Sections 7-12 and 14 of this report. They are
a Chartered Professional of the Australasian Institute of Mining and Metallurgy and have the required
qualifications and experience to act as a QP. Mitch is based in Takoradi, Ghana and is employed full-time
by GSR as Vice President Exploration.
Philipa Varris (not independent) is the QP responsible for Sections 4, 5 and 20 of this report. They are a
Chartered Professional of the Australasian Institute of Mining and Metallurgy and have the required
qualifications and experience to act as a QP. Philipa is based in London, UK and is employed by GSR as
Executive Vice President and Head of Sustainability.
All QP’s have conducted sufficient visits to Wassa site, as detailed in Table 2-1.
Table 2-1 Qualified persons and site visits
2.5 Effective Dates
- Effective date of the Wassa Mineral Resource: 31 December 2020
Company
GSR
GSR
GSR
Responsibility
Overall resposibility for GSR project management.
Mineral Reserves.
Sections 1-3, 6, 13, 15-19 and 21-27.
Mineral Resources.
Sections 7-12 and 14.
Sections 4, 5 and 20.
Site Visit
4 visits to Wassa in 2019-2020
Most recent 23 Nov – 4 Dec 2020
22 years based in Ghana for GSR.
6 visits to Wassa in 2020.
Most recent 12 – 22 Oct 2020
9 yrs in Ghana w ith GSR (2011-2019)
5 visits to Wassa in 2020
Most recent: 23 Nov – 3 Dec 2020
Qualified Person
Matt Varvari
- Mitchel Wasel
Philipa VarrisNI 43-101 Technical Report (March 2021) Wassa Gold Mine
- Effective date of the Wassa Mineral Reserve: 31 December 2020
- Effective date of the Economic Analysis for the Mineral Reserve: 31 December 2020
- Effective date of the Preliminary Economic Assessment: 31 December 2020
2.6 Previous Technical Report
Golden Star Resources filed the following Technical Report on Wassa with an effective date of 31 December
2018:
- Raffield, M., Wasel, M. and Varris, P. NI 43-101 Technical Report on Resources and Reserves,
Golden Star Resources, Wassa Gold Mine, Ghana
Page 40NI 43-101 Technical Report (March 2021) Wassa Gold Mine
3 RELIANCE ON OTHER EXPERTS
In the preparation of this Technical Report, the qualified persons in specific instances relied on studies,
reports, opinions or statements of experts who are not qualified persons. These include:
- Environmental impact assessment studies:
o “Golden Star (Wassa) Limited; Updated Tailings Storage Facility (TSF) 2 Project
Environmental Impact Statement”. Prepared by Golder Associates, November 2016,
regarding environmental impacts as reported in Section 18 and 20.
o “Golden Star (Wassa) Limited; Tailings Storage Facility (TSF) 2 Project Environmental Impact
Statement”. Prepared by Geosystems Consulting, February 2012, regarding environmental
impacts as reported in Section 18 and 20.
o “Wassa Expansion Project Environmental Impact Statement”. Prepared by Geosystems
Consulting, September 2015, regarding environmental impacts as reported in Section 18
and 20.
o “Environmental Impact Statement for the Wassa Project”. Prepared by Wexford Goldfields
Limited (WGL), 2004, regarding environmental impacts as reported in Section 20.
o “The Wassa Project Environmental Impact Statement”. Prepared by Scott Wilson, 2004,
regarding environmental impacts as reported in Section 20.
o “Satellite Goldfields Limited, Wassa Gold Project, Environmental Baseline Study”. Prepared
by SGS Laboratory Services (Ghana) Limited, November 1996, regarding environmental
baseline as reported in Section 20.
- “Final GSR Mining Title Opinion”. Prepared by REM Law Consultancy (Accra), February 2021,
regarding the good standing of the Wassa, Benso and Hwini Butre mining leases as reported in
Section 4.
Page 41NI 43-101 Technical Report (March 2021) Wassa Gold Mine
4 PROPERTY DESCRIPTION AND LOCATION
4.1 Location of Mineral Concessions
The Wassa Mine is located near the village of Akyempim in the Wassa East District in the Western Region of
Ghana, approximately 80 km north of Cape Coast and 150 km west of the capital, Accra. It lies between
latitudes 525’ and 530’ N and longitudes 1°42’ and 1°46’ E. The location of the Wassa Mine is shown in
Figure 1-1.
The Wassa Mine is operated under the Wassa mining lease which was issued on September 17, 1992. The
total surface area of the Wassa Mining Lease is 5,289 Ha, with approximately 595 Ha of disturbance from
GSWL’s activities. GSWL has applied for a reshape of the concession boundary to comply with recent
changes to cadastre grid requirements by the Minerals Commission, which will modify the total area of the
concession to 6,496 ha.
Figure 4-1 Wassa Mine Location in Ghana, West Africa (United Nations, 2018)
Page 42NI 43-101 Technical Report (March 2021) Wassa Gold Mine
In addition to the Wassa mining lease, GSWL holds the Hwini Butre and Benso mining leases, and several
prospecting licences in the Western Region of Ghana. GSWL’s mineral properties are shown in Figure 4-2.
Figure 4-2 Wassa Mine Location in Ghana, West Africa (GSR, 2021)
Figure 4-3 shows the locations of GSWL’s mineral concessions and operations:
- Wassa mining lease: Wassa is an operating underground gold mine comprising the following
mineralization domains: F Shoot, 419, B Shoot, 242, Starter, South-East, Mid-East and Dead Man’s
Hill. SAK comprises several deposits to the west.
- Benso mining lease: comprising the Subriso East, Subriso West, G-Zone, C-Zone and I-Zone
deposits.
- Hwini Butre mining lease: comprising the Father Brown, Adoikrom and Dabokrom deposits.
- Benso (Chichiwelli) exploration property: comprising two mineralized zones, Chichiwelli West and
Chichiwelli East.
- Manso exploration property: located east of Benso and Hwini Butre.
The properties and leases are spread along a trend of approximately 80 km southwest of the Wassa mine.
There are sufficient access and surface rights for GSWL’s operations.
Page 43NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 4-3 Location of operations and infrastructure and concession boundaries (GSR, 2021)
Page 44NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 45
4.2 Mineral Rights
The Constitution of Ghana vests title in every mineral in its natural state to the Government of Ghana. The
exercise of any mineral right in Ghana requires an appropriate mineral title to be issued by the Government
of Ghana acting through the Minister responsible for Lands and Natural Resources. The Minister of Lands
and Natural Resources administers, promotes and regulates Ghana’s mineral wealth through the Minerals
Commission, a governmental organization designed in accordance with the Minerals Commission Act 1993
and the Minerals and Mining Act, 2006 Act 703 (Minerals and Mining Act).
A person must apply to the Minerals Commission and be granted a mineral right by the Minister of Lands
and Natural Resources before they can search, survey, prospect, explore or mine for a mineral anywhere in
Ghana. There are different types of licenses (namely, reconnaissance and prospecting licenses, and mining
leases) for the different mining activities. Each type of licence details the activities that are permitted.
The Government of Ghana holds a 10% free-carried interest in all companies holding mining leases. The
10% free-carried interest entitles the Government to a pro-rata share of future dividends. The Government
has no obligation to contribute development capital or operating expenses.
Table 4-1 sets out the mineral rights held by GSWL (or those in which GSWL has an interest). GSR will from
time to time seek a title opinion from its legal counsel in Ghana to confirm its title in its material mineral
properties, and the good standing of the underlying mineral rights.
Table 4-1 Mineral rights held by GSWL
Name
Type of
Mineral right
No.
Issuing
Authority
Issue Date
Expiry
Date
Surface
Area
Third-Part
Ownership
Comments
Wassa
Mining Lease
LVB
87618/94
Minerals
Commission 17/09/1992 16/09/2022 52.89 km2
Government of
Ghana holds a
10% free
carried interest
Benso
Mining Lease
LVDGAST
37993462020
Minerals
Commission
25/08/2020
24/08/2031
19.45 km2
Government of
Ghana holds a
10% free
carried interest
Hwini Butre
Mining Lease
LVDGAST
38000372020
Minerals
Commission
25/08/2020
24/08/2031
43 km2
Government of
Ghana holds a
10% free
carried interest
Dwaben
(Safric)
Reconnaissance
Licence
LVB1624/06
Minerals
Commission
02/02/2006
(expired in
2020)
26.92 km2
Application to convert
reconnaissance licence
to prospecting licence
submitted to the
Minerals Commission in
November 2020
Benso
(Chichiwelli)
Prospecting
Licence
PL.2/1550
Minerals
Commission
27/09/2007
–
22.46 km2
Notice of grant of
extension of
prospecting licence
issued by the Minerals
Commission in January
2020
Abura
Abura
Prospecting
Licence
PL 2/135
Minerals
Commission
13/12/2018
12/12/2021
65.10 km2
Subject to
option
agreement
with Bowden
Gold Resources
Limited
Manso 1
Prospecting
Licence
PL 2/378
Minerals
Commission 10/01/2005
–
101.6 km2
Application to renew
prospecting licence
submitted to the
Minerals Commission in
August 2020
Manso 2
Prospecting
Licence
PL 2/337
Minerals
Commission 07/09/2007
–
21.38 km2
Subject to
option
agreement
with Pacific
Mining Limited
Application to renew
prospecting licence
submitted to the
Minerals Commission in
September 2020NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The Wassa Mine sits within the Wassa mining lease which comprises an area of 52.89 km2 lying to the north
and south of latitudes 525’ and 530’, respectively and bounded to the east and west by longitudes 142’
and 146’, respectively.
The Wassa mining lease was entered between the Government of Ghana and Satellite Goldfields Limited
(SGL) on September 17, 1992 for a term of 30 years, renewable. In 2002, the mining lease was assigned by
SGL to GSWL with the written consent of the Government of Ghana. GSWL is the registered legal and
beneficial holder of the Wassa mining lease. The Government of Ghana holds 10% of GSWL share capital.
4.3 Royalties and Other Payments; Encumbrances
GSWL pays to the Government of Ghana within thirty days from the end of each quarter a royalty at a rate
of 5% determined based on the total revenue of minerals produced during the quarter. This royalty is
payable prior to any adjustments from the Royal Gold stream (see below). Royalties are paid through the
Commissioner of Internal Revenue.
Payment of annual ground rent is made to the owner of the land except in the case of annual ground rent
in respect of mineral rights over stool lands, which are paid to the Office of the Administrator of Stool
Lands. A holder of a mineral right must also pay to the Minerals Commission an annual mineral right fee
determined based on the type of tenure. GSWL pays annual ground rate and annual fees in relation to all
the mineral rights it holds.
GSR is party to a gold purchase and sale agreement with Royal Gold, Inc. through its wholly owned
subsidiary RGLD Gold AG (RGLD). The agreement was initiated on 6 May 2015, amended on 29 Jun 2018,
17 October 2019 and most recently 30 September 2020. The stream covers all gold produced within
GSWL’s mineral concessions and requires GSR to deliver according to two tiers:
- Tier 1: 10.5% of all production to RGLD at a cash purchase price of 20% of spot gold until 240,000
ounces have been delivered; and
- Tier 2: thereafter, to deliver 5.5% of all production to RGLD at a cash purchase price of 30% of spot
gold.
Pursuant to the terms of the gold sale and purchase agreement, GSR is restricted from granting
encumbrances on the Wassa gold project without RGLD’s consent. In 2019, GSR entered into a credit
facility agreement with Macquarie Bank Limited pursuant to which GSWL’s mineral rights were, with the
approval of the Minister of Lands and Natural Resources and RGLD, encumbered to secure the repayment
of the loan.
At the end of December 2020, the remaining balance of the Tier 1 stream was 120,003 oz. The stream is
treated as a revenue adjustment.
4.4 Historic Environmental Liability and Indemnity
The Wassa operations were permitted under an environmental impact assessment developed for SGL in
- At commencement, Wassa was a heap leach operation fed by the Main pits complex comprising the
interconnected South-East, 242, B-Shoot, F-Shoot, South, Main South, and 419 pits. The predominant
liabilities of the original SGL operations, including heap leach area and waste dumps, have since been fully
encompassed by the GSWL operations.
In 2002, GSR purchased certain assets of SGL and liabilities for the operations transferred. In 2005, GSR
acquired St. Jude Resources (Ghana) Limited (SJR) and, with it, the Hwini Butre and Benso (HBB) properties
and their associated liabilities. Likewise, the development of the HBB operations by GSWL saw the
establishment of infrastructure that fully encompassed the previous areas of disturbance of SJR. The
establishment of the reclamation security agreement with the EPA in 2005 and the associated bond with
the EPA addresses security for reclamation and closure obligations.
There are no other legacy issues associated with the GSWL site.
Page 46NI 43-101 Technical Report (March 2021) Wassa Gold Mine
4.5 Permits and Authorization
In addition to the mineral rights specified in Table 4-1, GSWL requires certain permits and licenses to carry
out its activities, including:
- Mining operating permit:
The Minerals and Mining (Health, Safety and Technical) Regulations, 2012 (L.I. 2182) prescribe
technical and health and safety standards for mining operations and require a person who is
granted a mining lease to, before the commencement of operation of the mine, obtain a mining
operating permit from the Inspectorate Division of the Minerals Commission.
- Environmental permit:
The Environmental Assessment Regulations, 1999 (L.I. 1652) require that all developmental
activities likely to impact adversely on the environment be subject to environmental assessments.
Pursuant to these regulations, an undertaking which in the opinion of the Environmental Protection
Agency (EPA) has or is likely to have an adverse effect on the environment cannot commence
unless the undertaking has been registered and an environmental permit has been issued by the
EPA. The Minerals and Mining Act requires that all necessary approvals and permits required to be
obtained from the Forestry Commission and the EPA for the protection of natural resources, public
health and the environment.
The major environmental permits in place for the Wassa mine are:
o Wassa operations (EPA/EIA/112) and expansions (EPA/EIA/322) including South Akyempim
pits (EPA/EIA/190);
o Hwini Butre and Benso operations (EPA/EIA/175) and expansion (EPA/EIA/247).
o Wassa TSF 2 (EPA/EIA/383) and renewal (EPA/EIA/442); and
o Wassa Expansion project, including Wassa underground, Main pits and waste dump
expansion (EPA/EIA/508).
- Licence to export, sell or dispose of minerals:
The exportation, sale or disposal of minerals requires a licence from the Minister for Lands and
Natural Resources. Pursuant to section 46 of the Minerals and Mining Act., a mining lease
authorizes the holder to, inter alia, “take and remove from the land the specified minerals and to
dispose of them in accordance with the holder’s approved marketing plan.” Under the Minerals and
Mining (General) Regulations, 2012 (L.I. 2173), an application by a holder of a mining lease for a
licence to export, sell or dispose of gold or other precious minerals produced by the holder must be
accompanied by a refining contract and a sales and marketing agreement.
- Operating licence and permit for the acquisition, use, transportation and storage of explosives:
Under Regulation 23 of the Minerals and Mining (Explosives) Regulations, 2012 (L.I. 2177), the
construction of a building or other structure to be used as a magazine for the storage of explosives
is subject to an operating license delivered by the Minerals Commission. As required under
Regulation 32 of L.I. 2177, the storage of explosives in a magazine is also subject to a permit from
the Minerals Commission; the latter is valid for one year and is renewable on application. Under
L.I. 2177, an operating licence is required for the purchase and use or transportation of explosives.
There are separate operating licences for the purchase and use of explosives and for
transportation. Each is valid for a period of one calendar year and is renewable on application
made one month before the end of each year. Additionally, a permit is required for each occasion
on which explosives are being transported in respect of which the specific type and quantity of
explosives must be indicated.
- Licence to use water resources:
The use of water resources is regulated by the Water Resources Commission Act, 1996 (Act 522)
and the Water Use Regulations, 2001. Act 522 provides that no person shall (a) divert, dam, store,
abstract or use water resources; or (b) construct or maintain any works for the use of water
resources except in accordance with the provisions of the Act. Subject to obtaining the requisite
Page 47NI 43-101 Technical Report (March 2021) Wassa Gold Mine
approvals or licences, a holder of a mineral right may, for purposes of or ancillary to the mineral
operations, obtain, divert, impound, convey and use water from a river, stream, underground
reservoir or watercourse within the land the subject of the mineral right.
- Fire permit:
The Fire Precaution (Premises) Regulations, 2003 requires that a fire certificate be issued by the
Chief Fire Officer in respect of premises used as a place of work or for a purpose which involves
access to the premises by members of the public, whether on payment or not. The certificate is
valid for 12 months and is renewable.
GSWL conducts its operations in accordance with applicable laws and regulations in Ghana and is in
compliance with its permitting obligations in relation to its activities. With regards to environmental
matters, GSWL has undertaken environmental impact assessment studies on its concessions to support the
permitting of its mining projects and has considerable background data to support required environmental
permitting processes.
Page 48NI 43-101 Technical Report (March 2021) Wassa Gold Mine
5 ACCESSIBILITY, CLIMATE, LOCAL RESOURCES, INFRASTRUCTURE AND
PHYSIOGRAPHY
5.1 Accessibility
The Wassa Mine is near the village of Akyempim in the Wassa East District in the Western Region of Ghana.
It is 62 km north of the district capital, Daboase, and 40 km east of Bogoso, and is 80 km north of Cape
Coast and 150 km west of the capital Accra.
The main access to the site is from the east, via the Cape Coast to Twifo-Praso road, then over the
combined road-rail bridge on the Pra River. There is also an access road from Takoradi in the south via
Mpohor.
The satellite sites of Hwini Butre and Benso are respectively, 60 km and 35 km southeast of the main Wassa
site. They are accessible from Wassa via an unsealed access and haulage road. All sites lie within 15 km of
sealed public road but generally, the haul road to Wassa is the most reliable access.
Figure 4-3 in Section 4.1 shows a plan of the various locations and access infrastructure.
5.2 Physiography and Vegetation
The project area is characterized by gently rolling hills with elevations up to 1100 m RL, incised by an
extensive drainage network. The natural vegetation is an ecotone of the moist, semi-deciduous forest and
wet rainforest zones. It has been degraded due to anthropogenic activities, giving way to broken forest,
thickets of secondary forest, forb re-growth, swamps in the bottom of valleys, and cleared areas.
Extensive subsistence farming occurs throughout the area, with plantain, cassava, pineapple, maize, and
cocoyam being the principal crops. Some small-scale cultivation of commercial crops is also carried out,
with cocoa, teak, coconut and oil palm the most common. Forest patches are present on the steep slopes
and in areas unsuitable for agriculture.
Environmental assessments carried out in the project area over the last two decades (SGS 1996 and 1998,
WGL 2004, GSR 2015, Geosystems 2013, and Golder 2016) indicate that the biodiversity of the Wassa
operational area is of low ecological significance and conservation status.
5.3 Land Use and Proximity to Local Population Centres
The Wassa Mine is located in a rural setting with no major urban settlements within 30 km. It lies in the
Wassa East District, part of the Western Region of Ghana, 40 km north of Daboase (district capital), 65 km
north of Takoradi (regional capital) and 35 km north-east of the city of Tarkwa.
The nearest villages are Akyempim, Akyempim New Site (formally Akosombo, resettled early in Wassa
operations) and Kubekro. The Togbekrom community were resettled to Ateiku.
The Hwini Butre and Benso sites are approximately 35 km and 65 km, respectively, north-northwest of the
Port of Takoradi and south-east of Tarkwa. The key communities within and outside the concession are
Subriso, Odumase, Ningo, Akyaakrom, Mpohor, Benso, and Anlokrom. The total population of these
communities is approximately 10,000. The Benso Township is approximately 5 km from the Benso mine
site to the south and the Mpohor Township is approximately 2 km west of the Hwini Butre site.
The population data/estimates for the larger communities located within the Wassa concession boundaries
are shown in Table 5-1.
Page 49NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 50
Table 5-1 Communities neighbouring Wassa Mine
Land uses in the vicinity of GSWL operations are predominantly rural with agricultural, forestry,
agroforestry (palm oil and rubber plantations), and unauthorized small-scale mining operations.
5.4 Local Resources and Infrastructure
There are five other significant mining operations within 50 km of Wassa:
- Nsuta manganese mine, Ghana Manganese Company;
- Iduapriem gold mine, AngloGold Ashanti;
- Tarkwa gold mine, Gold Fields Ghana Limited;
- Damang gold mine, Gold Fields Ghana Limited; and
- Bogoso-Prestea gold mine, Future Global Resources.
Wassa Mine is in operation with required services, infrastructure, and community support to continue.
- Access is via public road to site with good overall access. Roads are sealed from Accra to within
15 km from site, then access is via formed, unsealed road. From site, travel by road to Takoradi is
generally 1.5-2 hours and 4-5 hours to Accra;
- Electrical infrastructure with access to power through the grid and on-site generation;
- On-site processing plant with capacity up to 2.7 Mtpa;
- On-site tailings storage facilities with sufficient permitted capacity;
- Waste rock storage facilities with sufficient permitted capacity;
- Access/haulage road from Wassa site, to the satellite Hwini Butre, Benso and Chichiwelli sites; and
- Access to skilled labour with the history and scale of mining in Ghana.
5.5 Climate and Length of Operating Season
The climate in the project area is classified as wet semi-equatorial. The Intertropical Convergence Zone
crosses the area twice a year, resulting in a bi-modal rainfall pattern with peaks in Mar-Jul and Sep-Oct.
During the dry season months of Nov-Feb, the climate is heavily influenced by the seasonal Harmattan
which brings dry and dusty winds from the Sahara across West Africa. Rainfall is mainly influenced by
south-west monsoon winds, which blow from the south-western part of the country.
Analysis of available rainfall data, obtained from the Ateiku Meteorological survey (1944 to 2009) indicates:
- Average annual rainfall is 1,996 ± 293 mm;
- Wettest month is June, with average rainfall of 241 ± 85 mm;
- Driest month is January, with average rainfall of 31 ± 35 mm;
- The wettest month on record is June 2009 with 475 mm of rainfall.
Local measurements taken at Wassa from 1998-2019 (at main site) and 2007-2014 (at TSF 1) are consistent
with the large data set from Ateiku. Local stations identified the bi-modal rainfall pattern and recorded an
average of approximately 1,659 mm/yr and the wettest month being June 2014 with 512 mm at TSF 1 and
417 mm at the main site.
Community
Divisional Area
Estimated Population
(SGS 1996)
Population
(WEDA 2013)
Akyempim
Mamponso
2,500
2,533
Akosombo
Mamponso
n/a
166
Kubrekro
Anyinabrem
300
335
Nsadweso
Anyinabrem
2,400
1,541
Togbekrom
Anyinabrem
Not measured
674NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Annual potential evapotranspiration is estimated to be approximately 1,337 mm/yr, indicating minimum
precipitation balance of +288 mm/year. In 2020, measured evaporation at the TSF site was in the order of
1,300 mm/year. Rainfall exceeds potential evapotranspiration from Mar-Jul and Sep-Oct with groundwater
recharge most likely to be prevalent during these periods. Relative humidity is consistent throughout the
year, ranging from 88% to 90%.
The climatic conditions mean that, with effective surface water management practices, mining operations
can continue year-round with short suspensions to open pit operations during storms, most of which are
short duration and can occur throughout the year. Underground mining operations are not directly
affected by weather events except where very large, long duration rainfall results in the safe capacity of pit
sumps being exceeded, requiring evacuation of the underground workings due to risk of inundation.
Normal operations are resumed once sumps are pumped down to safe levels.
Page 51NI 43-101 Technical Report (March 2021) Wassa Gold Mine
6 HISTORY
6.1 Wassa
6.1.1 Historic Mining
The Wassa area has experienced local small-scale and colonial mining activity at Wassa since the beginning
of the 20th century with numerous small pits and adits evident.
From 1988, the property was operated as a small-scale mining operation with a gravity gold recovery circuit
by WMRL, a Ghanaian company.
6.1.2 Satellite Goldfields Limited (1993-2002)
In 1993 WMRL formed Satellite Goldfields Limited (SGL) with the Irish companies Glencar Exploration
Limited and Moydow Ltd, assigning the Wassa mining lease to SGL.
Extensive satellite imagery and geophysical interpretations were carried out which identified a strong gold
target. Exploration drilling commenced in February 1994 and by March 1997 58,709 m of drilling had been
completed. Construction of the Wassa Mine was initiated in September 1998, after Glencar secured a
$42.5 M debt-financing package from a consortium of banks and institutions.
The operation was originally developed as an open pit mine with heap leach treatment of 3.0 Mtpa and
planned production of 100,000 oz/yr. First ore was mined from the open pit in October 1998.
During the first year of production, planned gold recovery of 85% from oxide ore in the heap leach was not
achieved due to high clay content of the ore and poor solution management. Attempts were made to
increase recovery, including doubling the leach solution application rate but recoveries for the oxide ores
above 55-60% could not be achieved.
The low gold recovery resulted in debt servicing issues and Wassa was marketed for sale. GSR started
negotiations to purchase Wassa in mid-2000. As part of due diligence, GSR initiated a drilling program in
March 2001 to test their geological model and extensions to some of the high grade orebodies.
SGL was placed into receivership in November 2001 and in April 2002, GSR concluded that the mineable
reserve at Wassa was 30% below the 648,000 oz stated by SGL. Negotiation continued until September
2002 when the agreement for GSR to purchase the 90% share of Wassa was announced.
6.2 Hwini Butre, Benso and Chichiwelli
6.2.1 Historic Mining
Early European reports indicate the Dabokrom area, around Hwini Butre, may have been a major source for
gold sold to Portuguese explorers when they first arrived in Ghana in the late 1400’s.
European interest grew in the 1800’s with the presence of gold and proximity to Sekondi-Takoradi, which
had developed as a port to service mines at Tarkwa, Prestea and Obuasi. Many exploration licences were
granted during the gold boom of 1898-1902 and by the 1930’s most of the area was under license to
various local and European interests.
At Dabokrom, a shaft was sunk by Oceania Consolidated in the 1930’s to follow the shallow dipping quartz
veins. The property was worked for several years but stopped in 1939 at the start of World War 2.
At Chichiwelli a shaft was sunk in 1918 following a quartz vein at the very north end of the Benso
concession, close to the Subri River Forest Reserve. Mining progressed to the 260 ft level but was
abandoned in 1924 after the mine was flooded.
The whole area has many historic workings which evidence mining activity, mostly from the 1930’s.
Page 52NI 43-101 Technical Report (March 2021) Wassa Gold Mine
6.2.2 Modern Exploration (1980’s-2005)
6.2.2.1 Hwini Butre
The Dabrokrom concession was acquired by BD Goldfields (BDG) during the 1980’s who invited Danish
company Lutz Resources Limited to carry out preliminary exploration on the property. The property
transferred to Hwini Butre Minerals (HBM) in the early 1990’s, which was controlled by Lutz.
HBM entered a joint venture with Placer-Outukumpu who drilled several holes around Dabokrom in 1993
to assess potential of the vein systems. They concluded that potential was limited by widely spaced veins
and little gold in the diorite host rock. Saint Jude Resources (SJR) acquired Dabokrom in 1994 and explored
the area until 2002 when work was suspended due to a legal dispute between SJR, BDG and the
Government of Ghana. The matter was resolved in 2005 before acquisition of the project by GSR.
SJR began exploring the concession in February 1995 which represented the first sustained exploration
program on the concession. SJR undertook ground geophysical surveys which included magnetic,
radiometric and induced polarization surveys; soil geochemical surveys were also completed on the
concession area, resulting in the identification of numerous targets. Trenching and pitting were conducted
in areas of geophysical and geochemical anomalies and over historical prospects or old workings in an
attempt to outline near surface mineralization. Subsequent drilling of the surface targets resulted in the
delineation of the Adoikrom, Father Brown and Dabokrom prospects along a combined strike length of 900
- Further exploration conducted in 2005 identified the Adoikrom North prospect. A total of some 22,100
m over 267 drill holes were completed on the main mineralized zones and the exploration targets.
6.2.2.2 Benso and Chichiwelli
Reconnaissance work at Chichiwelli, Subriso, Denerawah and Amantin was conducted by BHP Billiton from
1989-92, on what is now the Benso concession. This identified soil geochemical anomalies and follow-up
drilling was completed at Chichiwelli but results did not meet targeting criteria and the concessions were
relinquished. Tenure was then acquired by a local company, Architect Co-Partners, with a 150 km2
prospecting concession which covered Amantin, Subriso and Chichiwelli, as well as a large part of the
Subriso River Forest Reserve that was closed to exploration from 1996.
Canadian company Fairstar Exploration Limited took over the Benso concession in 1995 and carried out
extensive work, particularly at Subriso and Amantin, where considerable drilling was completed but ceased
by the end of the decade due to funding constraints. An agreement was reached in 2001 for SJR to take
over the exploration work.
In 2001, SJR completed an agreement with Fairstar and took over the exploration work. From early 2002 to
about mid-2004, SJR focused mainly on the Subriso area where substantial mineralization was outlined at
two prospects, Subriso East and West. Numerous other prospects, namely Subriso Central, I Zone and G
Zone were identified and drill tested, as was the Amantin area, which had also been drilled to a
considerable extent by Fairstar.
6.3 Production History, Previously Declared Resources and Reserves
6.3.1 Golden Star Resources (2003-present)
Since acquiring Wassa in 2003 GSR has produced 2.4 million ounces of gold and the mine has a remaining
life of six years as defined by the current Mineral Reserve.
Milestones at Wassa under GSR management are:
- 2003: definition drilling ahead of feasibility study for CIL plant.
- 2004: feasibility study completed and construction commences on CIL plant with open pit mining.
- 2005: CIL plant commissioned.
- 2006: acquired St Jude Resources (Hwini Butre and Benso concessions). Connected to grid power.
- 2007: commenced open pit mining at South Akyempim. Construction of haul road to Hwini Butre.
Page 53NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 54
- 2008: commenced open pit mining at Benso, processing at Wassa.
- 2009: commenced open pit mining at Hwini Butre and drilling to test underground potential.
- 2011: Hwini Butre mining moves from Adoikrom to Father Brown pit.
- 2012: commenced drilling to test underground potential below Wassa.
- 2013: upgraded plant to 2.7 Mtpa capacity with fresh ore, consolidated mining at Wassa Main pit.
- 2014: released positive Preliminary Economic Assessment for Wassa Underground and completed
Hwini Butre mining at Father Brown.
- 2015: completed positive Feasibility Study for Wassa UG and commenced development, along with
starting construction of TSF 2.
- 2016: mined first stope ore from Wassa UG in July and definition drilling continued to define wide
zones of mineralization in B-Shoot.
- 2017: commercial production declared at Wassa UG and deep definition drilling program defines
what was later to become the Southern Extension zone. UG averages 1,865 ore t/d.
- 2018: open pit mining of Main pit completed and UG ore mining rate increases to 2,945 t/d. Wassa
UG Inferred Mineral Resource reported growth to 5.2 Moz with addition of Southern Extension
zone.
- 2019: completed positive Feasibility Study for paste backfill commenced development. UG ore
mining rate increased to 3,895 t/d (1.4 Mtpa).
- 2020: completed construction of paste backfill plant and on-site gas-fired power generation. UG
ore mining rate increased to 4,480 t/d (1.6 Mtpa).
Annual production is shown in Table 6-1. Production in 2012 and 2013 includes contributions from Hwini
Butre and Benso.
Production peaked in 2013 at 187 koz with the plant operating at full capacity and high grade ore being
mined from the Father Brown pit at Hwini Butre. From 2014, open pit ore was sourced solely from the
Wassa Main pit until its completion in 2017. Lower grades resulted in production of around 100 koz/yr.
Mining transitioned to underground from 2016, with commercial production realized in 2017 and the
underground becoming the main production source by 2018. Since 2018, underground production has
steadily increased to maintain and exceed 150 koz/yr, with the addition of minor amounts of low-grade ore
from open pit stockpiles.
Table 6-1 Recent Production History, Wassa
Year
Open Pit & Stockpile
Underground
Total
Processed
Mt
Feed Grade
Au g/t
Produced
Au koz
Processed
Mt
Feed Grade
Au g/t
Produced
Au koz
Processed
Mt
Feed Grade
Au g/t
Produced
Au koz
2012
2.51
2.09
159
–
–
–
2.51
2.09
159
2013
2.70
2.29
187
–
–
–
2.70
2.29
187
2014
2.63
1.41
110
–
–
–
2.63
1.41
110
2015
2.50
1.46
109
–
–
–
2.50
1.46
109
2016
2.44
1.27
93
0.18
2.06
11
2.62
1.32
104
2017
1.93
1.27
76
0.69
3.03
61
2.62
1.73
137
2018
0.53
0.76
12
1.01
4.18
137
1.60
3.06
151
2019
0.16
0.65
3
1.39
3.57
153
1.55
3.27
155
2020
0.38
0.79
9
1.64
3.13
156
2.01
2.70
165NI 43-101 Technical Report (March 2021) Wassa Gold Mine
7 GEOLOGICAL SETTING AND MINERALIZATION
7.1 Regional Geology
The regional geological setting of the Ashanti belt has been described by several authors previously. The
most recent publication describing the geological setting of the sub-region was from Perrouty et al., in
Precambrian Research in 2012.
The Ashanti greenstone belt in the Western Region of Ghana is composed primarily of paleoproterozoic
metavolcanic and metasedimentary rocks that are divided into the Birimian Supergroup (Sefwi and Kumasi
Groups) and the Tarkwa Group. Both units are intruded by abundant granitoids and host numerous
hydrothermal gold deposits such as the Wassa, Obuasi, Bogoso and Prestea mines and paleoplacer deposits
such as the Tarkwa and Teberebie Mines.
Allibone et al. (2002) separated the Paleoproterozoic Eburnean orogeny into two distinct phases known as
Eburnean I and II. This classification was revised by Perrouty et al. in 2012 who proposed two distinct
orogenic events, the Eoeburnean orogeny and the Eburnean orogeny. The Eoeburnean orogeny predates
the deposition of Tarkwaian sediments and is associated with a major period of magmatism and
metamorphism in the Sefwi Group basement. The Eburnean event is associated with significant post
Tarkwaian deformation that affected both the Birimian Supergroup and overlying Tarkwaian sediments.
The Eburnean orogeny is associated with major north-west to south-east shortening that developed major
thrust faults, including the Ashanti Fault along with isoclinal folds in Birimian metasediments and regional
scale open folds in the Tarkwaian sediments. These features are overprinted by phases of sinistral and
dextral deformational events that reactivated the existing thrust faults and resulted in shear zones with
strong shear fabrics.
The Birimian series was first described by Kitson (1928) based on outcrops located in the Birim River
(around 80 km east of the Ashanti Belt). Since this early interpretation, the Birimian stratigraphic column
has been revised significantly. Before the application of geochronology, the Birimian super group was
divided in an Upper Birimian group composed mainly of metavolcanics and a Lower Birimian group
corresponding to metasedimentary basins. Subsequent authors have proposed synchronous deposition of
Birimian metavolcanics. Most recently, Samarium/Neodymium and U/Pb analyses have reversed the
earlier stratigraphic interpretation with the younger metasediments overlying the older metavolcanics.
Proposed ages for the metavolcanics vary between 2,162 ± 6 Ma and 2,266 ± 2 Ma. Detrital zircons in the
metasediments indicate the initiation of their deposition between 2,142 ± 24 Ma 2,154 ± 2 Ma. The Kumasi
Group was intruded by the late sedimentary Suhuma granodiorite at 2,136 ± 19 Ma (U/Pb on zircon,
Adadey et al., 2009).
Page 55NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 7-1 Location of Wassa on the Ashanti Belt (Perrouty et al 2012)
The Tarkwa super group was first recognized by Kitson (1928) and consists of a succession of clastic
sedimentary units, which have been divided in four groups by Whitelaw (1929) and Junner (1940).
The Kawere Group located at the base of the Tarkwaian super group is composed of conglomerates and
sandstones with a thickness varying between 250 m and 700 m. The unit is stratigraphically overlain by the
Banket Formation, which is characterized by sequences of conglomerates interbedded with cross-bedded
sandstone layers, the maximum thickness of this group being 400 m. The conglomerates are principally
composed of Birimian quartz pebbles (>90%) and volcanic clasts (Hirdes and Nunoo, 1994) that host the
Tarkwa Placer deposits.
The Banket formation is overlain by approximately 400 m of Tarkwa Phyllites.
The uppermost unit of the Tarkwa super group is the Huni Sandstone, comprised of alternating beds of
quartzite and phyllite intruded by minor dolerite sills that form a package up to 1,300 m thick (Pigois et al.,
2003). U/Pb and Pb/Pb geochronology dating of detrital zircons provide a maximum depositional age of
2,132 ± 2.8 Ma for the Kawere formation and 2,133 ± 3.4 Ma for the Banket formation (Davis et al., 1994;
Hirdes and Nunoo, 1994). These ages agree with the study by Pigois et al. (2003) that yielded maximum
depositional age of 2,133 ± 4 Ma from 71 concordant zircons of the Banket formation. According to all
concordant zircon histograms (161 grains) and their uncertainties, a reasonable estimation for the start of
the Tarkwaian sedimentation could be as young as 2,107 Ma.
Page 56NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Abundant granites and granitoids intruded the Birimian and Tarkwaian units during the Paleoproterozoic.
Eburnean plutonism in south-west Ghana can be divided into two phases between 2,180 to 2,150 Ma
(Eoeburnean) and 2,130 to 2,070 Ma (Eburnean) that is supported by the current database of U/Pb and
Pb/Pb zircon ages. Most of the granitoids intruded during both phases correspond to typical Tonalite–
Trondhjemite–Granodiorite suites. However, in the southern part of the Ashanti Belt, intrusions within the
Mpohor complex have granodioritic, dioritic and gabbroic compositions.
Dolerite dykes oriented north-south and east-northeast to west-southwest that are generally less than 100
m in thickness are abundant across the West African craton where they cross-cut Archean and
Paleoproterozoic basement. In south-western Ghana these dykes are well defined in magnetic data where
they are characterized by strong magnetic susceptibility. Dolerite dykes are observed to cross-cut
undeformed K-feldspar rich granites that formed during the late Eburnean, and are overlain by Volta basin
sediments with a maximum depositional age of 950 Ma (Kalsbeek et al., 2008). These relationships
constrain dyke emplacement to between 2,000 Ma and 950 Ma. In contrast some older dolerite/gabbro
dykes and sills were deformed during the Eburnean orogeny and are dated at 2,102 ± 13 Ma (U/Pb on
zircon, Adadey et al., 2009).
With the exception of some late Eburnean granitoids, dolerite dykes and Phanerozoic sediments, all other
lithologies have undergone metamorphism that generally does not exceed upper greenschist facies.
Studies on amphibole/plagioclase assemblages suggest the peak temperature and pressure was 500 to
650C and 5 to 6 kbar (John et al., 1999), dated at 2092 ± 3 Ma (Oberthür et al., 1998).
7.2 Local Geology and Mineralization
The Wassa property lies within the southern portion of the Ashanti Greenstone Belt along the eastern
margin of the belt within a volcano-sedimentary assemblage located at proximity to the Tarkwaian basin
contact. The eastern contact between the Tarkwaian basin and the volcano-sedimentary rocks of the Sefwi
group is faulted, but the fault is discrete as opposed to the western contact of the Ashanti belt where the
Ashanti fault zone can be several hundred meters wide.
Deposition of the Tarkwaian sediments was followed by a period of dilation and the intrusion of late mafic
dykes and sills.
The lithologies of the Wassa assemblage are predominantly comprised of mafic to intermediate volcanic
flows which are interbedded with minor horizons of volcaniclastics, clastic sediments such as wackes and
magnetite rich sedimentary layers, most likely banded iron formations. The volcano-sedimentary sequence
is intruded by syn-volcanic mafic intrusives and felsic porphyries.
The magnetic signature of the Ashanti belt is relatively high in comparison to the surrounding Birimian
sedimentary basins such as the Kumasi basin to the west of the Ashanti belt and the Akyem Basin to the
East as illustrated in Figure 7-2.
Rock assemblages from the southern area of the Ashanti belt were formed between a period spanning
from 2,080 to 2,240 Ma as illustrated in Table 7-1, with the Sefwi Group being the oldest rock package and
the Tarkwa sediments being the youngest. The Ashanti belt is host to numerous gold occurrences, which
are believed to be related to various stages of the Eoeburnean and Eburnean deformational event.
Structural evidences and relationships observed in drill core and pits at Wassa would suggest the
mineralization to be of Eoeburnean timing while other known deposits in the southern portion of the
Ashanti belt such as Chichiwelli, Benso and Hwini Butre are considered to be of Eburnean age.
The Eoeburnean deformation is best observed at Wassa where the deformational event has produced a
penetrative foliation with an associated lineation which is defined by mineral alignments. A period of
extension occurred between the Eoeburnean and Eburnean deformational events which resulted in the
formation of the Akyem Basin (Kumasi Group) to the northeast of the Wassa Mine and the Tarkwa group to
the west of the Wassa concession. Both metasedimentary sequences of the Tarkwa and Kumasi group
have not been affected by the penetrative foliation observed at Wassa.
Page 57NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The Eburnean deformation is divided in multiple events which vary in number depending on the authors as
summarized in Table 7-1. All deposits underlying the Wassa concession have been affected by the
Eburnean deformational events, the main penetrative foliation has been affected by at least three
Eburnean folding events which have resulted in a large scale refolded synform. The main foliation is sub
vertical and oriented northeast to south-west on the south-eastern flank of the Wassa mine fold whereas it
is dipping at around 45° to the south-southeast on the north-west flank of the Wassa mine fold.
Figure 7-2 Total magnetic intensity reduced to pole, of the Ashanti Belt (modified from Perrouty et al, 2012)
Page 58NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 59
Figure 7-3 Compilation of geochronology dating from the Ashanti Belt (Perrouty et al, 2012)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 60
Table 7-1 Deformational history of the Ashanti Belt (Perrouty et al, 2012)
In Birimian
Obuasi/Bogoso
Allibone et al, 2002
In Tarkwaian
Tarkwa,
Damang
Tunks et al, 2004
Regional
Eisenlhor et al, 1992
Regional
Feybesse et al,
2006
Milesi et al, 1992
Eoeburnean
2187 –
2158 Ma
Sefwi Group volcanism and
sedimentation
Volcanism,
Granitoids intrusion.
Regional
Metamorphism.
Birimian sediments
and volcanics.
Penecontemporan
eous Plutonism
(Dixcove type
granitoids).
Magmatic
accretion.
Plutonism.
Birimian
sedimentation.
D1, N-S shortening
Regional scale folding in the
Sefwi Group.
Possible Gold mineralization.
Onset of
deformation in a
“foreland thrust”
and Tarkwaian
deposition.
D2, Extension Phase
2154-2125 Ma
Kumasi Group sedimentation
D1
S1 parallel to bedding.
Flat-lying bedding
parallel shearing.
Eburnean
2125 –
2000 Ma
Tarkwa Basin Formation
(2107-2097 Ma)
D3, NW-SE shortening
Km scale folds in Birimian and
Tarkwaian.
S3 Subvertical crenulation
cleavage (NE-SE).
Thrust faults (Ashanti,
Damang…)
Metamorphism peak
(2092Ma).
D2, NW-SE shortening
Isoclinal folds with axial
surface parallel to the
regional faults and
shear zones.
Ashanti thrust fault.
D1, NW-SE
shortening
Km scale folds
(with subvertical
axial surface, S3).
Damang thrust
fault.
D1, NW-SE
shortening
S1 (NE-SE)
subvertical and
subparallel to
bedding in both
Birimian and
Tarkwaian Regional
folds (tight to
isocline).
D1, NW-SE
shortening
Thrust faults.
Tarkwaian
sediments
deposition, Syn
D1.
Metamorphism
(6kbar/550-
650°C).
D3
Low dip axial surface
fold at Obuasi.
S3 crenulation cleavage
overprinting S2. Final
stage of D2?
D2, Continuing
compression
S2 (NE-SE) fabrics
overprint S1
foliation.
S2 is defined by
aligned muscovite
and elongate
recrystallized
quartz grains.
Metamorphism.
Syncrogenic
plutonism (Cape
Coast type
granitoids).
D2/D3, NW-SE
shortening
Tarkwaian folds.
Strike-slip faults
and shearing.
Gold
mineralization.
Metamorphism
(2-3kbar/
200-300°C).
D4, NNW-SSE shortening
Sinistral shear reactivism D3
thrust.
S4 crenulation cleavage ENE
WSW.
Greenschist retrograde
metamorphism.
Remobilization and
concentration of gold particles
along the shear zone and at
the base of the Tarkwa Basin.
D4, NNW-SSE
shortening
Hm scale fold at
Obuasi.
D2, NNWSSE
shortening
Thrust faults and
minor folds.
D5 or syn-D4
Sinistral strike-slip
faults and shearing.
Gold mineralization.
D5
Recumbant folds <m.
Sub-horizontal crenulation
cleavage.
Last pyrite/gold mineralization
associated with quartz vein.
D3, ESE-WNW
shortening
Folds with
shallowly dipping
axial surfaces and
mineralized
quartz veins,
post-dating peak
of
metamorphism.
K-rich plutonism
(cross-cutting all
previous
structures).
Late plutonism.
D6, NE-SW shortening
Low amplitude folds +
crenulation cleavage ~N320/70
(RH).
Reverse faults oriented NW-SE.
D4
Faults oriented
NW-SE.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 7-4 Regional geology of the Ashanti belt, showing Wassa, GSR tenure and major deposits (GSR, 2020)
7.2.1 Wassa
The Wassa lithological sequence is characterized by lithologies belonging to the Sefwi Group and consisting
of intercalated meta-mafic volcanic and meta-diorite dykes with altered meta-mafic volcanic and meta
sediments which are locally characterized as magnetite rich, banded iron formation like horizons (Bourassa,
2003), as illustrated in Figure 7-5. The sequence is characterized by the presence of multiple ankerite
quartz veins which are sub-parallel to the main penetrative foliation. The lithological sequence is also
characterized by Eoeburnean felsic porphyry intrusions on the south-eastern flank of the Wassa mine fold.
Page 61NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 7-5 Wassa mine-scale geology (modified from Bourassa, 2003 and Perrouty et al, 2013)
The first deformational event (D1) at Wassa is of Eoeburnean timing and consists of North-South
Shortening. This pre-Tarkwaian event resulted in a penetrative foliation which transposed lithological
contacts along this main foliation. Early, gold bearing, syn-D1 quartz-ankerite veins were also formed
during the Eoeburnean event.
Page 62NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The second event of deformation (D2) is an extension period with no local deformation at the mine scale at
Wassa. Regionally, this event separates the Eoeburnean and Eburnean orogeny by an extension period of
approximately 40 Ma which resulted in the sedimentation of the Birimian and Tarkwaian basins.
The Eburnean orogeny is divided in three distinct deformational events, D3 is a Northwest-Southeast
shortening event which resulted in the inversion of regional detachment faults into thrust faults. At the
mine scale, this event generated a second penetrative foliation at Wassa and a first phase of Eburnean
folding. The D4 deformational event, a North Northwest-South Southeast shortening event resulted in the
sinistral reactivation of earlier faults at the regional scale and severely buckled the Wassa stratigraphic
sequence into moderately steeply dipping, tight fold patterns (F4 Fold) and a third penetrative foliation
(S4).The last deformational event, D5, is the result of sub-vertical compression which resulted in open
recumbent folds at Wassa and a fourth foliation located in the axial plane of the F5 folds and is generally
sub-horizontal, shallowly plunging to the South.
The deposit scale F4 fold is shown on a vertical section through the nose of this structure in Figure 7-6.
The various phases of Eburnean deformations and their effect on the host rocks are illustrated in:
- Figure 7-7:
o Top image shows syn-D1 veins and S1 foliation folded by and F3 fold;
o Bottom image shows syn-D1 veins, S1 and S3 foliations affected by a mesoscopic F4 fold;
- Figure 7-8:
o Top image shows syn-D1 veins folded and buckled by S5 foliation; and
o Bottom image shows syn-D1 veins, affected by both S4 and S5 foliations.
Figure 7-6 Vertical section through Nose of deposit-scale F4 fold, Wassa Main deposit
Page 63NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 7-7 Eburnean folds and foliations from Wassa mine, Starter pit
Page 64NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 7-8 Eburnean folds and foliations from Wassa mine, B-Shoot pit
Page 65NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The Wassa mineralization is subdivided into a number of domains: F Shoot, B Shoot, 242, South East,
Starter, 419, Mid-East and Dead Man’s Hill. Each of these represents discontinuous segments of the main
mineralized system which extends approximately 3.5 km along strike from surface and is still open at depth.
The SAK deposits are located approximately 2 km to the southwest of the Wassa Main deposit on the
northern end of a well-defined mineralized trend parallel to the Wassa Main trend. The SAK deposits are
also located on the western side of a major regional east dipping fault which separates the Wassa main
mineralization from this trend. The mineralization is hosted in highly altered multi-phased greenstone
hosted quartz-carbonate veins interlaced with sedimentary pelitic units. The SAK mineralization is
subdivided into a number of domains as well, SAK 1, 2 and 3, which are thought to be associated with tight
F3 fold closures which plunge steeply to the South west.
Mineralization within the Wassa Mine is structurally controlled and related to vein densities and sulphide
contents. Higher grade mineralization has been interpreted to be associated with tight isoclinal folding
(F3). These tight folds often have extenuated limbs that are weakly mineralized, where as the fold closure
was the focal point of remobilized fluids and associated gold. Mineralization in the limbs is generally
narrower, < 10 m and fold closer thicknesses and exceed 25-30 m thicknesses. Higher grade mineralization
has up and down dip extension of approximately 150 to 200 metres with a down plunge extension being
drill tested over 2,000 m from where it daylights in the Starter pit area to section 18,500 mN in the south,
where it remains open.
Figure 7-9 illustrates the tightly folded nature of the gold mineralization, as depicted by the black dotted
line showing high-grade zones associated with F3 fold closures and subsequent parasitic folding. The
mineralization is then subsequently folded by the deposit scale parasitic F4 folds.
Three vein generations have been distinguished on the basis of structural evidence, vein mineralogy,
textures and associated gold grades. Evidence further relates the majority of gold mineralization to the
earliest recognized vein generation which is believed to be syn-Eoeburnean. Gold grades broadly correlate
with the presence of quartz-dolomite/ankerite-tourmaline bearing quartz veins and the presence of
sulphide minerals (predominantly pyrite) within and around the quartz veins. Gold grades appear to be
spatially restricted to the quartz veins, vein selvages and the immediate wall rocks. The alteration haloes
developed around the veins and pervasively developed within the core of the deposit scale Wassa fold
contain lower grade mineralization.
Figure 7-9 Wassa section through 19,650 mN showing high-grade zones, F3 closures, parasitic folding
Page 66NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The combined and overprinted Eburnean deformational events (D3 to D5) render precise prediction of the
vein geometries and localities difficult in areas with wider spaced or little drillhole data. However, where
drilling density is tighter (12.5 m x 10 m), as with in the immediate underground mining areas it is possible
to construct both hanging and footwall contacts of the economic gold mineralization, Figure 7-10. The
higher grade zones of gold mineralization are constrained with in broader lower grade mineralized zones
that can be defined reasonably well with the wider spaced surface drillhole data, but to delineate the
geometry of the higher grade zones tighter underground grade control drilling is required. Figure 7-11, drill
cross section 18900N shows a simpler interpretation which is based on wider spaced surface drilling. As
indicated above further infill underground drilling is necessary to delineate the geometry of the high-grade
gold mineralization.
Figure 7-10 Wassa section through 19,925 mN showing interpretation with tight-spaced drilling
Figure 7-11 Wassa section through 18,900 mN showing interpretation and wide spaced (surface) drilling
Page 67NI 43-101 Technical Report (March 2021) Wassa Gold Mine
7.2.2 Hwini Butre
The Hwini Butre concession is underlain by three main deposits: Adoikrom, Dabokrom and Father Brown,
which are hosted within the Mpohor mafic complex, which consists mainly of gabbroic and gabbro-dioritic
intrusive horizons as illustrated in Figure 7-4 Regional geology of the Ashanti belt, showing Wassa, GSR
tenure and major deposits. Each of the three deposits have different mineralization styles.
The timing of the mineralization at Hwini Butre is considered to be of late to post Eburnean age with the
period of hydrothermal activity likely to have spanned a considerable length of time. At Father Brown and
Dabokrom, mineralization is associated with quartz vein systems which are locally surrounded by extensive,
lower grade, disseminated quartz stockwork bodies, especially at Dabokrom. The Father Brown deposit is
characterized by well-developed fault-filled quartz veins which are, as is the case for Dabokrom, light grey
with carbonate and mica accessory minerals and minor tourmaline and feldspar. Wall rock alteration is
commonly associated with elevated gold grades and consists of silicification with carbonates, muscovite
and sericite. Secondary strain fabrics are also present, with mylonitic and cataclastic fabrics common in the
heavily altered zones. Visible gold occurs as disseminations in discrete quartz veins and within zones of
silicification associated with pyrite. Gold is medium to coarse grained and generally occurs with pyrite and
appears to be free milling. As at Benso, arsenopyrite is largely absent from the Hwini Butre deposits.
At Adoikrom, the mineralization is shear hosted and characterized by the absence of quartz veins; gold is
associated with fine grained pyrite and intense potassic alteration. The higher grade core of gold
mineralization at Adoikrom is constrained within a moderately plunging, South West trending shoot which
has been drilled tested to approximately 1000 meters depth where it remains open.
Page 68NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 7-12 Hwini Butre section through 33,100 mN
7.2.3 Benso
The Benso concession is underlain by four main deposits: Subriso East, Subriso West, G Zone and I Zone. All
the deposits are characterized by similar style of mineralization. The Benso deposits are hosted in two
dominant rock types. Subriso West and I Zone are hosted within Intermediate feldspar porphyry intrusives
and meta-volcanics, where Subriso East occurs along the contact between carbonaceous phyllites and meta
volcanics. Mineralization at Benso is associated with late deformational stages of the Eburnean orogeny
and deposits are shear hosted along subsidiary structures.
Mineralogy is relatively simple with fine grained but visible gold disseminated in the shear fabric and
associated with pyrite which can be locally abundant. Zones of intense alteration with chlorite, carbonates
and epidote are common. Arsenopyrite is absent from the deposits.
7.2.4 Chichiwelli
The Chichiwelli deposit consists of two sub-parallel mineralized trends which hosts two distinct types of
mineralization. The Chichiwelli West trend is a shear zone hosted deposit with a quartz, carbonate, sericite
and potassic alteration assemblage, the mineralization is associated with pyrite. The Chichiwelli East trend
is a quartz vein associated deposit with an ankerite and sericite alteration assemblage. Mineralization is
also associated with pyrite along vein selvages and in the wall rocks.
Page 69NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The lithological assemblage at Chichiwelli West consists of mainly fine to medium grained dioritic intrusives
with local intercalation of basalt and feldspar porphyritic intrusives. Lithologies are moderately to strongly
foliated adjacent to the shear zone, the mineralization is bounded to the shear zone and associated with a
strong shear fabric. The shear zone mineralization is characterized locally by boudinage quartz and calcite
stringers with fine disseminated sulphides, mainly pyrite, and associated with a sericite and potassium
alteration assemblage with minor silicification. The Chichiwelli East lithological sequence is comprised
mainly of deformed diorite with local strain zones. The mineralization is characterized by milky white
quartz veins associated with potassium alteration and euhedral coarse grained pyrite.
Page 70NI 43-101 Technical Report (March 2021) Wassa Gold Mine
8 DEPOSIT TYPES
8.1 Wassa
The Wassa deposit is located on the eastern flank of the northeast trending Ashanti Belt, a
Paleoproterozoic greenstone belt which was formed and deformed, along with the dividing Birimian and
Tarkwaian sedimentary basins during the Eoeburnean and Eburnean orogeny. Most deposits found within
the Ashanti belt can be classified as lode gold deposits or orogenic mesothermal gold deposits, with the
exception of the Tarkwaian paleoplacer deposits which have a sedimentary origin. Orogenic gold deposits
are the most common gold systems found within Archean and Paleoproterozoic terrains, in the West
African shield, these deposits are typically underlain by geology considered to be of Eburnean age and are
generally hosted by volcano-sedimentary sequences.
- Dubé and P. Gosselin of the Geological Survey of Canada described these deposits as greenstone-hosted
quartz-carbonate vein deposits in the 2007 special publication No. 5 entitled Mineral Deposits of Canada.
The authors described these deposits as typically occurring in deformed greenstone belts and distributed
along major compressional crustal scale fault zones commonly marking the convergent margins between
major lithological boundaries. The greenstone-hosted quartz-carbonate vein deposits correspond to
structurally controlled complex deposits characterized by networks of gold-bearing, laminated quartz
carbonate fault-fill veins. These veins are hosted by moderately to steeply dipping, compressional brittle
ductile shear zones and faults with locally associated shallow-dipping extensional veins and hydrothermal
breccias. In these deposits, gold is mainly confined to the quartz-carbonate veins but can also occur within
iron-rich sulphidized wall rocks or within silicified and sulphide-rich replacement zones.
The Ashanti belt is considered prospective for orogenic mesothermal gold deposits and hosts numerous
lode gold deposits and paleoplacer deposits. As illustrated by Figure 7-4, several major gold deposits are
found within the Ashanti belt which can be classified into six different deposit types:
- Sedimentary hosted shear zones;
- Fault fill quartz veins;
- Paleoplacer;
- Intrusive hosted;
- Late thrust fault quartz veins; and
- Folded veins system.
The sedimentary hosted shear zone deposits are localized principally along a steep to sub-vertical major
crustal structures located along the western margin of the Ashanti belt referred to as the Ashanti trend.
The Ashanti trend shows a range of mineralization styles associated with graphitic shear zones, which
represents the principal displacement zone of a regional-scale shear zone that defines the mineral belt.
These styles include highly deformed graphitic shear zones containing disseminations of arsenopyrite as the
principal gold bearing phase and disseminations of sulphides in mafic volcanic rocks generally found in the
footwall of the main shear zones. The sedimentary hosted shear zone deposits which occur along the
Ashanti trend include Bogoso, Obuasi, Prestea and Nzema.
The second type of deposit found within the Ashanti belt are laminated quartz vein deposits containing free
gold. Fault filled quartz vein deposits also occur along the Ashanti trend but are only present at Obuasi and
Prestea. The third type of deposit are paleo-placer deposits within the Tarkwaian sedimentary basin which
are hosted within narrow conglomerate horizons intercalated with sandstone units characterized by iron
oxides cross beddings. Paleoplacer deposits occur in the southern portion of the Tarkwa basin and
examples include Tarkwa, Teberebie and Iduaprim. The fourth type of deposit found within the Ashanti
belt are intrusive hosted deposits which occur along second order structures such as the Akropong trend in
the Kumasi basin and the Manso trend in the Southern portion of the Ashanti belt. These deposits can be
hosted both within felsic and mafic intrusives and are characterized by a penetrative fabric where gold is
associated with pyrite and arsenopyrite. Examples of such deposits include Edikan and Pampe along the
Akropong trend and Benso and Hwini Butre along the Manso trend. The fifth type of deposit found within
Page 71NI 43-101 Technical Report (March 2021) Wassa Gold Mine
the Ashanti belt is late thrust fault associated quartz vein deposits. The Damang mine which is located just
west of Wassa is the only known thrust fault related deposit in the Ashanti belt. The deposit is
characterized by low angle; undeformed extensional and tensional veins associated with low angle thrust
faults. This type of deposit contrasts with the last type of deposit found with the belt, the multi-phase
folded Wassa vein deposit. The Wassa mineralization consists of greenstone-hosted, low sulphide
hydrothermal deposits where gold mineralization occurs within folded quartz-carbonate veins, as
illustrated in Figure 8-1. The Wassa deposit can therefore be classified as an Eoeburnean folded vein
system and is the only such deposit recognized to date within the Ashanti belt.
Host rocks in the Wassa mine area have been affected by at least four phases of ductile deformation,
producing a polyphase fold pattern at the mine scale. Discrete high-strain zones locally dissect this fold
system. The structural history of the Wassa area is important in that the various deformational events have
been responsible for the emplacement of the gold mineralization as well as the geometry of the zones
themselves. Mineralized zones at the Wassa Mine are related to vein swarms and associated sulphides that
formed during the Eoeburnean deformational event. All rock types underlying the Wassa Mine appear to
be altered to variable degrees with the most common alteration consisting of a carbonate-silica-sulphide
assemblage.
Figure 8-1 Syn-Eoeburnean veins from B-Shoot, 242 and South-east zones (modified from Perrouty et al, 2013)
8.2 Hwini Butre
The Hwini Butre deposits can be characterized as mafic intrusive hosted, orogenic shear zones. The
deposits are hosted within diorite and granodiorite intrusive rocks of the Mpohor complex. The Father
Brown deposit is characterized by well-developed fault-filled quartz veins (Figure 8-2), whereas the
Adoikrom deposit is a shear zone hosted deposit characterized by intense potassium and silica alteration
assemblage (Figure 8-3).
Analysis of geophysical surveys and topographical features have identified several north to north-northeast
trending regional features running through the area which are tentatively interpreted as boundary faults
along the margins of the Ashanti Belt. The Mpohor complex exhibits the underlying north-south trends but
also has extensive cross cutting features present particularly in the north-west orientation. These
structural features are second order or subsidiary structures splaying from primary structures.
Page 72NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 73
The Adoikrom, Father Brown and Dabokrom deposits occur in the south portion of the Mpohor complex
and appear to be controlled by a series of shallow to moderately dipping faults and shear structures with
dips varying from 20° to the south at Dabokrom and steepening to 65° to the northwest at Adoikrom.
Figure 8-2 Mineralization exposure in Father Brown pit, smoky quartz vein
Figure 8-3 Mineralization exposure in Adoikrom pit, potassic alteration
NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 74
8.3 Hwini Butre
The Benso deposits can also be characterized as mafic intrusive hosted, orogenic shear zones deposits,
which are hosted by Birimian metavolcanics into which coarse plagioclase porphyry units have intruded and
are generally conformable with the volcaniclastic units.
At Subriso East, the metavolcanics host complex quartz vein systems associated with intense shearing and
abundant sulphide mineralization (Figure 8-5). At Subriso West, the presence of intermediate porphyry
intrusive appears to play a more significant role (Figure 8-4) and quartz veining is less extensive and broad
scale silicification is more common. The contacts between metavolcanics and porphyry have been
identified as potential targets for higher grade gold mineralization.
The mineralization hosting structures generally dip steeply towards the west with foliation generally
parallel to the bedding. The aeromagnetic interpretation reveals a north to north-northeast striking fault
system along the course of the Ben River with several other fracture systems also evident with strikes
varying between the northwest and northeast. The Subriso East deposit is interpreted to dip less steeply to
the west at approximately 50°.
Oxidation associated with weathering is variable but generally limited. The weathering forms a layer of
lateritic clay rich material grading into a soft saprolite. The vertical depth is generally 10 m or less but can
reach depths of 30 m in places. There is a sharp boundary between oxide and fresh material with a narrow
and poorly developed transition zone.
Figure 8-4 Mineralization exposure in Subriso West
pit, sheared volcanics
Figure 8-5 Mineralization exposure in Subriso East
pit, fine grained pyrite
NI 43-101 Technical Report (March 2021) Wassa Gold Mine
8.4 Chichiwelli
The Chichiwelli deposits can also be characterized as mafic intrusive hosted, orogenic shear zones, the
deposits are hosted within diorite and granodiorite intrusive rocks. The mineralization zones at Chichiwelli
are similar to those observed at Benso, with the mineralized hosting structures generally dipping to the
east.
The Chichiwelli deposit consists of two sub-parallel mineralized trends which hosts two distinct types of
mineralization, as shown in Figure 8-7 and Figure 8-6. Mineralization at the Chichiwelli West zone is shear
zone hosted with a carbonate, sericite and potassic alteration assemblage, while mineralization along the
Chichiwelli East trend is quartz vein associated with an ankerite and sericite alteration assemblage.
Mineralization is spatially associated with pyrite at both deposits.
Figure 8-7 Mineralization at Chichiwelli West, shear
hosted
Figure 8-6 Mineralization at Chichiwelli East,
hydrothermal veins
Page 75NI 43-101 Technical Report (March 2021) Wassa Gold Mine
9 EXPLORATION
Extensive exploration work has been conducted on and around the Wassa concession. Previously, several
airborne and ground geophysical surveys consisting of aero-magnetics, radiometrics and Induced
Polarization (IP) were conducted on the properties. The geophysical surveys targeted geochemical
anomalies, which had previously been identified following multiple stream and soil geochemical sampling
programs.
9.1 Wassa
Modern exploration programs on the Wassa concession began in the early 1990s with satellite imagery and
geophysical surveys which identified geophysical lineaments and anomalies over small scale and colonial
mining areas. Stream and soil geochemistry sampling programs were conducted over the geophysical
anomalies and identified two linear gold in-soil anomalies as illustrated in Figure 9-1.
Figure 9-1 Wassa soil geochemistry and anomalies (GSR, 2018)
Exploration drilling commenced in February 1994 and, by March 1997, a total of 58,709 m of RC and DD
had been completed. In September 1997, consulting engineers Pincock, Allen and Holt completed a FS.
Only minimal exploration work was conducted by SGL between the completion of the FS in 1997 and the
2001 bankruptcy.
In March 2002, GSR started an exploration program as part of a due diligence exercise following the
ratification of a confidentiality agreement with the creditor of SGL. The exploration program consisted
mainly of pit mapping and drilling below the pits to test the continuity of mineralization at depth. The
concession was acquired later that year by GSR following the completion of the due diligence exercise.
Exploration drilling resumed in November 2002 under GSR with the aim to increase the quoted reserves
and resources for the feasibility, which was completed in 2003.
Simultaneously to the resource drilling program that targeted resource increases in the pit areas, GSR also
undertook grass roots exploration along two previously identified mineralized trends. The 419 area was
Page 76NI 43-101 Technical Report (March 2021) Wassa Gold Mine
located south of the main pits and the SAK anomaly was a soil target that had never been previously drilled
and was located west of the main pits. Deep auger campaigns were also undertaken in the Subri forest
Reserve, which is located in the southern portion of the Wassa Mining lease.
Figure 9-2 Wassa airborne magnetic coverage (GSR, 2004)
In March and April 2004, a high resolution, helicopter geophysical survey was carried out over the Wassa
Mining Lease and surrounding Prospecting and Reconnaissance Licenses (Figure 9-2). Five different survey
types were conducted, namely: Electromagnetic, Resistivity, Magnetic, Radiometric and Magnetic
Horizontal Gradient. The surveys consisted of 9,085 km of flown lines covering a total area of 450 km2 .
Flight lines were flown at various line spacing varying between 50 to 100 m depending on the survey type.
Page 77NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The geophysical surveys identified several anomalies with targets being prioritized on the basis of
supporting geochemical and geological evidence.
The exploration program in 2005 continued to focus on drill testing anomalies identified by the airborne
geophysical survey as well as infill drilling within the pit area to expand the reserve and resource base. The
resource definition drilling program focused mainly on SAK, South-East and the 419 area. The following
years were subject to more infill and resource definition drilling in the pit areas at Wassa. In 2011,
exploration drilling programs shifted towards drilling deep HG targets below the pits; this drilling continued
until 2015. Drilling was limited in 2016 with rigs in filling the first planned stoping areas to increase
confidence in the resource prior to underground mining. The 2017 drilling programs were two-fold, infilling
gaps in the previous drilling with in the proposed expanded open pit as well as testing the B shoot
underground mineralization both north and south, up and down plunge respectively. The southern
extension drilling initiated in 2017 continued into 2019 and utilized larger drill rigs to conduct directional
wedging and downhole motor work to delineate the deeper southern extensions of B and F shoot HG
mineralization.
9.2 Hwini Butre
GSR acquired SJR and the Hwini Butre concession in late 2005 and commenced exploration work in early
- GSR exploration activities concentrated on the previously defined mineralization at Adoikrom North,
Adoikrom, Dabokrom and Father Brown. The drilling program focused mainly on infill drilling and
extending the continuity of the deposits at depth. The previous drilling by SJR reached a maximum vertical
depth of approximately 130 m, whereas GSR extended the modelled mineralization at vertical depths of
over 250 m.
GSR also undertook regional exploration programs over the concession by targeting a number of
geochemical and geophysical anomalies previously identified by SJR, these anomalies were mainly tested
by use of rotary air blast drilling. A combination of 4 m deep auger and shallow auger at a grid spacing of
400 m by 50 m was also carried out to further test the existing gold in soil anomalies and gaps in the
geochemistry sampling over the Hwini Butre concessions.
In 2007 and 2008, GSR focused its Hwini Butre exploration activities on the northern portion of the
concession where several colonial gold occurrences such as Breminsu, Apotunso, Abada, Whinnie and
Guadium are located. Previous soil sampling in these areas identified several anomalies and the follow up
programs included deep auger and rotary air blast drilling. A total of 1,384 auger holes and 41 RAB holes
totalling 725 m were completed.
In 2009, 5,992 m RC (83 holes) and 2,100 m DD (21 holes) were completed on the Hwini Butre property
(Father Brown, Adoikrom and Dabokrom) to test the strike extensions of the zones and also upgrade the
existing quoted Mineral Resource. The drilling program also identified potential underground target
beneath the Subriso West pit. Induced Polarization geophysical surveys were conducted over the Hwini
Butre and Benso concessions in 2009. The program generated targets that were coincidental with
lithological trends and gold in soil anomalies.
The resource definition drilling program continued in 2010 at Father Brown, Adoikrom and Dabokrom
where 5,075 m of RC drilling (72 holes) and 5,207.3 m of DD drilling (24 holes) were completed. The drilling
program also tested the underground potential of the deposits with significant success. A deep auger
program totalling 746 m over 205 holes to test IP geophysical anomalies at Essaman was also completed.
In 2011 the deeper targets at Father Brown and Adoikrom were tested to evaluate the underground
potential of the deposits. In all, 13 DD holes totalling 3,689.6 m were drilled at Father Brown and
Adoikrom. RAB drilling, totalling 2,941 m (174 holes) were undertaken at Semkrom to test IP and
aeromagnetic/radiometric anomalies. In 2012, exploration concentrated on Father Brown and Adoikrom
infill and step out underground drilling program, with 33 DD holes totalling 10,094 m being completed. In
2018, exploration drilling resumed at Father Brown and Adoikrom to continue evaluating the underground
potential. The program combined RC and DD holes totalling 8,236.2 m. The 2018 drilling programs rolled
over into 2019 where another 28 holes were completed totaling 14,526.9 m (RC and DD ).
Page 78NI 43-101 Technical Report (March 2021) Wassa Gold Mine
9.3 Benso and Chichiwelli
GSR acquired the Benso and Chichiwelli concessions in late 2005 and commenced exploration work in early
2006, with exploration activities focusing on the previously defined mineralization at Subriso East, Subriso
West, I Zone and G Zone. The drilling program focused mainly on infill drilling and extending the continuity
of the deposits at depth. The 2006 exploration program was also the focus of regional exploration
programs over the concession by targeting a number of geochemical and geophysical anomalies previously
identified by SJR, these anomalies were mainly tested by use of rotary air blast drilling. A combination of 4
m deep auger and shallow auger at a grid spacing of 400 m by 50 m was also carried out to further test the
existing gold in soil anomalies and gaps in the geochemistry sampling over the Hwini Butre concessions.
Exploration on the Benso property in 2007 and 2008 concentrated on drill testing new zones of
mineralization delineated by the RAB drilling in 2006. A total of 81 holes and 10,232.3 m of RC and DD
drilling was completed at Subriso East, Subriso West, G Zone and I Zone. At Amantin, follow-up programs
included deep auger sampling on a 200 by 50 m grid and RAB drilling was undertaken to test the previously
defined soil anomalies. A total of 3,717 m of RAB drilling from 178 holes and 1,683.9 m of deep auger
drilling over 487 holes were completed at Amantin.
The 2009 exploration program at the Benso concession focused on resource delineation and definition
drilling at the Subriso East, Subriso West and G Zone deposits. A total of 3,159 m RC (35 holes) and 2,538.4
m DD were completed. IP geophysical surveys were conducted over the Benso concessions in 2009 and the
program generated targets that were coincidental with lithological trends and gold in soil anomalies.
The 2010 exploration activities at Benso included the continuation of the resource delineation and
definition drilling in and around the pits and also drilling off the potential underground target at Subriso
West. A total of 8,815 m RC (112 holes) and 8,286.2 m DD (18 holes) were completed. A deep auger
program totalling 1,114 m over 319 holes was undertaken to test IP targets at Subriso West.
In 2011, 12 DD holes, totalling 4,557 m, were drilled on the Benso property at Subriso West to close up the
spacing along strike and down dip of the HG zone of mineralization intersected beneath the pit. At
Amantin, a shallow RC program totalling 1,177 m (22 holes) was completed to follow up on widely spaced
RAB and RC intersections from earlier drilling programs. A deep auger (6 m) program totalling 907.5 m
from 174 holes were completed at K Zone and I Zone to test additional targets generated by IP survey
program.
Exploration activity at Benso in 2012 was limited to structural interpretation of the controls on
mineralization to determine the underground potential at Subriso West.
Page 79NI 43-101 Technical Report (March 2021) Wassa Gold Mine
10 DRILLING
Wassa is an advanced property so details of all drill results are not required in this report. This section
provides an overview of drilling and representative plans and cross-sections are shown in Section 7.2.
10.1 Surface Drilling
Drilling is carried out by a combination of DD, RC and RAB techniques. In general, RAB is used at early
stages for follow up to soil geochemical sampling and, during production, for testing contacts and
mineralization extensions around the production areas. RAB has a maximum drilling depth of 30 m.
RC pre-collar with diamond core tails drilling is used as the main method for obtaining samples for Mineral
Resource estimation and is carried out along drill lines spaced between 25 and 50 m along prospective
structures and anomalies defined from soil geochemistry and RAB drilling. RC drilling is typically extended
to depths of in the order of 100-125 m. The DD method is used to provide more detailed geological data
and where more structural and geotechnical information is required. Generally, the deeper intersections
are also drilled using DD and, as a result, most section lines contain a combination of RC and DD drilling.
RC and DD drilling was conducted with a GSR geologist was on site to align the drill rig and check the drill
head dip and azimuth. Downhole surveying was conducted using a single shot camera, for RC and DD holes
at the bottom of holes exceeding 30 m depths and then taken progressively every 30 m up hole. The single
shot camera recorded the dip and azimuth for each surveys which was validated and recorded by the GSR
geologists or was recorded by a Reflex survey instrument and captured in the database as well as being
filed in the respective drillhole file folders on site.
Drilling depths at Wassa Main have generally been less than 250 m but with the discovery of higher grades
below the Wassa Main pit in late 2011, hole depths have increased. In the 1st half of 2014, two gyro survey
instruments were utilized to resurvey several of the deeper holes. In total, 153 holes, drilled during 2012 to
2014, were resurveyed. The gyro survey readings were conducted every 10 m both in and out of the hole
and the values were then averaged. The 153 gyro surveyed holes were updated in the database and
subsequently used for the resource estimates. The gyro surveys showed that there was some deviation in
the holes below 250 m drilled depth. Deviations varied from location to location depending on drill
orientation with a general tendency for the hole to steepen and swing to the north.
Drilling of the deeper targets at Wassa has required the use of directional drilling methods. The deeper
holes, often exceeding 1000 meters, are drilled from surface using HQ sized core and this initial hole
(referred to as the “mother” hole) is drilled to the depth where the first directional hole would be started.
The directional hole (or “daughter” hole) is drilled using a smaller core size, NQ and is deviated from the
mother hole initially using a casing wedge which is oriented in the direction of the mineralized target. Once
the initial deflection has been achieved with the wedge, the hole deviation can be controlled using a down
hole directional motor which can change the dip and azimuth of the hole by approximately plus or minus
1.5 degrees over a 10-metre run. The direction of the hole can also be controlled by using various
combinations of down hole stabilizers and drill bits. The step out deeper drilling fences typically involve
two mother holes with three to four daughter holes from each of these. The deeper holes are surveyed,
down hole with either a Reflex multi-shot or gyro survey instrument. The surveys are taken while the hole
is being drilled as well as every 10 to 15 meters from the bottom of the hole once it has been completed.
Exploration data used in the Long-Range model for the Mineral Resource is summarized in Table 7-1.
The majority of the drilling has been conducted by GSR, although there are some drillholes completed by
previous concession owners that have been used to inform the Wassa long-range model (by SGL) and Hwini
Butre and Benso models (by SJR). Where drill data by prior ownership is used the data has be validated and
checked to the satisfaction of the QP for inclusion to inform interpretation and grade estimates.
Page 80NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 81
Table 10-1 Exploration data used for Mineral Resource models
All drillhole collars were surveyed using a Nikon Total Station (DTM-332) or Sokkia Total Station by a GSR
surveyor. Individual RC and DD holes are identified and marked in the field with poly-vinyl chloride (PVC)
pipes. RAB drill holes were surveyed in the field and identified and marked with wooden pegs.
10.2 Underground Drilling
Underground diamond drilling is performed using electric-hydraulic diamond drills utilizing the
underground mine’s 1,000 V power supply. Core drilled underground is HQ (63.5mm), NQ (47.6 mm) or
NQ2 (50.6 mm) in core size. The final drilling density for classification as Measured Mineral Resource is
designed to be 15 m along strike and 13 m down dip, or tighter. With the orebody generally striking north
south (on the mine grid), typical drilling azimuths range +/-30 degrees each side of 090˚ or 270˚ azimuth,
depending on whether the drills are set up on the hangingwall or footwall side of the orebody. Dips
generally range between +30˚ to -60˚.
Downhole surveying is conducted using a Reflex multi-shot downhole surveying tool. When collaring, a
single survey is taken at 10-12m depth. At the first survey, the drill hole orientation must fall within ±2o
azimuth and ±1.5o dip tolerance, when compared to design. For any hole where the first survey falls
outside of tolerance, the geologist has the discretion to either terminate the drill hole and re-collar at the
drilling company’s expense, or to continue the hole. At the completion of the drill hole, multi-shot surveys
are collected at 15 m intervals on the way out. All downhole surveys are collected by the underground
mine geologists. The drilling crews do not perform the surveys themselves.
Drill hole collar locations are captured by the underground mine surveying team. The surveyors use either
a Leica TS15 total station, or a Leica TS16 total station to record the collar position in X, Y, Z location. The
total station is accurate to less than two seconds in azimuth. In cases where the mine surveyors cannot
identify the drill hole collar site, the designed collar coordinates are recorded in the databases.
The Short-Range grade model used for calculation of the December 2020 Mineral Resource estimate,
within the active mining area, was completed in December 2020 and utilized 273 additional underground
holes totaling 34,275 meters.
10.3 Sampling
A standard approach to drilling and sampling on all GSR projects in Ghana. Sampling is typically carried out
along the entire mineralized drilled length.
Sample recovery is good across all deposits drilled to date. Ground conditions are generally good and air
drilling techniques (AC/RAB and RC) are avoided below the groundwater table where DD is applied.
For RC drilling, samples are collected every 1 m. Where DD holes have been pre-collared using RC, the
individual 1 m RC samples are combined to produce 3 m composites which are then sent for analysis.
Should any 3 m composite sample return a significant gold grade assay, the individual 1 m samples are then
sent separately along with those from the immediately adjacent samples.
Data Source
Purpose
No. Holes
Drill Metres
Grade Control (RC)
24,957
642,470
Pre-Existing (Dec18 Report)
Exploration (RC, DD)
3,422
500,282
UG Operational (DD)
847
93,896
Grade Control (RC)
411
12,142
2019-2020
Exploration (RC, DD)
59
48,036
UG Operational (DD)
371
56,914
Total
30,067
1,353,740NI 43-101 Technical Report (March 2021) Wassa Gold Mine
10.3.1 Diamond Drillholes
DD samples are collected, logged and split with a diamond rock saw in maximum 1.2 m lengths. The core is
cut according to mineralization, alteration or lithology. The core is split into two equal parts along a
median to the foliation plane using a core cutter. The sampling concept is to ensure a representative
sample of the core is assayed. The remaining half core is retained in the core tray, for reference and
additional sampling if required.
10.3.2 RC Drillholes
RC sampling protocols were established in 2003. The composite length of 3 m has been established to
allow a minimum of at least two composites per drillhole intersection based on experience from
exploration drilling and mining. The hangingwall and footwall intersections can generally be easily
recognized in core from changes in pyrite content and style of quartz mineralization.
The 3 m composite sampling methodology is:
- A sample of each drilled meter is collected by fitting a plastic bag on the lower rim of the cyclone to
prevent leakage of material;
- Bag is removed once the “blow-back” for the meter has been completed and prior to the
commencement of drilling the subsequent meter;
- Both the large plastic sample bags and the smaller bags are clearly and accurately labelled with
indelible ink marker prior to the commencement of drilling. This is to limit error and confusion of
drilling depth while drilling is proceeding;
- 3 m composite samples are taken by shaking each of the 1 m samples (approximately 20 kg) and
taking equal portions of the 3 consecutive samples into a single plastic bag to form one composite
sample (approximately 3 kg);
- Composite samples are taken using tube sampling, which uses a 50 mm diameter PVC tube which
has been cut at a low oblique angle at one end to produce a spear of approximately 600 mm
length;
- The technique assumes that a sample from the cyclone is stratified in reverse order to the drilled
interval. A representative section through the entire length of the collected sample is considered
to be representative of the entire drilled interval;
- PVC tube is shuffled from the top to bottom of the sample, collecting material on the way. The
“shuffling” approach ensures sample accumulated in the tube does not just push the remaining
sample away; and
- Material in the tube is emptied into the appropriately labelled sample bag and in the case of 3 m
composite samples, stored separately from the 1 m samples.
The 1 m sample collection methodology is:
- 1 m re-sampling of selected mineralized composite zones using the 20 kg field samples is
undertaken with a single stage riffle splitter;
- Splitter is clean, dry, free of rust, and damage is used to reduce the 20 kg sample weight to a 3 kg
fraction for analysis;
- Care is taken to ensure that the sample is not split when it is transferred to the splitter, and is
evenly spread across the riffles;
- When considered necessary, the sample is assisted through the splitter by tapping the sides with a
rubber mallet;
- Excessively damp or wet samples are not put through the splitter, but tube-sampled or grab
sampled in an appropriate manner. Alternatively, the sample is dried before splitting. A common
sense approach to wet sampling is adopted on a case by case basis;
Page 82NI 43-101 Technical Report (March 2021) Wassa Gold Mine
- Clods of samples are not forced through the splitter, but apportioned manually in a representative
manner; and
- Splitter is thoroughly cleaned between each sample using a brush. Where possible, the splitter is
cleaned using an air gun attached to the drill rig compressor.
10.3.3 RAB/AC Drilling
RAB and Air Core (AC) drilling is used for exploration but is not used to inform any of the current Mineral
Resource estimates.
RAB and AC samples are collected and bagged at 1 m intervals. As the samples are generally smaller in size
than the RC samples, 3 m composites are prepared by shaking the samples thoroughly to homogenize the
sample, before using the PVC tube to collect a portion of the three individual 1 m samples. After positive
results from the 3 m composites, the individual 1 m samples are split to approximately 2 to 3 kg using the
Jones riffle splitter and then submitted to the laboratory for analysis.
Page 83NI 43-101 Technical Report (March 2021) Wassa Gold Mine
11 SAMPLE PREPARATION, ANALYSES AND SECURITY
The measures implemented by GSR related to sample preparation, analysis and security are considered by
the Qualified Person to be consistent with standard industry practice and of sufficient quality to include in
the estimation of Mineral Resources.
11.1 Sample Preparation
Sample preparation on site is restricted to core logging and core cutting or RC and RAB sample splitting.
The facilities consist of enclosed core and coarse reject storage facilities, covered logging sheds and areas
for the splitting of RC and RAB samples. Sub-sampling of RC and RAB samples is carried out using a Jones
Riffle splitter.
11.2 Sample Dispatch and Security
Samples are collated at the mine site after core cutting or sample splitting and then transported to the
primary laboratory for the completion of the sample preparation and chemical analysis. Samples are
trucked by road to the laboratories in Tarkwa.
Sample security involves two aspects, namely, maintaining the chain of custody of samples to prevent
inadvertent contamination or mixing of samples, and rendering active tampering of samples as difficult as
possible.
The transport of samples from site to the laboratory is by road using a truck dispatched from the
laboratory. As the samples are loaded, they are checked and the sample numbers are validated. The
sample dispatch forms are signed off by the driver and a company representative. The sample dispatch
dates are recorded in the sample database as well as the date when results are received.
No specific security safeguards have been put in place by GSR to maintain the chain of custody during the
transfer of core between drilling sites, the core library, and sample preparation and assaying facilities. Core
and rejects from the sample preparation are archived in secure facilities at the core yard and remain
available for future testing.
11.3 Laboratory Procedures
Sample assays have been performed at either the Wassa Site Lab, SGS or Intertek (formerly named TWL).
Both commercial labs are located at Tarkwa. GSR submits quality control samples to each lab for testing
purposes.
Both SGS and Intertek laboratories are independent of GSR and are accredited for international
certification for testing and analysis.
- SGS, Minerals Division – Tarkwa: ISO 17025 and ISO 9001; and
- Intertek Minerals Ltd, Tarkwa: ISO/IEC 17025.
The sample preparation and analysis processes at the Wassa Site Laboratory (WSL), Intertek, and SGS differ
slightly. WSL was used as the primary laboratory for 3 m composite and grade control RC drill samples from
July 2007 onwards. The laboratory had previously operated as a metallurgical sample processing
laboratory at the Wassa mine site.
11.3.1 Wassa Site Laboratory
The sample preparation and analysis process at the WSL is as follows:
- Sample reception, sorting, labelling and loading;
- Dry entire sample (3 kg) at 110°C for between 4 and 8 hours;
- Jaw crush entire sample to 3 mm, and secondary Keegor crusher to 1 mm;
- Split 3 kg sample and pulverize for 3 to 8 minutes to 95% passing 75 µm;
Page 84NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 85
- Sample homogenization using a mat rolling technique, and sub-sample 1 kg into bulk leach
extractable gold (BLEG) roll bottle;
- Bottle roll for 6 hours with LeachWellTM accelerant. Allow to settle for 30 to 60 minutes;
- Filter 20 ml aliquot from bottle;
- Di-isobutyl Ketone extraction and atomic absorption spectroscopy (AAS) determination of gold
content; and
- 1 in 10 residue samples are retained for gold determination using fire assay.
11.3.2 Transworld/Intertek
TWL (now Intertek) was the primary laboratory for core samples until July 2007, when it was discontinued
due to the following issues:
- Contamination due to poor dust control in pulverizing area of the laboratory. Use of dust attracting
cloth gloves for sample handling. BLEG aliquot preparation area containing dirt and liquids, which
may result in sample cross-contamination.
- Large fluctuation in employee numbers (60 to 180), which resulted in a risk of training and quality
control issues when increasing employment numbers over a short period of time.
- The use of a manual data tracking and capture system, which increased risk of data entry errors.
GSR considered this to be a sub-optimal process for a commercial laboratory.
The sample preparation and analysis process used by TWL is illustrated in Figure 11-1.
Figure 11-1 Transworld Laboratories sample processing flow sheet
TRANSWORLD LABORATORIES(GH) LTD.-
BLEG +Leachwell Sample Analysis Flow Sheet
Detection Limit 0.01 ppm Au
3-5 kg Sample
Sample Receival and sorting
Dry entire sample
at 110oC (12 hours)
Jaw crush entire sample
<6mm
Riffle split 3.0 to 4.0 Kg
Retain residual split in
original receival bag.
If sample weight is greater than 5kg
Pulverise subsample
cone splitting is recommended
<75um
Homogenise and weigh
Retain residual pulp in
2.0 Kg into BLEG roll bottle
pulp bag
Add:
30g Ca(OH)2
10ml of 200ppm CN solution(2g NaCN)
1000 ml water
1 LeachWell Tablet
Place on Bottle roller –
roll for 6 hours
Remove from roller and
allow to settle for 2 hours
Discard all Tails
Filter 50ml sub sample
Wash Tails of 10th sample
Analysis for Gold by
into flask.
Fire assay Method
Extract into 5ml of DIBK
Atomic
Absorption
Analysis
Data Processing
and ReportingNI 43-101 Technical Report (March 2021) Wassa Gold Mine
11.3.3 SGS Tarkwa
The SGS laboratory (Tarkwa) was used for drill core samples from July 2007, to August 2017, with the
sample preparation and analysis process as follows:
- Sample received, entered in LIMS, worksheets, printed and samples sorted;
- Samples emptied into aluminium dishes;
- Dry entire sample at between 105 and 110°C for 8 hours;
- Jaw crush entire sample to 6 mm;
- Split sample using a single stage riffle splitter, to result in a 1.5 kg sub-sample;
- Pulverize sub-sample for 3 to 5 minutes, to give 90% passing 75 µm;
- Sample homogenization using a mat rolling technique, and put 1 kg of sample into the BLEG roll
bottle;
- Remaining sample is retained as pulp and crushed sample duplicates;
- Bottle roll for 12 hours with LeachWellTM accelerant. Allow to settle for 2 hours;
- Filter 50 ml of aliquot; and
- Di-isobutyl Ketone and AAS for gold grade determination.
During 2017, GSR discontinued using SGS laboratories and began shipping samples to Intertek Laboratories.
The Intertek lab sample flow sheet is shown in Figure 11-2. The reason for the change was poor sample
result turn-around time. Since the prior issues with Transworld/Intertek, ownership of TWL had changed to
Intertek who had implemented internationally recognised standards with changes in management and
procedures.
Figure 11-2 Intertek sample processing flow sheet
Page 86NI 43-101 Technical Report (March 2021) Wassa Gold Mine
11.4 Quality Control and Quality Assurance
Quality control measures are set in place to ensure the reliability and trustworthiness of assay data, and to
ensure that it is of sufficient quality for inclusion in the subsequent Mineral Resource estimates. Quality
control measures include written field procedures and independent verifications of aspects such as drilling,
surveying, sampling and assaying, data management and database integrity. Appropriate documentation
of quality control measures and analysis of quality control data are an integral component of a
comprehensive quality assurance program and an important safeguard of project data.
The field procedures implemented by GSR are comprehensive and cover all aspects of the data collection
process such as surveying, drilling, core and RC cuttings handling, description, sampling and database
creation and management. At Wassa, each task is conducted by appropriately qualified personnel under
the direct supervision of a qualified geologist. The measures implemented by GSR are considered to be
consistent with industry best practice.
The quality controls employed by GSR include:
- Field duplicates used to check sampling precision and deposit variability. Two separate samples are
collected at the drill site and bagged separately from which two individual samples are produced.
The results of these checks can be useful in highlighting natural variability of the grade distribution.
- Pulp duplicates used as a check of sampling precision and coarse gold in pulps. Two separate pulp
samples are prepared from a single coarse reject after sample splitting and on site preparation.
The results are useful in indicating problems with sample preparation and splitting.
- Repeats as a check of analytical precision and coarse gold. Two separate aliquots are prepared
from separate samples taken from the original coarse reject and the two samples results are
compared.
- Blanks for highlighting contamination problems and cross labelling when samples are mislabelled in
the laboratory.
- Standards as a check of analytical precision and accuracy.
GSR relies on both the laboratory operators QA/QC processes for assaying, as well as GSR’s own
independent QA/QC program. The GSR program includes inserting blanks, certified reference materials
(otherwise known as standards), and pulp or coarse reject duplicates into sample batches, before sample
submission to the lab. GSR also provides sample dispatch lists to the laboratories, to ensure that all
samples dispatched from site are received at the lab.
GSR has supplied QA/QC reports to various consultants over the numerous drilling campaigns since 2004,
and a summary of the historical and current QA/QC results is included here.
11.4.1 Comparison of Assay Methodologies
In 2003, during open-pit operations, it was recognized that there was a variance between primary and
duplicate assay grades of the same sample, as well as a variance between the planned mine grade to the
mill reconciled grade. The conventional 50g fire assay being used at the time displayed poor reproducibility
between field duplicates. This effect was also evident between pulp duplicates; although not as marked.
The conclusion was that a component of coarse gold was present in the samples, and contributed to poor
reproducibility between samples. It was recommended to switch to an analytical process that made use of
significantly larger sample masses, such as LeachWell™ assays.
To address this, GSR changed the assay procedure from the 50 gram fire assay method to a 1kg BLEG assay,
with a LeachWellTM accelerant. Gold grade was determined using an AAS finish. Initially, samples were split
by a rotary splitter and leached for six hours. Following the analysis of the leach tailings, the leach time was
extended to 12 hours.
Due to time constraints, the use of the rotary splitter was discontinued and a Jones Riffle splitter was used
to split sub-samples from the larger RC drill hole samples. The difference between the reproducibility of
fire assay versus larger BLEG assays is illustrated in Figure 11-3. It shows a significant improvement with
Page 87NI 43-101 Technical Report (March 2021) Wassa Gold Mine
respect to sample reproducibility between the fire assay and the BLEG methodologies. Using BLEG, 80% of
pairs report Half Absolute Relative Difference (HARD) precisions of less than 17%, compared to the 35%
precision attributable to the fire assay method. SRK recommended that GSR continue to monitor the
reproducibility of the sample grades from the paired data analysis.
Figure 11-3 HARD plot comparing fire assay and BLEG for field duplicates
11.4.2 Repeat (Coarse Reject) Duplicates 2011 to 2013
From 2011, GSR discontinued the use of pulp samples for determining repeatability. Instead, coarse reject
material (leftover material from the laboratory primary crush stage) was used as duplicate sample material.
During the sample prep stage, after the drill core passed through primary crushing, the excess coarse reject
material was collected and returned to Wassa. This material was then re-numbered and re-submitted to
the laboratory for repeat analysis. Coarse reject duplicates were used to monitor the sample preparation
processes of the laboratory.
The HARD plot of all coarse rejects for 2011 is presented in Figure 11-4. The results of this HARD analysis
show that approximately 89% of the 369 coarse duplicate samples fall within approximately 20% error and
76% fall within 10% error. This is acceptable for gold deposits of this type.
The HARD plot of all coarse rejects for 2012 is presented in Figure 11-5. The results of this HARD analysis
show that approximately 83% of the 2,173 coarse duplicate samples fall within approximately 20% error
and 60% fall within 10% error. This is acceptable for gold deposits like Wassa.
The HARD plot of all coarse rejects for 2013 is presented in Figure 11-6. The results of this HARD analysis
show that approximately 82% of the 2,962 coarse duplicate samples fall within approximately 20% error
and 56% fall within 10% error. This is considered to be acceptable for Wassa.
Page 88NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 11-4 HARD plot of all coarse rejects (2011) from SGS
Figure 11-5 HARD plot of all coarse rejects (2012) from SGS
Page 89NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 90
Figure 11-6 HARD plot of all coarse rejects (2013) from SGS
11.4.3 QA/QC Data Summary 2014 to early 2017
The analytical quality control data produced between 2014 and early 2017 is summarized in Table 11-1.
The data represents approximately 16% of the total number of entire samples for this period.
Table 11-1 Summary of analytical quality control data from 2014 to early 2017
SGS
WGS
Total
Comment
%
%
%
Sample Count
61,943
96,596
158,539
Blanks
622
1.0%
6,159
6.4%
6,781
4.28%
Coarse Sand
QC Samples
4,564
7.4%
4,302
4.5%
8,866
5.6%
ST074/9453
575
766
1,341
0.21 g/t
ST14/9501
–
405
405
0.43 g/t
ST16/9487
264
419
683
0.49 g/t
ST626
664
–
664
0.51 g/t
ST06/9481
89
280
369
1.02 g/t
ST06/7384
167
–
167
1.08 g/t
ST588
–
763
763
1.60 g/t
ST39/6373
–
168
168
1.67 g/t
ST602
324
–
324
1.91 g/t
ST482
635
516
1,151
1.94 g/t
ST575
476
–
476
2.43 g/t
G914-2
14
–
14
2.45 g/t
ST596
61
–
61
2.51g/t
ST37/6374
–
30
30
3.33 g/t
ST43/7370
–
955
955
3.37 g/t
G910-3
12
–
12
4.03 g/t
ST48/8462
175
–
175
4.82 g/t
ST517
1,108
–
1,108
5.23 g/t
GC Field Duplicates
6,567
10.6%
–
6,567
4.1%
Coarse Reject Duplicates
–
–
3,802
3.9%
3,802
2.4%
Total QC Samples
11,753
19.0%
14,263
14.8%
26,016
16.4%NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 91
11.4.4 Repeat (Coarse Reject) Duplicates 2014 to October 2020
Coarse reject samples from SGS and Intertek sample splits were re-numbered and re-submitted for repeat
analyses. Coarse reject duplicates were used to monitor the sample preparation stage at a laboratory.
Analysis of the HARD plots of coarse reject duplicates processed by SGS and Intertek suggested that
approximately 56% to 69% of gold assay samples had a HARD below 10% error. Approximately 77% to 96%
coarse duplicate samples fell within approximately 20% error. This variance is typical of coarse reject
duplicate pairs in gold deposits; indicating that SGS and Intertek can reasonably reproduce this type of
paired data.
The HARD plot of all coarse rejects for 2014 is presented in Figure 11-7. The results of this HARD analysis
show that approximately 83% of the 2,145 coarse duplicate samples fall within approximately 20% error
and 56% fall within 10% error. This is considered to be acceptable for Wassa.
Figure 11-7 HARD plot of all Surface Drilling coarse rejects (2014) from SGSNI 43-101 Technical Report (March 2021) Wassa Gold Mine
The HARD plot of all surface drilling coarse rejects for 2015 is presented in Figure 11-8. The results of this
HARD analysis show that approximately 88% of the 641 coarse duplicate samples fall within approximately
20% error and 69% fall within 10% error. This is considered to be acceptable for Wassa.
Figure 11-8 HARD plot of all Surface Drilling coarse rejects (2015) from SGS
The HARD plot of all coarse rejects for 2016 is presented in Figure 11-9. The results of this 83% of the 355
coarse duplicate samples fall within HARD analysis show that approximately 20% error and 61% fall within
10% error. This is considered to be acceptable for Wassa.
Figure 11-9 HARD plot of all Surface Drilling coarse rejects (2016) from SGS
Page 92NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The HARD plot of all surface drilling coarse rejects for 2017 is presented in Figure 11-10. The results show
that approximately 85% of the 750 coarse duplicate samples fall within approximately 20% error and 62%
fall within 10% error. This is considered to be acceptable for Wassa.
Figure 11-10 HARD plot of all Surface Drilling coarse rejects (2017) from SGS and Intertek
The HARD plot of all surface coarse rejects for 2018 is presented in Figure 11-11. The results show that
approximately 77% of the 2,399 coarse duplicate samples fall within approximately 20% error and 56% fall
within 10% error. This is considered to be acceptable for Wassa.
Figure 11-11 HARD plot of all Surface Drilling coarse rejects (2018) from Intertek
Page 93NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The HARD plot of all Surface drilling coarse rejects for 2019 (plus some 2018 results which were not
included in 2018 results) is presented in Figure 11-12. The results show that approximately 84% of the
4,079 coarse duplicate samples fall within approximately 20% error and 64% fall within 10% error. This is
considered to be acceptable for a Wassa.
Figure 11-12 HARD plot of all Surface Drilling coarse rejects (2019) from Intertek
The HARD plot of Underground drill core coarse rejects values for January to October 2020 is presented in
Figure 11-13. The results show that approximately 87% of the 1,280 coarse duplicate samples fall within
approximately 20% error and 63% fall within 10% error. This is considered to be acceptable for Wassa.
Figure 11-13 HARD plot of all Surface Drilling coarse rejects (2020 Jan-Aug) from Intertek
Page 94NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The HARD plot of coarse rejects values for the Father Brown and Adoikrom (HBB) drilling for 2018 and 2019
surface drilling is presented in Figure 11-14. The results of this HARD analysis show that approximately 86%
of the 946 coarse duplicate samples fall within approximately 20% error and 70% fall within 10% error. This
is considered to be acceptable for these deposits.
Figure 11-14 HARD plot of all Surface Drilling coarse rejects for 2018-19 for Father Brown & Adoikrom, from Intertek
11.4.5 Certified Reference Material
CRM material (otherwise known as standards) are used to monitor the accuracy, precision, and
reproducibility of the assay results. CRM materials were sourced from Geostats Pty Ltd. , and Gannet
Holdings Pty Ltd. Although the CRM material can be easily identified by the laboratory, the grade of the
standard is difficult to determine due to the large number of different standards used. Standards in use
between January 2003 and October 2020 are shown in Table 11-2 through to Table 11-12.
A total of 16,100 standards were submitted to SGS between 2008 and 2017. The standards submitted
largely performed within expected ranges and mean grades, similar to the expected values. Results
indicate that SGS reported assay values both higher and lower than the certified mean value, with some
variation to the detection limit. That said, 96% or more of the determinations typically fell within +/–5% of
the mean value. Standards submitted to SGS from 2014 to 2017 performed much better with 100% of the
determinations falling within +/–3% of the mean value and 75% falling within +/- 2% of the mean value.
A total of 4,320 standards were submitted to the Wassa site laboratory between 2014 and 2017. Standards
analyzed by Wassa site lab performed marginally worse with some individual samples beyond two standard
deviations of the expected value. These results could possibly be due to the mislabeling of samples. Due to
the lower accuracy of the Wassa site lab, along with the slowing down of open-pit operations, in-house
assaying was phased out during 2017.
In 2018, GSR began using Intertek Laboratory, as its primary laboratory. A total of 400 CRM were
submitted in 2018, with the UG drill core sample batches, with 89 percent or more of the determinations
typically falling within +/–2% of the expected value. Between January, 2019 – October, 2020, a total of
20,053 CRMs were submitted to Intertek with the underground core samples batches, with 77 percent of
the determinations typically falling within +/–2% of the expected value.
Page 95NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 96
The surface drilling programs in 2019 submitted an additional 2,584 CRM’s with the RC and diamond core
samples. These samples were also submitted to Intertek laboratories in Tarkwa and 100% of the samples
returned determinations falling with +/–2% of their certified value.
The HBB drilling program also utilized Intertek Laboratories, with 867 CRM’s being submitted with the RC
and core samples sent to the lab. The CRM’s returned 79 percent of the determinations typically falling
within +/–2% of the certified value.
In general, the performance of the standards inserted with samples submitted for assaying at SGS, Intertek
and Wassa site laboratories is acceptable. The majority of the failures appear to be caused by the
mislabelling of samples.
Table 11-2 CRM for 2003-2007 (TWL)
Table 11-3 Geostats CRM for 2008-2012 (SGS)
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
Gannet A
0.22
196
0.22
0%
Gannet B
2.52
185
2.57
+2%
Gannet C
3.46
21
3.53
+2%
Gannet D
3.40
75
3.40
0%
Gannet E
2.36
77
2.45
+4%
Gannet F
0.78
47
0.75
-4%
Gannet G
3.22
82
3.02
-6%
Gannet M
1.18
159
1.28
+2%
Gannet N
0.50
171
0.49
-2%
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
G901-10
0.48
82
0.51
+6%
G305-3
0.71
14
0.66
-7%
G901-2
1.70
32
1.54
-9%
G906-4
1.90
137
1.99
+5%
G999-4
2.30
36
2.40
+4%
G302-2
2.44
70
2.50
+2%
G901-1
2.50
38
2.38
-5%
G396-9
2.60
29
2.39
-8%
G900-7
3.19
193
3.22
+1%NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 97
Table 11-4 Gannet CRM for 2008-2012 (SGS)
Table 11-5 Gannet CRM for 2013 (SGS)
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
ST07/9453
0.21
476
0.21
+2%
ST14/9501
0.43
447
0.42
-3%
ST16/9487
0.49
110
0.51
+3%
ST16/5357
0.52
654
0.52
0%
ST486
0.57
124
0.54
-5%
ST17/2290
0.78
14
0.79
+2%
ST481
1.02
32
1.05
+3%
ST06/5356
1.04
115
1.06
+2%
ST322
1.04
18
1.07
+3%
ST06/7384
1.08
1881
1.04
-4%
ST384
1.08
173
1.06
-2%
ST39/6373
1.67
117
1.74
+4%
ST09/7382
1.93
205
1.87
-3%
ST482
1.94
695
1.98
+2%
ST5355
2.37
145
2.39
+1%
ST05/9451
2.45
538
2.53
+3%
ST05/6372
2.46
168
2.44
-1%
ST05/2297
2.56
78
2.49
-3%
ST486
2.63
49
2.59
-5%
ST10/9298
3.22
132
3.30
+3%
ST37/6374
3.33
129
3.08
-7%
ST43/7370
3.37
834
3.33
+1%
ST5359
3.91
131
3.97
+1%
ST359
3.93
87
3.96
+1%
ST48/8462
4.82
508
4.89
+1%
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
ST07/9453
0.21
645
0.22
+4%
ST14/9501
0.43
402
0.50
+17%
ST06/7384
1.08
39
1.05
-3%
ST482
1.94
528
1.99
+2%
ST05/6372
2.46
665
2.48
+1%
ST37/6374
3.33
579
3.29
-1%
ST48/8462
4.82
187
4.89
+1%NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 98
Table 11-6 Gannet CRM for 2014-2017 (SGS)
Table 11-7 Gannet CRM for 2014 to 2017 (Wassa Site Lab)
Table 11-8 Gannet CRM for 2018 (Intertek)
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
ST07/9453
0.21
575
0.21
0%
ST16/9487
0.49
264
0.49
0%
ST626
0.51
664
0.50
-2%
ST06/9481
1.02
89
1.03
+1%
ST06/7384
1.08
167
1.05
-3%
ST602
1.91
324
1.97
+3%
ST482
1.94
635
2.00
+3%
ST575
2.43
476
2.44
0%
G914-2
2.45
14
2.46
0%
ST596
2.51
61
2.51
0%
G910-3
4.03
12
3.96
-2%
ST48/8462
4.82
175
4.91
+2%
ST517
5.23
1108
5.20
-1%
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
ST07/9453
0.21
766
0.21
0%
ST14/9501
0.43
405
0.43
0%
ST16/9487
0.49
419
0.50
+2%
ST06/9481
1.02
280
1.00
-2%
ST588
1.6
763
1.61
+1%
ST482
1.94
516
1.95
+1%
ST37/6374
3.33
30
3.31
-1%
ST43/7370
3.37
955
3.36
0%
ST39/6373
1.67
168
1.66
-1%
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
G913-10
7.10
14
6.94
-2%
G915-3
9.22
23
8.98
-3%
G911-4
2.45
32
2.45
0%
G316-7
5.79
22
5.78
0%
G314-5
5.30
42
5.23
-1%
G314-3
6.68
7
6.59
-1%
ST588
1.6
69
1.60
0%
ST575
2.43
40
2.48
+2%
ST37/6374
3.33
22
3.15
-6%
ST43/7370
3.37
34
3.29
-2%
ST73-8281
1.52
95
1.51
0%NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 99
Table 11-9 Gannet CRM for 2019 Wassa UG (Intertek)
Table 11-10 Gannet CRM for 2020 Jan-Oct, Wassa UG (Intertek)
Table 11-11 Gannet CRM for 2019 Wassa surface drilling (Intertek)
Table 11-12 Gannet CRM for 2018-2019 Father Brown/Adoikrom surface drilling (Intertek)
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
ST638
5.29
2,652
5.14
-3%
ST675
4.91
3,308
4.99
+2%
ST43/7370
3.37
1,390
3.30
-2%
ST575
2.43
1,717
2.39
-2%
G912-3
2.1
254
2.06
-2%
ST601
2.09
2,734
2.06
-1%
ST602
1.91
1,010
1.97
+3%
ST588
1.6
3,488
1.59
-1%
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
ST638
5.29
853
5.07
-4%
ST675
4.91
335
4.99
+2%
ST43/7370
3.37
432
3.33
-1%
ST575
2.43
455
2.39
-2%
ST601
2.09
707
2.10
0%
ST602
1.91
171
2.00
+5%
ST588
1.6
547
1.60
0%
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
ST588
1.60
453
1.58
-2%
ST601
2.09
523
2.06
-1%
ST575
2.43
388
2.38
-2%
ST43/7370
3.37
257
3.29
-2%
ST675
4.91
584
5.02
+2%
ST638
5.29
379
5.18
-2%
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
ST588
1.60
100
1.57
-2%
ST602
1.91
161
1.97
+3%
ST601
2.09
8
2.00
-4%
G912-3
2.10
148
2.05
-2%
ST575
2.43
340
2.39
-2%
ST43/7370
3.37
7
3.24
-4%
ST675
4.91
98
5.03
+2%
G915-3
9.22
5
8.72
-5%NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 100
11.4.6 Blanks
Blank samples are routinely inserted into the sample stream to check for possible sample contamination
during the preparation and assaying process.
Pre-August 2018, the blank material used by GSR, Wassa consisted of coarse sand. The blank samples sent
to SGS laboratory consistently yielded values at or below the detection limit, with zero samples yielding a
value over 10 times the detection limit of gold. With no failures, the sample blanks performed extremely
well and indicated minimal, if any, sample contamination during assaying. From August 2018 to date,
coarse aggregate material (crushed granite) from the Winneba belt has been used as blank material and
inserted into the sample stream. These blanks have performed extremely well over the years as a check for
cross-contamination during sample preparation at Intertek.
From 2014 to 2017, blank material processed at the Wassa site laboratory performed more poorly, with
some samples yielding values close to, or above, 10 times the detection limit of gold. Over time, from 2014
to 2016, the blank samples’ performance noticeably declined. Further investigation of anomalously high
values indicated contamination in the sample preparation process in some cases. The Wassa site
laboratory was primarily used for assaying open pit grade control samples, with a very limited number (13)
of underground diamond drill holes processed by the Wassa site lab during 2017.
External lab analysed blank assay data from 2011 to Oct 2020 included 15,073 assays, all assayed by either
SGS or Intertek. Summary statistics for the blank material assays are shown in Table 11-13, Table 11-14 and
Table 11-15.
Table 11-13 Blank sample summary statistics 2011 to Oct-2020
Table 11-14 Blank sample summary statistics 2019, Wassa surface drilling (Intertek)
Table 11-15 Blank sample summary statistics 2018-2019 Father Brown/Adoikrom surface drilling (Intertek)
Sample Type
Year
Number
Minimum
(Au g/t)
Maximum
(Au g/t)
Median
(Au g/t)
Mean
(Au g/t)
Blanks
2011
278
0.01
0.01
0.01
0.01
Blanks
2012
194
0.01
0.27
0.01
0.01
Blanks
2013
210
0.01
0.11
0.01
0.01
Blanks
2014
56
0.01
0.07
0.01
0.02
Blanks
2015
69
0.01
0.03
0.01
0.01
Blanks
2016
553
0.01
0.03
0.01
0.01
Blanks
2017
930
0.01
0.04
0.01
0.01
Blanks
2017
498
0.01
0.03
0.01
0.01
Blanks
2018
1,089
0.005
0.66
0.01
0.01
Blanks
2019
7,177
0.005
0.08
0.01
0.01
Blanks
2020
2,074
0.005
0.08
0.01
0.01
Sample Type
Year
Number
Minimum
(Au g/t)
Maximum
(Au g/t)
Median
(Au g/t)
Mean
(Au g/t)
Blanks
2019
1419
0.01
0.03
0.01
0.01
Blanks
2020
15
0.01
0.05
0.01
0.01
Sample Type
Year
Number
Minimum
(Au g/t)
Maximum
(Au g/t)
Median
(Au g/t)
Mean
(Au g/t)
Blanks
2019
511
0.01
0.08
0.01
0.01NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 101
11.4.7 Umpire Laboratory Performance
Laboratory checks are performed to check on the reliability of the primary laboratory. In 2013 and 2014,
“round-robin” sample check studies were conducted using SGS, TWL (now Intertek) and the Wassa site
laboratory. SGS laboratory was the primary laboratory during this period. No additional studies have been
completed since then, but there are plans to implement another program in 2021.
In 2014, 252 quarter core samples were selected from drilling conducted between 2012 and mid-2014. The
intersections selected were high-grade intervals which averaged approximately 17 g/t Au. GSR has
previously conducted similar quarter core sampling studies on other GSR owned deposits. The
repeatability of the original results is often poor due to the change in sample size going to half the volume
from the original sample. The 2014 Wassa quarter core sampling study produced the same results, with
good repeatability between the original sample and the corresponding coarse sample reject, and much
poorer repeatability with the quarter core sample. The average grade for both the original assay and the
coarse sample reject duplicate compared well at 17 g/t Au, whereas the quarter core sample was less at 12
g/t Au. However, control sample standards that were submitted with these sample batches consistently
showed a negative bias, as seen in Table 11-16, so this can partially account for the lower average. The
HARD plots shown in Table 11-17 show the good correlation between the original assay value and the
coarse sample reject duplicate, but not when comparing the original assay to the quarter core samples
analysed at TWL Laboratory. Although the negative lab bias and the smaller sample volume attributes to
poor repeatability, the Wassa deposit has a high nugget gold distribution which alone will result in poor
repeatability. The variability of the gold distribution was recognized and GSR has put in sample protocols to
help reduce the variability, i.e. larger sample volumes, BLEG leach well analysis.
Table 11-16 Gannet CRM for quarter core sample analysis (Intertek)
Table 11-17 Summary HARD plot results for quarter core sample analysis
In 2013, 120 RC samples were split into three samples which were sent to each of the laboratories for gold
analysis. The sample batches also contained control samples to monitor the precision of the individual
laboratories.
The three laboratories all performed well with the best correlation being between SGS and the Wassa site
laboratory. The HARD plots for the laboratory comparisons are shown below in Table 11-18.
Table 11-18 Summary HARD plot results for 2013 round robin program
Standard
Certified Mean
(Au g/t)
Samples Submitted
(no.)
Mean Assay Grade
(Au g/t)
Laboratory Bias
ST517
5.23
5
4.98
-5%
ST482
1.94
9
1.78
-8%
ST16/9487
0.49
14
0.46
-6%
Laboratory
Samples
(no.)
<10% HARD
<15% HARD
<20% HARD
Correlation
Coefficient
Original SGS vs Check SGS
252
65%
81%
90%
0.94
Original SGS vs Check Intertek
252
32%
45%
57%
0.60
Check SGS vs Check Intertek
252
29%
44%
55%
0.45
Laboratory
<10% HARD
<15% HARD
<20% HARD
Correlation
Coefficient
SGS vs Wassa
65%
84%
92%
0.97
SGS vs Intertek
68%
84%
88%
0.97
Wassa vs Intertek
71%
84%
90%
0.98NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 102
The <20% HARD correlation for all the labs demonstrates how the larger RC chip samples provide a better
representation of grade. Approximately 90% of the 120 RC samples submitted for this study show a 20%
error, compared to the coarse reject core samples submitted in 2013 and 2014 which show a correlation of
approximately 80% of the data set with 20% error.
In 2012, a “round-robin” exercise was undertaken to check the reliability of Au assay results from the
primary laboratory, SGS. A total of 10% of all assays from the 1m samples received each month were
randomly picked for reanalysis. The data was grouped into six separate ranges, namely 0.00 to 0.50 g/t,
0.50 to 0.90 g/t, 0.90 to 1.20 g/t, 1.20 to 2.00 g/t, 2.00 to 2.50 g/t and greater than 2.50 g/t. The selection
in each range was manipulated until the 10% is achieved with a bias towards the mineralized intervals.
Three samples, each weighing about 3 kg were prepared from each original sample bag using the one-stage
riffle splitter. Four batches of 175 samples including duplicates and standards were dispatched to SGS,
WSL, TWL (Intertek), and ALS Minerals in Ghana-Kumasi (ALS). All samples were labeled with the same
identification numbers. A total of 157 assays were returned by each laboratory for analysis.
Statistical comparison of the data indicates that ALS returned lower grades and variance than SGS, WSL and
TWL (Intertek). SGS and TWL (Intertek) correlated well with similar minimum and maximum grades, and
standard deviation population distribution. The descriptive statistics from the round robin exercise are
included in Table 11-19.
Table 11-19 Round-robin descriptive statistics 2012
In 2017, GSR submitted 578 samples to both SGS and Intertek laboratories, inclusive of CRM. Statistical
comparison of the data indicated that TWL (Intertek) returned slightly lower grades and variance than SGS.
SGS and TWL (Intertek) correlated well with similar minimum and maximum grades, and standard deviation
population distribution. The descriptive statistics from the round-robin exercise are included in Table
11-20.
Table 11-20 Round-robin descriptive statistics 2017
When comparing the results from the two laboratories, the HARD analysis showed that approximately 84%
of the 584 repeat samples fell within approximately 20% error and 69% fell within 10% error. This was a
good correlation between the two laboratories and the decision was made to switch from SGS to TWL
(Intertek). The HARD results for the comparison between the two laboratories are shown in Table 11-21.
Table 11-21 Summary HARD plot results for 2017 round robin program
In 2018, GSWL changed its primary laboratory from SGS to Intertek Ltd. As part of the QA/QC protocols, to
check the reliability of the new primary laboratory, coarse rejects of samples analysed by Intertek were re
bagged with different identification numbers and submitted to SGS as checks, 761 samples were submitted
to SGS between January to August of 2020.
Laboratory
Samples
(no.)
Minimum
(g/t)
Maximum
(g/t)
Mean
(g/t)
Variance
Standard
Deviation
SGS
157
0.01
12.0
1.33
1.75
1.32
WSL
157
0.01
8.9
1.09
1.47
1.21
TWL/Intertek
157
0.01
11.68
1.15
1.68
1.30
ALS
157
0.01
9.32
1.02
1.31
1.15
Laboratory
Samples
(no.)
Minimum
(g/t)
Maximum
(g/t)
Mean
(g/t)
Variance
Standard
Deviation
SGS
584
0.01
113.00
3.33
60.79
7.80
TWL/Intertek
584
0.01
109.20
3.21
55.81
7.47
Laboratory
<10% HARD
<15% HARD
<20% HARD
Correlation
Coefficient
SGS vs TWL/Intertek
69%
78%
84%
0.97NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 103
Sample checks showed a strong correlation between the analytical methods of both laboratories. The
HARD results for the comparison between the two laboratories are shown in Table 11-22. Figure 11-15 and
Figure 11-16 show the HARD and corelation plots respectively.
Table 11-22 Summary HARD plot results for 2018 round robin program
Figure 11-15 HARD plot of 2018 Wassa duplicate analysis (Intertek vs SGS)
Figure 11-16 Wassa duplicates correlation plot (Intertek vs SGS)
Laboratory
<10% HARD
<15% HARD
<20% HARD
Correlation
Coefficient
Intertek vs SGS
73%
84%
90%
0.99NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 104
11.5 Specific Gravity Data
11.5.1 Open Pit
At Wassa SG determinations were carried out by GSR. SG was measured on representative core samples
from drill runs. This ensured representative SG data across all rock types irrespective of gold grade.
SG was measured at the core facility using a water immersion method. For each sample in the dataset, the
sample was weighed in air, then coated in wax and weighed in air and immersed in water. Historically, a
total of 606 determinations were collected on core samples.
The water immersion methodology was considered to provide accurate estimates of variations in bulk SG
throughout the Wassa gold deposits. After testing, each sample was carefully replaced at its original
location in the core box.
Samples were selected from all the different lithologies. The sampling procedure was guided by pit
location, lithology, depth, quartz contents (in oxide) and the oxidation state. A total of nineteen holes from
Dead Man’s Hill, South East, Starter, 419, 242, B-shoot and F-Shoot were selected with the results
presented in Table 11-23.
Table 11-23 Specific gravity test results, open pit
An additional 13 samples consisting of oxide (9), trans (1), fresh (2) and quartz (1) were sent to the Western
University College (WUC, Tarkwa) as independent checks. The average results were 1.76, 2.29, 2.73 and
2.59 g/cm3 respectively.
The SG determinations were considered accurate as the reconciliations between the mined tonnages and
those estimated from the resource models reconcile well.
11.5.2 Underground, 2017
In 2017 an SG study was completed to test whether higher grade mineralization being mined from
underground was heavier than waste rock and the lower grade material mined from the open pits. A total
of 40 samples were selected from four underground drill holes and were sent to Intertek Laboratories for
wax immersion SG determinations. The results from this study indicated that the higher grade
underground mineralization is heavier than the lower grade open pit material. Gold mineralization at
Wassa is directly related to the percentage of pyrite associated with quartz veining; in general, the higher
percentage of pyrite the higher the gold grades. The underground mining exploits these higher grade areas
of the mineralization with associated higher percentages of sulfides which in turn accounts for the heavier
mass of this material. The results of the study are summarized in Table 11-24.
Table 11-24 Specific gravity test results, underground drilling 2017
Material
No. Samples
SG Value (g/cm3 )
Standard Error
Oxide
213
1.80
2%
Transition
42
2.19
3%
Fresh
327
2.70
1%
Quartz Vein
24
2.56
1%
Hole ID
From
(m)
To
(m)
Interval Length
(m)
Au Grade
(avg. g/t)
SG
(avg. g/cm3 )
BS17-670-27
70.5
98.5
5.53
5.53
2.98
BS17-670-11
80.2
110.2
4.30
4.30
2.83
BS17-645-5
100.5
125.6
25.1
42.62
2.94
BS17-670-23
61.8
78.2
4.85
4.85
3.03NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 105
11.5.3 Southern Extension, 2018
In June 2018, GSR conducted a specific gravity measurement program. 723 samples from surface drill core
and 966 samples from underground core were assessed (Table 11-25 and Table 11-26). Results showed
average SG for the underground fresh ore is 2.8. The water displacement method to measure density was
employed, using paraffin sealed core samples.
Table 11-25 Specific gravity test results, underground drilling 2018
Table 11-26 Specific gravity test results, surface drilling 2018
11.5.4 2020 Drilling
In 2020, 58 check SG determinations were conducted on the limited surface drilling. No further SG
determinations were conducted on the UG core as lithologies have essentially remained the same. These
results have confirmed the overall density of 2.8 which has been used in the Mineral Resource Estimations.
These results are summarized in Table 11-5 below.
Table 11-27 Specific gravity test results, surface drilling 2020
Rock Type
No. Determinations
SG
(avg. g/cm3 )
Banded Magnetic Mudstone
67
3.02
Diorite
725
2.83
Felsic Intrusive
–
–
Phyllite
67
2.74
Quartz Vein
107
2.65
Total
966
2.81
Rock Type
No. Determinations
SG
(avg. g/cm3 )
Banded Magnetic Mudstone
32
2.70
Diorite
470
2.69
Felsic Intrusive
41
2.59
Phyllite
131
2.63
Quartz Vein
49
2.57
Total
723
2.63
Rock Type
No. Determinations
SG
(avg. g/cm3 )
Banded Magnetic Mudstone
5
2.75
Diorite
27
2.80
Felsic Intrusive
7
2.78
Phyllite
13
2.87
Quartz Vein
6
2.67
Total
58
2.77NI 43-101 Technical Report (March 2021) Wassa Gold Mine
12 DATA VERIFICATION
The measures implemented by GSR related to data verification are considered by the Qualified Person to
be consistent with standard industry practice and of sufficient quality to include in the estimation of
Mineral Resources.
Core logging and sampling procedures are considered consistent with industry standards. The Qualified
Person has supervised work completed by consultants to assess and validate the logging against the halved
drill core with no major errors identified.
“Blind” test samples are frequently sent to the laboratory and monthly batch results are analysed. Any
anomalous results are queried immediately. A small number of anomalous and/or poor results have been
noted over the years, but these have been identified and the reasons for the results fall into two main
categories, namely:
- Mislabelling of individual samples, standards, and blanks; and/or
- Individual batch issues corresponding to changes in the laboratory setup or calibration. In these
cases, re-assaying has been carried out.
12.1 Drilling Database
The procedures implemented by GSR involve several steps designed to verify the collection of drill hole
data and to minimize the potential for data entry errors. At Wassa, data entry and database management
involves two steps. Drill hole logs are captured directly into an SQL Acquire database via laptop computers,
which are linked to the main database. Acquire has built-in validation tools and drop-down menus,
designed to eliminate erroneous data entry during the core logging process.
Analytical data is checked for consistency by GSR personnel with oversight by the Qualified Person. Upon
reception of digital assay certificates; the assay results, along with the control sample values, are extracted
from the certificates and imported into the Acquire database. Failures and potential failures are examined
and, depending on the nature of the failure, re-assaying is requested from the primary laboratory. Analysis
of quality control data is documented, along with relevant comments or actions undertaken to either
investigate or mitigate problematic control samples.
12.2 Other Verifications by the Qualified Person
The QP for the Mineral Resource estimate is Mitch Wasel has been involved with the project since 2003
and data verification since then includes:
- Regular site visits to oversee and supervise drill programs, including adherence to procedures, and
oversight as it relates to quality control;
- Verification of core logging;
- Spot checks on the database to ensure it’s representative of hard copy data;
- Review and interpretation of QA/QC results (described in Section 11);
- Audits of laboratories;
- Comparison of RC and DD assays;
- Review of analytical methods, results of which informed the decision to move from AAS to BLEG
analysis (described in Section 11);
- Confirmation in the field of collar coordinates to verify drill hole locations; and
- Confirmation in the field of downhole surveys.
Page 106NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 107
13 MINERAL PROCESSING AND METALLURGICAL TESTING
13.1 Early Metallurgical Test Work
On obtaining ownership of the Project in 2002, GSR commissioned a feasibility study (FS) for a CIL operation
with the process engineering component undertaken by Metallurgical Process Development Pty Ltd. (now
known as MDM). The FS was completed in 2003. The metallurgical test work conducted in support of the
MDM FS was conducted on samples from the Wassa area. Samples were originally sent to SGS Lakefield in
Johannesburg for both variability and bulk sample test work. Further variability test work was conducted at
AMMTEC in Perth.
A total of 24 variability samples were tested; 10 of fresh mineralized material, six of oxide, and 8 samples
taken from the existing (now decommissioned and reclaimed) HL operation. Four bulk samples were also
tested, representing fresh, oxide, HL phase 1 and HL phase 2. The samples were all taken from the Wassa
Main area.
At a grind size of 75% -75 µm, and a 24-hour leach time, the fresh bulk sample achieved a leach recovery of
92%. The Bond Ball Mill Work Index (BWi) for this sample was 14.8 kWh/t. Under the same conditions, the
oxide bulk sample achieved a leach recovery of 93%. The BWi for this sample was reported as 8 kWh/t.
Minor preg-robbing behaviour was noted, and gravity recovery test work indicated that plant recoveries of
30 to 40% could be expected from a gravity circuit.
13.2 2015 Test Work Program
In 2015 as part of the Wassa Underground feasibility study, further metallurgical test work was completed.
The test work evaluated the performance of feed from underground with a series of half-core samples from
definition drilling. The physical characteristics and metallurgical response of these samples were compared
to those of a reference sample of current plant feed from that time (open pit sourced).
At the time of test work an exploration decline and bulk sample was obtained from underground, which
was expected to be representative of the underground feed material. The benefit of bulk sample
treatment through the plant resulted in a reduced test work program that included a series of six variability
and four crushability samples that were compared to a reference sample taken from the current open pit
ore feed.
The metallurgical test work was undertaken by SGS in Cornwall, UK and the samples were delivered and
logged in the middle of December 2014 with this initial phase of test work completed and the draft report
issued in early April 2015.
13.2.1 Metallurgical Variability, Crushability and Reference Samples
For the purpose of the metallurgical program, the material planned for future processing was differentiated
spatially by GSR into six underground domains or zones which are depicted in Figure 13-1 with further
details presented in Table 13-1.
Table 13-1 Ore zones represented by the variability samples
Zone
Northing
Relative Level
Tonnes
(‘000 t)
Grade
(g/t Au)
cont.Au
(koz)
Tonnes
share %
Metal
share %
from mN
to mN
from mRL
to mRL
Zone 1 upper
20,200
19937.5
857
682
598
4.74
91.2
15%
14%
Zone 1 lower
20,200
19937.5
682
607
707
6.78
154.1
18%
23%
Zone 2 upper
19,937.5
19690
782
632
723
6.28
146.1
18%
22%
Zone 2 lower
19,937.5
19690
632
507
538
4.32
74.7
14%
11%
Zone 3 upper
19,690
19500
657
557
772
5.02
124.6
20%
19%
Zone 3 lower
19690
19500
557
482
613
4.2
82.8
16%
12%
Total Processing Inventory
3,952
5.3
673.5
100%
100%NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 108
Figure 13-1 West view of metallurgical sample locations (GSR, 2015)
Six variability samples were selected, one for each zone from available HQ and NQ half cores. These core
sections were further cut in half, with one section used for the metallurgical test work and the remaining
quarter core sections retained for reference. Each sample of quarter cores weighed between 50 and 60 kg.
Four full core samples (with a segment removed for assay purposes) were selected for the crushability
tests. Each crushability sample consisted of 7 lengths of HQ drill core each approximately 200 mm in
length. From these, three samples were prepared for the UCS tests with the remaining core sections and
material from UCS testing prepared for the Bond crushability index (low energy crushing) tests.
A single reference sample was also obtained by hand selection from the workings in the Starter pit area at
around the 910 m level. Around 100 kg of material was taken and this sample was used for both
metallurgical and crushability test work.
Table 13-2 Summary and location of test work samples
Sample Type
Detail
Northing
Easting
Relative Level
Sub-samples /
Intersections
from
to
from
to
from
to
avg.
mN
mN
mE
mE
m
m
m
Reference
20,420
20,396
40,004
39,974
910
910
910
6
Variability
Z1U
19,972
20,043
40,113
39,984
828
682
763
6
Variability
Z1L
19,947
19,988
39,994
39,912
678
615
664
7
Variability
Z2U
19,770
19,846
40,084
39,930
753
653
713
5
Variability
Z2L
19,700
19,757
40,079
39,931
602
530
575
6
Variability
Z3U
19,531
19,576
40,023
39,979
602
562
585
4
Variability
Z3L
19,497
19,565
40,040
39,945
555
510
533
5
Crushability 1 BSDD347MET 19,492
19,489
40,024
39,999
587
514
553
8
Crushability 2
WMET4
20,053
20,050
40,014
39,999
767
748
753
8
Crushability 3
WMET5
20,036
20,036
39,980
39,975
722
713
719
8
Crushability 4
WMET6
20,017
20,016
39,976
39,964
716
652
700
8NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 109
The locations of the reference, variability and crushability samples are presented in Table 13-2 along with
the nominal ore zones selected. Some of the crushability samples selected were adjacent to rather than
completely within the representative ore zone. Crushability 1 was from depth to the south of Zone 3 Lower
while the other crushability samples were from different depth within Zone 1 Upper and Zone 1 Lower.
The reference sample was taken from the current workings in the starter pit area above and to the north of
Zone 1 Lower at 910 mRL.
13.2.2 Details of Metallurgical Test work
The metallurgical evaluation test work program included the following investigations:
- Scope of work for reference and variability samples:
o elemental scan: ICP multi-element analysis;
o analysis of sulphide and total sulphur;
o analysis of carbonate and graphitic carbon;
o diagnostic leach (gold deportment tests);
o BWi; and
o Bond abrasion index (Ai).
- Standard flowsheet treatment tests – to confirm recoveries and reagent additions / consumptions:
o grind calibration tests;
o gravity concentration;
o cyanide leaching of the gravity tails with pre-aeration; and
o settling tests.
- Scope of work for crushability and reference samples:
o unconfined compressive strength (UCS);
o Bond low impact crushing work index (CWi);
o BWi; and
o Ai.
13.3 Test Work Findings
13.3.1 Head Grade and Elemental / Chemical Analyses
The gold and silver head grades were determined by milling and screening at 106 µm with fire assay of the
two screen fractions. The results are summarized in Table 13-3.
Table 13-3 Screened head assay results
Sample
Overall Grade
Size fraction
Gold
Distribution
Silver
Distribution
+106 micron
-106 micron
Au g/t
Ag g/t
Share
Au g/t
Ag g/t
Au g/t
Ag g/t +106μm -106μm +106μm -106μm
Reference
1.53
0.1
1.9%
11.32
0.2
1.14
0.1
13.9%
86.1%
3.7%
96.3%
Zone 1 Upper
6.51
0.4
2.4%
28.29
1.6
7.03
0.4
10.3%
89.7%
8.8%
91.2%
Zone 1 Lower
7.99
0.6
2.3%
42.29
4.2
7.31
0.6
12.0%
88.0%
15.0%
85.0%
Zone 2 Upper
5.11
0.4
1.3%
17.26
1.0
4.38
0.3
4.2%
95.8%
3.5%
96.5%
Zone 2 Lower
4.64
0.2
2.4%
9.94
0.8
4.52
0.2
5.0%
95.0%
8.8%
91.2%
Zone 3 Upper
4.07
0.5
1.6%
9.45
0.6
4.42
0.5
3.6%
96.4%
2.1%
97.9%
Zone 3 Lower
5.26
0.6
2.2%
25.3
2.8
5.29
0.5
10.3%
89.7%
10.9%
89.1%NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 110
In all samples, the gold and silver analyses in the coarse fraction (+106 µm) is higher than for the finer
fraction (-106 µm).
An ICP elemental scan was undertaken on the reference and variability samples; in addition, the total
carbon and organic carbon as well as the total sulphur and sulphide sulphur were analysed using the Leco
method. Results are presented in Table 13-4.
Table 13-4 Elemental and chemical analysis results
Sample
1010A
2008A
3008A
4008A
5008A
6007A
7007A
(%)
REF1
Z1U
Z1L
Z2U
Z2L
Z3U
Z3L
Cu
0.003
0.019
0.011
0.01
0.01
0.008
0.01
Pb
<0.001
0.002
<0.001
<0.001
<0.001
<0.001
0.002
Zn
0.006
0.009
0.01
0.008
0.009
0.008
0.007
As
<0.001
0.001
0.003
0.001
0.001
0.001
<0.001
Cd
<0.0001
0.0003
0.0003
0.0003
0.0002
0.0002
0.0002
Ni
0.002
0.004
0.004
0.002
0.002
0.005
0.003
Co
<0.001
0.003
0.004
0.004
0.003
0.003
0.003
Mn
0.07
0.14
0.18
0.2
0.15
0.1
0.13
Bi
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
Sb
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
Hg
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
Te
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
Se
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
SiO2
78.46
74.96
65.39
66.51
59.42
65.39
57.55
Al
3.32
3.48
4.46
4.37
5.22
4.65
5.24
Fe
2.83
5.57
6.46
5.48
4.67
3.92
4.62
Mg
0.74
0.88
1.09
1.27
1.53
1.47
1.8
Cr
0.03
0.06
0.05
0.03
0.02
0.01
0.01
Ca
1.82
1.1
1.81
2.14
3.47
2.71
3.77
S
0.46
0.86
1.56
0.98
1.3
1.17
0.9
Na
0.92
0.96
1.46
1.93
1.98
1.57
2.16
K
1.36
1.7
1.79
1.57
1.38
2.11
1.6
% S (total)
0.46
0.86
1.56
0.98
1.3
1.17
0.9
% S (soluble)
0.02
0.03
0.04
0.04
0.04
0.03
0.03
% S (sulphide)
0.44
0.83
1.52
0.94
1.26
1.14
0.87
% C (total)
1.4
1.42
1.69
1.99
2.22
1.86
2.52
% C (organic)
0.03
0.02
0.03
0.02
0.03
0.02
0.02
% C (CO3)
1.37
1.4
1.66
1.97
2.19
1.84
2.5
The level of sulphide sulphur was higher in the higher grade variability samples than in the reference
sample. Similarly, the level of iron and other base metals was higher; however, the levels of the other base
metals is relatively low. NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 111
13.3.2 Diagnostic Leach
Diagnostic leaching is a method of quantifying the indicated deportment of gold in a sample and the
relative ease or difficulty with which the gold can be recovered. The sample is prepared by grinding to a
typical grind size likely to be employed (75% < 75 µm was selected) and is subject to a cyanide leach to
dissolve the free gold. The solids from the initial cyanide leach test are then sequentially pre-treated with
more aggressive acids to dissolve minerals that could be encapsulating the residual gold. Following each
pre-treatment stage the sample is again treated by cyanide leaching. As the level of sulphide minerals was
indicated to be higher in the higher grade underground material from the geological interpretation of the
core samples and confirmed from the elemental analyses presented in Table 13-5 the aim was to
determine whether the increased level of sulphide minerals was resulting in the samples being more
refractory to treatment for the recovery of gold.
In the diagnostic leach procedure, the samples are subject the following leach and pre-leach treatments:
- Direct cyanidation: recovers free and exposed gold.
- Hydrochloric acid pre-treatment: liberates gold encapsulated in carbonates, pyrrhotite, galena and
iron hydroxide minerals.
- Sulphuric acid (oxidative) pre-treatment: liberates gold encapsulated in sphalerite, labile copper
sulphate and labile base metal sulphide minerals.
- Nitric acid pre-treatment: liberates gold encapsulated in pyrite, arsenopyrite and marcasite.
- Carbon combustion: burns off any organic carbon releasing gold that had previously been
adsorbed by the carbon and not therefore amenable to recovery by cyanide leaching.
Residual gold and silver present after the above tests represent gold encapsulated in silica and other non
reactive gangue minerals.
Results of the diagnostic leach tests for gold are summarized in Table 13-5 and represented graphically
showing the deportment of gold in the samples in Figure 13-2.
Table 13-5 Summary of diagnostic leach results
Gold Deportment
Sample Reference
Ref 1
Z1U
Z1L
Z2U
Z2L
Z3U
Z3L
%
%
%
%
%
%
%
Cyanide Soluble
91.9
96.82
97.05
93.13
86.92
89.5
85.34
In Carbonates / Pyrrhotite
1.38
0.88
1.1
1.7
8.83
2.37
2.99
In Sphalerite and Labile Sulphides
0.66
0.58
0.23
0.73
1.22
0.97
2.18
In Pyrite and Arsenopyrite
2.53
1.22
1.26
3.3
1.91
4.01
7.01
In Graphitic Carbon
0.59
0.27
0.1
0.35
0.38
0.45
0.4
Residual Gold
2.93
0.23
0.25
0.79
0.74
2.71
2.08
TOTAL
100
100
100
100
100
100
100
The results generally indicated that the mineralogy and metallurgy of the samples are somewhat different
with some samples appearing to have potentially more gold locked or associated with different sulphide
minerals and others less when compared to the reference sample. Two samples (Z3U and Z3L) showed
potentially higher levels of gold encapsulated in pyrite while sample Z2L showed higher levels of gold
potentially associated with more reactive minerals such as pyrrhotite. The results were not seen to be
completely consistent with the gravity leach results discussed later.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 112
Low levels of preg-robbing potential were indicated from the gold liberated in the burn off stage. It should
be noted that due to assay detection limits some of the lower deportments may be marginally inaccurate.
Given a detection limit of 0.01 g/t Au, measurements below this level were assigned a nominal assay of
0.005 g/t Au; hence on the lower levels the deportment in these fractions could be slightly overstated.
It was reported in the diagnostic leach tests during the hydrochloric acid digestion that a reasonably
vigorous reaction took place on the majority of the variability samples with the generation of green foam.
This would tend to indicate a high level of carbonate and also acid soluble iron, possibly pyrrhotite.
Figure 13-2 Comparative indicated deportment of gold from diagnostic leach results
13.3.3 Crushability
Two separate tests were undertaken into the material strength and crushability by measuring the UCS and
the CWi test, which indicates a material’s resistance to crushing. In the UCS test, a sample is prepared by
cutting to pre-set dimensions (re-coring) and this is then subject to a compressive load to measure the
strength at which the sample fails. The Bond CWi test, also known as the low impact energy test, involves
two swinging weighted pendulums which are allowed to fall and impact simultaneously on the sample in
order to measure from what height the pendulum needs to fall to crush the sample. Both tests are
undertaken on multiple individual samples; 3 prepared samples in the case of the UCS tests and around 20
sample pieces for the Bond CWi test. The results of the tests are presented in Table 13-6.
Table 13-6 Results of Crushability Tests: UCS and CWi
Density
Depth
UCS Result (Mpa)
CWi (kwh/t)
Depth
t/m3
RL m
Average
Max
Min
Average
Std Dev
m RL
Reference
2.67
910
59.5
73.7
41.8
9.8
1.6
910
Crushability 1
2.93
550
64.7
76.9
54.3
9.7
1.3
550
Crushability 2
2.87
753
53.9
94.4
31.1
11.1
1.2
753
Crushability 3
2.71
720
167.4
244
90.7
11
2.1
720
Crushability 4
2.84
699
82.4
90
68.9
12.3
2.9
699
The UCS test results are seen to be variable, with a relatively large variation between the maximum and
minimum measurements on the different samples which mainly appear to relate to the sample tested NI 43-101 Technical Report (March 2021) Wassa Gold Mine
rather than the depth of the material. Results were generally in the 30 to 95 MPa range, indicating that the
materials tested were medium strong to strong, although one sample (Crushability 3) indicated to consist of
quartzite (massive quartz vein), rather than schist identified for the majority of the other samples tested,
recorded a very strong measurement of around 240 MPa. The other sample of the same type of material
measured 90 MPa, while a third sample shattered during preparation and cutting and failed to produce the
required test sample.
The CWi test results are in the easy to medium classification. Similar to the UCS results, the CWi test results
are also relatively variable with the reference sample (910 mRL) generally indicating results towards the
lower end of those measures; however, no real correlation can be see between the CWi results and relative
level of the sample tested as shown in Figure 13-3.
Figure 13-3 Variation of UCS and CWi results with depth (mRL)
13.3.4 Ball Milling Bond Work Index and Abrasion Index
For the 2003 FS into the treatment of the Wassa material by milling and CIL, test work was undertaken on
representative samples of primary ore, oxides and spent HL material. The BWi for the primary and oxide ores
were reported to be in the region of 14.6 and 8 kWh/t, respectively.
More recent investigations suggest that the BWi is generally noted to be increasing with depth. Based on
samples tested from three different drillholes from the Wassa starter pit area, SE Area and MSN Area, BWi
measurements, though somewhat inconsistent, appeared to indicate that the BWi was increasing with depth.
From 2015, with fresh open pit ore feed, the unit power draw presented for the two ball mills is shown to be
between 14.5 and 16.5 kWh/t treated. This results in a calculated BWi of around 14 – 16 kWh/t, based on
the reported mill feed and product sizes and power draw on the ball mills. An allowance has been included
in the calculations for mechanical and other losses between the drive motor and mill. In recent years with
the blend of underground and open pit the BWi continues to remain within the 14 – 16 kWh/t range.
The findings of the BWi and Ai investigations from the 2015 tests are presented in Table 13-7 and are
shown as a function of the average sample depth Figure 13-4 and Figure 13-5, respectively.
The BWi tests were undertaken at a closing screen size of 106 µm to give a mill product of around 75-80% <
75 µm.
In summary, the findings of the latest test work generally did not support the suspected increasing BWi with
further depth with the reference sample (910 m RL) showing the highest BWi reading.
Table 13-7 Results of 2015 BWi and Ai Tests
Page 113NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 114
Sample Description
BWi
Ai
Avg. Depth
kWh/t
RL m
Reference
15.7
0.394
910
Z1U Zone 1 Upper
15.3
0.33
763
Z1L Zone 1 Lower
14.7
0.276
664
Z2U Zone 2 Upper
14.9
0.228
713
Z2L Zone 2 Lower
14.5
0.175
575
Z3U Zone 3 Upper
14.4
0.229
585
Z3L Zone 3 Lower
13.9
0.152
533
Crushability 1 (347MET)
14
0.182
553
Crushability 2 (MET4)
15
0.205
753
Crushability 3 (MET5)
14.8
0.398
719
Crushability 4 (MET6)
14.8
0.326
700
Figure 13-4 2015 Ball Mill Bond Work Index against sample depth (mRL)
Figure 13-5 2015 Abrasion Index against sample depth (mRL)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 115
The abrasion index is a measure of the anticipated wear on components and consumables in the
comminution circuit and is applicable to wear in both crushers and mills (media and liners). Ai is generally
shown not to be increasing with depth and it appears that Ai is slightly lower on deeper samples. With the
exception of one sample (MET 5) of massive quartz vein, measured Ai is for the reference sample is higher
than all the other variability and crushability samples tested. This lower indicated abrasion index with
depth may result in the reduced consumption of grinding media and mill crusher liners as mining proceeds
deeper into the underground mining areas. All the samples fall into the slightly abrasive classification.
13.3.5 Gravity Gold and Leaching Tests
13.3.5.1 Gravity Tests
Gravity tests were undertaken by grinding a 1 kg sample to approximately 75% passing 75 µm and then
passing the sample through a Falcon centrifugal concentrator. The primary concentrate from the Falcon
was further processed on a Mozley shaking table, with the final concentrate weighed and sent for assay.
Tailings from the centrifugal concentrator and shaking table were subject to cyanide leach tests.
The results of the gravity concentration tests are presented in Table 13-8.
Table 13-8 Gravity Gold Recovery Test Results
Sample
Ref
Gravity Con Mass
Assay
Metal Recovery to
Gravity Con
g
Wt %
Au (g/t)
Ag (g/t)
% Fe
% S
(total)
Au %
Ag %
Ref1
3.3
0.33
84.33
8.0
19.59
15.61
18.19
26.4
Z1U
2.1
0.21
322.6
18.8
37.28
21.86
10.41
9.18
Z1L
4.9
0.49
322.3
19.3
38.24
26.92
19.77
15.01
Z2U
2.5
0.25
324.3
26.3
37.05
31.09
15.87
18.26
Z2L
3.0
0.30
211.6
13.4
35.84
44.15
13.68
19.14
Z3U
2.7
0.27
199.2
14.8
34.31
38.32
13.21
8.88
Z3L
2.4
0.24
282.8
24.1
28.80
29.76
12.90
10.52
Gravity recoveries were lower than previously reported. This is probably a function of the laboratory tests
which, for this stage of the investigation, were not optimized to maximize gravity gold recovery. It can also
be seen that the recovery from the reference sample is generally higher than on the variability samples.
In all gravity tests, concentrates contained a magnetic component that was readily picked up by a strong
rare earth magnet but not an iron magnet. This magnetic component was suspected to be pyrrhotite and
this was reported by SGS to be supported by the sulphur to iron ratios measured in the feed analyses.
13.3.5.2 Whole Ore Leach and CIL Evaluation Test
In order to investigate the effective leach parameters for the comparative leaching tests, a single leach test
was undertaken on the reference sample with and without carbon to confirm whether any preg-robbing
effect was evident. The results are presented in Table 13-9.
Table 13-9 Whole Ore Leach and CIL test results
Solution
(24h/48h)
Solid tails
Gold on Carbon
Overall
Recovery
Back Calc.
Head Grade
Au g/t
Ag g/t
Au g/t
Ag g/t
Au g/t
Ag g/t
Au %
Au %
Au
g/t
Ag g/t
Leach Test
1.13
0.08
0.105
0.05
–
–
–
–
1.55
0.15
Distribution
93.2%
67.0%
6.8%
33.0%
–
–
93.2%
67.0%
–
–
CIL Test
0.14
0.01
0.1
0.05
93.4
12.7
–
–
1.21
0.19
Distribution
14.3%
6.5%
8.3%
26.4%
77.4%
67.1%
91.7%
73.6%
–
–NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 116
The results generally indicated that no preg-robbing effect was evident with the recoveries without carbon
addition higher than those with carbon added to the leach (CIL test), although the gold reconciliation was
seen to be worse on the CIL test with a back-calculated gold head grade of 1.21 g/t Au compared to the
screened analysis head grade and leach test back-calculated head grade of 1.53 and 1.55 g/t Au
respectively.
13.3.5.3 Gravity Tails Leach Test Results
Leach tests were undertaken on the combined gravity tails from the centrifugal concentrator and
concentrate cleaning table. From the gravity tests and one of the diagnostic tests there was potential that
pyrrhotite could be present so the gravity tails samples were adjusted to pH 10.5 – 11 using lime and
aerated until the pH and dissolved oxygen levels stabilized generally in line with the plant practice of
injecting oxygen into the transfer lime from milling to CIL. Pyrrhotite is highly reactive and can result in
high consumptions of oxygen and cyanide in leach if not preconditioned.
Leach tests were conducted for 48 hours with samples taken at 2, 4, 6, 24 and 48h and analysed for gold
and silver in solution. An initial cyanide level of 1 g/l was used and cyanide levels in solution were
maintained at >0.5 g/l by dosing of additional cyanide as required. The tails solids were analysed for silver
and gold. No lead nitrate was added in the leach tests.
Leach test results of the gravity tails are presented in Table 13-10.
Table 13-10 Leach test results and reagent consumptions
Sample Reference
Gold Recovery %
Assayed Tails
Consumption kg/t
24h
48h
g/t Au
NaCN 24h
NaCN 48h
Lime as CaO
Ref1
77.22
88.69
0.09
0.43
1.31
0.88
Z1U
90.69
87.35
0.44
0.51
1.48
0.89
Z1L
86.72
87.64
0.68
0.40
1.15
0.75
Z2U
92.81
93.80
0.20
0.43
1.05
0.92
Z2L
87.81
88.06
0.42
0.15
0.91
0.88
Z3U
92.95
91.33
0.23
0.63
0.89
1.16
Z3L
94.57
93.25
0.18
0.63
1.01
1.11
Figure 13-6 Leach recovery kinetic curvesNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 117
It can be seen that in some tests, recoveries based on 48h leach solution analyses were lower than for the
those based on the 24h leach solution assays. This could be caused by analytical discrepancies or errors
based on solutions analysed or possibly some adsorption of dissolved gold onto the fine milled solids. As
no appreciable preg-robbing potential or effect was indicated in the diagnostic leach and comparative leach
and CIL tests, this is not considered to be a major concern as any weakly adsorbed gold would be recovered
on the plant due to the presence of activated carbon in the leach circuit.
The leach curves on the gravity tails appear to be relatively consistent with the exception of that for the
reference samples which shows slower kinetic especially at 24h, although results in similar overall
recoveries at 48h, shown in Figure 13-6.
13.3.5.4 Overall Gravity / Leach Recoveries
The overall recoveries from the gravity / leach test work are presented in Table 13-11. These are based on
the maximum leach recovery at either 24 or 48h and on the back-calculated head grade from the recovered
gold and tailings assays.
Table 13-11 Overall gravity leach recoveries
Sample
Reference
Gold Recovery %
Gravity
Leach
Overall
Ref1
26.41
88.69
91.68
Z1U
16.38
90.69
92.22
Z1L
22.69
87.64
90.44
Z2U
20.19
93.80
95.05
Z2L
15.37
88.06
89.90
Z3U
16.91
92.95
94.15
Z3L
20.41
94.57
95.68
In the gravity / leach tests, poor reconciliations were achieved between the back-calculated head grade and
the assay head grades from the screened analyses on the master samples with the back-calculated head
grades consistently being considerable lower than the head assay results by as much as 35% in two tests.
The comparison of the assay head compared to the back-calculated head grade for both the gravity leach
and diagnostic leach results are presented in Table 13-12.
Table 13-12 Reconciliation of assay and back-calculated head grades from test work
Sample
Assay Head Grade
From Diagnostics
From Gravity / Leach
Grade
Grade
g/t Au
g/t Ag
g/t Au
g/t Ag
g/t Au
g/t Ag
Reference
1.53
0.10
1.35
0.22
1.08
0.13
Z1U
6.51
0.43
6.74
0.89
4.18
0.31
Z1L
7.99
0.63
8.71
1.06
7.08
0.46
Z2U
5.11
0.36
5.10
0.62
4.03
0.38
Z2L
4.64
0.21
4.84
0.46
4.14
0.32
Z3U
4.07
0.45
4.12
0.33
3.20
0.30
Z3L
5.26
0.55
4.28
0.27
3.36
0.29
The correlations were better in the diagnostic leach tests compared to the gravity / leach tests with both
positive and negative discrepancies. Differences varied between -10% and +18% resulting in an overall
difference of only -2%.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 118
13.3.6 Settling Tests
Comparative settling tests were undertaken on the reference sample and one selected variability sample
(Z1L). Initial scoping tests were undertaken using five different flocculants with the settling tests
undertaken using Nasaco anion flocculants N2132 and N2326. The results show very similar settling
performance on the reference samples and one variability sample selected.
The settling test results are presented in Table 13-13.
Table 13-13 Comparative settling test results
Sample
Feed
Solids
pH
Flocculant
Flocculant
Dosage
Initial
Settling
Rate
Final
Solids
Content
Thickener
Underflow
Unit Area
%
g/t
m3 /m2 /day
%
m2 /t/d
Reference Test 1
9.43
10.5
N2132
50.04
1335.26
59
0.235
Reference Test 2
10.08
10.5
N2326
46.62
2897.86
61.8
0.261
Z1L Test 1
9.04
10.5
N2132
52.21
2414.88
56.5
0.225
Z1L Test 2
9.13
10.6
N2326
51.69
2637.79
56.9
0.223NI 43-101 Technical Report (March 2021) Wassa Gold Mine
14 MINERAL RESOURCES
14.1 Introduction
The Mineral Resource Statement presented herein represents an estimate for the Wassa Main deposit and
the satellite deposits Chichiwelli, Benso and Hwini Butre. The Mineral Resource Statement is presented in
accordance with the guidelines of NI 43-101.
The GSR exploration team was responsible for preparation of the long-range model (LR model) for the
Wassa Mineral Resource modelling exercise which included all topographic surfaces, weathering surfaces,
structural control lines and resulting Leapfrog Isoshells. SRK (Toronto), utilizing the inputs from the GSR
geologists, estimated gold grades for the LR model, whereas the short-range model (SR model), used within
the active mining area, Figure 14-1, was created by the GSR mine geologists with assistance from SRK
(Moscow). The Father Brown and Adoikrom Mineral Resource Estimates were created in a similar manner
with GSR providing drill hole intervals for HW, HG and FW mineralized zones to Resource Modeling
solutions (RMS) who provided 2D estimates of the grades and thicknesses. The Benso and Chichiwelli
Mineral Resource Estimates are historical models created by GSR geologists and SRK (Cardiff). The Mineral
Resource classification and statement was conducted by GSR under the supervision of S. Mitchel Wasel, a
For the SR model, the site’s mine geology group was responsible for the generation of the structural control
lines used to influence the grade interpolation in the model. SRK (Moscow) then performed the domain
generation and grade interpolation steps, as well as the depletion and validation of the block model. SRK
(Moscow) depleted the block model with asbuilt and CMS volumes provided by GSR. The completed block
model was also independently validated by the Wassa mine geology group.
Figure 14-1 Wassa long-range (grey) and short-range (cyan) Mineral Resource estimation model limits
Page 119NI 43-101 Technical Report (March 2021) Wassa Gold Mine
This section describes the Mineral Resource estimation methodology and summarizes the key assumptions
considered for the estimate. The Mineral Resource estimate reported herein is a reasonable
representation of the global gold Mineral Resource found at the Wassa Main and satellite deposits given
the current level of sampling. The Mineral Resources have been estimated in conformity with generally
accepted CIM “Estimation of Mineral Resource and Mineral Reserves Best Practices” guidelines and are
reported in accordance with NI 43-101. Mineral Resources are not Mineral Reserves and do not have
demonstrated economic viability. There is no certainty that all or any part of the Mineral Resource will be
converted into Mineral Reserve.
The databases used to estimate the Mineral Resources were audited internally by GSR. In the opinion of
the GSR QP, S. Mitchel Wasel, the current drilling information is sufficiently reliable to interpret with
confidence the boundaries for gold mineralization and that the assay data are sufficiently reliable to
support Mineral Resource estimation.
14.2 Mineral Resource Estimation Procedures
The Mineral Resource evaluation methodology involved a database compilation and internal validation
exercise by GSR. At Wassa, GSR was responsible for structural control lines, grade wireframes, topographic
and weathering surfaces. GSR provided SRK with borehole databases, structural control lines, grade
wireframes, topographic surfaces and weathering surfaces. At HBB, GSR was responsible for the HW, HG
and LG drillhole intervals, topographic and weathering surfaces and RMS estimated the gold grades and
mineralized zone thickness.
Prior to initiating the modelling and Mineral Resource estimation process, SRK reviewed the databases for
the Wassa project. The Father Brown and Adoikrom data was reviewed by RMS prior to gold grade
estimations.
After evaluating the available database, SRK proceeded with (Wassa), the data conditioning (compositing
and capping) for geostatistical analysis and variography. At Wassa, the grade wireframe modelling was
completed in Leapfrog Geo 4.4 under following the guidelines that GSR and SRK have established together.
The grade interpolation methodology was discussed between GSR and SRK, it was decided to use Ordinary
Kriging (OK) with local varying angles and local variograms for the estimation of gold grades based on the
structural complexity and folded nature of the deposit.
For the SR model, database compilation and internal validation checks were performed by GSR. The
database was then passed to SRK (Moscow) who performed a second data validation prior to commencing
modelling work. GSR was responsible for the generation of the structural control strings, which were used
to influence the domain shell creation and the grade estimation.
SRK (Moscow) then:
- Created the structural control meshes from the structural control strings;
- Created the domain shells;
- Coded the sub-block model with the domain information;
- Estimated grade using OK with locally variable anisotropy;
- Depleted the model with development and stope surveys; and
- Validated the model.
On completion, SRK (Moscow) submitted the Surpac and Leapfrog models to GSR Mine Geology for
independent validation.
The classification of the LR model and preparation of the Mineral Resource Statement utilizing both long
range and short-range estimates were conducted by GSR under the supervision of GSR’s QP, Mr. S.
Mitchel Wasel.
Page 120NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 121
14.3 Mineral Resource Database
14.3.1 Wassa
The Wassa database is made up of five individual drillhole databases, namely:
- GSR Wassa exploration database, which contains exploration drilling conducted by GSR since 2002;
- GSR Underground drilling database, which contains all of the diamond drill holes drilled from
underground;
- the All Wassa (AW) exploration database, which contains historical exploration drill holes from SGL;
- Satellite Open Pit grade control database, which is dominantly blast holes; and
- GSR Open Pit grade control database, which is dominantly RC holes.
The Satellite grade control database was not included in the Mineral Resource estimate as the blast holes
samples are considered not to be of a sufficient quality for use in the Mineral Resource estimate.
A completion date cut-off was applied to the GSR exploration and Underground drill hole databases. For
the 2020 year-end LR model estimate the cut off for surface and underground drilling was 31 January 2020
and for the SR model estimate the drilling results were up to 30 November 2020. These are the data sets
utilized for the subsequent Mineral Resources shown in Table 14-1.
Table 14-1 Wassa LR model drill hole database as at February, 2020
Database
Total
Type
Purpose
Holes
Metres
Pre-Existing
Grade Control
24,957
642,470
Exploration
3,422
500,282
UG Exploration
847
93,896
At February 20
Grade Control
411
12,142
Exploration
59
48,036
UG Exploration
371
56,914
Total
30,067
1,353,740
The later 30 November cut-off allowed addition of 273 underground drill holes totaling 34,275 m to be
included in the SR model estimate.
The borehole databases contain: collar details; downhole deviation surveys; gold assays; lithological
descriptions; alteration; structural data; major structures and vein descriptions. GSR and SRK have
performed validation routines to the database. Based on this assessment and checks described in Section
12, it is the opinion of the QP that the database is appropriate to inform the Mineral Resource estimate.
For the SR model, all data was initially stored in the GSR master acQuire database. The relevant Wassa
Mine geology data was then exported from acQuire in .csv format, to a Surpac-linkedMicrosoft Access
database. The database contained all Wassa related surface exploration drilling, all underground Mineral
Resource definition drilling, all underground channel sampling, all underground chip sampling, and all
underground sludge sampling data.
For the purpose of the short-range block modelling, the chip, channel and sludge data was excluded from
the estimation runs, leaving only the surface and underground diamond drill core and surface RC assay
data. GSR made this decision because, after statistical review of the data, SRK (Moscow) concluded that
the risk of biases existing in the chip, channel and sludge data exceeded the benefits from allowing these
additional samples to inform the estimation. Table 14-2 summarizes the number of drill holes contained in
the Surpac Access database, that were subsequently used for the short-range Mineral Resource estimate.
The Surpac Database only utilized surface drill holes that are in the immediate vicinity of underground
mine, whereas the LR model has a much larger extent and used all of the validated drill holes available. NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 122
Table 14-2 Wassa Underground short-range drill hole database as of December 1, 2020
Location
Type
No. Holes
Drill Metres
Wassa UG
DD
1,491
185,086
Wassa Surface
DD
841
302,253
Wassa Surface
RC
543
56,894
Total Drilling
DD + RC
2,875
544,233
14.3.2 Hwini Butre
The Father Brown/Adoikrom database is made up of Exploration DD and RC holes as well as RC grade
control drilling data.
The 2020 year-end Mineral Resource estimate utilized all of the drilling data that was available at the end
of 2019 which essentially remained unchanged as at the end of 2020, as summarized in Table 14-3.
Table 14-3 Father Brown/Adoikrom drill hole database as of December 2020
Location
Type
No. Holes
Drill Metres
Father Brown/Adoikrom
DD Exploration
435
66,229
RC Exploration
214
16,323
RC Grade Control
3,087
72,037
The borehole databases contain information including collar information, downhole deviation surveys, gold
assays, lithological descriptions, alteration, structural data, major structures and vein descriptions.
GSR has performed validation routines to the Mineral Resource database. Based on this assessment, and
the checks described in Section 12, it is the opinion of the QPs that the borehole database is appropriate to
form the basis of the Mineral Resource estimate.
14.3.3 Benso
SRK was provided with a Gemcom project directory containing the drilling data (Table 14-4) as audited by
GSR along with the geological wireframes, oxidation and topographic surfaces and block model parameters.
Additional information was provided as Excel spreadsheets documenting QA/QC data and results of density
determinations.
Table 14-4 Benso drill hole database as of December 2012
Location
Type
No. Holes
Drill Metres
Benso
RC
465
33,276
DD
321
37,623
Geotech
14
1,637
GC (RC)
2,362
57,970
14.3.4 Chichiwelli
SRK was provided with a Gemcom project directory containing the drilling data (Table 14-5) as audited by
GSR and the geological models subsequently produced by GSR including geological wireframes, oxidation
and topographic surfaces and block model parameters. Additional information was provided as Excel
spreadsheets documenting QA/QC data and results of density determinations.
Table 14-5 Chichiwelli drill hole database as of 2012
Location
Type
No. Holes
Drill Metres
Chichiwelli
RC
483
29,802
DD
23
3,692
Geotech
–
–
GC (RC)
–
–NI 43-101 Technical Report (March 2021) Wassa Gold Mine
As no mining has taken place at Chichiwelli, the topographic survey used for the 2010 Mineral Resource
statement remains current.
The “HBB other” tonnes and grade in the Mineral Resource statements in sub-section 14.9 also includes
three small deposits located in the Manso and Hwini Butre Prospecting and Mining licence areas. These
deposits are Abada, Adoikrom South and C3PR. The techniques used to estimate these deposits are
consistent with those reported for Chichiwelli.
14.4 Grade Shell Modelling
14.4.1 Wassa Mineralization Wireframes
The LR model wireframe modelling was carried out by GSR geologists using Leapfrog Geo 6.0 software.
Mineralized wireframes at Wassa are modelled using an indicator approach which uses a 0.4 g/t cut-off for
the low grade (LG) envelopes and a 1.5 g/t cut off for high grade (HG). Visual inspection of assay data
suggests that these respective lower cut-off levels are reasonable to separate barren from auriferous
sections intersected by each borehole. Mineralized shells are created using this indicator approach
combined with structural trend surfaces created by the site geologists and reviewed by SRK.
For the SR model, the cut-offs used to define LG or “halo” domain and HG or “mineralized” domain were
the same as those used for the LR model but the methodology used in by SRK using Leapfrog Geo 6.0
software was different in that grade thresholds were used instead of indicator. As per the LR model,
structural trend surfaces were used to influence the shape of the domain shells.
14.4.2 Wassa Indicator Interpolants – Background
An indicator interpolant works in a similar way to a grade shell, but rather than interpolating the raw grade,
all data above the given indicator grade value is assigned a value of 1 and all data below the indicator grade
value are assigned a value of 0. A shell is then generated at a defined iso-value, between 0 and 1. This
helps to remove the impact of very high grades which can result in “blow-outs” or unrealistic volumes that
can result from standard grade shell modelling of highly skewed data populations.
The indicator interpolant is influenced by an anisotropic structural trend, which is based on form surfaces.
The form surfaces represent vectors of grade continuity, where grade continuity is high along the modelled
form, and low across it. Due to the significantly deformed nature of the gold mineralization, this type of 3-
dimensional structural trend is vital to produce a geologically realistic shape of the indicator interpolants.
The SR model did not use the indicator interpolant method employed in the LR model. Rather, the domain
shells for the SR model were generated by directly interpolating the Au grade values above a nominated
threshold. The reason for the difference between the two modelling methodologies comes down to the
difference in drill spacing between the two models – wide spacing in the LR model and tighter drill spacing
in the SR model. To avoid “blow-outs” related to high grade values in widely spaced drill data, the LR
model seeks to limit the high grade values by restricting the volume of the domain shell generated around
that high grade assay. However, for the SR model, the drill spacing is much tighter, which reduces the
impact of any isolated high grade values. GSR has periodically reviewed the decision to use two different
modelling methodologies. At this time, GSR believes that this approach still provides the best estimate of
Au grades in each model.
14.4.3 Wassa Structural Trend
The structural HG mineralization trends at Wassa (Figure 14-2) has been created utilizing underground
mapping, open pit grade control data and available downhole diamond core structural data. A structural
consultant was engaged to assist with the creation of these trends in the southern portion of the Wassa
deposit, where there are currently Inferred Mineral Resources.
The structural trend lines were created on sections and then used to create a series of form surfaces, which
in turn were used to guide the interpolation of the grade isoshells and populate the local block angles for
search ellipse orientation and grade estimation. These form surfaces represent the broad F4 folding event,
a plunging synclinal feature which affects grade distribution at the mine scale, with some subtly different
Page 123NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 124
internal orientations attributed to the largest features associated with an earlier high strain folding event
(F3). In areas where tight underground drilling and mapping are available it is possible to create structural
controls surfaces that reflect the local mineralization geometry, often associated with smaller parasitic F4
and F3 folds.
Figure 14-2 Wassa LR model structural ‘Form’ surfaces (oblique view looking N up plunge), surfaces show deposit
scale F4 fold as well as rolling over of mineralization at depth
A total of 51 structural ‘form’ surfaces have been used for the creation of the LR model isoshells and local
varying block angles. Table 14-6 summarizes the parameters used to define the Structural Trend for each
model.
Table 14-6 Leapfrog trend inputs for creation of 1.5 g/t and 0.4 g/t LR model grade Isoshells
Trend Type
Compatibility
Trend Inputs
Strength
Global Mean Trend
Strongest Along Inputs
Version 2
All 51 modelled structural
‘form’ surfaces
7.0 to 10.0
N/A
An example of the resulting Structural Trend is presented in Figure 14-3.
W
E
400 mNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-3 North-facing cross sections showing structural form (18950 mN and 19170 mN)
For the SR model, in-mine and near mine structural control surfaces were created using oriented core
structural measurements, combined with underground structural mapping. This structural information was
used to create structural trend surfaces (Figure 14-4 and Figure 14-5) which represented the structural
geometry of the Au mineralization in the Wassa Mine area. A total of 68 surfaces were used in the
Short-Range model and represented the same fold geometries as seen in the LR model, but with greater
local definition.
Figure 14-4 Structural form surfaces used in the SR model
Table 14-7 summarizes the parameters used to define the Structural Trend for each model.
Page 125NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 126
Table 14-7 Leapfrog trend inputs for creation of 1.5 g/t and 0.4 g/t SR model grade Isoshells
Trend Type
Compatibility
Trend Inputs
Range
Strength
Global Mean
Trend Direction
Global Mean Trend
Ellipsoid Ratios
Strongest
Along Inputs
Version 2
68 modelled
structural ‘form’
surfaces
15
15
50 dip, 270 azi,
20 pitch
Maximum = 3
Intermediate = 2
Minimum = 1
Figure 14-5 Images showing the structural control surfaces on sections 19,750 mN and 19,635 mN. The images
show the longer, LR model defined control surfaces and the shorter, mine geology defined control surfaces
14.4.4 Wassa Indicator Interpolants – Process
Prior to generating the indicator interpolant shells, the raw assay file was composited to 3m, with a
minimum end composite length of 1.5m. Any composites less than the end composite length of 1.5 m were
not utilized in the interpolation. Indicator interpolants were defined at 0.4 g/t Au and 1.5 g/t Au threshold.
The indicator interpolants were restricted to be within a bounding box defined by the coordinates provided
in Table 14-8.
Table 14-8 LR modelling extents
Axis
Minimum extent
Maximum extent
X
39 050 E
40 850 E
Y
18 200 N
20 800 N
Z
-775 Z
1 100 Z
Table 14-9 summarizes the parameters that were applied to both the 1.5 g/t Au and 0.4 g/t Au models.
Table 14-9 LR Isoshell modelling parameters
Interpolant
Type
Range
Nugget
Iso-Value
Resolution
Volumes
Excluded
Spheroidal
100
0.5
0.35
2.5m
<5000m³NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 127
In order to better reflect the geometry of the Au mineralization at a local scale, and also to improve
continuity in areas of wider spaced drilling, GSR edited the indicator interpolant shells using indicator
polylines. Indicator polylines are digitized and editable strings that carry an associated numeric value which
is added to the assay data points on which the interpolant is based. In this instance, indicator polylines
with values of 1 (inside), 0 (outside) and indicator iso-value were added to the interpolant. The “iso-value”
indicator polylines allow the specific position of the outer limit of the shell to be locally edited. This helps
to influence continuity orientations at a smaller scale, ensuring F3 continuity and geometry could be
reflected in the resultant domain wireframes in well drilled areas, and assisted in improving the continuity
of the model in some of the more sparely drilled areas.
For the SR model, the raw assay intervals were composited down hole to a fixed 2m length. Any residual
lengths less than 1m were discarded. A composite cap of 30 g/t Au was applied to the data prior to grade
shell contouring.
Grade thresholds for the “mineralized” and the “halo” domains were defined at 1.5 g/t Au and 0.4 g/t Au
thresholds. The 1.5 g/t Au cut-off threshold was selected on the basis of a statistical and visual evaluation
of the grade distribution. This threshold has been periodically reviewed by GSR and is considered
appropriate. The low grade 0.4 g/t threshold has been in previous models Wassa and is considered
appropriate to define the low grade material that surrounds the higher grade core at Wassa.
The raw data interpolants were restricted within a bounding box defined by the coordinates provided in
Table 14-10.
Table 14-10 SR block model extents
Axis
Minimum extent
Maximum extent
X
39 580 E
40 300 E
Y
19 330 N
20 520 N
Z
300 Z
1 070 Z
The Leapfrog numeric model used the interpolant parameters shown in Figure 14-6.
Figure 14-6 Short-range isoshell modelling parameters (SRK, 2020)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 128
14.4.5 Wassa Long-Range Model
The final model, displayed in Figure 14-7, constitutes the following:
- >0.4 g/t Au – the iso-surfaced indicator interpolant;
- >1.5 g/t Au – the iso-surfaced indicator interpolant.
Figure 14-7 SE Isometric view of final LR model Leapfrog Isoshells (blue = >0.4 g/t, red = >1.5 g/t)
The two Mineral Resource Isoshells (wireframes) were constructed by GSR geologists with inputs from
structural consultants and SRK. These comprise a LG shell and HG shell, corresponding to a 0.4 g/t gold and
a 1.5 g/t gold threshold, respectively.
Figure 14-8 shows the two domain shells generated for the SR model. 0.4 g/t Au was used for the “halo”
domain threshold, and 1.5 g/t Au was used for the “mineralized” domain.
N
S
400 mNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-8 Long section looking East showing the mineralized and halo domain shells on 39,940E (top image).
Section on 39,940E (lower image) displaying the same data, cut by that section line, and the assay data used to
create the domain shells. RED = mineralized domain; BLUE = halo domain
14.4.6 Hwini Butre
The 2020 Mineral Resource estimates for Father Brown (FBZ) and Adoikrom (ADK) were a combined effort
by GSR and Resource Modelling Solutions (RMS). A different approach was taken compared to previous
and both of these deposits were modelled using a “vein modelling” technique, estimating both vein
thickness and grade.
GSR provided RMS with drill hole intercepts indicating hanging wall (HW) main mineralized zone or vein
(ADK or FBZ) (HG annotation) or footwall (FW) from and to intervals.
Each vein unit is modelled by estimating the position of the vein and each one of the thicknesses, HW, HG
and FW. The position of the vein is defined by the intercept with the top of HW unit, the first thickness is
the difference between the intercept of the contact between HW and HG with the top of HW, the second
thickness is defined by the difference between the contact HW and HG and the contact between HG and
FW and the third thickness is defined by the base of the FW contact.
Intercepts within a horizontal distance tolerance of 2.0m are used to calculate position and thicknesses in
order to check any possible relationship between these variables and determine whether or not
independent modelling is adequate for the modelling of each vein unit. The scatterplots between each
variable showed no significant correlation between the variables, therefore, the independent modelling of
each one of these variables in a stepwise manner is deemed appropriate.
Page 129NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The final vein model is defined by stacking the modelled thicknesses below the vein position model. A
cross section at U = -28.0m in transformed space is shown in Figure 14-9. Drill hole FBRGC0980075 in FBZ
in Figure 14-9 show discrepancies with surrounding data and are challenging to match, however, this
modelling workflow works very well on average. Note that these sections are shown in transformed
coordinates, after gold estimationsmodels were rotated back to the original Easting-Northing-Elevation
coordinates.
Figure 14-9 Model section at U=-28.0 in transformed space generated with 2.0 tolerance in V direction
14.4.7 Benso
Geology and mineralization domaining was undertaken by GSR. Mineralized wireframes were constructed
on 25 meter sections with the 2D polylines being snapped to drill hole grade intercepts using a nominal
grade cut-off of 0.5 g/t Au. The 2D polylines were then tied together to create a 3D mesh that was
subsequently used for volume and grade estimates. An oxidation surface was created in a similar manner
with the depth of weathering being delineated by a polyline on 25 m spaced drill sections and then used to
create a mesh surface. This oxidation surface was then used to code the subsequent block models,
distinguishing weathered from fresh rock.
The mineralization zones of Benso are structurally controlled with gold emplacement related to the density
of quartz veining and sulphide content.
Four estimation domains subdivided by oxidation state have been modelled for Benso, as follows:
- Subriso East (SE);
- Subriso West (SW);
- G-Zone; and
- I Zone.
The SE domain is physically separated from the others and strikes to the north with a dip to the west of
between 55-60°. The SW, G Zone and I Zone domains occur in sub-parallel structures and strike to the
north-west (320°) with a steep dip of 75-80° to the south-west. Because of this, it was decided to treat the
SE deposit as separate for the purposes of grade interpolation.
Only DD and RC drilling has been used for the subsequent grade estimation. The Mineral Resource
wireframes and drillholes are shown in Figure 14-10.
Page 130NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-10 Mineral Resource wireframes and drill hole locations for the Benso deposits (GSR, 2010)
14.4.8 Chichiwelli
Geology and mineralization domaining was undertaken by GSR and the mineralized zone modelling was
conducted in a method similar to the Benso deposits.
The mineralization zones of Chichiwelli are structurally controlled with gold emplacement related to the
density of quartz veining and sulphide content. The mineralization hosting structures generally trend
north-south and dip moderate-steeply to the east at 60°.
Two estimation domains have been modelled for Chichiwelli as follows:
- East Domain; and
- West Domain.
The East and West domains comprise some 10 individually separated wireframe solids.
Wireframes are based on a roughly 0.5 g/t Au grade value. In places composite grades fall below this
threshold value but have been included for the sake of maintaining continuity of the wireframe. The style
of mineralization seen at Chichiwelli is analogous to deposits observed elsewhere in the Wassa region and,
typically for shear zone hosted gold deposits, the mineralization grades tend to pinch and swell within the
defined mineralized bearing structures. The Mineral Resource wireframes and drillholes are shown in
Figure 14-11.
Page 131NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 132
Figure 14-11 Mineral Resource wireframes and drillhole locations for Chichiwelli (GSR, 2008)
14.5 Statistical Analysis and Variography
As with the previous LR model Mineral Resource estimates for Wassa, GSR contracted SRK (Toronto) to
conduct all of the Statistical Analysis and Variography. GSR provided SRK with all of the relevant DD assay
data, structural control lines and high and low grade mineralized wire frames (Leapfrog Isoshells).
Table 14-11 summarizes the gold statistics of the assays tagged by mineralized domains provided by GSR.
In May 2017, SRK evaluated four drill hole databases for the Wassa Gold Mine, and after discussions with
GSR, agreed to combine these databases as conditioning data to be used in grade estimation. This decision
has not since been revisited, and all four databases were combined once again.
For consistency with previous models, SRK chose to composite at 3.0-m lengths within the solid
wireframes. Unlike previous Mineral Resource models where all composites with length greater than 0.3 m
were kept in the estimation database, SRK chose to remove all composites smaller than 1.5 m (or 50% of
the composite length). Summary statistics for these composites are also provided in Table 14-11. There is
a slight change in the mean grade between assays and composites; however, assay statistics are length
weighted, while composite statistics are unweighted since length weights will not be used during grade
estimation.
Table 14-11 Summary Gold Statistics of Assays and Composites
Zone
Assays
Composites**
Count
Mean
Std
Dev*
Min*
Max*
CoV*
Count
Mean
Std
Dev*
Min*
Max*
CoV*
HG + LG
264,166
1.69
5.84
0.001
1547.97
3.45
93,387
1.71
3.84
0.001
185.07
2.24
HG
59,860
4.27
11.15
0.001
1547.97
2.61
20,094
4.32
6.95
0.001
185.07
1.61
LG
204,306
0.99
2.71
0.001
442.20
2.73
73,293
1.00
1.78
0.001
152.75
1.78
* StdDev = Standard Deviation; Min = Minimum; Max = Maximum; CoV = Coefficient of Variation
** Less 1.5 m residual composites, composite statistics are not length-weightedNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 133
In collaboration with GSR, SRK selected the capping value by comparing probability plots of gold
composites on a by-domain basis and plotting the mean grade and the number of affected data by the
chosen cap value shown in Figure 14-12. In recognition of the differences in drill density north and south of
19400N, and the potential impact of this spacing on high grade smearing, SRK separated the database into
a northern and southern dataset at 19,400 mN.
Figure 14-12 Probability Plot for LG (left) and HG (right) Domains North of 19400N (top row) and South of 19400N
(bottom row) (SRK, 2020)
In the northern area, SRK chose to cap HG composites at 50 g/t gold and LG composites at 22 g/t gold.
These capping thresholds are slightly higher than those chosen in the January 2019 Mineral Resource
model; however, given the data density, SRK does not foresee any overestimation issues. In the south, SRK
capped the HG composites at 20 g/t gold and LG composites at 15 g/t gold. Table 14-12 compares the
statistics for uncapped and capped composite gold grades.
Table 14-12 Comparison of Uncapped and Capped Gold Composite Grades – LR model
Zone
Composites
Capped Composites
Count
Mean
StdDev*
Max*
CoV*
Mean
StdDev*
Max*
CoV*
HG + LG
93,387
1.71
3.84
0.001
185.06
1.68
3.20
50
1.90
HG
20,094
4.32
6.95
0.001
185.06
4.21
5.67
50
1.35
LG
73,293
1.00
1.78
0.001
152.75
0.98
1.42
22
1.45
* StdDev = Standard Deviation; Min = Minimum; Max = Maximum; CoV = Coefficient of Variation
As with the previous short-range Mineral Resource estimates for Wassa, GSR contracted SRK (Moscow) to
conduct all of the mineralized wireframe modelling, Statistical Analysis and Variography. GSR provided SRK
with all of the relevant DD assay data and structural control lines .NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 134
The composite assay statistics for the SR model have been provided in Table 14-13. The target composite
length was 2.0m, but with small length adjustments made to avoid creating shorter composites at the end
of intersections. In the few cases where composites with a length less than 1m were generated, these
were discarded.
Table 14-13 Comparison of uncapped and capped gold composite grades – SR model
Zone
Composites
Capped Composites
Count
Mean
StdDev*
Max*
CoV*
Mean
StdDev*
Max*
CoV*
HG
24,023
4.92
8.16
217.64
1.66
4.34
4.44
20
1.02
LG
39,005
0.68
0.69
90.26
1.02
0.67
0.56
20
0.85
* StdDev = Standard Deviation; Min = Minimum; Max = Maximum; CoV = Coefficient of Variation
During the kriging estimate, the 2m Au composites were capped at 20g/t Au. This capping value has been
reviewed by GSR at various times throughout the Wassa Underground mine’s history. Mine reconciliation
data has shown that the 20g/t Au cap value has reconciled an acceptable level, with the capping considered
to have a conservative to neutral effect on the grade estimation, depending on which part of the Wassa
Underground deposit is being estimated. As such, the capping value remained unchanged during the latest
SR model creation. Histograms in Figure 14-13 and Figure 14-14 have been provided, showing the
uncapped 2m composite grade distribution for the two domains.
Figure 14-13 Histogram showing the uncapped 2m Au composite grade distribution for the mineralized domainNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-14 Histogram showing the uncapped 2m composite grade distribution for the halo domain
14.5.1 Wassa Local Angle Models (LR Model)
SRK generated local angles derived from triangulated facets of the structural trend surfaces provided by
GSR. This was achieved using Datamine Studio RM, and an initial angle data set for both dip and dip
directions. As before, the structural trend surfaces were generated using Leapfrog, and the mesh
resolution provided a smooth variation of the dip and dip direction angles.
The angles data set was then used to interpolate a block model of dip and dip directions, which was later
called upon for local estimation. The estimation of angles used inverse distance estimation with a power of
three, using an isotropic range of 500 m with up to six conditioning angle data. This is consistent with the
Mineral Resource models built since 2017.
14.5.2 Local Variogram Models
The local estimation approach chosen for the Wassa Gold Mine required the specification of local
variogram models. SRK assessed and modelled local variograms for the HG and LG domains, centred about
each anchor point. Anchor point locations were reviewed by GSR prior to finalization of their locations.
Table 14-14 summarizes the anchor point locations and their local orientations for variogram calculation
and modelling. The modelled local variograms for these anchor points are tabulated in Table 14-15. For
the LG domain, SRK relied on variograms based on the combined LG and HG capped composites due to the
challenges of inferring reliable variograms based solely on LG composites. One reason for the inference
challenge may be related to the spatial voids in the database where the HG domain resides. For anchor
points 6, 8 and 13, SRK used the HG domain variograms for the LG domain and adjusted the ranges
wherever possible to reflect the combined domain variograms.
For each domain (LG and HG), the local variogram parameters (Table 14-15) were then estimated to the
block model grid to be read into the grade estimation. In general, the local variograms should be smoothly
transitioning within the series. Abrupt changes in grade continuity, within a zone and between anchor
point locations, were not expected. Highly localized changes were addressed by the selection of anchor
point locations. To ensure smoothness of the local variograms parameters and consistency with the 2015
model, SRK used global kriging with a continuous spherical variogram with ranges of 1,000 by 750 by 500
metres.
Page 135NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 136
An example of the variograms for the HG and LG zones at two anchor points, 1 and 14 are shown in Figure
14-15 and in Figure 14-16.
Table 14-14 Local variogram orientations and anchor point locations
Anchor
Point
GSLib
Gems
Coordinates
ANG1
ANG2
ANG3
Azm
Dip
Azm
X
Y
Z
1
75
-88
0
75
-88
-15
40263
18575
136.5
2
79
-75
0
79
-75
-11
40164
18923
-322
3
270
-69
0
270
-69
180
40135
19155
438.5
4
285
-74
0
285
-74
195
40245
19575
1005.5
5
259
-77
0
259
-77
169
40005
19555
603.5
6
272
-61
0
272
-61
182
40015
19705
873.5
7
270
-75
0
270
-75
180
39975
19925
945.5
8
273
-85
0
273
-85
183
40245
19925
876.5
9
255
-77
0
255
-77
165
39945
19925
624.5
10
257
-37
0
257
-37
167
39975
20165
780.5
11
271
-75
0
271
-75
181
40255
20155
951.5
12
249
-65
0
249
-65
159
40045
20425
975.5
13
154
-41
0
154
-41
64
39835
20425
966.5
14
141
-46
0
141
-46
51
39555
20125
906.5
Table 14-15 Local variogram models by domain
Domai
n
AP
Nugget
Structure 1 (Exp)
Structure 2 (Sph)
Effect
CC
Ahmax
Ahmin
Ahvert
CC
Ahmax
Ahmin
Ahvert
LG
1
0.25
0.58
10
10
8
0.17
40
40
25
2
0.25
0.58
11
11
8.5
0.17
45
45
25
3
0.2
0.55
24
10
4
0.25
24
14
6
4
0.2
0.35
10
20
5
0.45
160
250
21
5
0.2
0.64
6
17
8
0.16
45
90
22
6
0.2
0.35
8
8
3
0.45
35
50
13
7
0.2
0.55
14
8
10
0.25
60
50
20
8
0.2
0.45
12
20
15
0.35
175
175
55
9
0.2
0.6
7
10
6.5
0.2
50
90
22
10
0.3
0.52
9.5
11
6
0.18
28
60
25
11
0.2
0.58
25
25
8
0.22
185
185
55
12
0.25
0.65
15
15
12.5
0.1
90
90
12.5
13
0.2
0.68
8
12
8
0.12
20
50
10
14
0.2
0.68
8
8
6
0.12
40
40
20
HG
1
0.25
0.58
10
10
6.5
0.17
35
35
25
2
0.25
0.68
11
11
8.5
0.07
25
25
15
3
0.3
0.25
24
24
5
0.45
32
32
14
4
0.2
0.35
10
20
5
0.45
160
250
21
5
0.2
0.67
8
18
8
0.13
55
100
22
6
0.2
0.45
10
10
3
0.35
30
22
13
7
0.2
0.5
25
8
8
0.3
60
55
12
8
0.2
0.35
35
35
5
0.45
175
175
55
9
0.2
0.65
6.5
11
6
0.15
30
100
35
10
0.2
0.62
6.5
4.5
7
0.18
25
55
40
11
0.2
0.53
31
31
12
0.27
185
185
55
12
0.25
0.38
15
15
6.5
0.37
110
25
7
13
0.3
0.68
10
10
8
0.02
75
75
30
14
0.3
0.68
10
10
8
0.02
75
75
30NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-15 HG Variogram from anchor point 1 (SRK, 2020)
Figure 14-16 LG Variogram from anchor point 14 (SRK, 2020)
Page 137NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 138
Local variogram models were not used in the SR model. The SR model used a different locally-variable
anisotropy (LVA) technique. Each location in the block model was assigned azimuth, dip and plunge
information based on the structural control surfaces and the overall variogram model. This orientation
information was then called upon during the estimation process to set the orientation of the variogram
model and search neighbourhood each block grade estimate.
The variogram parameters for the HG & LG mineralized domains were set as shown in Figure 14-17.
Figure 14-17 Variogram for the short-range HG & LG mineralized domains (SRK, 2020)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 139
14.5.3 Hwini Butre Father Brown – Adoikrom
The statistics were preformed on each of the domains for each individual zone, FBZ (HW, HG and FW) and
ADK (HW, HG and FW)
The descriptive statistics for the individual modelled domains are summarized in Table 14-16.
Table 14-16 Descriptive statistics for Hwini Butre modelled domains (uncapped & capped)
Zone
Domain
Capping
Count
Minimum Maximum
Mean
stdev
COV
Adoikrom
HW
Uncapped
807
0.00
13.42
1.31
1.265
0.965
Capped
807
0.00
5.00
1.00
0.793
0.791
HG
Uncapped
946
0.09
136.38
7.58
10.300
1.359
Capped
946
0.00
23.00
5.90
5.088
0.863
FW
Uncapped
855
0.00
12.01
1.19
1.058
0.893
Capped
855
0.00
5.00
0.95
0.802
0.843
Father
Brown
Zone
HW
Uncapped
1,130
0.01
37.62
0.81
1.796
2.214
Capped
1,130
0.01
5.00
0.60
0.741
1.231
HG
Uncapped
1,207
0.01
253.00
11.41
17.272
1.513
Capped
1,207
0.01
46.00
9.28
10.827
1.167
FW
Uncapped
1,120
0.00
40.10
1.02
2.458
2.402
Capped
1,120
0.00
5.00
0.74
0.789
1.068
Probability plotsfor eachvein unitfor eachdomain are generated andshown in Figure 14-18. The capping
values selected from the probability plots are summarized in Table 14-17.
Figure 14-18 Gold grade probability plot with outliers and far out thresholds highlighted (RMS, 2020)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 140
Table 14-17 Capping values selected from analysis of the probability plot
Deposit
Vein unit
Capped Values used
FBZ
FW
5
FBZ
HG
46
FBZ
HW
5
ADK
FW
5
ADK
HG
23
ADK
HW
5
The variography was performed for each deposit and for each vein unit (FBZ & ADK) using capped
composites. Experimental variograms are calculated for full range of possible azimuths with steps of 15
degrees totaling 24 directions. The direction with most continuous experimental points from visual
inspection of the 24 directions were utilized for nugget inference. These directions may not coincide with
the final major continuity direction when considering all experimental points for final model fit. The nugget
is inferred by fitting a single structure spherical variogram to the first few (up to three) experimental
variogram points.
The variogram nugget inference for all vein units in FBZ are shown in Figure 14-19. The directions utilized
for nugget inference are detailed in each plot in Figure 14-19.
Figure 14-19 Inferred nugget effect for gold grade in each vein unit for FBZ deposit (RMS, 2020)
The experimental variogram and fitted model for FW unit in FBZ is shown in Figure 14-20. The parameters
of the fitted model are summarized in Table 14-18. The experimental variogram and fitted model for HG
unit in FBZ is shown in Figure 14-21. The parameters of the fitted model are summarized in Table 14-19.
The experimental variogram and fitted model for HW unit in FBZ is shown in Figure 14-22. The parameters
of the fitted model are summarized in Table 14-20.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 141
Figure 14-20 Fitted experimental variogram points for gold grade in FW for FBZ deposit (RMS, 2020)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-21 Fitted experimental variogram points for gold grade in HG for FBZ deposit (RMS, 2020)
Page 142NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-22 Fitted experimental variogram points for gold grade in HW for FBZ deposit (RMS, 2020)
Page 143NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 144
Table 14-18 Fitted variogram parameters for gold grade in FW for FBZ deposit
Nugget
Structure 1
Structure 2
Contribution
0.000
0.851
0.149
Model Shape
exponential
exponential
Angle 1
43.3
43.3
Angle 2
0.0
0.0
Angle 3
0.0
0.0
Range 1
10.0
155.9
Range 2
16.3
10.0
Range 3
1.0
1.0
Table 14-19 Fitted variogram parameters for gold grade in HG for FBZ deposit
Nugget
Structure 1
Structure 2
Contribution
0.250
0.416
0.334
Model Shape
exponential
exponential
Angle 1
29.1
29.1
Angle 2
0.0
0.0
Angle 3
0.0
0.0
Range 1
10.0
77.3
Range 2
10.0
50.0
Range 3
1.0
1.0
Table 14-20 Fitted variogram parameters for gold grade in HW for FBZ deposit
Nugget
Structure 1
Contribution
0.283
0.717
Model Shape
exponential
Angle 1
72.6
Angle 2
0.0
Angle 3
0.0
Range 1
10.0
Range 2
10.0
Range 3
1.0
The variogram nugget inference for all vein units in ADK is shown in Figure 14-23. The directions utilized for
nugget inference are detailed in each plot in Figure 14-23 and the experimental variogram and fitted model
for FW unit in ADK is in Figure 14-24. The parameters of the fitted model are summarized in Table 14-21.
The experimental variogram and fitted model for HG unit in ADK is shown in Figure 14-25 and the
parameters of the fitted model in Table 14-22. The experimental variogram and fitted model for HW unit in
ADK is shown in Figure 14-26. The parameters of the fitted model are summarized in Table 14-23.
Figure 14-23 Inferred nugget effect for gold grade in each vein unit for ADK deposit (RMS, 2020)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-24 Fitted experimental variogram points for gold grade in FW for ADK deposit (RMS, 2020)
Page 145NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-25 Fitted experimental variogram points for gold grade in HG for ADK deposit (RMS, 2020)
Page 146NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-26 Fitted experimental variogram points for gold grade in HW for ADK deposit (RMS, 2020)
Page 147NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 148
Table 14-21 Fitted variogram parameters for gold grade in FW for ADK deposit
Nugget
Structure 1
Structure 2
Contribution
0.000
0.062
0.938
Model Shape
exponential
exponential
Angle 1
77.8
77.8
Angle 2
0.0
0.0
Angle 3
0.0
0.0
Range 1
15.0
15.0
Range 2
929.5
15.0
Range 3
1.0
1.0
Table 14-22 Fitted variogram parameters for gold grade in HG for ADK deposit
Nugget
Structure 1
Structure 2
Contribution
0.097
0.460
0.443
Model Shape
exponential
exponential
Angle 1
13.1
13.1
Angle 2
0.0
0.0
Angle 3
0.0
0.0
Range 1
32.8
21.9
Range 2
38.9
10.0
Range 3
1.0
1.0
Table 14-23 Fitted variogram parameters for gold grade in HW for ADK deposit
Nugget
Structure 1
Structure 2
Contribution
0.000
0.650
0.350
Model Shape
exponential
exponential
Angle 1
73.1
73.1
Angle 2
0.0
0.0
Angle 3
0.0
0.0
Range 1
15.0
58.4
Range 2
15.0
99.9
Range 3
1.0
1.0
The major direction of continuity for each variogram model for each deposit is inferred from the weighted
ranges of each variogram structure utilizing their contribution as weights. The major direction is rotated
back to original space and the results are summarized in Table 14-24.
Table 14-24 Fitted major variogram directions in original space
Deposit
Domain
Azimuth
Dip
Weighted
Anisotropy
FBZ
FW
118.9
26.5
2.1
FBZ
HG
131.6
18.5
1.4
FBZ
HW
86.9
38.5
1.0
ADK
FW
172.9
10.9
4.8
ADK
HG
4.1
11.7
1.1
ADK
HW
170.7
15.1
1.5NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 149
14.5.4 Benso
The statistics are based on composited assay values within the wireframes modelled by GSR; the data was
composited to 2 m lengths within the mineralized zones, and composites of less than 1.50 m were
removed.
The descriptive statistics for the individual modelled domains, split by oxidation state, are summarized
below in Table 14-25. The transition zone is relatively thin, and so has not been analysed separately. For
all datasets, zero values were checked in the database, and were set to 0.001 g/t.
Table 14-25 Descriptive statistics for Benso modelled domains (capped)
Domain
Oxidation
Count
Minimum
Maximum
Mean
Variance
COV
Subriso East
Oxide
266
0.001
30.81
2.11
15.18
1.85
Fresh
649
0.001
51.58
2.54
25.49
1.99
Total
915
0.001
51.58
2.42
22.51
1.96
Subriso West
Oxide
36
0.41
15.86
3.14
14.11
1.20
Fresh
571
0.001
223.83
3.88
147.39
3.13
Total
607
0.001
223.83
3.83
139.48
3.08
G Zone
Oxide
44
0.001
21.15
2.76
18.69
1.57
Fresh
570
0.001
52.33
2.04
11.1
1.63
Total
614
0.001
52.33
2.09
11.64
1.63
I Zone
Oxide
11
0.21
1.51
0.97
0.23
0.49
Fresh
86
0.11
18.18
2.72
10.96
1.22
Total
97
0.11
18.18
2.52
10.04
1.26
The four areas were combined into two areas for estimation purposes; namely Subriso East, and Subriso
West, G Zone and I Zone combined. The Subriso East domain is separated from the Subriso West, G Zone
and I Zone areas, and strikes roughly north-south, with a dip to the west of between 55 and 60°. The
Subriso West, G Zone and I Zone areas lie in sub-parallel structures, striking roughly to the north-west
(320°), with a steep dip of 75 to 80° towards the south-west. The descriptive statistics for the two separate
estimation domains are shown below in Table 14-26.
Table 14-26 Descriptive statistics for simplified Benso modelled domains (capped)
Domain
Count
Minimum
Maximum
Mean
Variance
COV
Subriso East
915
0.001
51.58
2.42
22.51
1.96
Subriso West, G Zone and I Zone
1318
0.001
223.83
2.93
71.05
2.88
Statistical distributions for the two domains are similar, with the histograms indicating that the distribution
is not normal, being highly negatively skewed. The log transformed gold grade data demonstrates there
may be several populations within the distribution and that the distribution approached log-normality.
HG caps were applied to the composite data as follows:
- Subriso East: 40 g/t cap; and
- Subriso West, G Zone, I Zone: 60g/t cap.
The estimation data sets noted above were used to derive variograms for estimation. In all cases, the grade
block model for each individual modelled solid was estimated using only the composites inside that solid.
Variography was undertaken on the log transformed data, with a short lag, omnidirectional, downhole
variogram used to derive the nugget effect. Directional variograms were then calculated within a rotated
plane aligned with the strike and dip of the modelled solids. The variogram parameters derived from the
modelled variograms are shown in Table 14-27. Variograms were back transformed before use in OK.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 150
Table 14-27 Variogram parameters for the Benso zones
Parameter
Subriso East
Subriso West, G Zone and I Zone
Co
0.25
0.19
C1
0.41
0.54
C2
0.34
0.27
a1 (strike)
20
20
a1 (dip)
15
8
a2 (strike)
50
50
a2 (dip)
40
30
14.5.5 Chichiwelli
The statistics are based on composited assay values domained within the mineralization wireframes
described previously, with sample data composited to 2 m lengths within the mineralized zones.
The statistics presented here are based on all drilling data that intersect the wireframes. The composites
inside the modelled bodies were also split into oxidation states, but as there was little information for the
transition zone, SRK combined the three oxidation states and used the combined oxidations datasets
throughout the statistical and geostatistical studies, and the subsequent grade estimation.
The descriptive statistics for the two separate estimation domains are shown below in Table 14-28.
Table 14-28 Descriptive statistics for Chichiwelli modelled domains (capped)
Domain
Count
Minimum Maximum
Mean
Variance
COV
East
418
0.001
41.1
1.75
17.64
2.41
West
559
0.001
46.3
1.69
10.14
1.89
HG capping was applied to both the East and West domains. The HG caps were determined on the basis of
the shape of the tail of the log histogram and the log probability plots. Capping reduces the extreme values
to a nominated capped value, which affects the mean grades of the 2.0 m composites, as indicated by Table
14-29.
Table 14-29 Chichiwelli high grade capping
Domain
Cap
Applied
Mean Grade
before Cap
Mean Grade
after Cap
Percentage
difference
(g/t)
(g/t)
(g/t)
(%)
East
25
1.75
1.65
-6.06
West
15
1.69
1.59
-6.29
The estimation data sets noted above were used to derive variograms for estimation. In all cases, the grade
block model for each individual modelled solid was estimated using only the composites inside that solid.
Variograms were modelled for the East and West domains separately. Variography was attempted for the
individual solids, but the resultant variograms were unable to be modelled. Raw variography resulted in
difficult to model variograms, and so a Gaussian transformation was applied to the data. The first stage
was to define the nugget effect from a short-lag omnidirectional variogram, which is calculated along the
drillhole, and then to model the variogram ranges from directional variograms from along strike, down-dip
and across dip directions. The directional variograms are then back transformed into “raw” space and used
for subsequent estimation. The back transformed variograms and resultant variogram parameters are
included in Table 14-30.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 151
Table 14-30 Variogram parameters for Chichiwelli zones
Parameter
East
West
Co
7.94
3.06
C1
3.60
1.59
Nugget Effect (%)
68.8
65.81
Range (m)
a1 (strike)
25
40
a1 (dip)
25
35
a1 (normal to strike)
8
4.7
14.6 Block Model and Grade Estimation
14.6.1 Wassa Long-Range Block Model
A 3D block model including rock type, gold, percent mineralization, density and class was constructed for
each of the modelling areas, Wassa short-range and long-range. The selection of the block size was driven
by the borehole spacing and mainly by the geometry of the auriferous zones, but also based on mining
parameters and in accordance with the previous Mineral Resource estimate. The LR models block size was
set at 10 x 10 x 5 m in the northing, easting and elevation directions, respectively along the mine grid. The
block model origins can be seen in Table 14-31.
Table 14-31 Wassa LR model definitions, upper left hand corner coordinates
Block Size
Origin*
Block Count
(m)
(m)
X
10
39,050
180
Y
10
18,200
260
Z
5
1,100
375
* Coordinates relative to mine grid.
A percent block model was used to evaluate tonnages. Tonnage for each respective block was obtained by
weighting volumes corresponding to the interpreted auriferous zones and the respective mean SG defined
by weathering profile.
The block model bulk density data was coded based on weathering surface which was built to define oxide
material from fresh material. The weathering surface defined the ‘top of fresh’ material; all blocks above
the ‘top of fresh’ surface were designated as oxide and material below the surface as ‘fresh’. The bulk
density values assigned to the block model were based on series of measurements made over the various
exploration phases going back to the initial GSR exploration program in 2002. The density values used for
the tonnage estimate were provided by GSR and are detailed below in Table 14-32.
Table 14-32 Average Bulk Density used for LR model
Weathering Type
Avg Bulk Density t/m3
Oxide
1.8
Fresh
2.8
For the SR model, the Surpac 3D block model contained the 20 g/t Au capped composite grade estimate,
the bulk density coding, the domain coding, the depletion coding, and the Mineral Resource classification
coding. The block size for estimation is effectively 5m cubes, with sub-blocking to 2.5 mN, 1.0 mE and 2.5
mRL. The block size was based on the Measured Mineral Resource drill spacing at Wassa. The Surpac block
model is structured with a 2.5 mN, 1.0 mE, and 2.5 mRL block size, and no sub-blocking, in order to
facilitate transfer of the block model between different software. The Surpac block model contained a total
of 9,041,540 blocks, with the origins outlined in Table 14-33. NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 152
Table 14-33 Wassa SR model definitions
Coordinate
Origin
Block Size (m)
No. of Blocks
X
39,600
1
272
Y
19,350
2.5
460
Z
320
2.5
292
As the Wassa Underground mine exists well below the bottom of the partial oxidation layer, the bulk
density in the model has been set to 2.8 (fresh rock). The 2.8 value comes from test work performed by
both GSR and Intertek during 2017 and 2018.
14.6.2 Wassa Mineral Resource Estimation Methodology
For the LR model, SRK implemented the same methodology since 2018 to construct the Mineral Resource
model, using ordinary kriging with local varying angles and local variograms for the estimation of gold
grades. The general steps required to implement the approach are:
- Construct locally varying angles models for dip and dip direction;
- Calculate and model local variograms for each series and interpolate these local variograms to
construct a model of local variogram model parameters;
- Estimate gold grades using ordinary kriging, calling upon the local models of dip, dip direction, and
variogram models; and
- Check estimated model using qualitative and quantitative methods.
Table 14-31 summarizes the block model definition used for the model area using the mine grid. No
rotation was applied. GSR opted to change the vertical size of a block from 3 m to 5 m to improve
alignment of the model to mine elevations. The vertical extent of the model has increased to encompass
the mineralization delineated by the deeper southern exploration boreholes.
The following sections summarize the method(s) used, assumptions made, and results obtained for each of
the four modelling steps.
For the SR model, the Mineral Resource estimation methodology involved:
- The construction of structural control surfaces that represented the orientation of the mineralized
structures in the local area;
- The generation of domains shells from the composited assay data, influenced by the structural
control surfaces;
- Coding of the block model framework with the domain shell information;
- Estimation of the Au grade into the block model, using the azimuth and dip information collected
from the structural control surfaces;
- The structural information was used to rotate the variogram model into the local mineralized trend
orientation. Estimation was performed using ordinary kriging;
- Coding of the model using solids created by the Wassa Mine Geology group to define Measured
and Indicated Mineral Resources. The classification was based on the drill density observed on a
section by section basis; and
- Depletions and validation of the model.
14.6.3 Wassa Grade Estimation
Using the models of local angles and local variograms, SRK performed the grade estimation using ordinary
kriging methodology. The LG and HG estimation used the parameters in Table 14-34. The parameters
differ from previous models and are based on an estimation sensitivity analysis conducted in January 2020.
The selection of an appropriate set of estimation parameters was based on ensuring a good quantile
quantile comparison of the resultant estimated grades distribution to change of support corrected
distributions for each of the LG and HG domains. This should ensure an appropriate level of smoothness.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 153
Table 14-34 LR model Estimation Parameters
Pass
Composites
Maximum
Composites per
Borehole
Search Ellipse
GSLIB
Min.
Max
Svx
Svy
Svz
A1
A2
A3
(m)
(m)
(m)
1
3
8
2
50
50
50
270
-50
0
2
2
12
4
90
90
50
270
-50
0
3
1
15
–
200
200
200
270
-50
0
The first estimation run required at least two holes with the aim to localize grade estimates. The second
pass was slightly more relaxed, requiring fewer samples found within a larger search radius. The third
estimation pass considered search ellipses sized at least twice the variogram ranges, with the aim of
estimating most of the blocks unvisited by the first two passes. As the estimation considered a stationary
search ellipsoid, these ranges were selected to ensure that local estimation yielded estimates that
conformed to the local anisotropy and local variograms.
After estimation of each domain, the LG and HG domain grades were then combined into a single block
grade based on a percentage weighted average of the estimated grade based on fill volume of the
respective Mineral Resource wireframes. These single block grades were used to generate the swath plots.
For the SR model, SRK (Moscow) performed the grade estimate using same estimation methodology
employed at the underground mine since the start of production. Hard boundaries were used to prevent
mineralized domain and halo domain information from mixing. Composites from inside the halo domain
were only allowed to influence the grade estimation inside the halo wireframe, whilst composites from
inside the mineralized domain were only allowed to influence the grade estimation inside the mineralized
wireframe. Grade estimation was performed using Ordinary Kriging. The parameters for the estimation
have been provided in Table 14-35.
Table 14-35 SR model estimation parameters
Pass
Composites
Maximum composites
per Borehole
Search Ellipse
Min
Max
Long
mX
Intermediate
mY
Short
mZ
1
6
18
5
60
30
15
2
4
24
No Limit
120
60
30
3
1
24
5
200
200
100
The variogram model was oriented along 270° azimuth, 50° dip, 20° plunge to the south.
14.6.4 Hwini Butre Father Brown – Adoikrom
The estimation is performed using ordinary kriging with uncapped and capped gold grades. The number of
composites and maximum search radius utilized for each vein unit in each deposit are shown in Table
14-36. The influence of outliers is visually evident in the HG unit.
Table 14-36 Kriging search parameters for each vein unit in each deposit
Deposit
Vein Unit
Maximum Search (m)
Maximum Composites
FBZ
HW
250
8
FBZ
HG
500
4
FBZ
FW
500
4
ADK
HW
250
4
ADK
HG
1000
24
ADK
FW
1000
2NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 154
Two block models were produced one for FBZ the other for ADK. No rotation was applied to the models.
Block sizes were chosen to reflect the geometry of the deposits. Grade data for each of the modelled units
was interpolated into the individual structures only. Block model parameters for FBZ and ADK are
summarized in Table 14-37 and Table 14-38.
Table 14-37 Father Brown block model parameters
Coordinate
Origin
Boundary size
Block Size (m)
X
175681.47
1443
1
Y
32345.73
683
2
Z
1176.72
482
2
Table 14-38 Adoikrom Zone block model parameters
Coordinate
Origin
Boundary size
Block Size (m)
X
175731.38
718
1
Y
32394.43
804
2
Z
1271.61
721
2
The density values used for the tonnage estimate were provided by GSR, and are detailed in Table 14-39.
Table 14-39 Hwini Butre rock density
Oxidation State
Value (t/m3 )
Fresh
2.7
14.6.5 Benso
A block model was produced for the whole Benso area. No rotation was applied to the model. Block sizes
were chosen to reflect the average spacing of drill lines along the strike. Grade data for each of the
modelled units was interpolated into the individual structures only, with soft boundaries between oxidation
states, and subsequently reported as oxide or fresh. Block model parameters for Benso are summarized in
Table 14-40.
Table 14-40 Benso block model parameters
Coordinate
Origin
Block Size (m)
No. of Blocks
X
173750
12.5
300
Y
56000
25
160
Z
1205
10
60
Block grades for each of the mineralized zones were estimated using OK. OK was carried out in four passes
for each mineralized zone, and the search parameters for the individual domains are shown in Table 14-41.
The discretization grid was set at 5 x 2 x 1 (xyz) in all cases. The search ellipsoids are relatively large
compared to the variogram ranges, but as there is quite a high data density the blocks were usually
estimated with data significantly closer than the edges of the ellipsoid. NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 155
Table 14-41 Benso ellipsoid search neighbourhood parameters
Domain
Search 1
Search 2
Subriso East
X
100
200
Y
80
160
Z
20
40
Min. Samples
4
4
Max. Samples
36
36
Subriso West,
G Zone and I
Zone
X
100
200
Y
80
160
Z
20
40
Min. Samples
4
4
Max. Samples
36
36
GSR modelled the oxidation surface to determine the boundary between oxide and fresh material. No
transition zone was modelled. The density values used for the tonnage estimate were provided by GSR and
are detailed in Table 14-42.
Table 14-42 Benso rock density
Oxidation State
Value (t/m3 )
Oxide
1.8
Fresh
2.7
14.6.6 Chichiwelli
A block model was produced for the whole Chichiwelli area. No rotation was applied to the model. Block
sizes were chosen to reflect the average spacing of drill lines along the strike. Grade data for each of the
modelled units was interpolated into the individual structures only, with soft boundaries between oxidation
states, and subsequently reported as oxide or fresh. Block model parameters for Chichiwelli are
summarized in Table 14-43.
Table 14-43 Chichiwelli block model parameters
Coordinate
Origin
Block Size (m)
No. of Blocks
X
631,093.64
12.5
100
Y
580,787.20
25
60
Z
1216 (max)
8
65
Block grades for each of the mineralized zones were estimated using OK. OK was carried out in four passes
for each mineralized zone, and the search parameters for the individual domains shown below in Table
14-44. The discretization grid was set at 5x2x1 (xyz) in all cases. The search ellipsoids are relatively large
compared to the variogram ranges, but as there is quite a high data density, the blocks were usually
estimated with data significantly closer than the edges of the ellipsoid. Octants were used on the 1st and
2 nd pass searches with three consecutive empty sectors, however they were not applied on the 3rd search
pass, hence the same number of minimum and maximum samples for the 2nd and 3rd searches.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 156
Table 14-44 Chichiwelli ellipsoid search neighbourhood parameters
Domain
Search 1
Search 2
Search 3
Rotation
Parameters
East
X
60
120
120
Azimuth: 20
Y
60
120
120
Dip: 60
Z
20
40
40
–
Min. Samples
3
3
3
–
Max. Samples
80
80
80
–
West
X
80
160
160
Azimuth: 20
Y
80
160
160
Dip: 60
Z
10
20
20
–
Min. Samples
3
3
3
–
Max. Samples
80
80
80
–
GSR modelled the oxidation surface to determine the boundary between oxide and fresh material. No
transition zone was modelled. The density values used for the tonnage estimate were provided by GSR and
are detailed in Table 14-45.
Table 14-45 Chichiwelli rock density
Oxidation State
Value (t/m3 )
Oxide
1.8
Fresh
2.68
14.7 Model Validation and Sensitivity
14.7.1 Wassa
SRK checked the resultant LR block model by considering: (1) visual comparisons of block grades and nearby
composites via a sectional approach; (2) swath plots for the combined LG and HG domains along northing,
easting and a vertical swath; and (3) change of support checks. Sectional checks showed good consistency
between the informing data and local estimated blocks, and also good conformity of grade trends to the
local folds in the mineralization. In general, the swath plots showed that in areas of abundant data, the
model matches well with the composite grades in that moving average window. Mismatches in the
informing composites and the average block grades are attributed to those regions of the model that are
sparsely sampled, specifically in the southern extent of the mineralized zone as shown in Figure 14-27.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-27 South-North Swath Plot Comparing Estimated Grades and Informing Capped Composites (SRK, 2020)
Histogram bars correspond to block tonnages in the February 2020 long-range Mineral Resource model
South of 19,400 North, the estimated grades and the composite grade profiles are more erratically
behaved. This is attributed to the presence of fewer composites with some very high-grade intersections,
and the continuity of the grade shells in the southern area. Mineral Resources in the southern portion of
the estimate have all been classified as Inferred Mineral Resources to reflect the lower confidence.
SRK anticipates that additional drilling in this area may impact the continuity of the grade domains and
dampen the influence of these higher-grade intervals. SRK understand that GSR have conducted
subsequent studies comparing 2018 to 2020 long- and short-range models; these comparisons
demonstrate that year on year, the impact of additional drilling has historically increased the Inferred and
Indicated Mineral Resources.
SRK also compared the ordinary kriging block model distribution with the declustered, change-of-support
corrected distribution of the informing composites for the LG and HG domains (Figure 14-28). Declustering
mitigates the influence of preferential sampling of borehole data; this often results in a distribution of
composites whose mean statistic is often comparable to that of the estimated model. Further, a change-of
support correction is applied to account for the volume difference between the composite scale and the
final block volume scale. Figure 14-28 shows the quantile-quantile comparison of the gold distribution
from the block model and the expected grade distribution following declustering and change-of support
corrections for the LG and HG domains. Overall, the mean grades from the block model are reasonably
close to those predicted from declustering. The quantile-quantile plot shows that the block model is
comparable to that predicted by the change-of-support for the HG domain, and slightly smoother than
predicted for the LG domain.
The preliminary block model was delivered on February 28, 2020 for further review by GSR. The sub
blocked Surpac model was delivered on March 3, 2020.
Page 157NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-28 Quantile-Quantile Comparison of Block Model Grades to Declustered Change-of-Support Corrected
Gold Distributions for LG (left) and HG (right) domains (SRK, 2020)
For the SR model, validation included the following processes:
- Sectional visual check to ensure that the mineralized domain was completely enclosed by the halo
domain;
- Sectional visual check to ensure that the mineralized domain enclosed continuous high grade assay
values and that the halo domain enclosed the lower grade isolated assay values;
- Sectional visual check to ensure that the domain shells were influenced by the structural control
surfaces;
- Sectional visual check to ensure that composite assay values and block model grades were
consistent with each other;
- Volume check, to ensure coded block model volumes are close to original wireframe volumes;
- Check that capping of the 2m composite assay values was performed correctly;
- Check between the block model and the 2m capped composite values statistics for similar values;
- Swath plots of the block grades versus the capped 2m composite values in the Easting, Northing
and Elevation directions to ensure that the block grade estimate was valid; and
- Comparison between the latest short-range block model tonnes and grade and the previous short
range block model tonnes and grade. Any difference in tonnes and grade was attributed to the
addition of new drilling.
Swath plots reporting the comparison between the block model estimated grade and the capped 2m
composite grade has been provided in Figure 14-29, Figure 14-30 and Figure 14-31.
Page 158NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 14-29 SWATH plot in the E-W direction X dimension. Blue line represents Block model Estimated grades and
Red is 2m drill hole composites grades (SRK, 2020)
Figure 14-30 SWATH plot in the N-S direction Y dimension. Blue line represents Block model Estimated grades and
Red is 2m drill hole composites grades (SRK, 2020)
Page 159NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 160
Figure 14-31 SWATH plot in the elevation direction Z dimension. Blue line represents Block model Estimated grades
and Red is 2m drill hole composites grades (SRK, 2020)
The data, as presented in the swath plots, showed that the block estimation respected the underlying drill
hole composite dataset and that the block model estimate was valid.
14.7.2 Hwni-Butre
14.7.2.1 Thickness models
In order to validate the thickness estimates a nearest neighbor model is generated for the thickness of each
vein unit of for each deposit. Swath plots comparing the data distribution, nearest neighbor estimates and
kriging estimates are generated. Table 14-46 shows a summary comparing the global mean of each model
for FBZ. The difference ranges from -6.34% to 7.67%.
Table 14-46 Global mean comparison between nearest neighbor and kriged thickness models for FBZ.
FBZ Variable
NN Mean
(m)
Kriging Mean
(m)
% Difference
HW Thickness
1.54
1.45
-6.34
HG Thickness
1.28
1.39
7.67
FW Thickness
1.23
1.25
1.89
Table 14-47 shows a summary comparing the global mean of each model for ADK. The difference ranges
from 0.93% to 12.41%.
Table 14-47 Global mean comparison between nearest neighbor and kriged thickness models for ADK. Variable
ADK Variable
NN Mean (m)
Kriging Mean (m)
% Difference
HW Thickness
1.92
2.08
7.63
HG Thickness
1.93
1.95
0.93
FW Thickness
1.15
1.31
12.41NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 161
14.7.2.2 Gold models
The gold grade data reproduction is also checked. The scatterplot of measured and estimated gold grades
at data locations for FBZ and ADK are shown in Figure 14-32. The least reliable estimates for FBZ are listed
in Table 14-48. The least reliable estimates for ADK are listed in Table 14-49. The scatter plots for both FBZ
and ADK indicate good data reproduction, Figure 14-32. Although the estimates, when compared to the
raw (uncapped) drill hole assay data are less accurate than the drill assay, all but one is under stating the
grade. This means the estimate is conservative in these areas.
Figure 14-32 Measured and estimated gold grades at data locations (RMS, 2020)
Table 14-48 List of least reliable estimates FBZ
Hole id
Min Zones
AUModified
Estimate
Error
A FBRGC0950072
HG
166.72
88.26
-78.46
B FBRGC0980109
HG
192.00
122.63
-69.37
C FBZDD059
HG
253.00
196.52
-56.48
D FBRGC0950039
HG
140.60
92.76
-47.84
E FBRGC0980164
HG
91.92
51.63
-40.29
Table 14-49 List of least reliable estimates ADK
Hole id
Min Zones
AUModified
Estimate
Error
A ADKGC164
HG
8.71
57.97
49.26
B ADKGC042
HG
106.71
59.87
-46.84
C ADK-62
HG
136.38
101.67
-34.71
D ADKGC0960037
HG
104.92
73.22
-31.70
E ADK-71
HG
8.17
33.48
25.30
In addition to the validation above a nearest neighbor model was generated for each vein unit for each
deposit for uncapped and capped gold grades. Swath plots comparing the data distribution, nearest
neighbor estimates and kriging estimates were generated. The swath plots for HG units in the FBZ zone are
shown in Figure 14-33. Table 14-50 shows a summary comparing the global mean of each model for FBZ.
The difference ranges from -3.8% to 8.3%.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 162
Figure 14-33 Swath plot comparison of composites, nearest neighbor estimates and kriging estimates for uncapped
and capped grades in HG for FBZ deposit (RMS, 2020)
Table 14-50 Global mean comparison between nearest neighbor and kriged Gold models for FBZ
Variable
Vein Unit NN
Mean
Kriging Mean
% Difference
AUModified
FW
0.33
0.36
8.28
AUModified3
FW
0.30
0.30
1.72
AUModified5
FW
0.31
0.32
3.38
AUModified
HG
4.20
4.51
6.92
AUModified30
HG
3.71
4.00
7.39
AUModified46
HG
3.83
4.14
7.41
AUModified
HW
0.33
0.32
-3.17
AUModified3
HW
0.33
0.31
-3.79
AUModified5
HW
0.33
0.32
-3.48
A nearest neighbor model was generated for the ADK estimate for each deposit for uncapped and capped
gold grades. Swath plots comparing the data distribution, nearest neighbor estimates and kriging estimates
were generated and plots for HG units are shown in Figure 14-34. Table 14-51 shows a summary
comparing the global mean of each model for ADK. The difference ranges from -043% to 3.09%.
Figure 14-34 Swath plot comparison of composites, nearest neighbor estimates and kriging estimates for uncapped
and capped grades in HG for ADK deposit (RMS, 2020)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 163
Table 14-51 Global mean comparison between nearest neighbor and kriged Gold models for ADK
Variable
Vein Unit NN
Mean
Kriging Mean
% Difference
AUModified
FW
0.58
0.58
1.14
AUModified3
FW
0.57
0.58
1.28
AUModified5
FW
0.58
0.58
1.13
AUModified
HG
5.03
5.19
3.09
AUModified16
HG
4.77
4.75
-0.43
AUModified23
HG
4.87
4.93
1.26
AUModified
HW
0.91
0.92
0.85
AUModified4
HW
0.9
0.91
0.93
AUModified5
HW
0.9
0.91
0.91
Swath plots comparing the nearest neighbor estimates and kriging estimates for the densely sampled area
for FW, HG and HW units in FBZ deposit were created. The swath plot restricted to the densely sampled
areas does not show bias when compared to the nearest neighbor estimates for any of the vein units in the
FBZ deposit. Table 14-52 shows a summary comparing the global mean of each model for FBZ. The
difference ranges from -0.9% to 2.2%.
Table 14-52 Global mean comparison between nearest neighbor and kriged Gold models for FBZ within the densely
sampled area
Variable
Vein Unit
NN Mean
Kriging Mean
% Difference
AUModified
FW
0.77
0.78
1.23
AUModified3
FW
0.71
0.72
1.29
AUModified5
FW
0.73
0.74
1.4
AUModified
HG
10.39
10.29
-0.92
AUModified30
HG
8.58
8.58
0.04
AUModified46
HG
9.41
9.38
-0.29
AUModified
HW
0.62
0.64
2.24
AUModified3
HW
0.57
0.58
0.57
AUModified5
HW
0.59
0.59
0.89
Swath plots comparing the nearest neighbor estimates and kriging estimates for the densely sampled area
for FW, HG and HW units in ADK deposit were also constructed. The swath plot restricted to the densely
sampled areas does not show bias when compared to the nearest neighbor estimates for any of the vein
units in the ADK deposit. Table 14-53 shows a summary comparing the global mean of each model for ADK.
The difference ranges from -1.9% to 0.5%.
Table 14-53 Global mean comparison between nearest neighbor and kriged Gold models for ADK within the densely
sampled area
Variable
Vein Unit NN
Mean
Kriging Mean
% Difference
AUModified
FW
0.99
0.99
0.51
AUModified3
FW
0.96
0.96
0.11
AUModified5
FW
0.97
0.97
0.33
AUModified
HG
6.39
6.38
-0.13
AUModified16
HG
5.52
5.53
0.08
AUModified23
HG
5.84
5.84
0.04
AUModified
HW
1.11
1.09
-1.89
AUModified4
HW
1.06
1.05
-0.86
AUModified5
HW
1.07
1.06
-0.99NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 164
In order to determine how the estimate performed in areas of sparse drill hole data Swath plots comparing
the nearest neighbor estimates and kriging estimates for FW, HG and HW units in FBZ were created. The
swath plot restricted to the sparsely sampled areas is consistently lower for nearest neighbor estimates for
the FBZ deposit except for the HG unit at high U coordinate. High U coordinate correspond to extrapolation
at deeper area of the deposit. Table 14-54 shows a summary comparing the global mean of each model for
FBZ. The difference ranges from -4.8% to 9.6%.
Table 14-54 Global mean comparison between nearest neighbor and kriged Gold models for FBZ within the sparsely
sampled area
Variable
Vein Unit NN
Mean
Kriging Mean
% Difference
AUModified
FW
0.29
0.32
9.57
AUModified3
FW
0.27
0.27
1.80
AUModified5
FW
0.27
0.28
3.77
AUModified
HG
3.73
4.07
8.43
AUModified30
HG
3.34
3.65
8.71
AUModified46
HG
3.41
3.74
8.88
AUModified
HW
0.31
0.30
-4.46
AUModified3
HW
0.31
0.29
-4.79
AUModified5
HW
0.31
0.30
-4.50
Swath plots comparing the nearest neighbor estimates and kriging estimates for the sparsely sampled area
for FW, HG and HW units in ADK deposit were also created. The swath plot restricted to the sparsely
sampled area shows consistently lower nearest neighbor estimates for the HW unit for the ADK deposit.
The nearest neighbor estimate is mostly higher for the FW unit. The HG unit for ADK show reasonable
match with exception of high U coordinates. The high U coordinates correspond to the deeper zones of the
deposit. Table 14-55 shows a summary comparing the global mean of each model for ADK. The difference
ranges from -0.5% to 1.4%.
Table 14-55 Global mean comparison between nearest neighbor and kriged Gold models for ADK within the
sparsely sampled area
Variable
Vein Unit NN
Mean
Kriging Mean
% Difference
AUModified
FW
0.55
0.56
1.20
AUModified3
FW
0.55
0.55
1.39
AUModified5
FW
0.55
0.56
1.21
AUModified
HG
4.95
5.12
3.31
AUModified16
HG
4.73
4.71
-0.46
AUModified23
HG
4.82
4.88
1.34
AUModified
HW
0.90
0.91
1.04
AUModified4
HW
0.90
0.91
1.04
AUModified5
HW
0.90
0.91
1.04
It is the opinion of the QP that the validation exercises of the block model above show that the estimate is
robust and accurate with errors within acceptable ranges.
14.7.3 Benso
The block models were validated by comparing the block model mean grades with the declustered
composite mean grades and through validation slices through the block models.
The mean grades for each of the estimated block models were compared to the declustered mean grade
for the composite input data. Each of the modelled zones was compared separately. The differences
between the declustered mean composite grades and the block grades are relatively small, indicating that
the model is similar to the input data on a global scale.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The block model was also compared to the composite grades within defined sectional criteria in a series of
validation slices, the results of which are displayed on graphs to check for visual discrepancies between
grades along the defined coordinate line. The expected outcome of the estimation process is to observe a
relative smoothing of block model grades around the composite values.
Overall, the estimation of the Benso domains is robust and the results have been verified to a reasonable
degree of confidence. Globally, the block model average grade is relatively similar to that of the
declustered input data, indicating that no biases have been introduced.
The sectional validation slices show a reasonable correlation between the composite grades and the block
model grades and it appears that a reasonable degree of smoothing has taken place for the majority of the
domains.
14.7.4 Chichiwelli
The block models were validated by comparing the block model mean grades with the declustered
composite mean grades and through validation slices through the block models.
The mean grades for each of the estimated block models were compared to the declustered mean grade
for the composite input data. Each of the modelled zones was compared separately. The differences
between the declustered mean composite grades and the block grades are relatively small with the largest
differences up to 10% for a few of the less well sampled domains, indicating that the model is similar to the
input data on a global scale.
The block model was also compared to the composite grades within defined sectional criteria in a series of
validation slices, the results of which are displayed on graphs to check for visual discrepancies between
grades along the defined coordinate line. The expected outcome of the estimation process is to observe a
relative smoothing of block model grades around the composite values.
Overall, the estimation of the Chichiwell domains is robust and the results have been verified to a
reasonable degree of confidence. Globally, the block model average grade is relatively similar to that of the
de-clustered input data, indicating that no biases have been introduced.
The sectional validation slices show a reasonable correlation between the composite grades and the block
model grades and it appears that a reasonable degree of smoothing has taken place for the majority of the
domains.
14.8 Mineral Resource Classification
Block model quantities and grade estimates for the Wassa HBB Project were classified according to the CIM
Definition Standards for Mineral Resources and Mineral Reserves (10 May 2014).
Mineral Resource classification is typically a subjective concept. Mineral Resource classification should
consider the confidence in the geological continuity of the mineralized structures, the quality and quantity
of exploration data supporting the estimates and the geostatistical confidence in the tonnage and grade
estimates. Appropriate classification criteria should aim at integrating all concepts to delineate regular
areas at similar Mineral Resource classification.
The geological modelling honors the current geological information and knowledge. The location of the
samples and the assay data are sufficiently reliable to support Mineral Resource evaluation.
The sampling information was acquired primarily by diamond core and RC drilling on sections spaced at
variable distances between the different deposit areas.
In situ dry bulk density has been estimated to a sufficient level to inform tonnages.
Using the above criteria a 3D surface and solid were created to separated areas of higher confidence
(Indicated Mineral Resources) from those of less confidence (Inferred Mineral Resources).
Page 165NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 166
14.8.1 Wassa
GSR classified the long-range Mineral Resource model and SRK used these to code an interim model
constructed in January 2020, Figure 14-35. The GSR classification surfaces and solids did not change from
the January 2020 Interim model and were also used to classify the final model created in February 2020.
All blocks above the Indicated Mineral Resource surface and within the solid mesh were classified as
Indicated Mineral Resources. No Mineral Resources were classified as Measured in the long-range
Resource model.
Indicated Mineral Resources were classified where drilling was up to 50 m spacing, with Inferred Mineral
Resources being classified where drill spacing was greater than 50 m.
SRK noted that blocks classified as Indicated blocks are informed by composites within an average distance
less than 22 m from the estimated block, with more than 4 holes on average (Figure 14-36). Inferred
Mineral Resources were supported by informing composites within an average distance of 56 m of the
estimated block from an average of 2 holes.
Figure 14-35 Wassa LR model Indicated Mineral Resource classification surface and solids. All blocks above surface
and within solid mesh were classified as Indicated Mineral Resources (GSR, 2021)
To provide quantitative support analyses for the classification scheme adopted by GSR, SRK extracted some
statistics pertaining to the classified blocks based on an optimized pit generated by GSR. For this analysis,
SRK used a cut-off grade of 0.4 g/t gold and 2.1 g/t gold for open pit and underground Mineral Resources,
respectively.
Table 14-56 shows the breakdown of the Open Pit blocks above 0.4 g/t gold cut-off grade, based on Mineral
Resource category, domains and also distance metrics to the nearest 3 holes. The Indicated blocks account
for 99% of the contained metal within the pit, of which 38% comes from the HG and 61% comes from the
LG domain. Overall, the open pit blocks are based on an average of 15 m distance to the closest 3 holes (or
equivalently 25 metre drillhole spacing) and are mostly estimated in the first estimation pass.
Table 14-57 shows a similar breakdown for underground blocks above 2.1 g/t cut-off, based on Mineral
Resource category, domains and also distance metrics to the nearest 3 holes. Unlike the open pit blocks,
only 22% of underground blocks are classified as Indicated with the remaining 78% Inferred. Indicated
blocks are largely supported by data from 4 or more holes estimated in the first pass, found within 21 m of
the block and corresponding to drillhole spacing that is 25 m or less. Inferred blocks comprise 78% of metal
content from underground blocks, of which 71% is from the HG domain and 7% from LG. Statistical analysis
showed that approximately 60% of the metal within Inferred blocks are in areas of less than 100 m drillhole
spacing, 30% in areas of 100-150 m spacing, 5% from 150- 170 m and 5% from greater than 170 m spacing.
N
S
400 mNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 167
Figure 14-36 Estimation metrics associated to Indicated (top) and Inferred (bottom) classified Resources (SRK, 2020)
Table 14-56 Composition of Classified Blocks for Open Pit Extraction Above a Cut-Off Grade of 0.4 g/t Gold
Category
3 Holes
within
(m)
Avg.
Pass
Avg. No.
Holes
Avg.
Data
Dist for
Estimate
(m)
Avg.
Dist to 3
holes
(m)
Max.
Dist to 3
holes
(m)
Tonnage
Contained
Metal
(oz)
% Metal
Indicated
1.0
4.6
20.3
15.3
113.6
27,629,017
1,303,918
99%
HG
1.0
4.6
20.7
13.4
41.3
3,760,615
504,887
38%
unlimited
1.0
4.5
27.4
0.0
0.0
1,801
217
0%
25
1.0
4.9
15.1
8.3
16.8
1,814,004
226,671
17%
50
1.0
4.4
26.4
18.5
32.6
1,815,578
258,562
20%
140
1.1
3.4
31.6
26.5
41.3
129,231
19,437
1%
LG
1.0
4.7
20.2
15.6
113.6
23,868,402
799,031
61%
unlimited
1.3
4.3
26.1
28.4
113.6
223
12
0%
25
1.0
4.8
14.1
9.6
17.0
10,825,800
354,562
27%
50
1.0
4.6
23.4
18.7
33.9
11,577,012
391,625
30%
140
1.0
4.1
32.9
29.5
61.2
1,465,366
52,832
4%
Inferred
1.2
3.7
37.7
37.2
66.1
148,215
9,532
1%
LG
1.2
3.7
37.7
37.2
66.1
148,215
9,532
1%
50
1.0
4.7
26.3
22.0
29.4
20,339
1,935
0%
140
1.2
3.5
39.7
39.9
66.1
127,876
7,598
1%
Total
1.0
4.6
20.3
15.4
113.6
27,777,231
1,313,451
100%NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 168
Table 14-57 Composition of Classified Blocks for Underground Extraction Above a Cut-Off Grade of 2.1 g/t Gold
Category
3 Holes
within
(m)
Avg.
Pass
Avg. No.
Holes
Avg. Data
Dist for
Estimate
(m)
Avg.
Dist to 3
holes
(m)
Max.
Dist to 3
holes
(m)
Tonnage
Contained
Metal (oz)
% Metal
Indicated
1.0
4.3
21.1
16.0
74.5
13,176,385
1,873,291
22%
HG
Domain
4800
1.0
4.3
20.8
15.2
51.8
11,116,448
1,673,516
20%
unlimited
1.0
3.9
33.6
0.0
0.0
8,783
1,119
0%
25
1.0
4.6
14.0
8.6
17.2
6,579,654
1,085,569
13%
50
1.0
4.3
26.6
19.7
34.0
2,484,389
324,510
4%
140
1.1
3.2
35.4
31.6
51.8
2,043,622
262,319
3%
LG
Domain
8800
1.0
4.2
23.0
19.9
74.5
2,059,937
199,774
2%
unlimited
2.0
1.0
17.2
73.0
74.5
1,161
80
0%
25
1.0
4.7
13.5
9.7
16.4
764,421
79,349
1%
50
1.0
4.5
24.0
19.5
34.3
646,069
61,059
1%
140
1.0
3.3
33.2
32.5
55.8
648,286
59,287
1%
Inferred
1.9
2.0
54.1
66.2
199.0
51,682,594 6,678,108
78%
Domain
4800
1.9
2.0
54.2
65.2
190.9
45,714,950
6,083,754
71%
unlimited
2.3
1.4
67.2
90.0
190.9
15,774,728
2,113,514
25%
25
1.1
3.9
19.3
10.4
16.1
70,945
8,392
0%
50
1.0
3.4
28.6
22.0
34.0
1,059,985
124,326
1%
140
1.7
2.3
48.1
53.4
98.8
28,809,293
3,837,522
45%
Domain
8800
1.8
1.9
53.3
73.1
199.0
5,967,644
594,354
7%
unlimited
2.1
1.3
58.5
96.4
199.0
3,172,757
338,150
4%
25
1.0
4.3
17.9
11.2
14.8
12,218
918
0%
50
1.0
4.1
27.6
21.8
32.4
99,418
8,440
0%
140
1.7
2.4
50.0
54.9
97.3
2,683,251
246,846
3%
Total
1.6
2.6
44.8
52.0
199.0
64,858,979 8,551,399
100%
For the SR model, Mineral Resource classification was performed by wireframing the Measured and
Indicated Mineral Resources, based on drill spacing displayed on section. For sections between 20,500 mN
and 19,725 mN, sections were spaced every 12.5 m along northing. For sections 19,725 mN to 19,350 mN,
sections were spaced every 15.0 m along northing.
For Measured Mineral Resources:
- between 20,500N and 19,725N, defined in areas where the drill intercepts were consistently no
greater than 10m apart, up dip or down dip, along the mineralized structures, on each 12.5mN
spaced section; and
- Between 19,725N and 19,350N, defined in areas where the drill intercepts were consistently no
greater than 13m apart, up dip or down dip, along the mineralized structures, on each 15.0mN
spaced section.
For Indicated Mineral Resources:
- Indicated Mineral Resources were classified for blocks in the model that were not classified as
Measured Mineral Resources but were within a domain shell, trimmed against a boundary solid,
used to define the limits of the use of the SR model in the final model. Outside of this boundary,
the LR model is relied upon. The boundary solid typically extended outwards from the tightly
defined Measured resource a maximum distance of approximately 100 to 120 meters vertically or
horizontally.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
An example demonstrating the classification of resources on the 645m RL has been provided in Figure
14-37. The image shows the mineralization classified as either Measured or Indicated Mineral Resources in
the SR model. The image also shows mineralization that is located outside the boundary solid. Mineral
Resources and classification for this material would be informed by the LR model.
Figure 14-37 645m RL section showing resource classification, boundary solid and drill holes (GSR, 2020)
Page 169NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 170
14.8.2 Hwini Butre – Father Brown – Adoikrom
Mineral Resource Classification for Hwini Butre generally follows the same general principles as those
applied at Wassa. Classification has been assigned using a combination of drillhole spacing, geological and
confidence in mineralization interpretation, as well as slope of regression values from the estimation
process. The classification was modelled visually by digitizing a wireframe in order to define contiguous
zones of confidence.
The surface used to define Mineral Resource classification was extended approximately half the drill hole
spacing on section, as this is where confidence in the geological interpretation was considered to reduce.
Indicated Mineral Resources have been defined in the areas of Father Brown and Adoikrom where drilling is
sufficient to demonstrate geological and grade continuity to a reasonable level. The Inferred Mineral
Resources have been constrained by two 3D solids that have included the wider spaced drilling at depth
(100 to 200m spacing), shown in Figure 14-38. All other material outside of the 3D mesh/surface
constraints remained unclassified.
Figure 14-38 Father Brown and Adoikrom Indicated Mineral Resource surface and Inferred Mineral Resource solids.
All material above Magenta surface was classified as Indicated Mineral Resources all material below surface and
within cyan (ADK) and red (FBZ) 3D meshes was classified as Inferred Mineral Resource
N
S
200 m
ADK Inf
FBZ Inf
IND SurfaceNI 43-101 Technical Report (March 2021) Wassa Gold Mine
14.8.3 Benso
Classification for Benso generally follows the same principles applied at Wassa and Hwini Butre.
Classification has been carried out using a combination of drillhole spacing, geological and wireframe
confidence and was modelled by digitizing a wireframe.
The Indicated Mineral Resource wireframe was extended approximately half the drill hole spacing on
section, as this is where confidence in the geological interpretation was considered to reduce. Indicated
Mineral Resources have been defined in the Subriso East, Subriso West and G Zone areas of Benso where
drilling is sufficient to demonstrate geological and grade continuity to a reasonable level (nom. 25 x 25 m).
14.8.4 Chichiwelli
Classification for Chichiwelli generally follows the same general principles as those applied at Wassa, Hwini
Butre and Benso, with classification carried out using a combination of drillhole spacing, geological and
wireframe confidence, and was modelled visually by digitizing a wireframe.
Wireframes were digitized for East Domain and West Domain, with the areas inside the modelled solids
considered to be Indicated Mineral Resources, and outside, Inferred Mineral Resources.
The majority of the Chichiwelli Mineral Resource has been classified as Indicated Mineral Resources. For
the three additional deposits covered by the Chichiwelli MRE, an Inferred classification has been applied.
14.9 Mineral Resource Statement
The Mineral Resources have been prepared in accordance with CIM Definition Standards for Mineral
Resources and Mineral Reserves, adopted by the CIM Council on May 10, 2014, and the CIM Estimation of
Mineral Resources and Mineral Reserves Best Practice Guidelines, adopted by CIM Council on November
29, 2019.
Mineral Resources are reported inclusive of Mineral Reserves.
The Wassa Mineral Resource Estimates are a combination of the long-range (LR) and short-range (SR)
models.
The “reasonable prospects for eventual economic extraction” (RPEEE) requirement implies that the
quantity and grade estimates meet certain economic thresholds and that the Mineral Resources are
reported at an appropriate COG, taking into account extraction scenarios and processing recoveries.
In order to determine the quantities of material offering “reasonable prospects for economic extraction” by
open pit mining, GSR used a pit optimizer and reasonable mining assumptions to evaluate the proportions
of the block model (Indicated and Inferred blocks) that could be “reasonably expected” to be mined from
an open pit. The assumptions of open pit mining were only assumed for the Benso, Chichiwelli and HBB
other prospects. No open pit Mineral Resource are reported herein for Wassa.
The optimization parameters are based on actual costs from the operations. The reader is cautioned that
the results from the pit optimization are used solely for the purpose of testing the “reasonable prospects
for economic extraction” by an open pit and do not represent an attempt to estimate Mineral Reserves.
GSR considers that the blocks located within the conceptual pit shells show “reasonable prospects for
economic extraction” and can be reported as a Mineral Resource.
The underground Mineral Resources were reported above an economic cut off based on a $1500/ ounce
gold price and mining, processing and general administrative costs that were adjusted from actual costs at
the Wassa underground operation. Table 14-58 and Table 14-59 shows the Mineral Resource statements
for the Wassa main and HBB deposits.
Page 171NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 172
Table 14-58 Wassa Measured and Indicated Mineral Resource, as at 31 December 2020
Table 14-59 Wassa Inferred Mineral Resource, as at 31 December 2020
Notes to the Mineral Resource estimate:
- The Mineral Resource estimate complies with the requirements of National Instrument 43-101 and
has been prepared and classified in accordance with the CIM Definition Standards for Mineral
Resources and Mineral Reserves, adopted by the CIM Council on May 10, 2014, and the CIM
Estimation of Mineral Resources and Mineral Reserves Best Practice Guidelines, adopted by CIM
Council on November 29, 2019;
- Measured and Indicated Mineral Resources are reported inclusive of Mineral Reserves;
- Underground deposits within the Mineral Resource are reported at a cut-off grade of 1.4 g/t;
- Open pit deposits within the Mineral Resource are reported at a cut-off grade of 0.55 g/t, within
optimized pit shells calculated at a $1,500 /oz gold selling price;
- The Mineral Resource models have been depleted using appropriate topographic surveys;
- Mineral Resources are reported in-situ without modifying factors;
- No open pit resource has been reported for the Wassa deposit, as engineering studies have
determined Wassa will be mined by underground methods only; and
- All figures are rounded to reflect the relative accuracy of the estimate.
Measured & Indicated Mineral Resource, at 31 December 2020
Meas. & Ind.
Mineral Resource
at 31 December 2019
Measured Resource
Indicated Resource
Meas. & Ind.
Mineral Resource
Mt
Au g/t
koz
Mt
Au g/t
koz
Mt
Au g/t
koz
Mt
Au g/t
koz
Wassa OP
–
–
–
–
–
–
–
–
–
29.18
1.29
1,206
Wassa UG
5.90
4.45
843
18.96
3.55
2,162 24.85
3.76
3,005 16.20
3.89
2,027
Father Brown
/Adoikrom UG
–
–
–
1.31
7.96
335
1.31
7.96
335
0.91
8.67
254
Benso OP
–
–
–
1.38
2.50
111
1.38
2.50
111
Chichiwelli OP
–
–
–
1.11
1.75
62
1.11
1.75
62
HBB Other OP
–
–
–
0.62
1.21
24
0.62
1.21
24
2.51
2.32
187
TOTAL
5.90
4.45
843
23.37
3.59
2,694 29.26
3.76
3,537 48.81
2.34
3,675
Inferred Mineral Resource
at 31 December 2020
Inferred Mineral Resource
at 31 December 2019
Mt
Au g/t
koz
Mt
Au g/t
koz
Wassa OP
–
–
–
0.62
1.31
26
Wassa UG
70.50
3.39
7,689
58.82
3.75
7,097
Father Brown
/Adoikrom UG
2.66
5.30
454
1.88
6.08
367
Benso OP
0.05
3.37
5
–
–
–
Chichiwelli OP
0.05
2.22
4
–
–
–
HBB Other OP
0.77
1.31
32
0.42
2.14
29
TOTAL
74.02
3.44
8,183
61.74
3.79
7,519NI 43-101 Technical Report (March 2021) Wassa Gold Mine
14.10Mineral Resource Risks
During estimation of the Mineral Resources, the following risks were identified:
- At Wassa, the geometry of gold mineralization is complex and will require tight spaced drilling prior
to extraction.
- The Inferred Mineral Resource in the southern portion of the Wassa deposit is informed by wide
spaced drilling. It is the opinion of the QP that the global estimate in this area is within the
accuracy limits to be classified as an Inferred Mineral Resource but the geometry of the mineralized
zones will change with additional definition drilling.
- In the Southern portion of the Wassa LR model, additional definition drilling may impact the
continuity of the grade domains and dampen the influence of higher-grade intervals. GSR have
conducted subsequent studies comparing 2018 to 2020 long and short-range models. The
comparisons demonstrate that historically, the addition of more drilling has resulted in larger
Inferred and Indicated Resource estimates.
- Reporting of the Wassa underground resource at 1.4 g/t within the modelled 1.5 g/t isoshell may
result in tonnages being underestimated and grades overstated. During 2021, the modelling
parameters will be reviewed as to ensure the estimate is appropriate for the cut-off grade.
- The Inferred Mineral Resources at FBZ and ADK have been classified based on drill hole spacing in
excess of 100m in some cases and there is risk associated with the grade estimates in these areas.
The wider spaced drilling has however demonstrated the continuity of the mineralized structure
and through further drilling the average grade of the inferred resource should be realized.
Beyond the risks disclosed here and in Section 25.2 not material risks have been identified.
Page 173NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 174
15 MINERAL RESERVES
15.1 Cut-off Grade
The cut-off grade applied for the Wassa UG Mineral Reserve is 1.9 g/t for stoping and development. This is
a decrease from 2.4 g/t for the previous declaration, with the change driven by lower operating costs,
achieved from increasing underground mining rates that have been sustained through 2019 and 2020.
Table 15-1 Wassa UG cut-off grade calculation
An assessment was completed during 2020 for cut-offs from 1.5-3.0 g/t. Stope shapes were generated for
each cut-off, indicative schedules were developed by applying vertical advance benchmarks and costs were
estimated using fixed and variable rates (lower $/t at higher rates).
Preliminary NPV’s (pre-tax) were calculated at $1,300 /oz and results showed peak NPV generated across
the range of 1.6-2.0 g/t . 1.9 g/t was selected as the cut-off for calculation of the Reserve as the associated
5,000 t/d ore mining rate (1.8 Mtpa), is considered close to full capacity of the current mining system.
Figure 15-1 Wassa UG cut-off optimization
Unit
Realisation Costs
Mining
$/t
Processing
$/t
TSF & Projects
$/t
Site G&A
$/t
Total, Realisation Cost
$/t
Dilution Adjustment
%dil
Net Realisation Cost
$/t
Selling Costs/Adjustments
Government Royalty
% sales
RG Stream Adjustment
% sales
Total, Sell Cost/Adjustments
$/oz
Revenue
Gold Price
$/oz
Processing Recovery
%rec.
Total, Realised Revenue
$/cont.oz
$/cont.g
Cut-off Grade
Reserve Cut-off Grade
g/t
Parameter
32.41
18.32
1.13
9.17
61.03
5.0%
8.4%
5.0%
64.08
1.9
1,300.00
95.0%
1,060.80
34.11
174.20NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 175
15.2 Modifying Factors
Modifying factors were applied to calculate the Wassa UG Mineral Reserve as follows:
- Stopes: based on back analysis of actual stope performance from 2020.
o Mining Dilution: 5.0%
o Mining Recovery: 96.1%
- Development: based on back analysis of actual stope performance from 2020.
o Mining Dilution: 0.0%
o Mining Recovery: 100.0%
Diluting material is assumed to contain no gold.
The effective modifying factors for the combined stope and development ore yield:
o 100.8% of in-situ ore tonnes;
o 95.8% of in-situ grade; and
o 96.6% of in-situ contained ounces.
Modifying factors were determined from analysis of the stope performance for 2020 to end of November
and are a more conservative approach than the previous declaration which assumed 0% dilution and 100%
stope recovery. The change is mostly due to improving systems for monitoring and tracking stope
excavation performance.
15.3 Mineral Reserve Statement
The Mineral Reserves have been prepared in accordance with CIM Definition Standards for Mineral
Resources and Mineral Reserves, adopted by the CIM Council on May 10, 2014, and the CIM Estimation of
Mineral Resources and Mineral Reserves Best Practice Guidelines, adopted by CIM Council on November
29, 2019.
Table 15-2 Wassa Mineral Reserve, as at 31 December 2020
Notes to the Mineral Reserve estimate:
- The Mineral Reserve estimate complies with the requirements of National Instrument 43-101 and
has been prepared and classified in accordance with the CIM Definition Standards for Mineral
Resources and Mineral Reserves, adopted by the CIM Council on May 10, 2014, and the CIM
Estimation of Mineral Resources and Mineral Reserves Best Practice Guidelines, adopted by CIM
Council on November 29, 2019;
- The Mineral Reserve is reported at a cut-off grade of 1.9 g/t, calculated at a $1,300 /oz gold selling
price;
- Modifying factors are applied as 5.0% dilution and 96.1% recovery for stopes;
- Material based on Measured Mineral Resources are reported as Proven Mineral Reserves;
- Material based on Indicated Mineral Resources are reported as Probable Mineral Reserves;
Mineral Reserve, at 31 December 2020
Mineral Reserve
at 31 December 2019
Proven Reserve
Probable Reserve
Mineral Reserve
Mt
Au g/t
koz
Mt
Au g/t
koz
Mt
Au g/t
koz
Mt
Au g/t
koz
UG, Panels 1 & 2
4.28
3.28
451
4.48
2.99
430
8.75
3.13
881
7.42
3.72
889
UG, Panel 3
–
–
–
2.06
2.94
195
2.06
2.94
195
–
–
–
Open Pit
–
–
–
–
–
–
–
–
–
9.92
1.57
500
Stockpiles
0.69
0.58
13
–
–
–
0.69
0.58
13
1.06
0.62
21
TOTAL
4.97
2.91
464
6.54
2.97
625
11.50
2.94
1,089 18.41
2.38
1,410NI 43-101 Technical Report (March 2021) Wassa Gold Mine
- Material based on Inferred Mineral Resources are excluded from Mineral Reserve;
- Economic analysis of the Mineral Reserve demonstrates economic viability at $1,300 /oz gold price;
and
- All figures are rounded to reflect the relative accuracy of the estimate.
15.4 Mineral Reserve Risks
The Mineral Reserve estimate could be materially affected should assumptions not be realized for:
- Underground mining productivity and unit costs;
- Geotechnical conditions requiring a material change to the mine design;
- Processing performance (throughput and recovery) and unit costs; and
- Failure to maintain operating permits in good standing.
Page 176NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16 MINING METHODS
16.1 Mineral Resources Considered in Mining Plan
The Wassa Underground Mine (WUG) commenced development in 2015 and declared commercial
production in January 2017.
The Wassa property has an established record of successful permitting applications from project
commencement in 1998 to present. These are detailed in Section 20.1.2.
16.1.1 Mineral Resource Inclusions
Mineral Resources considered in this assessment are as at December 2020 and consist of two geological
models:
- Short-Range (SR) Model (bm201201_v4):
Estimate for mineralization proximal to current underground mine. SR model is applied north of
19,350 mN and below 745 mRL to the 350 mRL. It contains material classified as Measured and
Indicated Resource.
- Long-Range (LR) Model (srkwasmar20e):
Estimate for mineralization in all areas not defined by the SR model and is applied from 19,240 to
19,350 mN and above 745 mRL. It contains material classified as Measured, Indicated and
Inferred Mineral Resource and Inferred Mineral Resources are excluded from consideration.
Figure 16-1 Mineral Resources considered in Mineral Reserve and models applied
Page 177NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16.1.2 Definitions
Figure 16-2 illustrates the following definitions used to describe the different mining quantities.
- Panel: Each panel defines a progressive phase of definition drilling and capital development. The
definition can be flexible but new panels are defined by their requirement for new access
infrastructure (eg: Panel 3 vs Panel 1-2), a change in mining method (Panel 2 vs Panel 1) or a new
phase of definition drilling followed by an investment decision (eg: Panels 4, to 5, to 6, etc).
- Area: Areas are semi/continuous zones of mineralization, which require extraction in a connected
sequence but are geotechnically independent from other areas within the panel. Panels can extend
across multiple areas where the panel boundaries are designed to permit sequence independence.
- Stope: A stope is a single production excavation which follows a defined sequence to complete the
production cycle (eg: development, drilling, blasting, loading, filling).
- Lift: Stopes across multiple levels are mined in a series of lifts, as they progress through each level,
i.e. a four-lift stope is four levels high.
Figure 16-2 Schematic of Wassa location descriptors
16.2 Mining Locations
The underground mine has been divided into 3 zones which are shown in the plan in Figure 16-3 and
longitudinally in Figure 16-4.
- Panels 1 & 2:
Current zones of mining, include B-Shoot, F-Shoot and Hanging-wall. Panel 1 is from 20,400 mN,
south to 19,730 mN (+/-10m) and vertically from 745 mRL to 520 mRL. Panel 2 lies further south,
from 19,700 mN (+/-10m) to 19 240 mN and vertically from 695 to 345 mRL. Mineral Resource in
the mine plan for Panels 1 and 2 is classified as Measured and Indicated. Natural surface level is
nominally 1,000 mRL meaning Panels 1 and 2 range from approximately 250 to 650 m depth.
- Panel 3:
The upper mine zones of B-Shoot, F-Shoot and 242, were included in the December 2019 Mineral
Reserve Statement to be mined by open pit methods. This assessment now proposes a change to
underground extraction (refer 16.3.1.1.1 for discussion).
Panel 3 runs from 20,200 mN, south to 19,700 mN (+/-10m) and vertically from 945 down to 745
mRL. Mineral Resources in the plan for Panel 3 are all Indicated. The zone also contains Inferred
Mineral Resource that is not included in the mine plan. Panel 3 ranges from approximately 50 to
250 m depth.
Page 178NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 16-3 Wassa mine design and asbuilt, plan view (GSR, 2021)
Page 179NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 16-4 Wassa mine design and asbuilt, longitudinal view
16.3 Current and Upper Mining Zones (Panels 1-3)
This section covers the extraction of ore north of 19,240 mN, being Panels 1, 2 and 3.
Wassa commenced underground development in 2015 and stoping production in 2017. During the
establishment of the underground mine, open pit mining was occurring in parallel to deplete the Main and
242 pits. Open pit mining was completed in 2017.
Figure 16-5 Wassa underground production history
Page 180NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 181
16.3.1 Mine Design
Panels 1, 2 and 3 will continue to be mined by underground methods using the Long Hole Open Stoping
(LHOS) method, with 25 m level spacing.
16.3.1.1 Stoping Methodology
16.3.1.1.1 Upper Zones Method Change
The December 2019 Mineral Reserve included mineralization above the current underground workings and
below the Main pit, as well as below the 242 pit, to be extracted by open pit methods. These upper zones
are now collectively referred to as Panel 3.
During 2020, trade-off reviews were completed to determine the optimal extraction method.
The trade-offs showed that the optimal extraction method for the upper zones was by underground, rather
than open pit. The advantages of underground extraction being:
- Improved selectivity: enables focus on extraction of high margin mineralization. This has resulted
in a decrease in total ounces, but metal removed from the inventory is the higher unit cost, lower
grade material.
- Reduced capital demand: the smaller scale underground plan will have a lower upfront capital
demand than the large cutbacks required for open pit extraction. This further enables bringing
forward production from the upper zones.
- Elimination of interactions: between active open pit and underground operations.
Table 16-1 Upper mine inventory change, OP to UG
16.3.1.1.2 Panels 1 and 3
- Stope length is 25 m along strike with 6-10 m pillars between.
- Stope width is full width of the orebody which can be up to 35 m but is usually 15-25 m.
- Stopes are mined with uphole blastholes drilled from below. The stope lifts are extracted in a top
down sequence; each stope lift is extracted below the open stope void above. Up to four stope lifts
are extracted to create a continuous excavation up to 100 m high.
- In Panels 1 and 3, the 100 m height limit usually enables full extraction of the orebody without the
need for sill pillars. Where this is not the case, a sill pillar is left in the level between the sets of
stopes.
- Mined voids are generally left open with some loose rock fill to dispose of waste or for
opportunistic pillar recovery.
- Narrower ore zones (<15 m) are mined as longitudinal stopes with progressive placement of rock
fill to minimize ore loss in pillars.
- Stopes at the south end of Panel 1 will utilize paste backfill within approximately 100 m of the
panel boundary. Use of paste further north is limited by distribution pressures.
16.3.1.1.3 Panel 2
- The introduction of paste backfill permits a change to increase the extraction ratio.
- Primary stope length is 20 m with 20 m pillars left between, which will then be mined as secondary
stopes after filling and curing of the primaries.
Design Inventory
Tonnes
‘000 t
Au grade
g/t
cont.Au
‘000 oz
* Implied Grade of Variance ounces/tonnes
Variance
-7,857
1.21*
-305
Underground
Open Pit
9,920
1.57
2,063
2.94
195
500NI 43-101 Technical Report (March 2021) Wassa Gold Mine
- Stope width is full width of the orebody which can approach 50 m but is usually 15-25 m.
- Primary stopes are mined with uphole blastholes drilled from below. The stope lifts are extracted
in a top-down sequence; each stope lift is extracted below the open stope void above, shown in
Figure 16-6. Up to four stope lifts are extracted to create a continuous excavation up to 100 m
high, which are filled with paste fill as a single fill mass.
- Secondary stopes are mined with blastholes drilled from below with each stope lift extracted in a
bottom-up sequence, shown in Figure 16-7. To minimize paste exposure in the side-walls, each
stope lift is planned to be filled before extracting the lift above. As experience with paste fill
increases, there is an opportunity that the secondary stopes could be extracted in multiple lifts
before filling. This would deliver a more productive mine schedule but this plan assumes the more
conservative approach.
- Combined stope excavations up to 100 m high are planned before a sill pillar is introduced. The
first sill pillar in Panel 2 lies between the 520 and 545 mRL levels.
- Sill pillars can be extracted after the secondary stopes are backfilled and sill pillar extraction
assumes 60% recovery of the full stope.
Figure 16-6 Stope cycle for Panel 2 primary stopes
Figure 16-7 Panel 2 primary/secondary stope extraction sequence, transverse stopes
The primary / secondary sequence in Panel 2 extracts the first pass of stopes to full design height (4-lifts,
100 m), mining every second stope along strike (the primary stopes), with pillars left between. The pillars
are extracted as secondary stopes after sufficient primary stope voids complete paste backfilling.
In Panel 2, extraction of the first pass of primary stopes is well progressed. Paste backfilling and
subsequent mining of the first secondary stopes is planned in 2021.
Figure 16-8 shows progression of the generic primary/secondary sequence, which includes:
- The first stope is generally located in the centre of the block and the mining front radiates from the
centre toward the peripheries, with primary stopes mined to full height of the block (4-lifts, 100 m).
Page 182NI 43-101 Technical Report (March 2021) Wassa Gold Mine
- Secondary stopes follow the primary stope front with a lag distance of 120-140m along strike to
create a sufficient buffer from active primary stopes and development.
- Secondary stopes will initially be constrained to one lift per stope, to limit exposure dimensions of
the paste fill mass in stope walls.
- Extraction of the sill pillar commences when there is a sufficient distance from secondary stopes in
the blocks above and below. Each crosscut into the sill pillar is scheduled to be redeveloped in time
for the uphole stopes to be mined.
- This resulting sequence has primary stope extraction almost, if not fully, complete before the first
secondary stope is mined. It creates a production profile which is high in the early years of primary
stoping, then slows as secondary stopes are mined and becomes low when the block is only
producing from stopes in the sill pillar.
Figure 16-8 Stope cycle for Panel 2 secondary stopes
16.3.1.2 Stope Design
Mine design for Panels 1-3 was completed by the Wassa mine technical team in January 2020 as part the
planning for the December 2020 update of the Mineral Reserve.
Optimal stope shapes were developed from the Mineral Resource block model using Datamine Mineable
Shape Optimizer (MSO) software. MSO is a design algorithm which processes a geological block model
against user defined geometrical parameters to produce optimized stope shapes. MSO inputs were:
- Cut off Grade: 1.9 g/t
- Stoping width (minimum/maximum): 5 – 100 m
- Minimum pillar between adjacent stopes: 10 m
- Minimum hanging/foot-wall dip angle: 80°
Optimization shapes were validated by manual checks to remove outliers and updated with production
designs where applicable.
Page 183NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16.3.1.3 Development Design
The methodology used for the development design was:
- Operating development, Levels: both in ore and waste, designed to provide access for drilling and
loading of stopes;
- Capital development, Decline: linking of level accesses with inclined development (1:7 grade),
including stockpiles to facilitate development;
- Capital development, Levels: infrastructure on each level located at the required access position
along strike, to enable the stope extraction sequence (access, stockpiles, electrical cuddy, paste fill
access, footwall accesses); and
- Capital development – Infrastructure: attachment of infrastructure to the main decline and level
accesses, including: ventilation network extensions, sumps and drainage system, and emergency
egress (escapeway) network.
Panels 1 and 2 are accessed via the Daniel Owiredu Portal (formerly Portal 1), located in the Starter Pit. The
Main decline is positioned east of B-Shoot which has variable dip. Maximum ramp grade is 1:7 and follows
the plunge of the deposit south toward the deeper levels of Panel 2. Levels are accessed every 25 metres
through level access drives connecting the ramp to each level’s footwall drive.
The upper zones will be mined as Panel 3 with two new decline accesses due to their spatial distance from
the Main decline:
- Upper B-Shoot decline portal will be in the southern end of the Main pit and connects the Main
decline at the 760 mRL. Duplicating the main decline enables the B-Shoot Upper material to be
extracted in parallel with Panels 1 and 2, plus also forms part of a haulage loop system.
- 242 decline will be mined in the footwall of the 242 shoot which is north of the mineralized zone. It
is remote from any B-Shoot infrastructure and will be an independent ramp.
Figure 16-9 shows an isometric view of the asbuilt and planned underground development for Panels 1 to
- Figure 16-10 shows a typical level layout for Panels 1/2.
Figure 16-9 Oblique view of Wassa Panels 1-3, asbuilt and planned development
Page 184NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Panel 1
Decline
Panel 2
UG Workshop
570 Diamond Drill
Drive (DDD)
Figure 16-10 Typical level layout, Panels 1-2 570 mRL
Figure 16-11 Oblique view of Panels 3 242 Area, planned development and stopes
Page 185NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 186
Figure 16-12 Oblique view of Panels 3 B-Shoot Area, planned development and stopes
16.3.1.4 Design Quantities
The design quantities defining the Mineral Reserve (as at 31 December 2020) and are summarized in Table
16-2.
Table 16-2 Wassa Panels 1-3, design quantities for Mineral Reserve
Panels 1-2
B-Shoot
Panel 3
B/F-Shoot
Panel 3
242
Ore Mined, Development
‘000 t
1,143
166
93
g/t
2.98
2.85
3.70
‘000 oz
110
15
11
share% oz
X
X
X
Ore Mined, Stopes
‘000 t
7,611
1,079
724
g/t
3.15
2.71
3.25
‘000 oz
771
93
76
Ore Mined, Total
‘000 t
8.755
1,245
818
g/t
3.13
2.71
3.30
‘000 oz
881
109
87
Ore Mined, Total
‘000 t
10,818
g/t
3.09
‘000 oz
1,076
Development, Total
m
44,173
Dev’t Capital
m
20,392
Dev’t Operating
m
23,781
Vertical Development
m
2,776
Mined to Waste
‘000 t
2,469
Paste Backfill
‘000 m3
2,967NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16.3.2 Geotechnical
Geotechnical characterization and design parameters used in the mine design for Panels 1-3 are based on:
- Wall mapping in permanent openings and ore drives to define the structural discontinuities;
- Geotechnical data available in from surface exploration and underground drilling logs;
- Logs of underground boreholes that had been subject to detailed geotechnical logging;
- A limited set of laboratory strength and deformation test results;
- Empirical support classification assessment to determine the support requirement for the
permanent drives;
- Empirical Stability Graph (Mathews et al, 1981) assessments to determine the maximum stable
spans of the stopes; and
- Numerical modelling to assess the stability and stress distributions around the stope spans and the
crown pillar.
Geotechnical characterization has been done using Q classification values (Barton et al, 1974), for input to
the Empirical Stability Graph Method, and Geological Strength Index (GSI, Marinos et al 2007) classification
values.
16.3.2.1 Structural Data
A number of faults have been identified orientated at right angles to the limbs of the fold. These are normal
faults with downthrows of up to 5 m. They are characterized as fairly tight with little to no evidence of
shearing adjacent to the contacts. Some were identified to contain in-filling material.
The rock mass structure has little variance between each lithology. The small scale discontinuities can be
related to the major scale deformational processes that have affected thedeposit. Several joint sets have
been identified from the relevant data sources and have been considered for the mine design criteria.
Based on the structural assessment of the geotechnical mapping, the joint sets presented in the stereonet
plot shown in Figure 16-13 and summarized in Table 16-3 were used for the stope stability assessment.
Figure 16-13 Stereonet plant of Wassa joint set database
Page 187NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 188
The dominant discontinuity sets in all domains, shown in Figure 16-13 are:
- The orebody parallel foliation (F);
- A moderately north-east dipping joint set (J1);
- A joint set trending south-east (J2);
- Joint set J3 is a moderately developed sub-horizontal set; and
- Joint set 4 (J4) is steeply dipping, north trending.
In this analysis, the mean discontinuity orientations presented in Table 16-3 have been used.
Table 16-3 Joint sets used for stope design
16.3.2.2 In-Situ Stress
Over-coring stress measurements were completed in September 2019 to measure in-situ stress levels in the
mine.
The measurements were taken at two sites using the CSIRO HI-Cell method. The sites are located in the
hanging-wall at 645-DD7 and in the footwall at the 570 decline.
The stress measurement was rated as Excellent for the 570 decline according to the stress test rating
system used by the service supplier (industry standard). The 645-DD7 stress measurement was disregarded
due to the test site being considered within the mining induced stress zone of excavations and not a valid
reflection of the virgin in-situ stress field.
The results from the-570 decline are shown in Table 16-4 and the interpreted depth gradient is shown in
Figure 16-14.
Table 16-4 570 decline stress measurement
Discontinuity Set
Dip
Dip Direction
Comments
Foliation
16.53
11.61
Tightly healed foliation planes
J1
–
–
Set of tightly healed North-east trending joints
J2
1.64
1.33
Set of tightly healed South-east trending joints
J3
1.66
1.37
Set of sub-Horizontal North-west trending joints
J4
19.83
14.31
Set of steeply dipping North trending joints
Principal Stress
Magnitude
(Mpa)
Depth
(m)
Ratio
Gradient
(MPa/m)
Dip
Direction
Major
26.5
430
2.23
0.062
4°
339°
Intermediate
18.9
430
1.59
0.044
6°
69°
Minor
11.9
430
1.00
0.028
83°
219°NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 189
Figure 16-14 Principal stress measurement Magnitude vs Depth
16.3.2.3 Rock Quality
Based on the structural assessment of the geotechnical mapping, the rock mass quality is classified Very
Good, using Barton’s (Barton et al, 1974) classification and Geological Strength Index (GSI) rating systems.
Table 16-5 contains the rock mass condition data of the Wassa geotechnical domains, which were used for
the stope stability assessment and ground support design.
Table 16-5 Wassa rock mass characterization parameters (Barton et al, 1974)
0
200
400
600
800
1000
1200
1400
1600
0
20
40
60
80
100
120
Magnitude (MPa)
Principal Stress with Depth
Expected Wassa Mine Stress Gradient
Wassa 645 Site 1 Stress Measurement
Wassa 570 Site 2 Stress Measurement
Parameter
Footwall / Orebody / Hanging-wall
Source
MIN
MAX
Average
Rock Quality Desc.
RQD%
85
90
85
Geotechnical and mapping
Joint Number
Jn
6
9
6
Borehole structural data and mapping
Joint Roughness
Jr
3
4
3
Detailed geotechnical logs & mapping
Joint Alteration
Ja
1
0.75
1
Detailed geotechnical logs & mapping
Q’
43
53
48
Rock Mass Quality
Very Good
Very Good
Very Good
Geol. Strength Index
GSI
78
80
78
Underground mapping & inspections
Unconfined Compressive
Strength
UCS
Mpa
110
160
135
Rocklab laboratory test result
Unconfined Tensile
Strength
UTS
MPa
16
18
17
Rocklab laboratory test result
Young’s Modulus
GPa
70
80.5
75.3
Rocklab laboratory test result
Poisson’s Ratio
0.28
0.32
0.3
Rocklab laboratory test result
Density
t/m3
2.79
2.81
2.8
Rocklab laboratory test result
Depth below Surface (m)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16.3.2.4 Geotechnical Design, Development
Barton’s Q support classification system was applied to estimate the support requirement for the
development headings, which are nominally designed at 5.5 m wide.
Using and Excavation Support Ratio (ESR) of 1.3, as defined by Barton and Grimstad (1993) for permanent
mine openings, results are plotted in Figure 16-15. The development excavations are plotted in red and are
assessed to be within Category 1 (No Support Required). This aligns with observations of a Very Good rock
mass with little or no fallout and spalling.
Notwithstanding the results of the analysis, GSR applies a standard reinforcement pattern of friction bolts
and surface mesh to the back and upper walls of all development headings. This level of support plots in
Category 3 (Systematic Support) in Figure 16-15.
Figure 16-15 Support, Barton’s Q-Index chart (Barton and Grimstad, 1993)
16.3.2.5 Geotechnical Design, Stopes
16.3.2.5.1 Modified Stability Number
The Q’ value derived from the geotechnical characterization (Barton et al, 1974) has been used, along with
the stability graph parameters A, B and C to determine the Modified Stability Number (N’) (Potvin, 1988)
for stope back, side-walls (hanging/foot) and end-walls.
The stress parameter A was estimated by calculating the gravitational stress generated from the weight of
the overburden rock above the mining. The structural parameters B and C were derived from an
assessment of the interaction of the dominant joint sets with the stope boundaries.
Calculated N’ for the Q’ value derived from the rock mass characterization for both the longitudinal and
transverse stopes are presented in Table 16-6 and Table 16-7.
Page 190NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 191
Table 16-6 Modified Stability Number (N’) for Panels 1-3, transverse stopes (Potvin, 1988)
Table 16-7 Modified Stability Number (N’) for Panels 1-3, longitudinal stopes (Potvin, 1988)
Parameter
Stope Wall, Transverse
Comments
Back
Side
End
Q’
47.9
47.9
47.9
From mapping and core RQD, Jn, Jr, Ja
UCS, Sigma C
Mpa
130
130
130
Average intact rock strength
Depth
m
500
500
500
Average depth below surface, Panel 2
Max. Principal Stress, Sigma
1
Mpa
13.5
13.5
13.5
Estimated overburden stress
Stress : Strength Ratio
1:
9.6
9.6
9.6
Factor A
1.0
1.0
1.0
Angle between Stope Face &
Daylighting Joint
15°
15°
45°
Critical Joint for all back and
side-walls is J3, end-wall is J4.
Factor B
0.2
0.2
0.5
Potential Failure Mode
Gravity
Slabbing
Slabbing
Gravity or Slabbing
Dip of Stope Face
0°
90°
64°
Factor C
2
8
5
N = Q’ x A x B x C
19.2
76.7
119.8
N-value for all stopes >=64° slope
Parameter
Stope Wall, Longitudinal
Comments
Back
Side
End
Q’
47.9
47.9
47.9
From mapping and core RQD, Jn, Jr, Ja
UCS, Sigma C
Mpa
130
130
130
Average intact rock strength
Depth
m
500
500
500
Average depth below surface, Panel 2
Max. Principal Stress, Sigma
1
Mpa
14.6
14.6
14.6
Estimated overburden stress
Stress : Strength Ratio
1:
8.1
8.1
8.1
Factor A
0.9
0.9
0.9
Angle between Stope Face &
Daylighting Joint
15°
45°
15°
Critical Joint for all back and
side-walls is J3, end-wall is J4.
Factor B
0.2
0.2
0.5
Potential Failure Mode
Gravity
Slabbing
Slabbing
Gravity or Slabbing
Dip of Stope Face
0°
64°
90°
Factor C
2
4.9
8
N = Q’ x A x B x C
17.3
106.3
69.0
N-value for all stopes >=64° slopeNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 192
16.3.2.5.2 Stable Slope Design Geometry
Table 16-8 summarizes the calculated range of stable stope and design geometries for the expected rock
mass conditions for Transverse and Longitudinal Open Stoping Methods in Panels 1-3. The orientation of
the measurement axes is shown in Figure 16-16.
Table 16-8 Stable stope dimensions, Panels 1-3
Figure 16-16 Stope axes measurements
The nominal designs for transverse and longitudinal stopes were plotted on the Matthews Stability graph
and are shown in Figure 16-17 and Figure 16-18. All faces plot in the stable portion of the graph, without
additional support.
This indicates that for a 30 m wide ore zone, stopes of 20 m width by 100 m height will be stable which is
confirmed by field observations of current excavations.
Stope Dimension
Transverse Stope
Longitudinal Stope
MIN
MAX
Design (m)
MIN
MAX
Design (m)
Height
m
25
100
100
<15
25
25
Strike Length
m
25
25
25
<60
70
70
Width across Strike
m
15
30
25
<15
15
15
Dip, end/side-walls
65°
65°
65°
65°
65°
65°NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 16-17 Matthews Stability Graph, transverse stopes (Mathews et al, 1981)
Figure 16-18 Matthews Stability Graph, longitudinal stopes (Mathews et al, 1981)
Page 193NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16.3.2.6 Geotechnical Design, Major Pillars
16.3.2.6.1 Existing Pillars, B-Shoot
A crown pillar exists between the Main pit where B-Shoot has been mined below from underground. In
addition, there are a number of sill pillars remaining between mined stopes underground, which are a mix
of open void and loose rock fill.
Stability analysis was conducted using Phase 2 software which calculated factors of safety:
- Crown Pillar, B-Shoot Main pit and 720-N1 stope = 1.58
- Sill Pillar, 720-N1 and 745-S1 = 1.58
This indicates that in both situations a stable pillar can be maintained, Figure 16-19.
Figure 16-19 B-Shoot Pillars, modelled factors of safety from Phase 2 software, (GSR, 2018)
16.3.2.6.2 Future Pillars, Panel 3
Panel 3 stopes are proposed to be excavated close to the 242 and Main B-shoot pits.
At the time of modelling the B-Shoot pillars, stope designs for Panel 3 were not complete, so no assessment
was completed.
The indicative minimum design thickness of the crown pillars is approximately 20 m which is considered
reasonable at this early stage but further geotechnical investigation will be required to confirm stability
prior to mining.
Page 194NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16.3.2.7 Geotechnical Design, Ventilation Shafts
Ventilation shafts are planned for Panels 2 and 3 which will be excavated by raisebore with some possible
use of drilling and blasting. The proposed locations of the ventilation shafts have not been geotechnically
assessed and will require geotechnical data collection (drill holes) and evaluation to assess ground
conditions to determine the unsupported diameter.
The first major ventilation shaft is planned to be raisebored in 2021 and includes drilling of a diamond drill
hole for geotechnical logging prior as part of the work program.
16.3.3 Hydrogeology
Hydrogeological investigations were undertaken in 2016 and 2019. Key conclusions for the Panel 1-3 were:
- Inflow of groundwater occurs along discreet zones of faulting and fracturing.
- Hydraulic testing of the underground mining regions to depths of 800 m below surface showed
generally the formation is not water bearing and has generally very low permeability, although
localized high permeability zones have been identified at depth with potential permeability of up to
2 l/s measured.
- Pit sumps in B-Shoot (Starter and Main) and 242 are possibly hydrogeologically connected to the
underground workings. They have dual-use as surge sumps to manage surface runoff and staging
points for the underground dewatering system. This functionality means that generally, sumps
aren’t full but do hold sufficient water that there is potentially a recirculating groundwater load.
A main dewatering system was constructed in 2020 and planned for commissioning in 2021. Addition of
the new pump station will allow the Starter pit sump to be dedicated for collection of incident rainfall and
surface runoff, which will reduce sump inventory and likely reduce flows from hydraulic connection.
16.3.4 Backfill
Different backfill systems and stoping methods are used across Panels 1-3.
16.3.4.1 Rock Fill
In Panels 1 and 3, the nominal stope design mines stope voids, left unfilled, with ore pillars between.
Uncemented rock fill is applied in irregular locations to increase recovery of mineralization by avoiding the
creation of, or enabling the recovery of, ore pillars. Rock fill is sourced from development waste and tipped
directly into stope voids by truck, or rehandled by loader from stockpile.
16.3.4.2 Paste Fill
A feasibility study for the application of paste backfill at Wassa was completed by Outotec in 2018. Plant
construction was completed at the end of 2020, Figure 16-20, and the full system is planned for
commissioning early in 2021. Design capacity is 4,000 t/d of dry tailings processed to produce 120 cu.m/h
of cemented paste fill. Depending on utilization, comparable plants support mining rates of 1.5-2.6 Mtpa.
16.3.4.2.1 Test Work
The feasibility study program tested material characterization, rheology and strength and concluded Wassa
tailings to be suitable for production of paste fill:
- Dewatering, including thickening and vacuum filtration, was achieved through proven unit
processes typical of most backfill plants;
- Typical primary stopes sizes (20 mL x 20 mW x 25 mH) will require 4.5% cement to achieve the
required strength of 270 kPa. Secondary stopes will require 3% cement to achieve the minimum
threshold strength of 150kPa; and
- Underground distribution is amenable to gravity distribution (rather than pumping) with the
location of the surface plant relative to the underground stopes.
Page 195NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16.3.4.2.2 Filter and Mixing Plant
Paste fill will be produced in a filtration and mixing plant with the following processes:
- Tailings will be pumped as the full-stream discharge from the CIL plant in batches with automated
changeover and flushing between the alternate discharge to the TSF. The pipeline corridor has
secondary containment over the 3 km length.
- Tailings are processed in thickener and underflow thickened tailings are held in an agitated storage
tank which which creates buffer capacity between the batches of tailings pumped from CIL and
continuous filtration.
- Ceramic disc filters produced tailings cake which is delivered by conveyor to a paste mixer where
binder (cement) and thickened tailings are added to achieve the required density and binder
content.
- Surplus water (thickener overflow) is recycled to the process water network for re-use in the main
processing plant.
- Mixed paste is transferred into a hopper which discharges to a borehole which supplies the
underground distribution network.
The paste plant is operated from a dedicated control room with access to monitoring data from pressure
sensors in the underground distribution network. In addition, the CIL plant control room can monitor
operations and alarms in the paste plant, with both control rooms able to operate the tailing pumping
processes from the CIL to paste plants. The paste plant is shown in Figure 16-20.
Figure 16-20 Wassa paste plant Dec-2020, thickener and storage tank in foreground
Page 196NI 43-101 Technical Report (March 2021) Wassa Gold Mine
16.3.4.2.3 Underground Distribution
Underground distribution is via a borehole to the 620 mRL, approximately 440 m long, shown in Figure
16-21. The borehole is duplicated for redundancy and to allow periodic cleaning to prevent blockage.
Paste will be distributed by 8 inch steel pipes and can be distributed by gravity to all stopes in Panel 2.
Stopes in the south end of Panel 1 can also be reached by modifying the fill mix to include more moisture,
which will require offsetting increased binder addition.
Figure 16-21 Paste fill distribution modelling
16.3.5 Ventilation
Primary ventilation flows at Wassa are modelled using VentSim software with the model validated using
results of volume and pressure surveys through the mine.
16.3.5.1 Design Criteria
Ghanaian mining regulations prescribe:
- Maximum velocity of 6 m/s in travelling roadways;
- Minimum flow 0.06 m3 /kW/s for diesel engine capacity;
- Minimum velocity of 0.2 m/s in headings, 0.1 m/s in large openings;
- 32.5ºC wet bulb maximum working temperature; and
- Carbon monoxide must be continuously monitored in return airways and information transmitted
to surface.
The ventilation system is designed to meet these regulations as a minimum, with airflow volumes in
Panels 1-3 determined based on the following criteria:
- Up to 9 working areas at any time;
- 50 m3 /s, per working area.
Page 197NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 198
16.3.5.2 Network Design, Panels 1 and 2
The current installed ventilation network, servicing Panels 1 and 2 has surface connections clustered north
of the operating mining areas.
Primary intake points are:
- Daniel Owideru Portal (Portal 1) collared in the Starter Pit; and
- Portal 3, 670 mRL intake shaft and 695 mRL waste pass, collared in the Main Pit.
Primary exhaust points are:
- Portal 2, collared in the Starter Pit with 4 x 132 kW fans in parallel at the portal entrance; and
- 695 mRL exhaust shaft, collared in the Main Pit with 2 x 280 kW fans in series on the 695 mRL level.
A ventilation review was completed by SRK(US) in 2020 which included updating the ventilation model for
current and future operations. Surveyed and modelled airflows as measured in October 2020 are shown in
Table 16-9. Model accuracy is considered adequate by SRK.
Table 16-9 Wassa ventilation model calibration, Dec-2020
To adequately ventilate the complete extraction of Panels 1 and 2, additional main airways and other
changes to the current circuit are required to provide intake and exhaust capacity south of the current
working areas:
- Construction of a 5.5 m diameter exhaust shaft from surface to 570 mRL, with installation of new
primary fans;
- Construction of a 5.5 m diameter intake shaft from surface to 575 mRL; and
- Removal of the exhaust fans in Portal 2 and reversing airflow to become intake.
The new circuit will increase total airflow to approximately 590 m3 /s, with 190 m3 /s exhausting via the
existing 695 mRL fans and 400 m3 /s via the new southern exhaust shaft (RAR1). This will provide sufficient
flow to operate 9 working areas with 50 m3 /s per location. Figure 16-22 shows the Panel 1 and 2
ventilation circuit to end of life.
Construction of the two new shafts and installation of the new primary exhaust fans are budgeted to
commence in 2021 and be completed early 2022.
% Error
Intake Airways
Portal 1 (DO Portal)
m3/s
-11%
Portal 3
m3/s
-7%
670 mRL Intake Shaft
m3/s
+3%
670 mRL Waste Pass
m3/s
–
Intake, Total
m3/s
-4%
Return Airways
Portal 2 (4 x 132 kW)
m3/s
-4%
695 mRL Level (2 x 280 kW)
m3/s
-12%
Intake, Total (1,088 kW)
m3/s
-8%
Fan Pressure
Portal 2
kPa
-1%
695 mRL Level
kPa
+16%
1,105
1,284
441
406
Unit
Survey
1,436
1,426
415
400
221
212
220
194
Location
Measure
8 3
119
149
4 9
VentSim Model
9 3
128
145
4 9NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 16-22 Wassa Panels 1 and 2 ventilation circuit to end of life
16.3.5.3 Panel 3
16.3.5.3.1 B-Shoot Upper
The Upper B ventilation circuit integrate with Panel 2 with connections for both exhaust and intake (via
decline) at 745 mRL, shown in Figure 16-23. An optional exhaust shaft will be included in the mine plan to
provide ventilation independence (approximately 100 m3 /s), enabling activity in B-Shoot to be ventilated
without compromizing capacity to the main Panel 2 production area.
The ‘Extended Haulage Ramp’ shown in Figure 16-23 is a ramp to create a haulage loop in Panels 1 and 2.
Figure 16-23 Wassa Panel 3, B-Shoot Upper ventilation circuit
16.3.5.3.2 242
The 242 mining area is spatially separated from the rest of the underground mine and has an independent
ventilation network. Preliminary ventilation designs are preliminary only but reflect a conservative design
approach to ventilate the area.
The current design is shown in Figure 16-24 with the following features:
- Exhaust via a connecting ramp to the Main pit. As well as exhaust ventilation, this drive will be
used for definition drilling and as a second egress.
- Intake via the access decline.
Page 199NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 16-24 Wassa Panel 3, 242 ventilation circuit
The two exhaust fan positions in Panel 3 plan to re-use the four 132 kW fans currently located in Portal 2.
Although detailed models are not yet completed, it is anticipated that, given the similarity to their current
duty, with two fans in parallel each position provides approximately 100 m3/s to ventilate two working
areas in each area.
16.3.6 Mining Services
16.3.6.1 Electrical
The underground electrical system has been designed and installed according to Ghanaian mining
regulations and to efficient mining standards and will have high availability, medium utilization and low
operating maintenance. The high voltage circuit above 570 level is 6.6 kV and 1 kV for low voltage. The
high voltage circuit below 570 level in Panel 2 will be 11kV, with 1kV outlets for mining equipment. The
total underground feed from both the 6.6kV and 11kV circuits is approximately 13.0 MVA., split 5.0MVA to
the 6.6kV circuit via the Starter Pit and 8.0MVA to the 11kV circuit via a borehole to 570 level.
Panel 3’s electrical circuit will use the 6.6kV circuit because of Upper B and 242’s proximity to the already
installed infrastructure. Panel 2 below 570 level will use the 11kV circuit. Refer to Figure 18-4 for the site’s
basic electrical layout line diagram.
16.3.6.2 Compressed Air
The compressed air system comprises 2 x 90 kW compressors located on surface at the Starter Pit portal.
Compressed air is distributed underground via a 110 mm poly pipe down the main decline. Due to pressure
drop along the reticulation and incremental increases in duty, an additional compressor is planned.
16.3.6.3 Service Water
A 30,000 litre water tank is installed above the portal area to supply the underground mine with service
water for drilling, dust suppression and general use. The service water tank is filled using the 90 kW Flygt
pump that is permanently installed in the Starter pit sump. Service water is reticulated throughout the
mine by 110 mm HDPE lines installed in the primary headings and reducing to 63 mm HDPE for supply to
end use locations.
16.3.6.4 Underground Dewatering
The underground mine dewatering system is designed and installed to remove both ground water and service
water (collectively called mine water), including up to 10% by volume solid particles.
The mine dewatering system contains the following staging in the upper part of the mine:
- 18kW decline face pumps which pump to sumps on operating levels;
- 37kW pumps transfer initially settled water to either mono pumps or 90 kW Flygt pumps, which
pump to the starter pit sump outside the main portal.
Page 200NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The system dewaters to the Starter Pit sump at a rate of 35 l/s and, where required, up to 65 l/s. The F Shoot
mining area will continue to use this system; the rest of the B Shoot mining areas will use a recently installed
permanent pump station on 620 mRL.
The permanent pump station at the 620 mRL level can pump 80 l/s over a 440m total dynamic head. The
pump station pumps directly to the surface via a borehole to surface settling and discharge routes. The
station uses cascading settling sumps to drop out as many solids as possible prior to pumping to surface.
The station uses multistage pumps to meet the total dynamic head and flow rate required. A borehole
connects the pump station to surface with a 200 mm NB steel rising main installed.
As the mine progresses at depth beyond the 620 mRL level, additional staging pumps will be utilized and
directed to the 620 mRL pump station. These pumps will be similar to existing pumps with sublevel 37 kW
Flygt pump and for main dewatering at depth a 90 kW Flygt pump and, if required, supported by a 55 kW
Mono pump. A reduced dewatering system above the 620 mRL pump station will remain in place to
intersect inflow at higher levels and dewater to the Starter Pit sump on surface. The dewatering system is
shown in Figure 16-25.
The recently installed 620 mRL pump station is shown in Figure 16-26.
Figure 16-25 Underground dewatering longitudinal view
Page 201NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 16-26 620 mRL main pump station
16.3.7 Mining Schedule
Mining quantities for Panels 1-3 were scheduled using MineSched software, with spatial links between
development and stoping, and capacity constraints which reflect the methodology and sequence outlined
above.
The mine schedule calculates all physical quantities which are input into the cost estimate.
- Definition Drilling: geological diamond drilling required to define the mineralization. Drilling is
capitalized where the material being targeted is not yet classified as Mineral Reserve or production
is planned two or more years after drilling.
- Development: Lateral and ramp development to access and support stoping. Heading types which
support production from a number of stopes are classified as capital (decline, stockpiles, level
access, footwall drives, vent access, orepass access, dewatering) and access for production from
one stope are operating (stope crosscut, ore drives).
- Vertical Development: Vertical development (long hole raise or raisebore) for ventilation, egress,
orepass or other infrastructure, which are all capitalized. Raising required for stope blasting is not
quantified and is included in the $/t unit cost for stope blasting.
- Backfill: Paste fill volume placed.
- Waste Material: waste generated from lateral and vertical development activities, including any
material which may be placed as rock fill.
- ROM Material: Material generated from development and stoping and sent for processing.
- Haulage: Estimated haulage quantities, calculated from planned tonnes mined and average
one-way lead distance.
Page 202NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 203
The key scheduling constraints applied were:
- Maximum advance rate from a single heading: 4.5 m/d for decline, 6.0 m/d for other lateral;
- Maximum total advance rate: 27 m/d (820 m/mth);
- Maximum ore tonnage from a single stope: 3,000 t/d; and
- Maximum total tonnage: 6,200 t/d in 2021 and 6,800 t/d thereafter when Panel 3 development
commences.
Milestones assumed in the scheduling of Panels 1-3 are:
- Continued extraction from Panels 1 and 2 from 2021;
- Initial development from Panel 3 in mid-2022;
- Stoping commences from Panel 3 in 2025;
- Sill pillar extraction in Panel 2 commences 2024;
- Development completed 2025;
- Primary and secondary stopes completed in 2025; and
- Sill pillar extraction (and all other activity) completed in 2026.
The schedule quantities are shown in Table 16-10.
Table 16-10 Wassa mining schedule quantities for Mineral Reserve plan
CY21
CY22
CY23
CY24
CY25
CY26
Definition Drilling
Resource Dev’t & Infill
‘000 dd.m
36.0
5.0
15.0
5.0
–
–
Grade Control
‘000 dd.m
13.5
12.3
13.1
12.2
6.5
–
Total Dev’t
‘000 dd.m
49.5
17.3
28.1
17.2
6.5
–
Development
Capital
m.adv
2,582
5,943
6,756
5,111
–
–
Operating
m.adv
7,272
4,996
5,289
5,926
296
–
Total Dev’t
m.adv
9,855
10,939
12,045
11,037
296
–
Vertical Development
v m
977
891
464
443
–
–
Backfill
‘000 fill.m3
546
597
592
621
445
166
Material Movement
Waste, tonnes
‘000 t
463
657
737
609
3
–
ROM, tonnes
‘000 t
1,784
1,826
1,804
1,939
2,020
1,445
ROM, Au grade
g/t
3.08
3.11
3.29
3.07
2.94
3.10
ROM, cont.Au
‘000 oz
176.7
182.5
190.6
191.3
191.0
144.1
Total Movement
‘000 t
2,247
2,483
2,541
2,549
2,023
1,445
Haulage
Tonnes x Kilometres
Mtkm
6.8
8.0
8.7
9.3
6.7
4.8
Avg. Distance
km
3.01
3.22
3.43
3.64
3.33
3.33
1,076.3
13,287
44.3
3.33
20,392
23,781
44,173
2,776
2,967
2,469
10,818
3.09
Total/avg
118.6
61.0
57.6NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 16-27 Lateral development schedule for Mineral Reserve
Figure 16-28 Ore mining schedule for Mineral Reserve
Page 204NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 16-29 Underground Production History and Mineral Reserve plan
16.3.8 Mobile Equipment
The current mining fleet at Wassa is a mixture of the original low-cost, pre-owned fleet from when the
mine was established and new units which have been commissioned as the project has modernized and
productivity has grown. The forward plan at Wassa assumes that this cycling out of older units with new
equipment will continue:
- Development Jumbos: Current fleet is four Sandvik DD421 twin-boom jumbos which continue as
the standardized development machine.
- Production Drills: Current fleet is three rigs, one each of Sandvik DL411/421/431 which are the
same class machine (89-115 mm top-hammer) with different boom configurations. This machine
will continue as the standardized blasthole drilling machine, possibly with different boom
configuration or replacement of a longhole drill with a small raisebore/boxhole rig for stope slots.
- UG Loaders: Current fleet is four 18 t class LHD’s (two older Cat R2900G and one Sandvik LH517)
and two 21 t class machines (Sandvik LH621), which will be standardized to the LH621. Fleet
numbers in early years have been adjusted to reflect operation of the smaller units until they are
cycled out of the fleet.
- UG Truck: Current fleet is eight 40 t class articulated trucks (Volvo A45G) which are planned to
upgrade to 60 t class machines (Volvo A60H), with the first larger truck budgeted for 2021. Fleet
numbers in early years are adjusted to reflect the smaller units until they are cycled out of the fleet.
Machine numbers for the mobile equipment fleet categories were estimated using the productivity
assumptions shown in Table 16-11 and the resulting fleet schedule is shown in Table 16-12.
Page 205NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 206
Table 16-11 Mobile fleet productivity assumption
Table 16-12 Mobile fleet schedule for Mineral Reserve plan
Development Jumbo
4
5
5
5
1
–
Production Drill
2
2
2
3
3
2
UG Loader
6
5
4
4
3
3
UG Truck
8
9
7
8
6
4
ROM & Ancillary
9
1 0
1 0
1 0
8
6
CY26
Machine Type
CY21
CY22
CY23
CY24
CY25
UofM
Development Jumbo
m.adv
Production Drill
sto.t
UG Loader
all.t
UG Truck
tkm
ROM & Ancillary
all.t
Machine Type
Tonne Kilometres
Driving Quantity
119,250
Total Tonnes, Ore+Waste
22,500
Capacity per Unit
Description
per mth
Metres Advanced, Total
220
Stope Tonnes
65,000
Total Tonnes, Ore+Waste
60,000NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 207
17 RECOVERY METHODS
17.1 Processing History
Wassa started industrial scale processing in 1998 utilizing a heap leach (HL) to recover gold from the ore.
The process involved crushing, screening and agglomeration of the mined feed material before being
stacked on leach pads which were irrigated with a weak cyanide solution to recover the gold. The solution
was processed through carbon columns, stripped from the loaded carbon and smelted through to gold doré
bars. Actual recoveries of 55-60% did not achieve planned recovery of 85% which led to the suspension of
operations in 2001.
In 2003 a feasibility study commenced to evaluate construction of the current CIL plant. The study results
were positive and the plant was constructed in 2004 and commissioned in 2005. The CIL plant uses
crushing, milling and CIL and was designed to process 3.5 Mtpa from a feed blend comprising 45% fresh
material, 25% oxidized material and 30% reclaimed spent HL material. Spent HL material reclaimed from
the pads was added to the mill feed via a scrubber until this material was depleted in 2014. After that, mill
feed consisted of fresh material from the open pit until 2016 when underground material was introduced
to the feed. Open pit mining was completed in 2018 and since then, the predominant feed has been
underground ore with supplementary addition of open pit stockpiles fresh, low grade ore.
Table 17-1 Historic plant production, grades and recoveries
17.2 Flow Sheet Description
Gold recovery is achieved using conventional CIL technology, although the plant itself contains a few
atypical features due to its history and development.
The plant flowsheet has transitioned from the historical HL processing and currently consists of the
following operations:
- A four-stage fine crushing circuit incorporating an open circuit primary jaw crusher followed by
secondary, tertiary and quaternary cone crushers with the secondary and tertiary crushers
operated in closed circuit with sizing screens. A single secondary, two tertiary and four quaternary
crushers give a nominal crushed product size from the crushing circuit of 80% <8 mm.
- Two independent milling circuits, each comprising a 5.03 m diameter x 6.7 m long ball mill fitted
with 3 MW motors feeding individual clusters of classifying cyclones. Reported mill product size is
around 80% <75 µm.
- Two separate gravity gold recovery circuits using 48” Knelson centrifugal concentrators process a
portion of the classifying cyclone feed in each mill circuit.
CY06
CY07
CY08
CY09
CY10
CY11
CY12
CY13
CY14
CY15
CY16
CY17
CY18
CY19
CY20
Feed, from Heap Leach
Tonnes
‘000 t
928
324
147
214
188
8
146
9 6
–
–
–
–
–
–
Au grade
g/t
0.64
0.30
0.73
0.59
0.39
0.24
0.30
0.30
–
–
–
–
–
–
Feed, from Open Pit
Tonnes
‘000 t
2,824
2,863
2,506
2,434
2,579
2,507
2,695
2,629
2,495
2,444
1,926
526
161
375
Au grade
g/t
1.34
1.52
2.78
2.36
2.01
2.09
2.27
1.40
1.46
1.27
1.27
0.76
0.65
0.79
Feed, from Underground
Tonnes
‘000 t
–
–
–
–
–
–
–
–
–
–
178
691
1,075
1,388
1,636
Au grade
g/t
–
–
–
–
–
–
–
–
–
–
2.06
3.03
4.18
3.57
3.13
Total Feed
Tonnes
‘000 t
3,691
3,752
3,187
2,653
2,648
2,767
2,515
2,841
2,725
2,495
2,623
2,617
1,601
1,549
2,011
Au grade
g/t
0.90
1.17
1.40
2.67
2.22
1.90
2.08
2.17
1.36
1.46
1.32
1.73
3.06
3.27
2.70
cont.Au in Feed
‘000 oz
107
141
143
228
189
169
168
198
119
117
112
146
157
163
174
Recovery
Gravity
g/t
19.3% 19.1% 22.7% 26.5% 27.0% 49.6% 51.4% 35.4% 22.6% 24.0% 22.2% 25.8% 28.4% 25.7%
CIL
g/t
72.8% 74.8% 72.4% 68.3% 67.3% 45.0% 43.1% 57.3% 70.8% 69.5% 71.9% 69.9% 67.1% 69.3%
Total
g/t
88.8%* 92.1%* 93.9%* 95.1%* 94.8%* 94.3% 94.6% 94.5% 92.7% 93.4% 93.5% 94.0% 95.7% 95.6% 95.0%
Au Produced
‘000 oz
98*
130*
135*
217*
179*
160
159
188
110
109
104
137
151
155
165
* CY06-09 recovered includes metal to GIC, Produced is poured only
Total/avg
2,051
1.92
35,983
3.43
4,968
2,100
0.52
28,964
1.76
65.3%
94.4%
29.1%
2,226NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 208
- The gravity concentrate from the Knelson concentrators is leached using an intensive leach reactor
in combination with an electrowinning cell to recover the precious metals as a sludge prior to
refining. The tails from the centrifugal concentrators are returned to the milling circuits.
- Classifying cyclones and pre-leach thickener. The thickener underflow feeds a transfer vessel
together with the secondary cyclone underflow where cyanide is added before the slurry is
transferred to the CIL circuit. Oxygen is injected into the transfer line after the transfer pumps.
The transfer pipeline acts as an In-Line Reactor (ILR), where most leaching occurs.
- Adsorption occurs in the counter current CIL circuit, consisting of six stages of agitated vessel each
of 2500 m3 , providing an overall residence time of 18-20 hours at a 7,400 t/d mill capacity.
Hydrogen peroxide is added periodically to CIL tank 1 to maintain the dissolved oxygen level.
Activated carbon is retained in each tank using interstage basket screens and is moved counter
current to the slurry flow using submerged vertical spindle pumps in each tank. Loaded carbon is
recovered from the first CIL stage.
- Loaded carbon is acid washed and then stripped of gold using caustic soda in an 11.5 t pressure
Zadra elution system with the gold electrowon onto steel mesh before smelting.
- Eluted carbon is thermally regenerated and returned to the last stage of the CIL circuit.
- The gravity gold concentrate and electrowon gold are smelted separately to produce doré bars.
- Additional supporting facilities include:
o Two, 2.1 t/d capacity pressure swing absorption oxygen plant located in the milling area;
o emergency diesel powered generators.
The key plant design and operating parameters are shown in Table 17-2 and a schematic flowsheet for the
Wassa plant is presented in Table 17-2. The schematic incorporates the new densifying cyclone and
thickening circuit currently being installed.
The Wassa process plant is currently operating below design capacity due to limited feed supply. 2.0 Mt of
ore was processed in 2020 compared to nameplate capacity of 2.7 Mtpa.
The Wassa process operation achieved certification with the International Cyanide Management Code in
early November 2009 and was recertified in 2017 and again in 2020.
Table 17-2 Key plant design and operating parameters
Parameter
Unit
Fresh Ore Feed
Design
Current Operations
Nominal throughput
Mtpa
2.65
1.60
Crushing Circuit Product
% passing
80%< 8mm
80%< 8mm
Crushing Circuit Utilization
%
75
75
Plant Design Availability
%
92
92
Mill product grind
% passing
70%<75 micron
70%<75 micron
CIL Feed Density, Design/Current
% Solids
40
40 (CIL tanks – measured)
CIL Feed Density, with thickener
% Solids
44-46
44-46
CIL Retention Time (calculated)
h (total)
20
33NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 17-1 Wassa processing plant flow sheet
Page 209NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 210
17.2.1 Plant Accounting
Plant throughput is reported based on the belt weighers installed on the conveyors feeding the two ball
mills from the crushed material stockpile. There is also a belt weigher installed on the crushing circuit
product to the crushed material stockpile.
Plant performance and accounting is assessed based on samples of feed and tailings taken automatically
using inline slurry samplers, which are composited into 12 h shift accounting samples. The feed sample is
taken after the milling and gravity circuit before transfer to the CIL circuit and the gold recovered by gravity
and smelted separately is added to calculate the plant feed grade. The feed and tail slurry samples are
analysed using bottle roll laboratory tests to assess the BLEG tests.
Slurry samples are filtered and washed and solids are pulverized to 95% <75 µm before being subject to
BLEG (bulk leach extractable gold) bottle roll extraction. BLEG tests are run for 8 hours at high cyanide
concentration. Solutions from BLEG test and slurry filtrate are analysed by gold extraction into an organic
phase and then measured by atomic adsorption spectroscopy (AAS). Extended BLEG tests are also done to
confirm that all the recoverable gold has been extracted during the standard BLEG leach period. The BLEG
tails are periodically fire assayed to determine residual gold in the samples not recovered in the BLEG tests
(gold potentially locked in silica, pyrite or other sulphide minerals). Initially, a BLEG factor was used in
assessment of the total gold in the plant tails to determine the overall plant gold recoveries. However, GSR
has continuously improved its BLEG testing process so that the tests achieve complete gold dissolution.
Periodic fire assays on the residue of the tails from the BLEG tests confirm the efficiency of the BLEG tests.
The gold recovered by gravity is leached, electrowon and smelted separately and this is added to the gold
in the mill product sample to determine the gold grade in the feed. A sample is taken of crushed ore from
the feed to the ball mills and this is used as a check measurement on the plant feed grade although is not
used for accounting purposes.
Reconciliation is undertaken monthly between the gold produced and the gold present in the feed and
tails. This also considers the changing gold inventory on the plant from month start to month end. Based
on the reconciliation the reported head grade is adjusted to correlate with the monthly gold production.
17.3 Processing Schedule
Table 17-3 shows the processing schedule quantities for the Mineral Reserve plan.
Table 17-3 Processing schedule quantities for Mineral Reserve plan
CY21
CY22
CY23
CY24
CY25
CY26
Feed, from Underground
Tonnes
‘000 t
1,711
1,893
1,996
2,228
2,001
338
Au grade
g/t
3.14
3.01
2.95
2.95
2.89
3.03
cont.Au in Feed
‘000 oz
173
183
190
211
186
3 3
Feed, from LG Stockpile
Tonnes
‘000 t
361
100
–
–
–
225
Au grade
g/t
0.62
0.61
–
–
–
0.61
cont.Au in Feed
‘000 oz
7
2
–
–
–
4
Total Processed
Tonnes
‘000 t
2,072
1,993
1,996
2,228
2,001
563
Au grade
g/t
2.70
2.89
2.95
2.95
2.89
2.06
cont.Au in Feed
‘000 oz
180
185
190
211
186
3 7
Recovery
g/t
94.4%
94.3%
94.1%
93.9%
93.6%
90.8%
Au Produced
‘000 oz
170
175
178
199
174
3 4
Total/avg
10,167
2.99
976
686
0.62
1 4
10,852
2.84
990
93.9%
930NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 17-2 Processing schedule for Mineral Reserve plan
Figure 17-3 Gold Production schedule for Mineral Reserve plan
Page 211NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 17-4 Processing Production History and Mineral Reserve Plan
Figure 17-5 Gold Production History and Mineral Reserve plan
Page 212NI 43-101 Technical Report (March 2021) Wassa Gold Mine
18 INFRASTRUCTURE
The locations of mining areas and major infrastructure at Wassa are shown in Figure 18-2, including:
- Main roads, towns and power lines;
- Open pit voids and waste storage areas;
- Processing facilities;
- Tailings storage facilities; and
- Site accommodation.
Key infrastructure locations around the main site area are shown in Figure 18-1 and a site layout in Figure
18-2, which shows both the local mine grid and UTM grid (WGS84 30N). Figure 18-3 shows the same site
layout image plus the underground workings surveyed at the end of December 2020.
Figure 18-1 Wassa key infrastructure (GSR, 2018)
Page 213NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 18-2 Wassa site layout (GSR, 2021)
Page 214NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 18-3 Wassa site layout and underground workings (GSR, 2021)
18.1 Electrical Infrastructure
18.1.1 Power Supply
Wassa has two power supply sources. The site is connected to the national grid, along with on-site power
generation.
Grid power from the national power supplier (VRA) via a network operated by GridCo comes from a 161 kV
line to local substation where power is transformed down through a 33 MVA transformer to 34.5 kV. The
grid connection has been the primary site power supply since commissioning in 2006.
An on-site power station was constructed during 2020 to improve long-term reliability of the power supply.
The plant is owned and operated by Genser under an agreement and contains two 34.5kV, 16.5MW gas
turbines. The plant was commissioned in early 2021 and now supplies all site power except for the site
accommodation camp.
With on-site generation, the grid connection is retained, permitting use of the grid for standby supply.
Page 215NI 43-101 Technical Report (March 2021) Wassa Gold Mine
18.1.2 Site Distribution
Power is supplied to the main site substations at 34.5 kV with a major upgrade completed in 2020.
- The processing plant and other surface facilities are fed via the GSR substations, which are 16 MVA
and 18 MVA capacity and distribute at 6.6 kV. They are sized for the plant to operate at the full
2.7 Mtpa throughput rate.
Figure 18-4 Site electrical distribution
- The underground mine is supplied by three 34.5/6.6 kV substations:
o One 5.0 MVA capacity transformer with two 2000 kVA 400 V diesel generators with
switching and transformers to distribute at 6.6 kV to distribution substations in the
underground mine and associated locations, where it is locally stepped down as required to
1000 V, 415 V and 240 V. Spare switches are available for future requirements.
o Two 4.0 MVA transformers were added in 2020 when distribution was expanded to provide
capacity for the paste plant and ventilation fans required to extract the Reserve.
Distribution voltage was increased from 6.6kV to 11kV and the project included installing a
new switch yard to split the feed between the 34.5kV/6.6kV circuit servicing mine via the
Portal bench and the new 34.5kV/11kV circuit which connects to a ring main unit at 570
level via a single point suspended 185mm2 XLPE cable in a raisebored service hole.
The 11kV project has capacity to be readily expanded and Figure 18-4 shows a simplified
line diagram, with the conceptual expanded HV circuit shown in yellow shading.
Page 216NI 43-101 Technical Report (March 2021) Wassa Gold Mine
18.2 Surface Water Management
Water diversion structures are installed as required to prevent inflow of surface runoff from the
surrounding topography. Within the pit crests, water inflow is a combination of rainfall and groundwater.
Each of the four catchments within the Main pit complex (Figure 18-5) have a storm water collection sump
which is designed for a 1:100 year, 24 hour duration event (241 mm). Catchment modifications have been
completed to manage flow directions and capacity requirements at each sump. The dewatering discharge
from the pit sumps is used across the site (eg: process plant, dust suppression) and excess water is directed
to settling and drainage systems prior to release.
Figure 18-5 Wassa Main pit catchments
- Starter Pit: has direct connectivity to underground workings via the two portals at 905 mRL. The
sump below the portal entrances has 115% of the capacity required for the design rainfall event.
Service and emergency pump systems are installed to maintain low operating levels and provide
surge capacity to draw down the sump during and after a rainfall event.
o Service – 45 l/s (electric submersible pump with 160 mm HDPE pipe); and
o Emergency – 165 l/s (diesel pump set with 2x 160 mm HDPE pipes).
- B-Shoot Pit: has direct connectivity to underground workings via the portal, waste rock pass and
vent shaft breakthoughs at the 844 mRL. The sump in the bottom of the B-Shoot pit has 200% of
the capacity required for the design event.
A single diesel pump set with 2x 160 mm HDPE pipes is installed with 150 l/s capacity.
- 242 Pit: currently has limited connectivity to underground workings through groundwater seepage
only. However, this will change with underground development of the Panel 3, 242 area, although
Page 217NI 43-101 Technical Report (March 2021) Wassa Gold Mine
the surface water management plan will remain consistent with the current strategy to catch water
in the 242 pit sump to prevent entry into underground workings.
Current sump capacity is 360% of the design requirement and will reduce to 138% when the new
portal at 940 mRL is cut to establish the underground workings.
A single diesel pump set with 2x 160 mm HDPE pipes is installed with 150 l/s capacity.
- South East Pit: currently has limited connectivity to underground workings through groundwater
seepage only. Sump capacity is 240% of the design requirement.
A single diesel pump set with 2x 160 mm HDPE pipes is installed with 150 l/s capacity.
- The pump network is maintained regularly and sufficient spare equipment is on site including one
of the electric submersible pumps and two of the diesel pump sets.
18.3 Workshops and Other Site Buildings
The following engineering workshops are in place to support site operations:
- Processing Fixed Plant: located near the processing plant to support its activity.
- Surface Mobile Equipment: located between the administration area and equipped with offices,
overhead cranage, services and welding bay to support the former open pit mining fleet.
- Underground has three workshop areas to support the underground mining fleet:
o Surface, located near the underground offices with offices, services and 1000 V power
supply for equipment testing;
o Starter pit portal bench: lube and service bay, with 1000 V test panel; and
o Underground workshop at 595 mRL: this facility is in the final stages of construction
(excavation, support, concreting and water management are complete) and is planned for
completion in 2021-Q2. It will be used to service drilling equipment and loaders and
reduce tramming time to surface.
- Light Vehicles: located near the warehouse.
Other buildings on site include:
- Administration offices;
- Kitchen and messing facilities;
- Diesel fuel storage;
- Warehouse and dry goods storage;
- Metallurgical laboratory; and
- Core processing and logging facility.
18.4 Site Accommodation
Employees reside both on-site, or in surrounding towns and villages.
On-site accommodation is located at the Tara Camp 3 km northwest of the mine site as well as at Camp 2
located within the Akyempim village.
Facilities include:
- Accommodation for both single employees with some houses for families;
- Company medical and health clinic including primary care, laboratory, pharmacy, radiology
ambulance and detention services;
- Kitchen and messing facilities;
- Recreation facilities including gymnasium, tennis court, swimming pool and bar; and
- Commissary.
Page 218NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Accommodation is currently being expanded to provide additional capacity to permit more personnel to
reside on site during their roster-cycle and reduce risk of pandemic exposure. The accommodation
expansion project is shown top-left of Figure 18-6.
Figure 18-6 Tara Camp
18.5 Waste Rock Storage
The waste dumps are located adjacent to the Main and South Akyempim pit complexes. Waste from
underground operations is either placed in underground stope voids or hauled to the waste dump locations
shown in Figure 18-7.
Waste dumps were designed and then permitted in 2017, to allow an additional 88 Mt of storage of waste
from the underground and Main pits Cut 3 cutback. The 419 waste rock dump, south of the Main pit, is the
currently active waste placement area. The permitted storage at the site is sufficient for the waste volume
scheduled to be mined alongside the Mineral Reserve.
Page 219NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 18-7 Waste dump locations (Golder, 2016)
Dumps are designed with 10 m bench height with 10 m wide berms and consider operational and
rehabilitation phases. For operations, as-dumped designs have 37° batter angles (natural angle of repose)
with wider berms and final rehabilitation applies 25° batters to achieve the overall slope of 22°. A nominal
dump section is shown in Figure 18-8.
Asbuilt and designed dumps include the following features:
- Adequate drainage to ensure that any discharge from the waste dump is contained for settlement
and/or monitoring, to enable compliance with the EPA effluent discharge limits.
- The top surface of the dump, and any berms partway up the dump slopes, are constructed to shed
water away from the surface of the dump.
- Water collecting drains are constructed around the perimeter of the dump to route discharges and
runoffs into settlement and monitoring ponds.
Figure 18-8 Section through nominal waste dump design
Page 220NI 43-101 Technical Report (March 2021) Wassa Gold Mine
18.6 Tailings Storage
There are two tailings storage facilities at Wassa which are described below and shown in Figure 18-9:
- TSF 1:
TSF 1 is located northwest of the processing plant at the head of a southerly draining valley and
immediately adjacent to the historical leach pad area. Ground levels range from 1000 mRL on the
valley floor to above 1060 mRL on the surrounding hills.
It is a cross valley impoundment created by the construction of a main embankment in the south
with confining saddle embankments at the north of the facility. Containment to the east and west
is provided by natural ridges. Access is via unsealed access road west of the plant site area.
The catchment area of TSF 1 is estimated to be approximately 140 Ha, of which 124 ha is covered
with tailings as the facility proceeds through closure revegetation trials.
Deposition into TSF 1 ceased in 2019 with paddock deposition completed to achieve the
approximate closure surface topography requirements of the closure landform.
Re-vegetation trials commenced in 2017 towards the next land use and by the end of 2020
revegetation planting was mostly complete.
- TSF 2:
TSF 2 is located in the valley system that trends eastward from the north embankment of TSF 1. It
is approximately 2.5 km from the processing plant and 1.3 km downstream of TSF 1 Saddle Dam 5.
TSF 2 has a footprint of 260 ha, of which 72 ha have been developed to date, and lies within a total
project area of 340 ha including buffer zones.
The remaining capacity of TSF 2 is well in excess of that required for processing of ore defined by
the Mineral Reserve, both before and after allowing for use of tails solids in paste backfill.
Figure 18-9 Wassa TSF 1 and TSF 2 aerial view (August 2020)
Figure 18-10 is a photograph taken from the north of TSF 1, looking southeast in November 2020. In the
image the following features can be seen:
- Revegetated TSF 1 to the right;
- Active deposition into TSF 2, Cell 1 in background left; and
- Basin preparations of TSF 2, Cell 2 in the foreground.
Page 221NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 18-10 View from north of TSF 1 looking southeast (November 2020)
18.6.1 History
TSF 1 was commissioned August 2004 to meet the tailings storage needs for the mine life associated with
construction of the CIL plant. Since starter embankment construction, embankments raises have been
designed, permitted and constructed up to the final elevation at 1039 mRL.
During planning for TSF 2 in 2009 and 2010, alternatives were considered for additional tailings capacity,
with four potentially feasible options:
- Two different locations for new TSF’s;
- Increasing elevation of TSF 1 to 1049.5 mRL; and
- Increasing elevation TSF 1 whilst progressing a new TSF.
The selected option was to construct a new facility (TSF 2). The new TSF required development of a
Resettlement Action Plan (RAP) which ultimately determined the RAP scope to include resettlement of the
entire community of Togbekrom.
In compliance with the requirements of the EPA’s Environmental Assessments Regulations, 1999 (L.I.
1652), GSWL registered a new TSF project with the EPA in May 2010 and obtained authorization to proceed
to permitting in July 2010. An Environmental Scoping Report was submitted to the EPA in March 2011 and
later, and EIS was submitted for the construction and operation of the proposed TSF 2. The EIS was
approved by the EPA in April 2013 (EPA/EIA/383) and conditions of the EIA permit led to GSWL re-designing
the TSF 2 facility to accommodate a geomembrane liner.
While conducting the impact assessments and the preparation of the EIS, GSWL sought permission to raise
the TSF 1 by an additional 5 m and for continued deposition between August 2011 and May 2015. All
embankments have subsequently been constructed to the final permitted elevation of 1039 mRL.
Page 222NI 43-101 Technical Report (March 2021) Wassa Gold Mine
In March 2015, GSWL obtained permitting to expand TSF 1 into the disused heap leach area that was
located directly east of TSF 1. The 16.2 ha extension provided 2.09 Mt additional storage capacity
conventional deposition (embankment spigotting) and in over 2.17 Mt of capacity, primarily through
paddock deposition (spigotting from day walls) across the entire TSF 1, to achieve the optimal drainage
design, ahead of TSF 1 closure.
GSWL applied to the EPA in July 2014 for the renewal of the TSF 2 permit in compliance with the
requirements of the EPA Environmental Assessment Regulations, 1999 (L.I. 1652) and Section 3.7 of the
EPA Permit (EPA/EIA/383) after the facility was re-designed to accommodate a geomembrane liner. The
EIS for TSF 2 was updated in January 2014, following advice from the EPA permitting was issued in January
2016 with an effective date of November 2015 (EPA/EIA/442).
The development of TSF 2 necessitated resettlement of some 105 households within the Togbekrom and
surrounding hamlets to New Ateiku, approximately 10 km north. All the affected people affected by the
project were successfully relocated to their new homes in Q1 of 2013. The RAP has been successfully
completed.
TSF 2 has current design capacity of some 41 Mt of tailings, which provides approximately 15 years capacity
at 2.7 Mtpa throughput. It will be constructed in three cells and 11 stages. The cellular design provides
flexibility to modify stage raises and enable dry season construction for various throughput rates.
At the time of permit renewal, the TSF 2 design had been revised to a cellular arrangement with lining of
the entire basin with HDPE geomembrane. In February 2016, the Mines Inspectorate Division of the
Minerals Commission directed that, as per the Minerals and Mining Regulations, 2012 (L.I. 2182), the TSF 2
design be constructed with a compacted soil liner (CSL). As GSWL was well advanced with development of
TSF 2 at the time, dispensation was granted for HDPE lining of TSF 2 Cell 1, with all future cells and stage
raises to incorporate a compacted soil liner.
TSF 2 Cell 1 construction commenced in July 2016. Verbal approval from the Inspectorate Division to start
deposition was given in February 2017 and EPA approval followed in April. Deposition started May 2017.
In July 2017, the Mines Inspectorate Division had completed their review and recommended the re-design
of TSF 2 with a compacted soil liner to the Chief Inspector of Mines for approval.
In 2017, GSWL commenced an EIA to support the submission of a Supplementary EIS for TSF 2 Cell 2. The
Supplementary EIS was submitted to the EPA in October 2018 with the compacted soil liner design (Figure
18-11). The TSF 2 Cell 2 Supplementary EIS was permitted in August 2020 and Environmental Permit issued
in November 2020 (EPA/EIA/533).
Page 223NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 18-11 TSF 1 and TSF 2 layout (Geosystems, 2018)
Page 224NI 43-101 Technical Report (March 2021) Wassa Gold Mine
18.6.2 TSF 2 Details
18.6.2.1 Geotechnical Characterization
A detailed geotechnical investigation comprising sub-soil, in-situ and laboratory testing of soils of the TSF 2
basin was carried out by Knight Piésold Consulting Ltd using test pitting, cable percussion drilling, standard
penetration testing, permeability testing, moisture content, grading, Atterberg Limits tests, consolidation
tests, triaxial testing on undisturbed soil samples and falling head permeability tests.
Results established the soil profile of the basin, the strength of the foundation soils, and the permeability of
the different soil types, to inform in the design of the TSF embankments, base and environmental
protection features.
The TSF 2 basin is characterized by a rugged and dissected ground profile that defines the soil profiles in the
area according to topographical location. Two main soil types are found in the TSF footprint:
- Alluvial soils formed by deposition of eroded materials from the surrounding hills; and
- Residual soils formed in-situ from the chemical weathering of the underlying base rocks.
Soils can be classified as either of:
- High ground and side-slope soils that are found along slopes and crests of hills, plateau and other
high ground that characterizes the TSF footprint; or
- Basin valley and embankment foundation soils that dominate the valleys and low-lying areas.
Guelph permeability tests conducted on nearby surface soils in the valley floor indicated that in some areas
the soils have very low permeability (lower than 1.0 x 10-8 m/s). In-situ falling head permeability tests
showed that the residual soils, at depths greater than 1.0 m, have a relatively high permeability.
Laboratory falling head permeability tests corroborated the field studies and showed that in the valley
floor, very low permeability strata exists to approximately 1.0 m depth.
18.6.2.2 TSF 2 Design
The TSF 2 design comprises three cells separated by embankments, a temporary embankment and a series
of perimeter saddle dams, providing primary containment to ensure that tailings are contained within the
valley basin. Other key environmental protection features of the design to enable efficient and appropriate
water management include:
- Lining of the base with geomembrane and/or compacted soil liner;
- Spillway;
- Decant barge;
- Secondary confinement;
- Ground water drains; and
- Basin under-drains.
The TSF 2 design assumed a processing rate of 2.7 Mtpa. The facility is designed for a storm capacity of:
- Containment of a 1:100 year, 24 hour duration event with allowance for wave run-up and no flow
through the spillway; and
- Safe discharge of a 1:1000 year, 24 hour duration event.
The design of the TSF 2 meets the requirements of the Minerals and Mining (Health, Safety and Technical)
Regulations, 2012 (L.I. 2182) and takes due consideration of the recommendations of the International
Committee on Large Dams (ICOLD), the Australian Committee on Large Dams (1999) and the Canadian Dam
Association guidelines (2007).
Page 225NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 226
Following release of the Global Industry Standard on Tailings Management in August 2020, GSR engaged its
Engineer of Record to complete a gap analysis against the standard which is expected to be completed in
TSF 2 is being constructed in stages and stage storage capacities are presented in Table 18-1. Alternative
stage raises have been evaluated to facilitate annual raising during suitable construction weather
conditions (Knight Piésold, 2017).
The useful life of TSF 2 will be prolonged by the commencement of paste fill in 2021. On average 40-60% of
tails solids are estimated to be used in paste fill and deposited underground.
Beach and bathymetry surveys conducted in September 2020 indicate the current design allows for
approximately 33 Mt of further capacity. The Mineral Reserve plan requires processing of 10.8 Mt of ore
and schedules estimate 5.0 Mt of the resulting tails solids will be used for paste backfill. Even with the
most conservative of paste fill estimates, TSF 2 has more than sufficient design capacity to support
extraction of the Mineral Reserve.
Table 18-1 TSF 2 stage design details
18.6.2.3 Stability Analysis
Stability analyses were conducted for static and seismic loading conditions and static post liquefaction
conditions for critical embankments and stages using SLOPE/W® and the Morgenstern-Price method of
analysis, which considers force and moments equilibrium of circular slips.
A conservative peak seismic design horizontal ground acceleration of 0.1 g, obtained from “Seismicity of
Southern Ghana: Causes, Engineering Implications and Mitigation Strategies” by N.K. Kumapley (1996), was
employed in the pseudo static analyses.
For the stability analyses on the upstream slopes, the worst-case scenario was considered, where no
tailings are present in front of each embankment stage. For the stability analyses of the downstream
slopes, the worst-case scenario was also considered, where the TSF was full to capacity in front of each
stage raise (1 m below crest). Modelling scenarios assessed drained and undrained conditions and worst
case-phreatic conditions. The assumed conditions combine to present a conservative analysis.
The minimum Factor of Safety (FOS) values calculated for all conditions on both the downstream and
upstream slopes were found to meet, and in some conditions exceed the Minerals and Mining (Health,
Safety and Technical) Regulations, 2012 (L.I. 2182) requirements for factors of safety.
Stability of the facility was also assessed under the condition where, following the design seismic event, the
tailings may be subjected to liquefaction. Seismic stability assessment of the various embankments was
conducted in the undrained condition for upstream failure and static drained condition for downstream
failure. Tailings were modelled with a residual post-liquefied undrained strength but with no earthquake
loading. The minimum FOS values calculated for the post-liquefied condition of the downstream and
upstream slopes meet and, in some conditions exceed, the regulatory requirements.
Storage
Cell
Crest
Beach
Density Stage
Cum.
Stage
Cum.
Mth
Annual
mRL
mRL
t/m3
Mt
Mt
mth
mth
m/mth
m/yr
1
1,011.5 1,010.5
1.10
3.24
3.24
14.4
14.4
1.3
15.0
1
1,018.5 1,017.5
1.10
3.63
6.87
16.1
30.5
0.4
5.2
1
1,203.0 1,022.0
1.10
3.14
10.01
14.0
44.5
0.3
3.9
1
1,010.0 1,009.0
1.10
3.34
13.35
14.8
59.3
1.2
14.6
3
1,001.0 1,000.0
1.10
3.01
16.36
13.4
72.7
1.0
12.1
3
1,007.8 1,006.8
1.10
2.90
19.26
12.9
85.6
0.5
6.3
2+3
1,012.5 1,011.5
1.25
3.35
22.61
14.9
100.5
0.3
3.8
2+3
1,015.0 1,014.0
1.29
3.33
25.94
14.8
115.3
0.2
2.0
2+3
1,017.4 1,016.4
1.33
3.52
29.46
15.6
130.9
0.2
1.8
2+3
1,020.0 1,019.0
1.37
3.64
33.10
16.2
147.1
0.2
1.9
2+3
1,023.0 1,022.0
1.40
7.86
40.96
34.9
182.0
0.1
1.0
Levels
3
5
9
1 0
1 1
2
Stage
1
8
7
Embankment
Capacity
Duration/Life
Rate of Rise
Inundation
Height
Area
m
18.5
25.5
ha
34.6
46.0
30.0
61.5
4
18.5
37.8
14.0
36.5
6
20.8
37.3
33.0
111.2
37.0
133.5
25.5
71.0
28.0
98.8
30.4
110.5NI 43-101 Technical Report (March 2021) Wassa Gold Mine
19 MARKET STUDIES AND CONTRACTS
19.1 Market Studies
All gold from Wassa is shipped to a South African gold refinery under a long-term sales contract. Shipping is
in the form of doré bars, which average approximately 90% gold by weight with the remaining portion
being silver and other metals. The sale price is generally set with reference to the London p.m. fix on the
day of the shipment to the refinery.
Gold is a freely traded commodity on the world market and whilst the selling price is subject to fluctuation,
the volume of gold produced at Wassa will not be material to the supply/demand balance and will not
influence the selling price.
This report considers two gold price assumptions:
- Base Case: for Mineral Reserve estimation and economic test – $1,300 /oz flat; and
- Consensus Case: consensus long-term forecast of 27 banks and financial institutions, as at the end
of January 2021:
o 2021 – $1,944.26 /oz;
o 2022 – $1,879.70 /oz;
o 2023 – $1,772.87 /oz;
o 2024 – $1,715.61 /oz; and
o 2025 and beyond (long-term) – $1,584.68 /oz.
19.2 Contracts
The following major contracts are in place to support the Wassa operations:
- Gold sales contract is in-place with Rand Refinery in South Africa;
- Electricity supply (on-site gas generation) – Genser Energy Ghana;
- Fuel and lubricants supply – Ghana Oil Company;
- Electricity transmission from VRA – GRIDCo;
- Electricity supply – VRA;
- Explosives and associated systems – AEL (AECI Ghana Ltd);
- Medical services – International SOS;
- Bulk lime supply – Carmeuse Lime Products (Ghana);
- Site security – Magnum Force Security; and
- Freight forwarding and logistics – Racing Link Express.
All contracts are currently valid and in good standing. Terms, rates and charges of contracts are considered
consistent with industry norms. Contract management processes are in place and resourced so that
contracts re-tendered and/or renewed as they approach expiry.
Page 227NI 43-101 Technical Report (March 2021) Wassa Gold Mine
20 ENVIRONMENTAL STUDIES, PERMITTING AND SOCIAL OR
COMMUNITY IMPACT
20.1 Relevant Legislation and Required Approvals
The minerals and mining sector in Ghana is governed by Act 703. It requires mines to obtain environmental
approvals from relevant agencies as outlined in Table 20-1. Ghanaian environmental legislation is well
developed and enforced by the Environmental Protection Agency (EPA).
20.1.1 Permitting Requirements in Ghana
20.1.1.1 Environmental Assessment Requirements
Environmental aspects in Ghana are regulated by the EPA Act, 1994 (Act 490). The EPA’s primary legislation
for regulation and monitoring of mineral operations are the Environmental Assessment Regulations, Legal
Instrument 1652 of 1999 (L.I. 1652), which cover requirements for:
- Environmental permitting;
- Environmental Impact Assessment (EIA);
- Preparation of preliminary environmental reports and environmental impact statements (EIS);
- Environmental certificates;
- Environmental Management Plan (EMP); and
- Reclamation bonding.
The EPA grants environmental approval to projects through an Environmental Permit, which is issued
subject to the findings of an EIA, which is documented in an EIS and also covers social aspects. For a mine,
an EIS must include a reclamation plan and a provisional EMP. Prior to formal review by the EPA, the EIS
may be subject to public exhibition and hearing, with responses from regulators and community to be
incorporated into the EIS before an Environmental Permit is granted.
Two years from receipt of an Environmental Permit, an Environmental Certificate is required from the EPA
to confirm:
- Commencement of operations;
- Acquisition of all permits and approvals;
- Compliance with mitigation commitments in the EIS and/or EMP; and
- Submission of annual reports to EPA as required.
Within 18 months of commencing operations an EMP must be submitted to and be approved by the EPA. A
provisional EMP is included in the EIS which is then updated and incorporated into the mine’s active EMP
which is updated every three years over the mine’s life. EMP’s are submitted to and approved by the EPA.
Mines in Ghana are required to have a reclamation plan (Regulation 14 of L.I. 1652) and mining operations
submit annual environmental reports (Regulation 25 of L.I. 1652) and monthly environmental monitoring
results to EPA, with commentary where values exceed limits and response plans as required.
Relevant guidelines and standards are provided under Act 490, including the Mining and Environmental
Guidelines (1994) which provide guidance for: EIS and EMP contents; reclamation plans; EIA procedures;
effluent and emission standards; ambient quality and noise levels; and economic instruments.
The EPA conducts routine monitoring of environmental parameters for mines and the results obtained are
cross-checked with the monthly results submitted by operations and compared to relevant standards.
The EPA is empowered to suspend, cancel, or revoke Environmental Permits in the event of a breach of L.I.
1652, the permit conditions or the mitigation commitments in the EMP.
Page 228NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 229
Table 20-1 Primary environmental approvals for mines in Ghana
20.1.1.2 Minerals and Mining Requirements
Act 703 establishes laws on the process for obtaining mineral rights, the administration and management
of these rights and protection of the environment. Supporting Act 703 are the Minerals and Mining
Regulations, 2012 which cover:
- General aspects (L.I. 2173);
- Compensation and resettlement (L.I. 2175);
- Explosives (L.I. 2177);
- Support services (L.I. 2174); and
- Health, safety and technical requirements (L.I. 2182).
Regulatory institution
Approvals & Permits
Compliance
Environmental Protection
Agency
Established under the
Environmental Protection
Agency Act, 1994 (Act
490), responsible for
enforcement of
environmental regulations.
Environmental Permit
Under Section 18 of the Mining Act, 2006 (Act 703), and the
Environmental Assessment Regulations, 1999 (L.I. 1652), of the EPA, the
holder of a mineral right requires an Environmental Permit from the EPA
in to undertake any mineral operations.
Approved Environmental Management Plan
EMP to be submitted within 18 months of commencement of operations
and updated every three years (Regulation 24 of L.I. 1652).
Environmental Certificate
Must be obtained from EPA within 24 months of commencement of an
approved undertaking (Regulation 22 of L.I. 1652).
Reclamation plan
Mine closure and decommissioning plans to be prepared and approved
by the EPA (Regulation 14 of L.I. 1652).
Reclamation bond
Mines must post a reclamation bond based on an approved reclamation
plan (Regulation 22 of L.I. 1652).
Reporting
Mines submit monthly returns and
annual environmental reports to the
EPA.
Inspections
EPA undertakes regular inspections to
ensure compliance.
Enforcement
EPA may suspend, cancel or revoke
an Environmental Permit or
certificate and prosecute breaches.
Minerals Commission and
Mines Inspectorate
Division
Established under the
Minerals and Mining Act,
2006 (Act 703), the
Minerals Commission
administrate mineral rights
in trust for the people of
Ghana.
Exploration and mining operating plans
Operating Permit from Inspectorate Division required to commence
operations. Changes to operating plans to be approved by the Chief
Inspector of Mines.
Emergency response plan
An approved emergency response plan must be in place.
Resettlement plan
Resettlement plans to be approved by the district planning authority,
according to requirements for compensation & resettlement in L.I.
Closure Plan
Closure plan to comply with Regulations 273 to 277.
Other
A number of other minor permits and licences are required to support
operations (eg: explosives).
Reporting
Mines submit monthly and quarterly
returns.
Inspections
Mines Inspectorate undertakes
regular inspections to ensure
compliance.
Enforcement
Regulations 21 and 22 allow the
Mines Inspectorate to issue
improvement and/or prohibition
notices for contraventions of the
Regulations.
Water Resources
Commission
Established under the
Water Resources
Commission Act, 1996 (Act
522), WRC is responsible
for regulation and
management of the use of
water resources.
Approvals for water usage
Under Section 17 of the Mining Act, 2006 (Act 703), the holder of a
mineral right may obtain, divert, impound, convey and use water from a
watercourse or underground reservoir on the land of the subject of the
mineral right, subject to obtaining the requisite approvals under Act 522.
The Water Use Regulations, 2001 (L.I. 1692), regulate and monitor the
use of water.
Reporting
Holders submit quarterly and annual
reports to the WRC.
Inspection
WRC can inspect works and ascertain
abstraction volumes.
Enforcement
Act 522 and L.I. 1692 prescribe
sanctions for breaches.
Forestry Commission and
Forestry Services Division
In accordance with Section 18 of the Mining Act, 2006 (Act 703), a
holder of a mining right must obtain necessary approvals from the
Forestry Commission.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The following regulations have particular relevance to environmental and social management:
- Minerals and Mining (Health, Safety and Technical) Regulations 2012 (L.I. 2182): requirements for
approval of mine closure plans and TSF hazard classes outlining requirements for embankment
design, factors of safety, impoundments, freeboard, discharge systems, safety arrangements,
monitoring, planning, auditing and closure.
- Mining General Regulations 2012 (L.I. 2173): promote preferential employment of Ghanaians and
procurement from Ghanaian suppliers. Mines prepare localization plans to achieve this and submit
periodic reports (monthly, six-monthly and annual) detailing Ghanaian and expatriate staff
numbers, payments of salaries and wages, royalty and corporate tax.
- Mines (Support Services) Regulations, 2012 (L.I. 2174): extend the requirement to preferentially
employ Ghanaians to providers of services to mines.
- Mines (Compensation & Resettlement) Regulations, 2012 (L.I. 2175): require that people displaced
to conduct mining operations are resettled to suitable alternative land and that livelihoods and
living standards are improved. The resettlement plan must be approved by the district planning
authority and then given effect by the Minister responsible for Mines.
GSWL has submitted its localization plan to the Minerals Commission covering expatriate staff and the
company remains in full compliance with the regulatory requirements.
GSR is listed on the Ghana stock exchange and continues to submit its annual financial reports as required.
20.1.1.3 Water Resource Legislation Requirements
The Water Resources Commission Act, 1996 (Act 552) establishes the Water Resources Commission (WRC)
and sets requirements regulating the use of water resources. The Water Use Regulations, 2001 (L.I. 1692),
and Drilling Licence and Groundwater Development Regulations, 2006 (L.I. 1827), complement the Act by
specifying the requirements for obtaining permits for water use, water rights, and priorities for water use;
and water drilling licences, and well construction requirements; respectively.
20.1.2 Permitting of Existing Operations
A summary of environmental approvals held by GSWL is provided in Table 20-2 and can be summarized as:
- 1998 – Satellite Goldfields Limited (SGL): EIS effected approval for development of Wassa, including
the original extent of the Main pits complex (South East, 242, F-Shoot, B-Shoot, South, Main South
and 419 pits) and processing via a heap leach operation.
- Sep-2002: GSR purchased the project, recommencing operations under Wexford Goldfields Limited
(WGL), with ownership 90% GSR and 10% Government of Ghana.
- 2004 – WGL: EIS effected approval to construct and commence processing via carbon-in-leach (CIL)
and establishment of the tailings storage facility (TSF 1).
- 2005: GSR acquired St Jude Resources (SJR) and with it, Hwini Butre and Benso properties to the
south.
- 2006: Permitting to extend open pit mining to South Akyempim.
- 2007: Hwini Butre and Benso (HBB) EIS permitted expansion of open pits with processing at Wassa.
- 2010: GSWL (Wassa) Pits Expansion EIS permitted cutbacks at 242, South, Main South, F & B
Shoots. A further EIS effected approval of the Benso G-Zone waste rock dump.
- 2011, 2012, 2013: TSF 1 stage raises to 1035.5 mRL, 1037 mRL and 1039 mRL respectively.
- 2015: TSF 1 extension, establishment of TSF 2 and permitting of underground exploration.
- 2016: TSF 2 re-design and re-permitting.
- 2017: Permitting to incorporate underground mining, pit cut back and waste dump extensions.
- 2020: Permitting of TSF 2 Cell 2.
Page 230NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 231
Table 20-2 Environmental approvals obtained for Wassa mine
Approval
Permit No.
Date of Issue Expiry Date
Comments
Environmental Protection Agency – Environmental Permits to commence operations
Approval of the Satellite Goldfields Limited
Wassa project EIS
n/a
1998
There are no formal approval documents on
record
EIA and EMP for Exploration in Subri River
Forest Reserve
n/a
2004
There are no formal approval documents on
record
Environmental Permit for the Wassa Power
Project
Form D
(0010335)
7-May-2004
n/a
Based on Volta River Authority Wexford Power
Project 161 kV Power Transmission Line Bogoso
to Akyempim Environmental Scoping Report
(2003)
Environmental Permit to pursue operations
EPA/EIA/112
18-Mar-2004
n/a
Based on Wexford Goldfields Limited Wassa
project EIS (2004)
Hwini Butre Permit
EPA/EIA/175
24-Feb-2006
n/a
St Jude Resources (Ghana) Limited based on
Hwini Butre EIS and Subriso EIS
Benso Subriso Permit
Detox Plant and Discharge to Kubekro Creek
Approval
Letter
23-Dec-2005
n/a
South Akyempim Environmental Permit
EPA/EIA/190
2-Jun-2006
n/a
Based on EIS on South Akyempim Project (2005)
Hwini Butre/Benso Project Environmental
Permit
EPA/EIA/247
2-Oct-2007
n/a
Based on the Hwini Butre and Benso EIS (2005)
Wassa Pits Expansion Project Environmental
Permit
EPA/EIA/322
20-Dec-2010
n/a
Based on Wassa Pits Expansion EIS (2010)
G-Zone Waste Rock Dump Environmental
Permit
EPA/EIA/323
13-Dec-2010
n/a
Based on Supplementary EIS for G-Zone Waste
Dump (2010)
TSF 1 embankment raise to 1035.5 mRL
Letter
4-Aug-2011
n/a
TSF 1 embankment raise to 1037 mRL
Letter
9-May-2012
n/a
Environmental Permit for Mineral Exploration
(Manso)
EPA/PR/PN/770
4-Sep-2012
3-Sep-2014 New permit not presently required
TSF 2 Permit
EPA/EIA/383
5-Apr-2013
4-Oct-2014
Based on corresponding EIS (2013)
TSF 1 embankment raise to 1039 mRL
Letter
12-Apr-2013
n/a
Father Brown/Dabokrom Supplementary EIS
Letter
Invoiced 14-
Jan-2014
Based on Father Brown/Dabokrom Impact
Prediction Study (2012)
TSF 1 extension Environmental Permit
EPA/EIA/419
13-Mar-2015
n/a
Based on TSF 1 extension EIS (2014)
TSF 2 (re-design) Environmental Permit
EPA/EIA/442
25-Nov-2015
n/a
Based on TSF 2 EIS (2015)
Wassa Underground Exploration Permit
EPA/PR/PN/929
3-Jul-2015
4-Jul-2017
Transitioned to EPA/EIA/508
Wassa Expansion Project Environmental Permit
EPA/EIA/508
30-Oct-2017
n/a
Based on Wassa Expansion EIS (2016)
TSF 2 Cell 2
EPA/EIA/533
28-Aug-2020
n/a
Based on TSF 2 Cell 2 SEIS (2018)
Environmental Protection Agency – Environmental Certificate
Environmental Certificate
EPA/EMP/055
Sep-2006
Sep-2009
2006-2009 EMP
Environmental Certificate
EPA/EMP/093
Apr-2011
Apr-2014
Submitted as required by law in 2010.
EPA approved for period 2011-2014
Environmental Certificate
Invoiced
2014
Submitted as required by law in 2013. 2014-17
EMP renewal processed by EPA in 2014
Environmental Certificate
EPA/EMP/221
Jun-2020
Dec-2021
Submitted as required by law in 2017
EPA approved for period 2020-2021
Water Resources Commission
Permission to divert Adehesu creek at South
Akyempim
n/a
6-Dec-2006
n/a
Water Use Permit Diversion of Ben and Subri
Streams
n/a
27-Mar-2008
n/a
Water Use Permit (C Zone fish cages)
GSWLID455/17
27-Jun-2017
26-Jun-2020
Application for renewal submitted Aug-19 and
permit issuance pending. No activity underway.
Water Use Permit (Mpohor)
GSWLID212/19
1-Jan-2019
31-Dec-2021
Water Use Permit (Benso)
GSWLID193/19
1-Jan-2019
31-Dec-2021
Water Use Permit (Akyempim)
GSWLID134/1/20
1-Jan-2020
31-Dec-2022
Water Use Permit (dewater Wassa Main and
Starter)
GSWLID134/2/20
1-Jan-2020
31-Dec-2022
Water Use Permit (bores and 242)
GSWLID134/3/20
1-Jan-2020
31-Dec-2022
District Assembly
Togbekrom Resettlement Plan
WEDA/DEV 15
9-Jan-2013
n/a
Wassa East District Assembly
Awunakrom Resettlement Plan
AWDA/DEV 21
4-Mar-2013
n/a
Ahanta West District AssemblyNI 43-101 Technical Report (March 2021) Wassa Gold Mine
20.1.3 Environmental Certificate and EMP for Overall Operations
GSWL (then WGL) received the first Environmental Certificate for Wassa for the period September 2006 to
September 2009. Since that time GSWL has routinely submitted the 3-yearly EMP as required to maintain
the Environmental Certificate in good standing.
The most recent renewal was initiated by submitting the updated EMP to the EPA in December 2017.
Following review by the EPA, the Environmental Certificate was invoiced in June 2018, the EMP was
finalized and resubmitted, then the Environmental Certificate was issued in 2020.
The Environmental Certificate and the EMP cover all concessions managed by GSWL including Wassa, Hwini
Butre (suspended), Benso (suspended) and associated infrastructure including the HBB access road.
20.1.4 Notable Conditions of Approval
The Environmental Permit and EIS require a reclamation bond to be posted within one year of commencing
operations. The initial reclamation bond for Wassa was posted in November 2004 has been updated
periodically as new projects or changes are approved. At the end of 2020 the GSWL bond was $13,672,231.
The mining leases contain conditions relevant to environmental management. The Wassa Mining Lease
(LVB7618/94), Benso Mining Lease (LVB26871/07), and Hwini Butre Mining Lease (LVB1714/08) contain
conditions to limit encroachment of mining activities on community infrastructure, disturbance of
vegetation, conservation of resources, reclamation of land and prevention of water pollution.
20.1.5 Permitting of Future Operations
Future changes to the plan which would likely trigger the need for a new permitting are:
- Increasing processing capacity above 2.7 Mtpa;
- Introduction of infrastructure or a new activity outside the permitted footprint, specifically
construction of a hoisting shaft to service the Southern Extension area, although infrastructure that
can be located within the current open pit excavation is not expected to be subject to EIS/EIA.
If required, the indicative approval timeline for an EIS/EIA process is approximately 2.5 years.
20.2 International Requirements
20.2.1 Environment and Conservation
The Government of Ghana is party to a number of international treaties relating to the environment:
- Ramsar Convention on Wetlands of International Importance (there are five designated Ramsar
sites along the coast of Ghana but none in the Wassa project area).
- Convention of International Trade in Endangered Species.
- United Nations Framework Convention on Climate Change.
Ghana has more than 1,000 IUCN-management protected areas, including 317 forest reserves
(EarthTrends, 2003). There are two forest reserves near the Wassa project area; the Bonsa River Forest
Reserve and the Subri River Forest Reserve. Approximately 12 km of the Hwini Butre Benso access road
traverses the Subri River Forest Reserve.
20.2.2 Human Rights
In 2005 GSR, with full support of its Board of Directors wrote to the UN Secretary General as a statement of
commitment to adopt the United Nations Global Compact (www.unglobalcompact.org) and GSR continues
to integrate the Global Compact principles in its business activities.
GSR’s 2019 Corporate Responsibility Report (formerly Sustainable Development Report) is the 14th public
report on how the company is contributing to advance Ghana’s performance against the Sustainable
Development Goals in the Global Compact.
Page 232NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The 2019 report incorporated enhanced disclosures including:
- Global Reporting Initiative (GRI) standards;
- Sustainability Accounting Standards Board (SASB), Metals and Mining Sustainability Accounting
Standards;
- Mining Local Procurement Reporting Mechanism (Mining LPRM);
- World Gold Council, Conflict Free Gold Standard disclosure;
- Investor Mining and Tailings Safety Initiative (IMTSI) disclosure; and
- World Gold Council, Responsible Gold Mining Principles (RGMPs) disclosure.
20.2.3 Anti-Corruption
The Government of Ghana was designated Extractive Industries Transparency Initiative compliant in 2010.
To support this GSR provides annual public reports, declaring payments to the Government of Ghana, with
significant contributions made by GSR businesses to the end of 2019:
- GSWL payment of more than $259 M over the previous decade; and
- In 2019, the expected royalty distributions from GSWL operations including those to the Office of
the Administrator of Stool Lands, Traditional Authorities, Stool Lands and District Assemblies, was
over $10.2 M.
GSR are registered in the US and Canada, so are subject to the US Dodd-Frank Wall Street Reform and
Consumer Protection Act, the US Foreign Corrupt Practices Act and the Canadian Corruption of Foreign
Public Officials Act. Internal GSR policies address these items for GSR management.
20.2.4 Voluntary Codes
GSR has adopted a number of voluntary international codes and standards pertaining to corporate
responsibility and apply to the Wassa operations:
- Cyanide management – full certification to International Cyanide Management Code since 2010;
- TSFs – current TSF 1 and TSF 2 designs align with the ICOLD requirements;
- Gold mining and processing – as a member of the World Gold Council, GSR ascribes to the
Responsible Gold Standard and the Responsible Gold Mining Principles; and
- Resettlement, land acquisition, and compensation – since 2009, GSR has ensured all resettlement
projects conform to the International Finance Corporation’s Performance Standard 5 on Land
Acquisition and Involuntary Resettlement.
GSR has corporate assurance processes which include independent review, audit and/or validation to
ensure conformance of the principles ascribed in these codes and standards.
20.3 Environmental and Social Setting
20.3.1 Biophysical Setting
The concession area falls within the wet semi-equatorial climatic zone of Ghana and is characterized by an
annual double maxima rainfall pattern occurring in the months of May to July and September to October.
Average annual rainfall measured at the nearest meteorological station (Ateiku) is 1,996 ± 293 mm.
Average annual rainfall measured at the Wassa weather station is approximately 1,750 mm.
20.3.2 Hydrology
20.3.2.1 Existing Catchment and Flow Paths
The Wassa operations lie within the Pra River basin which is one the two major rivers draining south
western Ghana. The Pra Basin is located in south central Ghana (Figure 20-1) and is extensive, with several
river systems traversing the basin.
Page 233NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Topographic elevation of the Pra basin is from sea level, up to 800 m. The highest elevations are to the
north and at the eastern edges of the basin, where elevations of 800 m are common. The southern
sections are relatively flat to slightly undulating and there are a few peaks in the central regions. The
nature and orientation of the highlands determine the flow direction of the drainage network in the basin.
The Wassa mining lease area is drained by tributaries of the Pra, namely the Toe to the far south, Kubekro
to the east and the Petetwum to the north. The Petetwum River flows directly into the Pra River and is fed
by the Petetwum, Nankadam, and Kumue streams. The Subiri River, locally known as Subri, which drains
the western end of the concession, is a tributary of the Bonsa.
Figure 20-1 Pra River basin and location of Wassa
The topography of the Wassa site area is generally undulating, dissected by steep-sided valleys and incised
by an extensive, largely dendritic drainage network (Figure 20-2).
The project site is located high in its local catchments such that most surface water comes from rainfall
runoff, rather than stream flows entering the site.
Page 234NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 20-2 Wassa topography and drainage with sub-catchments
20.3.2.2 Surface Water Management
Multiple surface water studies have been undertaken over the project’s life, the most relevant to the
current project being:
- 2015 feasibility study to establish underground mining (SRK); and
- Various studies in 2010-2014 for initial TSF 2 permitting and subsequent redesign and permitting
(Knight Piesold and Geosystems Consult).
Established surface water management features on site include a stream diversion around the processing
plant and administration area, TSF drainage diversions and a French drain to prevent water inflow to the
southern end of the Main pit area. These water management features were engineered and constructed as
permitted through EIS/EIA processes.
In addition to these main features, secondary drainage works are in place around site to direct water runoff
from dumps and roads, away from active mining areas or toward dewatering infrastructure.
Surface water management features are maintained by the surface earthworks and underground mining
workgroups as needed.
20.3.3 Hydrogeology
The Wassa site falls in within the Birimian Province and it is characterized by aquifers of the Birimian
metasediments and metavolcanics and the Tarkwaian aquifers.
Extensive baseline studies were conducted in 1995 and 1996 by Minerex Environmental Limited prior to the
development of Wassa operations which were extended by subsequent EIA/EIS processes.
In 2015 and 2019 expanded hydrogeological field studies were conducted by Golder Associates to testing
hydrogeological conditions in the underground Mineral Resource. Hydraulic (packer) testing was
conducted on selected exploration holes to provide data for conceptual and numerical hydrogeological
models. The two programs found the main lithological units to be saprolite, saprock, fractured and fresh
bedrock.
Page 235NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Groundwater typically occurs in a shallow, weathered zone aquifer and a fractured deeper bedrock aquifer.
The aquifers have overall low permeability (4 x 10-7 m/d), significantly enhanced along tabular zones where
interconnected joint sets, faulting and/or quartz vein occur (6 x 10-2 m/d).
Inflow to the underground workings occurs along these discreet zones of faulting and fracturing (Figure
20-3), however these higher permeability areas are isolated, forming a very small percentage of the overall
rock mass and therefore only localized higher inflow in the underground workings (Figure 20-4).
Figure 20-3 Conceptual underground water flow path model (Golder, 2016)
Page 236NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 20-4 Conceptual groundwater model (Golder, 2016)
Ground water elevation contours show that generally the groundwater flows in a south-westerly direction
following the major topographical features, with the site primarily drained by the Kubekro catchment
network of streams. Near the active open pits, the prevailing hydraulic head is towards the open pit in
response to the active pit dewatering (Figure 20-5).
Page 237NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 20-5 Groundwater contours and flow (Golder, 2016)
Page 238NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 20-6 Conceptual geo-environmental model, E-W section (Golder, 2016)
At Wassa shallower gold deposits have been extracted from pits with voids now empty or in various stages
of backfilling with waste rock. Waste rock not used for backfilling is stockpiled in waste rock dumps
adjacent to or west of the Main pit complex (Figure 20-6). Precipitation on these catchments and storm
water inflow into mining areas also contributes to underground water make.
To understand these influences environmental stable isotope (ESI) signatures were investigated by Golder
in 2017 to identify the origin of water ingress into the underground workings. ESI analysis provides the
measurable variation of the stable isotopes against the natural values (Dansgaard, 1964). The analysis
found that key pits share a common water source with the underground water bearing zones which
suggests the pits and underground workings are hydraulically connected.
Due to the potential connection between the surface and underground workings, water volumes in the pits
are monitored to ensure water inventory is managed. These controls complement the surface water
management systems described in Section 18.2.
Data from the various hydrogeological studies have informed numerical groundwater model (FEFLOW)
development. The model suggests that the permeability will decrease with depth in the saprolite to act as
a confining horizon (Golder, 2016). Groundwater recharge is considered low (approximately 10 mm/a or
0.5-1.0%). The reported dewatering rates pumped to the underground mine range from 5-10 l/s and from
the underground mine ranges from 45-120 l/s. The implications are:
- The drawdown (dewatering cone) from the operations is not expected to have any significant effect
on existing (community) groundwater boreholes;
- Groundwater in the shallow weathered zone and deeper bedrock aquifers flows from the elevated
areas towards the rivers, following the topography;
- Preliminary modelled underground water production is within current permitted abstraction; and
- The receiving environment will not receive underground mine leachate in the recovered state and
no decant is expected to occur. Additionally, leachate from mine waste rock dumps is controlled by
the cone of depression and is not expected to impact on the receiving environment.
Page 239NI 43-101 Technical Report (March 2021) Wassa Gold Mine
20.3.4 Geochemistry
The Wassa rocks show a calcium-alkaline affinity. Metasediments, metavolcanics and diorite have an
apparent enrichment in rare earth elements compared to primitive mantle, whilst the metamorphic rocks
appear to be deep water sedimentary in origin.
Total element concentrations and extent of enrichment were assessed using the geochemical abundance
index (GAI) (after Fortescue 1992 and Price 1997) and show a high enrichment in bismuth, sulphur and
tungsten in all rock types except for quartz vein (low sulphur). Rocks are also enriched in arsenic, boron,
lithium, antimony, barium, tellurium, cadmium and copper. These elements are environmentally significant
as they are associated with sulphides, carbonates and phosphates, which are reactive minerals.
The potential for acid rock drainage (ARD) was originally assessed in the original Wassa EIA (SGS, 1998).
Subsequent studies (SGS 2002, Scott Wilson 2004, Golder 2016 and 2019) have expanded knowledge of the
geochemical regime. Representative samples of open pit and underground host rock lithologies have been
analysed utilizing X-ray diffraction (XRD), X-ray fluorescence (XRF) (whole rock analysis), leach extraction tests
and acid base accounting.
A study for the Southern Extension Inferred Mineral Resource, utilized samples identified from geochemical
logging of over 1,853 m of core and targeted areas of geochemical risk – rock expected to be subject to blast
fracture or overbreak and demonstrating acid rock drainage risk, contact zones, weak zones of heavy foliation
or friability and similar. These studies have been complemented by extensive review of elemental analyses
including 21,000 inductively coupled plasma mass spectrometry (ICP-MS) results and 18,800 portable XRF
analyses.
The study findings were:
- The sulphur content of rock materials from the pits, dumps and underground is highly variable.
- The acid potential (AP) of the different rock types from the pits (mean=5.2 kg CaCO3 eqv/t), waste
(mean=4.6 kg CaCO3 eqv/t) and underground (mean=6.7 kg CaCO3 eqv/t) is generally low. This
becomes more variable across all lithological units in the Inferred Mineral Resource (mean 2.6 –
33 kg CaCO3 eqv/t, max 32 – 155 kg CaCO3 eqv/ton).
- The neutralization potential (Bulk NP) of rock samples from pits (mean=97 kg CaCO3 eqv/t), waste
rock (mean=92 kg CaCO3 eqv/t) and underground (mean=111 kg CaCO3 eqv/t) is generally very high
and continues in Inferred Mineral Resource across all lithological units (mean 52 – 162 kg CaCO3
eqv/t) except quartz vein (0.15 kg CaCO3 eqv/t).
- Ankerite represents a significant proportion of total carbonates in the rock at Wassa. Whilst
ankerite has limited neutralizing capacity under oxidizing field conditions, the paste pH (8.3-10.1) is
generally alkaline indicating availability of excess buffering capacity. Acid-neutralizing dolomite is a
major mineral in the diorite, phyllite and mafic rocks in the Inferred Mineral Resource.
- Classification of ARD potential (Morin & Hutt 2007, MEND 2009) shows that the majority of rock
samples are not potentially acid generating (Figure 20-7 to Figure 20-10). Diorite, phyllite and
mafics in the Southern Inferred Resource have 8.5% of samples with potential for generating acid.
- Alternative classification methods (Price et al. 1997, Soregaroli & Lawrence 1997) also indicate the
majority of samples have no acid generating potential (Figure 20-11 to Figure 20-14).
Analysis of the geochemistry of the rocks intersected at Wassa has consistently shown that the rock
lithologies, ore and waste, are not acid generating (NAG) which is validated by over two decades of mining.
Whilst there are some samples from the Southern Inferred Mineral Resource area that are potentially acid
generating they are not common, only in isolated intervals and the majority (88%) of samples from this
area having low or no risk of acid-generation. This suggests the overall chemistry of the water make is will
be circum-neutral.
Page 240Figure 20-7 Paste pH vs NPR for Open Pit
Figure 20-8 Paste pH vs NPR for Waste
Figure 20-9 Paste pH vs NPR for Underground
Figure 20-10 Paste pH vs NPR for South Inferred
Figure 20-11 NPR vs S% for Open Pit
Figure 20-12 NPR vs S% for WasteNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 242
Figure 20-13 NPR vs S% for Underground
Figure 20-14 NPR vs S% for South Inferred
20.3.5 Water Quality
Baseline studies (MEL 1996c) found that groundwater in valley areas had been resident in the aquifer
longer and is more saturated with respect to calcium carbonate (higher calcium bicarbonate signature)
than groundwater from more elevated plateau areas (neutral ionic signature and low ionic strength).
Shallow groundwater in the area generally ranges from slightly acidic to basic, reflecting the nature of the
soils, as well as the lack of connection between the aquifers. Studies show shallow groundwater is often
acidic (Geosystems 2013, 2015) and water quality in deeper bores reflects greater saturation of neutralizing
minerals resulting from greater confinement, and associated longer residence time, of the deeper aquifer.
Nitrate and nitrite concentrations are low, as is phosphorus concentration of groundwater, reflecting the
low contents in the rocks from which the soils develop and the intense leaching of the soils.
Water quality is monitored at Wassa operations for both surface and ground water (GSWL Annual
Environmental Report 2019). Sites have been routinely sampled since 2003 with external laboratory
analysis conducted since 2012. The parameters analysed are compared to the Water Resources
Commission’s Raw Water Criteria and Guidelines for Domestic Water Use, as well as the EPA’s sector
specific effluent quality guidelines for discharges into natural water bodies (EPA guidelines).
Surface water in the vicinity of the open pits, on average, conforms to the EPA Effluent Quality Guidelines.
Occasional peaks in suspended sediment and nitrogen from the operations are removed by mine
dewatering treatment processes. Elevated levels of iron reflect the baseline conditions and rock
geochemistry. GSWL’s interpretation of the data is that both surface water and groundwater quality has
remained consistent with the findings of the Wassa Gold Project Environmental Baseline Study (SGS, 1996)
and EIS (SGS, 1998) and associated specialist studies (MEL 1996a, b and c) throughout operations.
The groundwater quality at Wassa and therefore the mine water inflows and discharges are affected by the
host rock geochemistry as well as the geo-environmental context. To understand the quality of
leachate/water expected from the underground mine synthetic precipitation leaching procedure (SPLP) and
net acid generation leach tests (NAG leach) were conducted (Golder 2016, 2019).
Leachate generated by NAG leach tests represents complete and instantaneous oxidation and leaching of
all reactive minerals and can be considered an indication of worst-case drainage quality. Under field
conditions, sulphide oxidation and release of elements occurs gradually and as such, concentrations in mine
drainage are expected to be lower than NAG leachate chemistry at any given time (INAP, 2010).
Results indicate that measured constituents will not exceed water quality guidelines in the underground
mine drainage. The underground mine drainage for the current underground workings and the broader
Mineral Resource area were predicted to be generally neutral to alkaline with low concentrations of TDS,
sulphate and metals. This is validated by the history of routine underground mine water quality sampling.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
20.3.6 Air Quality
Air quality is routinely monitored at Wassa by monthly 24-hour measurement of total suspended particulate,
particulate matter, depositional dust, oxides of nitrogen and nitrogen dioxide.
Prevailing air quality is also monitored at communities near the operational area and results generally exhibit
low levels of particulates. This reflects the mostly rural nature of the area and sources which are mostly
anthropogenic and include domestic activities such as open fire cooking, agriculture and movement of
people. The exception is the seasonal Harmattan which brings dry and dusty winds from the Sahara across
West Africa.
2017 impact assessment studies incorporated predictive modelling using the AERMOD dispersion model.
Modelling results predict ground level concentrations and deposition rates of modelled emissions using a
regional mesoscale meteorological dataset (MM5) over the modelling domains.
Results predicted that even with worst-case conditions and without mitigation, ground level concentrations
of key emissions at the nearest sensitive receptors met the majority of the applicable Regulations. As
modelling illustrated that cumulative conditions of worst-case weather (single worst 24 hr) and seasonal
Harmattan peaks may exceed 24 hr ground level concentrations for PM10 and TSP the operations employ an
array of dust suppression mitigations throughout dry season conditions.
Model predictions have since been validated by air quality monitoring results with mine derived emissions
demonstrated as within regulated ambient air quality guidelines.
20.3.7 Noise and Vibration
Noise is routinely monitored at the nearest neighboring villages of Akyempim and Kubreko. Results show
that noise emanations are predominantly local anthropogenic sources and not the result of activities at
Wassa.
Studies were undertaken for the 2017 impact assessment using CadnaA software (ISO 9613 compliant) to
model sound propagation under a variety of meteorological conditions. Meteorological data derived from
the MM5 data was utilized to develop a baseline noise model calibrated to the existing monitoring results.
Results predicted that even with worst-case conditions and without mitigation, noise levels at receptor sites
were within EPA guidelines for ambient noise in all modelled scenarios. Model predictions have since been
validated by noise monitoring results which have measured no mine derived exceedances.
The 2017 impact assessment also carried out modelling for blast induced vibration utilizing the United States
Bureau of Mines (USBM, 1980) ground vibration propagation equations, and the ICI formula for estimation
of air blast overpressure (ICI, 1990). Results predicted that even with worst-case conditions, ground vibration
and blast overpressure at the nearest receptors were within levels in the Minerals and Mining (Explosives)
Regulations (L.I. 2177).
Model predictions have since been validated by blast monitoring results that demonstrate conformance to
regulatory limits.
20.3.8 Biodiversity
A number of biodiversity surveys have been conducted across Wassa:
- 1996: baseline study prior to the commencement of operations, covering the entire site
(SGS, 1996).
- 2010: Main pits expansion, covering the open pit areas and potential waste dump locations.
- 2012: TSF 2 footprint in a valley north of TSF 1 (Geosystems, 2015).
20.3.8.1 Flora
Wassa is located in a transitional area between moist, semi-deciduous forest and wet rainforest zones.
Baseline conditions illustrated degraded vegetation, impacted by logging and farming activities. Whilst the
Page 243NI 43-101 Technical Report (March 2021) Wassa Gold Mine
baseline study (1996) did not record any endangered plant species, under ongoing pressure conservation
status of species is routinely reclassified.
As at 2016 the IUCN had identified Tieghemella heckelii as endangered, and Mitragyna stipulosa,
Turraeanthus africanus, and Guarea cedrata as vulnerable. Three species identified in the baseline study at
Genus level that may have modified conservation status in the present day, including Terminalia,
Entandrophragma and Pterocarpus-sp. These are primarily timber tree species overexploited for a variety
of uses.
For species of conservation significance, GSR actively propagates a number of these for use in mine site
revegetation. Since 2010, more than 22,000 seedlings of these species have been propagated for use in
mine site reclamation. The TSF 2 EIS (Geosystems 2013, 2015) indicates this mitigation should not only
reverse the impact from disturbance, but also improve the local conservation status of these species.
Additionally, areas identified as hosting high quality unprotected remnant forest stands have been
specifically avoided for future mine activities.
20.3.8.2 Forest Reserves
There are two forest reserves in the vicinity of Wassa:
- Bonsa River Forest Reserve; and
- Subri River Forest Reserve.
The satellite site at Benso is 17 km west of the southern part of the Subri River Forest Reserve and 12 km of
the Hwini Butre Benso access road traverses the reserve. The Globally Significant Biodiversity Area within
the Subri River Forest Reserve is not impacted by the road.
The Subri River Forest Reserve covers approximately 590 km2 and is an actively managed reserve currently
logged on a 40-year cycle with approximately 2,590 ha of the reserve used for silvicultural research. The
reserve forms part of the watershed between the Bonsa and Pra Rivers and is traversed by their tributaries,
resulting in extensive areas of swampy vegetation.
20.3.8.3 Fauna
The 1996 baseline study found no species of small mammal, bats, birds, herpetofauna, or amphibians of
outstanding conservation merit. Of the large mammals, several species were reported as being of
conservation significance, although it was necessary to traverse more than 10 km into the Forest Reserve to
observe any of these species, likely due to high hunting pressures and impacts of logging activities, which
have continued since 1996. Notable species observed in the various surveys and their current classification
are:
- Necrosyrtes monachus (Hooded Vulture) – critically endangered, owing to indiscriminate poisoning,
trade for traditional medicine, hunting and persecution;
- Kinixys homeana (Hinge-back tortoise) – vulnerable;
- Psittacus erithacus (Grey Parrot) – vulnerable, owing to international pet trade;
- Scotonycteris ophiodon (Pohle’s Fruit Bat) – near threatened;
- Phataginus tricuspis (African White-bellied Pangolin) – vulnerable;
- Anomalurus pelii (Pel’s Flying Squirrel) – near threatened in 1996, data deficient currently.
The 2012 survey for the TSF 2 assessment included terrestrial and aquatic species. Of the 314 ha surveyed,
0.3% was uncultivated and the fauna of the project area was relatively impoverished, likely reflecting
indiscriminate hunting and agricultural clearing. The study found no species of Lepidoptera, amphibians,
reptiles, birds or aquatic species listed as having conservation significance by IUCN. Of the mammal species
identified, a single African White-bellied Pangolin was located in the wider project area.
Page 244NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 245
20.3.9 Social Setting
20.3.9.1 Administrative Setting, Settlements and Land Ownership
The Wassa Mine is located in a rural setting with no major urban settlements within 30 km. It lies in the
Wassa East District, part of the Western Region of Ghana, 40 km north of Daboase (district capital), 65 km
north of Takoradi (regional capital) and 35 km north-east of the city of Tarkwa.
The nearest villages are Akyempim, Akyempim New Site (formally Akosombo, resettled early in Wassa
operations) and Kubekro. The Togbekrom community was resettled Ateiku to permit construction of TSF 2.
Table 20-3 Communities around Wassa
The District Assembly is the supreme organ charged with the administration and supervision of
development activities in the district and the District Chief Executive is the most senior government official.
In addition to the governmental administration, the project operates within the Wassa Fiase Traditional
Area, with its Paramountcy at Tarkwa. Within the traditional structure, the Paramount Chief (Omanhene) is
the head and exercises traditional control over the divisional and sub-divisional chiefs (Adikro) of
communities (traditional towns and villages).
The 1992 Constitution of Ghana provides for three categories of land ownership or holding: customary
(stool/skin) lands (78%); state (or public) lands (20 %); and vested (or public) lands (2 %). Customary lands
are managed by traditional authorities in accordance with customary laws, although the State exerts
considerable control over administration of these lands. Land access is only available under leasehold.
As the lands within the Wassa concession are mineralized, the minerals are state-owned with the mineral
rights granted to GSWL under the Minerals and Mining Act, 703, 2006. The Constitution of Ghana (1992),
State Lands Act (1962), Minerals and Mining Act 703 (2006), Minerals and Mining (Compensation and
Resettlement) Regulations (2012), Mining and Environmental Guidelines, Environmental Protection Agency
Act 490 (1994) and Environmental Assessment Regulations (1999) each have provisions pertaining to land
access, including land acquisition, land and farm compensation and resettlement.
All land affected by activities proposed in this assessment are traditionally in the ownership of the
Mamponso Stool of the Wassa Fiase Traditional Area. The relationship between the Divisional Stool Chiefs
and the inhabitants is based on tenancy, where tenants typically pay annual rent as a portion of their
annual crop returns.
20.3.9.2 Socioeconomic Setting
The Wassa Mining Lease (LVB 87618/94) area is 52.89 km2 and by December 2019, was subject to
approximately 940 ha of disturbance from mining and associated activities. GSWL has provided
compensation for a total of 1,294 ha of land due to both direct disturbance and for buffer areas.
Socioeconomic study of Wassa mine host communities’ highlights:
- Land Use – prior to mining, the main use was farming, mostly cocoa with lesser crops of oil palm,
maize intercropped with cassava, and plantain. There were also compound farms around villages
and hamlets for crops of coconut, cocoyam, avocado pear, citrus, mango, maize and cassava in
mixtures. There were no commercial plantations farmed and commercial logging was almost
Community
Divisional Area
Estimated Population
(SGS 1996)
Population
(WEDA 2013)
Akyempim
Mamponso
2,500
2,533
Akosombo
Mamponso
n/a
166
Kubrekro
Anyinabrem
300
335
Nsadweso
Anyinabrem
2,400
1,541
Togbekrom
Anyinabrem
Not measured
674NI 43-101 Technical Report (March 2021) Wassa Gold Mine
entirely restricted to the portion of the Subri River Forest Reserve. This remains consistent today,
with addition of land use for the mine and supporting activities.
- Livelihood – prior to mining, most people were dependent on crop farming which was also the
principal source of employment. Farming was dominated by migrant farmers from other regions of
Ghana, using land owned by indigenous families on a leasehold basis. More recently, livelihoods
are still mostly agricultural with approximately two-thirds of economically active people employed
in agriculture and one quarter in mining/quarrying, manufacturing and wholesale/retail sectors.
- Housing – more than half of homes in the district are constructed from mud/earth, roofing
materials are generally metal sheet.
- Water Supply – most people in the district obtain water for drinking and domestic use from
boreholes or rivers/streams with one-fifth of households using external pipes and/or public
standpipes.
- Energy – less than half of households use mains electricity for lighting and most use wood or
charcoal for cooking.
- Sanitation – most households cannot access formal waste disposal facilities. Most waste is
dumped in public open space and liquids are generally disposed in compounds/streets or gutters.
- Communications – approximately one-third of the population over 12 years of age own mobile
phones and very few households have landline telephones.
- Health – malaria is a common illness experienced by the catchment communities and remains a
serious public health concern nationally. It is regarded as a leading cause of morbidity and
mortality, especially among pregnant women and children under five years (NDPC & UNDP 2010).
Other common ailments in the area are respiratory tract infections and diarrhoea.
- Education – literacy in the Western Region was 58.2 % in 2008, biased toward males (68%) and
remains largely unchanged at the most recent census. Attendance of primary and middle/junior
school is higher in the Wassa East District than the Western Region generally and in 2010 literacy
for ages over 11 years was 75%. Recently, there has been increasing female attendance at the
primary and junior school levels although approximately 10% fewer females complete school than
males (NDPC & UNDP 2010).
20.4 Environmental and Social Management
20.4.1 Golden Star Corporate Commitment
GSR has policies pertaining to:
- Environment;
- Community Relations;
- Human Rights;
- Community Development and Support; and
- Safety, Health and Wellbeing.
To support these policies, GSR demonstrates management commitment through provision of dedicated,
skilled personnel in the disciplines of environment, safety, health, community affairs, resettlement and
security. In 2020, GSWL employed 81 people in these disciplines, representing 11% of the total workforce.
Environmental expenditure in 2020 represented approximately 2% of total operating expenditure.
GSR supports achievement of its corporate policies through training and development of its workforce.
Over 49,000 personnel hours were committed to training at the Wassa operations in 2019.
Page 246NI 43-101 Technical Report (March 2021) Wassa Gold Mine
20.4.2 Social Investment
20.4.2.1 Golden Star Development Foundation
The primary vehicle for GSR’s social investments is the community-led Golden Star Development Foundation,
which is funded annually with $1/oz Au produced and 0.1% of pre-tax profit. Under the foundation umbrella,
GSWL works with local Community Mine Consultative Committees (CMCC), government bodies, and third
party non-governmental organizations (among others) to strategize and implement a variety of community
development projects and programs.
In 2020, GSR contributed over $0.20 M to the foundation, bringing contributions to date to over $4 M.
20.4.2.2 Golden Star Oil Palm Plantation (GSOPP)
Golden Star Oil Palm Plantation (GSOPP) is a community-based oil palm plantation company established in
2006 as a non-profit subsidiary of GSR.
GSOPP applies the small-holder concept of sustainable agribusiness, which addresses environmental, food
access, and community concerns. Currently, development is sponsored by GSR as part of its local economic
development program. The goal is that plantations will become self-supporting in the future as small-hold
farmers pay back their start-up loans to GSOPP to sustainably fund future investment.
GSR commits $1/oz Au produced to the program, resulting in over $8.1 M in funding as at year end 2019. To
date, GSOPP has established 1,512 ha of plantations and in 2019, produced and sold over 13,000 tonnes of
oil palm fruit.
In 2018, GSOPP was expanded into the parts of TSF 1 that had reached closure elevation and in 2020 the
development planting at TSF 1 was completed.
Figure 20-15 GSOPP oil palm plantation on TSF 1
Page 247NI 43-101 Technical Report (March 2021) Wassa Gold Mine
20.4.2.3 Capacity Building and Livelihood Enhancement
Employment, particularly for youth, continues to be the foremost concern to the Wassa catchment
communities. Education and training initiatives are extended through community out-reach programs,
which aim to impart lasting educational benefits.
The Golden Star Skills Training and Employability Program (GSSTEP) provides training in practical and
technical skills to young people in sectors unrelated to mining, contributing to diversification of the local
economy’s employment base. This program has also been integrated into many of the negotiated
resettlement agreements that conform to the IFC Performance Standard 5 on involuntary resettlement.
Inaugurated in 2009, by the end of 2019, 14 GSSTEP programs had been run, for over 600 youth providing
skills in masonry, commercial cookery, carpentry, mobile phone repairs, building, electrical, beading and
jewellery making, hair dressing, fabric bag and sandal making.
In 2013, GSWL initiated a pilot Community Youth Apprenticeship Program (CYAP), which provided local
residents a one-year work program at Wassa. The pilot project enrolled 44 young people from 15
catchment communities in various disciplines but mostly mechanical trades. As a result of CYAP, local
graduates were better positioned to fill skilled employment vacancies within the company to further boost
local hiring. Following from the success of CYAP, the program is being implemented again in 2020 to
provide a further pool of local youth vocation training in the mining sector.
Since 2010 GSR has provided opportunities for extended education with over 800 attachment/work
experience students, over 700 tertiary graduates through the Ghana national service program, 164
graduate traineeships, 84 apprenticeships and 143 post-graduate sponsorships.
GSR also provides scholarships for underprivileged students attending secondary school. Since 2008, the
company has provided scholarships for over 1,080 children. A further 3,000 registered dependents of
employees are also supported through annual educational subsidies.
20.4.2.4 Corporate Responsibility
In accordance with its commitment to the UN Global Compact, GSR supports and respects internationally
proclaimed human rights within their sphere of influence. GSR’s policies on Community Relations and
Human Rights outline the commitment to create a company culture where the protection of human rights
are an integral and sustainable part of the operations, including performance management systems.
GSR periodically conducts human rights reviews with major suppliers and results reported to the GSR
Corporate Responsibility Committee. This provides further assurance that GSR is not complicit in any
human rights abuses, even where they may be occurring indirectly through the supply chain.
GSR has processes and training in place to prevent harassment and discrimination.
GSR has a safety management system and safety improvement programs to minimize harm and embed
safety management into the operations. Recent improvements include:
- Risk management system enhancements;
- Crisis and emergency management system upgrades and training;
- Safety culture surveys; and
- Safety leadership training.
GSR engages in accurate, transparent, and timely two-way consultation with local stakeholders to
communicate about the business and address the needs of local partners. Regular dialogue with
stakeholders is conducted via public meetings, open houses, and sensitization forums. Improved
understanding of stakeholders’ issues and concerns helps to realize sustainable solutions.
As a catalyst for sustainable economic development in the host communities, GSR plays a role in enhancing
relationships with partners to maximize benefits accrued to the stakeholder communities. The aim of
Page 248NI 43-101 Technical Report (March 2021) Wassa Gold Mine
investments in local communities is to have a strategic approach which creates lasting, meaningful benefits
for local communities and contributes a positive long-term legacy around the operations.
In the area of security and human rights, in 2014, GSR commenced a program of training and awareness
with its security personnel and military personnel, in the Voluntary Principles on Security and Human
Rights. By the end of 2019, over 740 security personnel had been trained and the Voluntary Principles are
now part of induction for new security personnel.
20.4.2.5 Environmental and Social Management System
Environmental management is addressed through an Environmental and Social Management System (EMS)
developed in-line with an ISO 14001 EMS. It provides the operation with a program which addresses the
legal and corporate needs for monitoring and reporting. The EMP and the associated Environmental
Certificate provide the legal framework for GSWL environmental management, whilst EIS’ and associated
Environmental Permits provide the legal framework for project developments.
Community management at GSWL is conducted by specialist community affairs and development
personnel. GSWL has established a series of CMCC’s with the local communities and an Apex CMCC collects
the recommendations and presents them to the company entities (eg: Golden Star Development
Foundation) on behalf of the three concession areas (Wassa, Hwini Butre and Benso). The aim is to ensure
full representation across the GSWL operations occurs without interference from GSWL.
The CMCC’s are responsible for selecting development projects and assisting with understanding of
community concerns and needs. Development opportunities for the stakeholder communities are funded
by either the Golden Star Development Foundation, or directly from GSWL.
In November 2019 GSWL reached milestone Memoranda of Understanding (MOU) with its Wassa host
communities. Developing the MOU’s involved all four catchment communities, two resettlement
communities and two divisional areas. Representatives included the Traditional Council, Queen Mothers,
Members of Parliament, Districts Assembly, as well as specific representation from both women and youth
to ensure inclusion and diversity. Implementation of the MOU’s, covering Relationship and Sustainable
Livelihoods, Local Employment and Contracts, and Development Foundation, commenced in 2020 with the
re-constitution of the CMCC. Institutionalization of the agreed new modalities will continue in 2021.
GSWL maintains a grievance mechanism enabling catchment communities to document concerns and
grievances for investigation and/or action. The mechanism is well publicized by GSWL and used actively by
the community and other stakeholders. Details of registered grievances and resolutions are recorded and
reported internally and to the regulators.
20.5 Environmental and Social Issues
Environmental and social issues – those that could affect permitting, operations and/or social licence – can
be material to the company.
Community expectations and sensitivities have the potential to affect social licence, land access and permit
issuance. Issues of primary concern for local stakeholder communities include employment, involvement in
local supply chain and amenity. Management of these issues is pivotal to strengthening of relationships
and ensuring business continuity.
20.5.1 Employment
The main socioeconomic concern for most stakeholders in the local community is employment, where
working at the mine is viewed as a preferred occupation. The mine life for the Mineral Reserve and
potential of the large Inferred Mineral Resource, is expected to receive local support. The potential for
employment growth will be tempered by expected productivity increases, requiring ongoing management
of expectation in host communities.
Page 249NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Enhanced productivity is assumed to be driven by more efficient stoping methodology, increasing
application of technology and efficiencies due to the economies of scale, as installed capacity becomes fully
utilized. GSR will continue to focus on the development of vocational skill in the host communities to
create an enabling environment for local employment and associated enhanced business continuity.
Whilst the operations will not provide full employment to all people seeking work, the Memorandum of
Understanding on Local Employment and Contracts provides agreed modalities for affirmative action to
employ from local stakeholder communities.
- All vacant positions are advertized locally first, then nationally;
- Local people are used exclusively for unskilled positions, and preferably for skilled positions;
Wassa draws most of its workforce from the Western Region. To support the commitment to local
employment, GSWL has the CYAP program discussed above to build local vocational capacity.
20.5.2 Local Procurement
The GSWL MOU on Local Employment and Contracts builds on the history of building local procurement
capacity around Wassa. The MOU specifies specific contract services to be provided by local community
companies (eg: heavy equipment and quarrying) and additionally commits that if a local community
company rates equally with non-local on the tender assessment criteria, they will be awarded the works.
In partnership with the German development agency (GIZ), the National Vocational Training Institute (NVTI)
and the District Assembly, Golden Star and GSWL have joined a partnership program focussed on improving
the employment situation of over 2,000 people in the catchment communities through upskilling and value
chain development. Program activities include technical training for certification, enterprise coaching and
development, support to industry association development, upgrading of secondary technical education
and training of lead farmers, amongst other elements.
20.5.3 Resettlement and Compensation
Where physical, social and/or economic displacement is anticipated, GSWL applies the requirements of the
International Finance Corporation, Performance Standard 5 for land acquisition and involuntary
resettlement. If compensation is required for future operations this it is done in accordance with
applicable laws, and GSWL Farm Compensation and Land Acquisition procedures. Previous application of
these processes by GSR has shown that resettlement can be achieved with positive outcomes, evidenced
most recently with the resettlement of the Togbekrom community to Ateiku in 2013.
20.5.4 Unauthorized Small-Scale Mining
In Ghana, small-scale artisanal mining is termed galamsey. It is mostly unauthorized or illegal and is often
associated with environmental degradation, safety hazards and general community and social concerns.
20.5.4.1 Strategic Approach
GSR has numerous proactive programs to support the maintenance of land access security and reduce local
community uptake of illegal and conflicting land uses, including:
- Extensive social enterprise initiatives, such as the Golden Star Oil Palm Plantation (GSOPP) that
provide sustainable alternative livelihoods and wealth creation.
- Local content including local procurement programs to retain and enhance the value of the
operations retained by host communities, eg LOCOM’s partnership at the former GSR Bogoso
Prestea mine resulted in redirecting 250 former illegal miners to providing contract services to
support the mine’s operations, to the order of $30 M of works over recent years, enabling local
employment and opportunity.
- Ongoing review of tenure and relinquishment of concessions deemed non-prospective, avoids
potential competition over access land or minerals. GSR has undertaken programs of engagement
and collaboration with the Minerals Commission, legal small-scale mining associations and
community organizations to cede areas of concessions to facilitate legal small-scale mining.
Page 250NI 43-101 Technical Report (March 2021) Wassa Gold Mine
- Designing closure plans that recognize the potential next land use as legal small-scale mining so
that synergies between large and small-scale mining can be leveraged.
- Youth skills development programs to provide skills training and support for small and micro
enterprise business initiation, providing mainstream employment and income generating activities.
- School sustainability clubs to educate children on environmental, safety, health and sanitation
issues, enabling educated decision making on livelihoods as they leave school to seek employment.
- Maintenance of a three-tiered engagement structure with host communities with each forum
incorporating a wide array of community representation including women and youth.
20.5.4.2 Security Management
GSR discloses annually against the World Gold Council Conflict-Free Gold Standard although Wassa is not
located in a country or region designated as conflict affected or high-risk. GSR’s Policy on Human Rights
highlights the company’s commitment to implement programs on ethical conduct and human rights in
support of the Voluntary Principles on Security and Human Rights.
GSR engages private security companies at Wassa for site access control, patrol, protection services,
security monitoring and intelligence gathering. Security providers are:
- Trained in the Voluntary Principles on Security and Human Rights; and
- Do not bear arms, in compliance with Ghanaian law.
General security services are complemented by public security support for bullion movements which is
arranged with local Police. Where public security intervention is required, this can be requested through
the District or Regional Security Councils.
GSWL records any incidents of incursion by members of the community into active mining or reclamation
areas in the company incident reporting system. The system is designed so that that all incidents are
investigated, with corrective actions identified and implemented to prevent reoccurrence.
GSR reports security related incidents verbally to the District Security Council via meetings and direct
contact, mining related incidents to the Minerals Commission via statutory submissions and
pollution/environmental related incidents to the Environmental Protection Agency via the statutory report
submissions. In the case of illegal mining incursions these are typically be reported to all three regulators.
In the community relations context, GSR engages with traditional leaders, opinion leaders and local elected
government representatives for involvement as necessary in the investigation, management or other
intervention related to any land use or competition related issues.
GSR is of the opinion that galamsey around Wassa has little potential to impact the current or future
operations. The main project site is well secured, with other infrastructure located between the Wassa
main pits complex and the nearest community. Generally, the removal of unauthorized persons from the
wider project area has posed no difficulty, with persons moving on as requested. The underground mine
entrance is located within the existing open pit complex, such that unauthorized small-scale mining is not
expected to adversely affect the underground operations.
20.5.5 Process Water Balance and Discharge to Environment
The process water balance model at Wassa indicates that under normal conditions discharges from the TSF
to the receiving environment should not be required. In the event discharge is required, there is an
approved detoxification plant to treat cyanide from supernatant waters. No discharges from TSF have been
required since 2010.
20.5.6 Geochemistry
Characterization testing of ore and waste rock evidence low potential for acid generation (Section 20.3.4).
Geochemical management incorporates ongoing characterization of core to assess the geochemical
Page 251NI 43-101 Technical Report (March 2021) Wassa Gold Mine
properties of future ore and waste sources for variability against the current predicted state of all materials
having low acid generation potential.
20.5.7 Legacy Issues
GSR has been responsible for managing Wassa for over 20 years. In 2002, when GSR assumed
responsibility, Wassa was an open pit operation with heap leach processing. Since then, the former heap
leach area has been encompassed within TSF1 and most of the open pit excavations have been
rehabilitated or expanded by subsequent mining.
Disturbances by the legacy operations are covered by the Reclamation Security Agreement and Wassa
closure plan and financially addressed by the company asset retirement obligations as well as the bond
required by the EPA. There are no other legacy issues associated with the GSWL site.
20.5.8 Amenity
GSR conducts regular environmental monitoring and continues to demonstrate high levels of conformance
to regulatory standards for water, air, noise and vibration. The involvement of local host community
members in elements of the monitoring program, grievance mechanisms, as well as transparent reporting
of performance in stakeholder engagement, also contributes to understanding of management of amenity.
20.6 Closure Planning
Closure concepts and provisional plans are included in the various permitting documents received over the
project’s life and are updated in the Environmental Management Plan (three yearly update). The annual
Mining Operating Plan also contains details related to closure and reclamation.
Rehabilitation and closure of the existing operations (including processing plant, TSF’s, pit excavations,
waste dumps and transport corridor) are covered under the EMP, Reclamation Security Agreement and
associated bank guarantee (bond). As new expansions are permitted, GSWL develops a conceptual closure
plan that is incorporated into the applicable EIS.
GSR applies two methodologies for estimation of closure costs:
- Asset Retirement Obligations (ARO), as defined by International Financial Reporting Standards; and
- Practical Closure Plan (PCP).
Both methodologies are updated annually and utilize:
- Costing of works assumes mixture of mine operations and standalone contractors;
- No provision for ongoing water treatment as the closure plan assumes, and modelling indicates,
mine workings will be flooded but will not result in decant; and
- Post-closure community costs are excluded as none are anticipated or currently committed.
The methodologies differ in that:
- Scrap value is excluded from the ARO;
- Infrastructure handover, eg handover of roads to local government or buildings to host
communities, is excluded from the ARO; and
- Progressive reclamation and operational synergies are excluded from the ARO.
This economic analysis assumes the costings in the PCP will be realized, as the company has continued to
demonstrate realization of progressive revegetation (eg TSF revegetation) and operational synergies (eg
concurrent backfilling of pits with waste rock), and host community have established an expectation of
hand-over of key community infrastructure.
For the purposes of conservatism, an additional $3.0 M has been added to allow for unanticipated future
disturbance associated with the extended operating life.
Page 252NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 253
Closure costs include all tenure associated with GSWL including Wassa, Hwini Butre and Benso concessions.
Table 20-4 Closure cost estimates, at Dec-2020
Methodology
Asset Retirement Obligation
(ARO, $M)
Practical Closure Plan
(PCP, $M)
Wassa Concession, current disturbance
16.53
11.61
Benso Concession, current disturbance
1.64
1.33
Hwini Butre Concession, current disturbance
1.66
1.37
Total
19.83
14.31NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 254
21 CAPITAL AND OPERATING COSTS
21.1 Introduction
GSR’s prepared capital and operating cost estimates with the following bases:
- All costs are in US dollars (US$/$). This is consistent for both historic actuals and forward looking
expenditures, where the majority of costs (including local Ghana costs) are aligned to US$,
negating the effect of exchange rates.
- Expenditures aligned to physical schedules over the life of the project.
- Forward estimates calibrated to 2020 actual spend (Jan-Dec 2020).
21.2 Capital Costs
Wassa is currently operating at full production, as defined by the current Mineral Reserve and future
capital expenditure consists of:
- Growth Capital: to expand or increase capacity of the operation from the current established base,
including expediting primary access to new mining areas to increase extraction rates.
- Sustaining Capital: for ongoing access of production areas within the established operation.
21.2.1 Cost Estimation, Capital
21.2.1.1 Major Projects
Major Projects are one-off expenditures for specific projects required to deliver the project plan.
Estimate basis and timing of expenditures are shown in Table 21-1.
It is notable that there are no major project costs for the processing plant or other surface infrastructure.
Currently installed processing and infrastructure capacity are sufficient to meet the planned higher mining
rates so capital expenditure in these areas is sufficiently allowed for in the Minor Projects classification.
Table 21-1 Cost estimate, Major Projects for Mineral Reserve plan
21.2.1.2 Mine Development
Mine Development capital costs are estimated as an allocation of a share of mining operations costs
attributable to capital works, factored by physical quantities.
- Lateral Development: factored by lateral development metres advance (m.adv);
- Vertical Development: 100% to capital for raises at average rate of $5000/m for all profiles (vary
from 1.8, 2.4, 3.5 to 6.0m diameter); and
- Overheads: factored by total material mined (all.t).
Timing
Year
Upper Mine, Establish
2022
Vent, Fans RAR1
2020-21
Expenditure
$ ‘000
Description
5,000
7,500
Portal construction & establishment of services.
Development commences mid-2022
Fans (1.5-2MW) pow er dist. (shaft in Mine Dev’t).
Budget 2021 has shaft in 2021 and fans 21-22NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 255
Table 21-2 Mine development capital allocation for Mineral Reserve plan
21.2.1.3 Minor Projects
Minor Projects are the capital expenditures required to support delivery of the physicals schedule.
- Are additional to the share of operations costs that are recharged to capital;
- Estimation method is fixed/variable model, driven by a physical quantity; and
- Base is actual spend.
Minor Projects are estimated in the following groups:
- Mining UG: including, but not limited to: power distribution, ventilation equipment, dewatering
equipment and facilities, mine water and compressed air services, major maintenance projects,
technical equipment and support facilities.
- Geology UG: definition drilling in the following categories:
o Resource Development: intended to upgrade inferred resource to indicated. Timing is to
be completed ahead of capital investment for mining panel (decline and access
development).
o Resource Infill: increase drill density of indicated material to reduce spatial risk to permit
accurate development positioning. Timing is to provide a drilled inventory 2-3 years ahead
of stoping.
- Processing: including, but not limited to: major maintenance projects, corrosion management,
insurance spares, technical equipment and support facilities.
- G&A: including, but not limited to: accommodation and administration facilities, IT infrastructure,
supply facilities, light vehicles, sustainability projects and emergency equipment.
- TSF: incremental raises of the TSF. Tails quantities are reduced to account for tails solids used in
paste backfill. 2021 costs are per the 2021 budget and will deliver the Stage 2 cell expansion,
thereafter expenditure is estimated on a $/t basis to construct cell raises for the quantity of tails
required the following year.
Table 21-3 Cost estimate, Minor Projects for Mineral Reserve plan
CY21
CY22
CY23
CY24
CY25
CY26
Lateral Development
$M
7.8
17.7
19.9
15.4
–
–
Share to Capital
%
54.3%
56.1%
46.3%
–
–
–
Vertical Development
$M
4.9
4.5
2.3
2.2
–
–
Share to Capital
%
100.0%
100.0%
100.0%
100.0%
–
–
Mine Overheads
$M
0.6
1.1
1.1
0.9
–
–
Share to Capital
%
12.4%
22.1%
23.2%
18.2%
–
–
Total
$M
13.2
23.2
23.4
18.5
–
–
Share to Capital
%
55.4%
56.8%
46.5%
258.0%
–
–
3.7
13.2%
78.3
–
Total/avg
60.7
44.3%
13.9
100.0%
UofM
Mining UG
ug.all.t
Geology UG
ug.ddm.cap
Processing
mill.t
G&A
mill.t
TSF
mill.t.tsf
Tonnes Processed
0.50
Expenditure
$ ‘000
33,173
Description
Resultant Rate
$/ROM.t mined
Driving Quantity
Total Material Mined, UG
18,268
Tonnes Processed
1.69
9,789
Tails Solids to TSF
0.90
3.07
–
Definition Drilling, UG
–
5,459NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 256
21.2.1.4 Mobile Fleet
Fleet schedules have been determined and calculated for the following machine categories:
- Development Jumbo;
- Production Drill;
- UG Loader;
- UG Truck; and
- Ancillary, includes all minor equipment (eg: Integrated toolcarrier, charging units, ROM Loader,
Rockbreaker) which for estimation are considered a like-for-like fleet.
Light vehicles are included in the Minor Projects cost allowances.
Table 21-4 Mobile Fleet, categories
Detailed fleet schedules are presented in Table 21-5 and the capital replacement schedule is shown below.
Nominal machine type, cost and life are based on the current preferred fleet and 2021 budget estimates.
Table 21-5 Cost estimate, Mobile Fleet replacement schedule for Mineral Reserve plan
21.2.2 Capital Allocations, Growth and Sustaining
Growth capital is defined as that required to materially increase capacity or extend mine life. For this
study, capital expenditures are allocated to growth where they relate to expanding operations to new
mining areas.
- Major Projects: Infrastructure required to expand the underground mine, being the southern
exhaust ventilation upgrade (RAR1) and establishment of the upper mining zone (Panel 3).
- Mine Development: Capital development to access new mining areas.
- Definition Drilling: drilling for Panel 3 (Upper mine).
- Minor Projects, excluding definition drilling: share of these costs, weighted by proportion of Mine
Development cost for growth. Includes mining, processing and G&A.
- Mobile Fleet: weighted share, as per Minor Projects.
The allocation methodology of growth capital has an expected accuracy of +/-30%, where the error will
result in misallocation of capital to either of growth/sustaining.
CY21
CY22
CY23
CY24
CY25
CY26
Development Drill
- units
–
2
1
–
–
–
$M
–
2.80
1.40
–
–
–
Production Drill
- units
–
–
–
1
1
–
$M
–
–
–
1.40
1.40
–
UG Loader
- units
–
1
–
1
–
–
$M
–
1.40
–
1.40
–
–
UG Truck
- units
1
2
1
3
–
–
$M
0.97
1.93
0.97
2.90
–
–
ROM & Ancillary
- units
1
1
–
–
–
2
$M
0.40
0.40
–
–
–
0.80
Total
- units
2
6
2
5
1
2
$M
1.37
6.53
2.37
5.70
1.40
0.80
Total/avg
3
4.2
2
2.8
2
2.8
7
6.8
4
1.6
1 8
18.2
Life
years
Development Jumbo
7
Production Drill
7
UG Loader
6
UG Truck
4
ROM & Ancillary
8
Type
Sandvik DD421
Sandvik DL421
Sandvik LH621
Volvo A60H
various
Nominal Cost
US$ ‘000
1,400
1,400
1,400
965
400
Nominal UnitNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 257
Table 21-6 Capital cost summary for Mineral Reserve plan
21.3 Operating Costs
Operating costs have been estimated as follows:
- Analysis of 2020 Jan-Dec YTD actual spend;
- Analysis of share of fixed and variable cost for each activity, at the cost element level (eg: fuel,
labour, consumables);
- Calculation of periodic spend, driven by scheduled units of a physical activity; and
- Review of step change fixed costs where higher physical rates are planned.
21.3.1 Cost Estimation, Operating
Operations costs are estimated in the following groups.
- Mining, Development: operating share of lateral development, including labour, energy,
consumables and equipment maintenance for drilling, blasting, ground support, loading, hauling
and secondary ventilation. Cost estimate is driven by lateral development advance and based on
2020 actuals.
Costs are factored up from current rates, linearly with the average haulage distance each year, to
reflect the increasing trucking fleet and ventilation needs. Rates are consistent, ranging from
$2,945 – $3,010 /m.adv.
CY21
CY22
CY23
CY24
CY25
CY26
Growth Capital
Mine Development
$M
5.1
8.9
9.0
3.6
–
–
Mining UG
$M
–
–
–
–
–
–
Definition Drilling
$M
5.1
0.7
2.1
0.7
–
–
Processing
$M
–
–
–
–
–
–
Site G&A
$M
–
–
–
–
–
–
TSF
$M
–
–
–
–
–
–
Mobile Fleet
$M
–
–
–
–
–
–
Projects, Ventilation
$M
4.8
2.8
–
–
–
–
Projects, Other
$M
–
5.0
–
–
–
–
Total Growth
$M
15.0
17.4
11.1
4.3
–
–
Unit Cost per Proc.t
$/t
7.69
8.18
6.16
2.20
–
–
Unit Cost per rec.oz
$/oz
8 8
9 8
6 2
2 4
–
–
Sustaining Capital
Mine Development
$M
8.1
14.3
14.4
14.9
–
–
Mining UG
$M
6.4
6.8
6.9
7.0
6.0
–
Definition Drilling
$M
–
–
–
–
–
–
Processing
$M
1.1
1.1
1.1
1.1
1.1
–
Site G&A
$M
3.7
3.7
3.6
3.7
3.7
–
TSF
$M
4.6
1.4
1.6
2.2
–
–
Mobile Fleet
$M
1.4
6.5
2.4
5.7
1.4
0.8
Projects, Ventilation
$M
–
–
–
–
–
–
Projects, Other
$M
–
–
–
–
–
–
Total Sustaining
$M
25.3
33.9
29.9
34.5
12.2
0.8
Unit Cost per Proc.t
$/t
13.01
15.93
16.57
17.81
6.04
0.48
Unit Cost per rec.oz
$/oz
149
192
166
192
6 8
6
Total Capital
Growth
$M
15.0
17.4
11.1
4.3
–
–
Sustaining
$M
25.3
33.9
29.9
34.5
12.2
0.8
Total
$M
40.3
51.3
41.0
38.8
12.2
0.8
Unit Cost per Proc.t
$/t
20.70
24.12
22.73
20.00
6.04
0.48
Unit Cost per rec.oz
$/oz
237
290
227
215
6 8
6
Total/avg
26.6
–
8.6
–
–
–
–
7.5
5.0
47.7
4.15
4 7
51.7
33.2
–
5.5
18.3
9.8
184.3
16.02
18.2
–
–
136.6
11.87
133
47.7
136.6
180NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 258
- Mining, Production: ore production from stoping, including labour, energy, consumables and
equipment maintenance for slotting, drilling, blasting, loading and hauling. Cost estimate is driven
by stope ore tonnes and based on 2020 actuals.
Costs are factored up from current rates, linearly with the average haulage distance each year, to
reflect the increasing trucking fleet and ventilation needs. Rates vary from $21.41 /stope.t in 2021,
to $19.70 /stope.t in 2025 (last year of full production). Rates decrease slightly over time with
increasing stope tonnage offsetting the cost impact of longer haulage distances.
- Mining, Backfill: labour, energy, consumables and maintenance for the paste filter plant,
underground distribution and stope barricades. Cost estimate is driven by volume of paste placed
and, as there is not operating history (commissioning planned for 2021-Q1) costs are per the 2021
site budget, informed by the 2018 feasibility study (nominally $17/m3 from 2021).
Backfill volumes assume all 95% of ore voids are filled.
- Mining, Surface Haulage: haulage of ore from the portal bench to processing run-of-mine pad,
including labour, energy, consumables and equipment maintenance for loading and hauling. Cost
estimate is driven by total ore tonnes and based on 2020 actuals.
- Mining, Overheads: general support services for the underground mine, including labour,
consumables and services for technical, management and administrative personnel. Cost estimate
is driven by total tonnes mined and based on 2020 actuals. Cost estimate is driven by grade control
drill metres and based on 2020 actuals.
- Mining, Geology: labour, consumables and contractor drilling costs for grade control drilling (from
Indicated to Measured), muck sampling and technical support.
- Processing: labour, energy, consumables, maintenance and services for the processing plant,
including crusher feed, comminution, leaching, tailings deposition and laboratory. Cost estimate is
driven by ore tonnes processed and based on 2020 actuals.
- General and Administration (G&A): labour, consumables, maintenance and services for the site
G&A functions, including general management, human resources, community and social
responsibility, safety, security, emergency services, environmental, finance, supply and information
technology. Cost estimate is driven by ore tonnes processed and based on 2020 actuals.
- Refining: transport, security, refining and transaction costs for selling gold. Cost estimate is driven
by ounces produced and based on 2019 actuals ($4.50/oz), as 2020 costs were inflated ($9.00/oz)
during the period of Covid-19 disruption where gold was transported out of Ghana on charter
flights, rather than regular commercial services which have since returned.
Table 21-7 Cost estimate, Operating for Mineral Reserve plan
UofM
Mining, Development
m.adv
Mining, Production
stope.t
Mining, Backfill
fill.m3
Mining, Surface Haulage
ROM.t
Mining, Overheads
ug.all.t
Mining, Geology
ug.ddm.op
Processing
mill.t
G&A
mill.t
Refining
rec.oz
1.27
9,665
Description
Lateral Development
Stope Material
Paste Backfill
ROM Material
Driving Quantity
Resultant Rate
$/ROM.t mined
7.05
18.24
4.87
220,378
Tonnes Processed
20.37
99,942
Tonnes Processed
9.24
Grade Control Drilling, UG
13,767
0.89
24,399
Total Material Mined, UG
2.26
197,269
52,640
Expenditure
$ ‘000
76,247
4,610
Au Produced
0.43NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 259
Table 21-8 Operating cost summary for Mineral Reserve plan
21.4 Closure Costs
Closure costs are as estimated annually and this assessment applies the Practical Closure Plan values
discussed in Section 20.6.
Closure costs for all concessions under GSWL are allowed for, including Wassa, Benso and Hwini Butre to
the south.
Consistent with the mine closure plans, closure costs are planned to occur both progressively over the mine
life (for Benso and Hwini Butre) and at the completion of operations (for Wassa).
There is potential that Wassa earthworks may be brought forward once final waste dump volumes and
designs are confirmed which could result in $3-5 M of the Wassa costs being brough forward to occur in
parallel with the HBB work.
Table 21-9 Closure cost summary for Mineral Reserve plan
CY21
CY22
CY23
CY24
CY25
CY26
Mining
Development
$M
21.9
14.9
15.6
17.8
6.1
0.0
Production
$M
30.0
32.2
32.3
33.7
38.5
30.7
Paste Backfill
$M
9.4
10.0
9.9
10.3
8.2
4.8
Surface Haulage
$M
1.6
1.8
1.9
1.9
1.5
1.1
Overheads
$M
4.1
3.8
3.8
4.0
4.5
4.1
Refrigeraton
$M
–
–
–
–
–
–
Geology
$M
3.0
2.9
3.0
2.9
2.0
–
Total Mining
$M
70.1
65.5
66.4
70.5
60.8
40.7
Unit Cost per ROM.t
$/t
39.29
35.89
36.82
36.35
30.10
28.15
Unit Cost per rec.oz
$/oz
412
371
368
391
340
295
Processing
Processing
$M
37.1
39.6
35.2
37.0
38.1
33.4
Total Processing
$M
37.1
39.6
35.2
37.0
38.1
33.4
Unit Cost per Proc.t
$/t
19.08
18.62
19.50
19.09
18.88
19.97
Unit Cost per rec.oz
$/oz
218
224
195
206
213
242
Site G&A
Site G&A
$M
16.7
17.1
16.4
16.7
16.9
16.1
Refining
$M
0.8
0.8
0.8
0.8
0.8
0.6
Total Site G&A
$M
17.5
17.9
17.2
17.5
17.7
16.7
Unit Cost per Proc.t
$/t
8.99
8.44
9.53
9.03
8.77
10.00
Unit Cost per rec.oz
$/oz
103
101
9 5
9 7
9 9
121
Total Operating
Mining
$M
70.1
65.5
66.4
70.5
60.8
40.7
Processing
$M
37.1
39.6
35.2
37.0
38.1
33.4
Site G&A
$M
17.5
17.9
17.2
17.5
17.7
16.7
Total Operating
$M
124.7
123.1
118.8
125.1
116.6
90.7
Unit Cost per Proc.t
$/t
64.11
57.89
65.85
64.48
57.74
54.32
Unit Cost per rec.oz
$/oz
733
696
658
694
652
657
76.2
197.3
52.6
9.7
24.4
–
13.8
374.0
Total/avg
220.4
104.6
699.0
60.76
34.57
365
220.4
220.4
19.16
215
99.9
682
374.0
4.6
104.6
9.09
102
Total
Wassa
–
–
–
–
–
–
1.2 3.5 3.5 2.3
1.2
Benso
–
–
0.1 0.4 0.4 0.3 0.1
–
–
–
–
Hw ini-Butre
–
–
0.1 0.4 0.4 0.3 0.1
–
–
–
–
Total
–
–
0.3 0.8 0.8 0.5
1.4 3.5 3.5 2.3
1.2
$1.4M
$11.6M
$1.3M
$14.3M
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 260
22 ECONOMIC ANALYSIS
The Wassa Mineral Reserve has been valued using discounted cash flows at an appropriate discount rate to
determine a Net Present Value (NPV). The effective date is 31 December 2020.
Sensitivity analyses were performed for variations in gold price, gold grade, operating costs and capital
costs to determine their relative importance as value drivers.
The economic analysis includes mining and processing of ore defined by the Mineral Reserve only.
22.1 Assumptions
Table 22-1 below shows the key inputs and assumptions used to develop the economic model.
The discount rate selected for the NPV calculation is 5% which reflects GSR’s view of the cost of capital, and
risk associated with the project, commodity price and country of operation.
Analyses have been conducted using two gold price assumptions:
- Base Case: for Mineral Reserve estimation and economic test – $1,300 /oz flat; and
- Consensus Case: consensus long-term forecast of 27 banks and financial institutions, as at the end
of January 2021:
o 2021 – $1,944.26 /oz;
o 2022 – $1,879.70 /oz;
o 2023 – $1,772.87 /oz;
o 2024 – $1,715.61 /oz; and
o 2025 and beyond (long-term) – $1,584.68 /oz.
Table 22-1 Key life of mine inputs and assumptions used in the economic model for Mineral Reserve
Parameter
Unit
Mine Life
years
Underground Mining
ROM, Development
Mt
g/t
cont.koz
ROM, Stope
Mt
g/t
cont.koz
ROM, Total
Mt
g/t
cont.koz
Waste Mined, Total
Mt
Development, Capital
km.adv
Development, Operating
km.adv
Vertical Dev’t, Capital
‘000 vm
LG Stockpile
Mt
g/t
cont.koz
Processing
Throughput Capacity
Mtpa
Au Recovery, Average
%
Au Recovery, Minimum
%
Au Recovery, Maximum
%
Au Produced & Sold
koz
Au Sales
Au Price, Base Case
$/oz
Au Price, Consensus Case
avg. $/oz
Price Escalation
Inflation
%
1.4
3.01
136
9.4
3.11
940
10.8
3.09
1,076
2.5
20.4
Value
6
23.8
44.2
0.7
0.58
13
2.70
94.1%
–
94.7%
0% (nil)
1,751
1,024
1,300NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 261
22.2 Stream, Taxes and Royalty
22.2.1 Stream
Royal Gold holds a two tier gold stream over the Wassa LOM production:
- Tier 1: delivery of 10.5% of all production at 20% of gold price until 240,000 ounces have been
delivered; and
- Tier 2: delivery of 5.5% of all production at 30% of gold price for all ounces thereafter.
The opening balance of the Tier 1 stream for this economic analysis is 120,003 oz.
22.2.1.1 Taxes and Royalty
The income tax rate in Ghana is 35% of taxable earnings. The royalty rate is 5% of gross revenue. The
government of Ghana holds a 10% free carried interest in the project. Taxation calculations have been
prepared by GSR based on current application and legislation which may be subject to change beyond the
scope of this assessment.
22.3 Economic Results, Base Case
The Mineral Reserve base case presents a positive economic return at $1,300 /oz with after-tax NPV at 5%
of $121.1 M (100% Basis). Table 22-2 shows the projected cash flows from the economic analysis and Table
22-3 shows the detailed results of the evaluation (NB: IRR cannot be calculated as all year cash flows are
positive).
Table 22-2 Cash flows, Mineral Reserve economic analysis – Base case
Figure 22-1 Cash Flows by Year for Mineral Reserve – Base case
Unit
Net Revenue (post Stream)
$M
Operating Costs & Royalties
$M
Cash Flow from Operations
$M
Tax
$M
Capital, Growth & Sustaining
$M
Cash Flow after Tax & Capital
$M
Pre-tax NPV (5%)
$M
Post-tax NPV (5%)
$M
Pre-tax IRR
%
Post-tax IRR
%
212.2
121.2
Value
1,219.9
703.5
147.5
108.4
184.2
147.5
n/a
n/aNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Table 22-3 Mineral Reserve economic analysis – Base case
Page 262NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 263
22.4 Economic Results, Consensus Case
The Mineral Reserve is economically viable at the consensus price ($1,944 – 1,585 /oz), with an after-tax
NPV at 5% of $335.6 M (100% Basis). Table 22-4 shows the projected cash flows from the economic
analysis and Table 22-5 shows the detailed results of the evaluation (NB: IRR cannot be calculated as all
year cash flows are positive).
Table 22-4 Cash flows, Mineral Reserve economic analysis – Consensus case
Figure 22-2 Cash Flows by Year for Mineral Reserve – Consensus case
Unit
Net Revenue (post Stream)
$M
Operating Costs & Royalties
$M
Cash Flow from Operations
$M
Tax
$M
Capital, Growth & Sustaining
$M
Cash Flow after Tax & Capital
$M
Pre-tax NPV (5%)
$M
Post-tax NPV (5%)
$M
Pre-tax IRR
%
Post-tax IRR
%
560.2
335.6
Value
1,643.6
703.5
394.2
262.2
184.2
394.2
n/a
n/aNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Table 22-5 Mineral Reserve economic analysis – Consensus case
Page 264NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 265
22.5 Sensitivity
Sensitivity analyses were completed for the Mineral Reserve for both the Base and Consensus cases.
Results presented are NPV at 5% discount rate, after tax.
Table 22-6 Sensitivity results for the Mineral Reserve at different gold prices and discount rates
Discount
Rate
1,200/oz
Base
1,300/oz
1,400/oz
1,500/oz
1,600/oz
1,700/oz
Consensus
1,751/oz
avg.
1,800/oz
1,900/oz
0%
$93 M
$147 M
$202 M
$257 M
$311 M
$360 M
$394 M
$421 M
$475 M
5%
$75 M
$121 M
$168 M
$214 M
$260 M
$302 M
$336 M
$353 M
$400 M
7.5%
$67 M
$110 M
$153 M
$196 M
$239 M
$278 M
$311 M
$325 M
$368 M
10%
$61 M
$101 M
$141 M
$181 M
$221 M
$256 M
$289 M
$300 M
$340 M
22.5.1 Economic Sensitivity of Base Case
Figure 22-3 Sensitivity analysis of the Mineral Reserve base case ($1,300 /oz)
Table 22-7 Sensitivity results of the Mineral Reserve base case ($1,300 /oz)
Sensitivity
-30%-
-25%-
-20%-
-15%-
-10%-
-5%-
+0%
+5%
+10%
+15%
+20%
+25%
+30%
Gold price
$ M
-82
-33
1
3 1
6 1
9 1
121
151
181
212
242
272
302
Processed gold grade
$ M
-78
-31
2
3 2
6 2
9 1
121
151
181
212
244
276
308
Growth capital cost
$ M
134
132
130
128
125
123
121
119
117
115
113
110
108
Sustaining capital cost
$ M
157
151
145
139
133
127
121
115
109
103
9 7
9 1
8 5
Operating cost: mining
$ M
217
201
185
169
153
137
121
105
8 9
7 3
5 7
4 1
2 5
Operating cost: processing
$ M
177
168
159
149
140
131
121
112
102
9 3
8 4
7 4
6 5
Operating cost: G&A
$ M
147
142
138
134
130
125
121
121
117
113
108
104
100
Sensitivity
-2.5%- -2.0%- -1.5%- -1.0%- -0.5%-
+0%
+0.5% +1.0% +1.5% +2.0% +2.5%
Gold Recovery
$ M
106
109
112
115
118
121
124
127
130
133
136NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 266
22.5.2 Economic Sensitivity of Consensus Case
Figure 22-4 Sensitivity analysis of the Mineral Reserve consensus case (av. $1,751 /oz)
Table 22-8 Sensitivity results of the Mineral Reserve consensus case (av. $1,751 /oz)
Sensitivity
-30%-
-25%-
-20%-
-15%-
-10%-
-5%-
+0%
+5%
+10%
+15%
+20%
+25%
+30%
Gold price
$ M
9 0
131
172
213
254
295
336
376
417
458
499
540
581
Processed gold grade
$ M
9 3
134
174
214
255
295
336
376
416
458
502
545
588
Growth capital cost
$ M
349
346
344
342
340
338
336
333
331
329
327
325
323
Sustaining capital cost
$ M
371
365
359
353
347
342
336
330
324
318
312
306
300
Operating cost: mining
$ M
431
415
399
383
368
352
336
320
304
288
272
256
240
Operating cost: processing
$ M
392
382
373
364
354
345
336
326
317
308
298
289
280
Operating cost: G&A
$ M
361
357
352
348
344
340
336
331
327
323
319
314
310
Sensitivity
-2.5%- -2.0%- -1.5%- -1.0%- -0.5%-
+0%
+0.5% +1.0% +1.5% +2.0% +2.5%
Gold Recovery
$ M
315
319
323
327
331
336
340
344
348
352
356NI 43-101 Technical Report (March 2021) Wassa Gold Mine
23 ADJACENT PROPERTIES
There is no relevant information relating to adjacent properties.
Page 267NI 43-101 Technical Report (March 2021) Wassa Gold Mine
24 OTHER RELEVANT DATA AND INFORMATION
24.1 Southern Extension PEA Introduction
24.1.1 Cautionary Statement
The Preliminary Economic Assessment (PEA) is conceptual and outlines a mining inventory which is entirely
based on an Inferred Mineral Resource. Inferred is the lowest level of confidence for a Mineral Resource
and there is no certainty that further geological drilling will result in the determination of higher Mineral
Resource classification, nor that production and financial outcomes will be realized. Mineral Resources that
are not Mineral Reserves do not have demonstrated economic viability.
The term ‘ROM material’ is used in this assessment to describe potentially economic Mineral Resource
included in the mining and processing plans.
Where the term “ore” is used in various parts of this section it is to use common terms describe items of
mine infrastructure (eg: “ore pass”, “ore bin”, “ore drive” etc.) and metallurgical aspects (“whole of ore”)
without implying economic value.
24.1.2 Basis to Include Inferred Mineral Resources in a Potential Mill Feed Plan
The Wassa underground mine commenced development in 2015 and declared commercial production in
January 2017. There is a history of successfully converting Mineral Resources (including inferred) to
production from underground using the methods outlined in this assessment.
The Wassa property has an established record of successful permitting applications from project
commencement in 1998 to present. These are detailed in Section 20.1.2 (Permitting of Existing
Operations).
On these bases, GSR considers it reasonable to include Inferred Mineral Resources in the PEA mining
production and processing plans for the purpose of informing the PEA economic assessment.
In the event that any of the ROM material is upgraded to enable classification as Mineral Reserve, it will be
declared as such but ROM material should not be considered Mineral Reserve on the basis of this
assessment. Section 15 of this Technical Report should be referred to for the declared Wassa Mineral
Reserve.
24.1.3 Scope of the PEA
The scope of the PEA is to outline an underground mining method, together with supporting infrastructure
and sustainability plans, to extract the potentially economic portion of the Wassa Gold Mine Inferred
Mineral Resource.
The PEA has been prepared within the following framework:
- Underground mining rate increased to fully utilise the installed processing capacity (2.7 Mtpa);
- Production schedules to appropriately consider conversion risk of the Inferred Mineral Resource;
- Methodologies and design quantities based on proven, currently available technologies;
- Costs to reflect current operational experience; and
- Minimise capital demand needed to establish full production.
The intent of the framework is to present a deliverable plan which can be executed with GSR’s current
operational and financing capacity.
Potential enhancements outside this framework are presented as opportunities outside of the PEA
outcomes and can be investigated as part of the forward work plan.
Page 268NI 43-101 Technical Report (March 2021) Wassa Gold Mine
There are no significant changes required for the processing plant to process the potential feed schedule.
Surface infrastructure needed to support the mining method is ventilation and refrigeration related,
including raisebored shafts, exhaust fans and refrigeration plant. The majority of the proposed capital plan
expenditure is contained in underground lateral and vertical development mining. The PEA mining method
relies on paste fill; the paste fill plant was constructed in 2020 and is to be commissioned in Q1 2021.
Based on the mining plan described in the PEA, no additional material permitting is expected to be
required. GSR and GSWL have extensive experience in the Ghanaian regulatory regime and have
throughout the operations history obtained all required regulatory permitting within projected timelines.
The Ghanaian regulatory regime itself is well defined and permitting processes are defined by regulation.
Should future studies identify the requirement for any additional permitting there is no reason to expect
that these would be unduly delayed.
24.1.4 Definitions
The following descriptors are used for the Southern Extension mining quantities. They are consistent with
those used for Panels 1-3 with some additional features.
- Panel:
Each panel defines a progressive phase of definition drilling and capital development. The
definition can be flexible but new panels are defined by their requirement for a new phase of
definition drilling followed by an investment decision (eg: Panels 4, to 5, to 6, etc).
- Area:
Areas are semi/continuous zones of mineralization, which require extraction in connected
sequence but are geotechnically independent from other areas within the panel, for the purposes
of stope sequencing. Areas can extend across multiple panels where the panel boundaries are
designed to permit sequence independence.
- Block:
Blocks are groups of stopes, mined as independent production districts. Generally 125 m high, they
consist of four production levels, plus a sill pillar to separate from the block above. They are
established to facilitate efficient stope production with separable mine infrastructure (vent, access,
materials handling) so minimize the interactions between different blocks.
- Stope:
A stope is a single production excavation which follows a defined sequence to complete the
production cycle (eg: development, drilling, blasting, loading, filling).
- Lift:
Stopes across multiple levels are mined in a series of lifts, as they progress through each level, ie: a
four-lift stope is four levels high.
- Split:
Where the width of mineralization is larger than the allowed stope width, stopes will be broken
into a series of splits across strike.
The descriptors are illustrated in Figure 24-1
Page 269NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 24-1 Illustration of Wassa location descriptors
24.2 Mineral Resources used in the PEA
The Mineral Resources considered in the PEA are as at December 2020 and are entirely Inferred Mineral
Resource. The Long-Range model (srkwasmar20e) was used, south of 19,240mN or below 300 mRL.
Mineral Resources above and north of this area inform the Mineral Reserve and are excluded from the PEA.
Figure 24-2 Mineral Resources considered in Southern Extension PEA (LR model only)
Page 270NI 43-101 Technical Report (March 2021) Wassa Gold Mine
24.3 Mining Methods
24.3.1 Introduction
The Southern Extension has the potential to expand the underground production profile if the Inferred
Mineral Resource is successfully converted to production. Figure 24-3 and Figure 24-4 respectively show
the scale of the Southern Extension and the arrangement of the mining areas across the deposit.
The Southern Extension will be accessed from existing underground workings via two declines, one on each
side of the production panels. Panels 4-8, shown in Figure 24-3, continue in numbering from those in the
current and upper mining zones.
Duplicate Ramp
(Haulage Loop)
Panel 4
Panel 5
Panel 6
Panel 7
Panel 8
Figure 24-3 Longitudinal Section looking east, showing the Southern Extension Panels
Page 271NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Panel 4
Panel 5
Panel 6
Panel 7
Panel 8
Figure 24-4 Cross sectional view, Southern Extension, highlighting the width and complexity across the deposit
24.3.2 Mine Design
24.3.2.1 Introduction
The general layout of the Southern Extension zone is shown in Figure 24-5. The large mineralized footprint
in the southern zone is accessed from two declines, east and west of the mineralization. The distribution of
mineralization varies between the upper (4-6) and lower (7-8) panels. The layout of the production blocks
is also different in the upper and lower panels.
- Panels 4-6: Three large production blocks on the east side with numerous smaller production
blocks to the west. Blocks are spread across and along strike of the deposit, creating multiple
independent production blocks.
- Panels 7-8: Reasonably uniform and continuous blocks on both sides of the deposit, merging at
depth. More consistent geometry could be influenced by relatively wide spaced drilling (all of the
Southern Extension classified as Inferred Resource), but panels 7 and 8 have the lowest drill hole
density). However, should the geometry break apart with further drilling, the mining and access
strategy is flexible in that the modular production blocks, with access from the two declines, can be
moved around to match the geometry of the defined mineralization.
Page 272NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 24-5 Oblique view of the Southern Extension showing twin decline layout (looking northeast)
24.3.2.2 Stoping Methodology
The majority of stopes in the Southern Extension zone will be mined using bottom-up, transverse Long Hole
Open Stoping, with occasional longitudinal stopes where deposit widths are less than 15 m. Nominal stope
lift dimensions are 20m along strike, up to 30m wide and 25 m height (level spacing), regardless of stope
type and sequence used. The number of lifts mined in a single stope varies depending on the stope type
and sequence, with between one and four lifts per stope (25-100 m height).
24.3.2.2.1 Transverse Stoping
Transverse stopes are designed where planned width is above 15 m. Transverse stopes are planned to
extract the majority of the mineralization and have the following characteristics:
- On each level, the stope is accessed by a single crosscut, mined from the footwall drive through the
full thickness of mineralization and centrally located along the 20m strike span.
- Each lift will be opened by a slot, proposed to be mechanically excavated with a boxhole from the
lower level of the lift, leaving a cap before breakthrough into the top drill access. Blast holes will be
drilled down from the top access in transverse rings.
- For the lowest lift in a production block, an intact trough will be left on each side of the crosscut.
o The trough consists of material that is inefficient to recover with the stope above (complex
blasting and difficult remote loading).
o Troughs will be angled so that blasted material rills toward the extraction crosscut,
improving the overall productivity over the stope life.
Page 273NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 274
o Material can be recovered with the extraction of the sill pillar from the block below.
o For all lifts above, the lower level will be formed by the fully opened crown of the lift
below, so will not require troughing.
Generic sections for a primary transverse stope are shown in Figure 24-6, and the generic extraction
sequence for the stope cycle is shown in Figure 24-7.
Figure 24-6 Schematic of a 4-lift primary transverse stope (illustration not to scale)
Sill
Lift 1
Sill
Lift 4
Lift 3
Lift 2
Lift 1
Filled
Filled
Cross Section
Longitudinal Section
A
A
A
A
Trough
Trough
Footwall
Drive
Cross Cut
Trough
Trough
Drawpoint
Production
rings
Broken
stocks
Plan
Drawpoint
Cross-cut
Uphole stope
removes sill
Footwall
Drive
Drawpoint
Cross-
20 m
25 m
25 m
25 m
25 m
25 m
12 – 30 m
20 m
25 m
Uphole lift
Downhole liftsNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 275
Figure 24-7 Generic downhole stope activity sequence
24.3.2.2.1.1 Primary/Secondary Sequence
The primary secondary sequence extracts the first pass of stopes to full-height (4-lifts, 100 m) stopes,
mining every second stope along strike (the primary stopes), with alternating pillar between. The pillars are
extracted later as the secondary stopes after sufficient stope voids complete paste backfilling.
The primary/secondary sequence has advantages:
- Quick ramp-up of production rate after stoping commences. Minimal interactions between
primary stopes due to the pillars in between each.
- Lower strength paste backfill or waste rock from development, can be applied in secondary stopes,
to reduce cost (although not considered in this assessment due to the low level of the study).
Lower
Middle
Upper
1
2
3
4
5
6
–
–
Boxhole Drilling
Blast, Mass
–
–
Loading
Loading
Loading
Loading
Boxhole Drilling
Boxhole Drilling
–
–
Prod. Drilling
Prod. Drilling
Blast, Slot
Blast, for Void
Lower
Middle
Upper
12
–
7
8
9
10
11
Loading
Loading
Loading
Loading, Cleanout
Paste Fill
–
Paste Fill
Fill Capping
–
–
–
–
Paste Fill
–
Blast, Slot
Blast, for Void
Blast, MassNI 43-101 Technical Report (March 2021) Wassa Gold Mine
The primary/secondary sequence has disadvantages:
- Creates higher mining induced stress conditions in the pillars which can be problematic during
extraction of the secondary stopes and potentially the primary stopes.
- Mining rate during latter stages of the block is reduced as extraction of the sill pillars cannot
commence until late in the block life as a higher proportion of the block tonnes need to be
extracted to create sufficient distance between active secondary stopes and those extracting the
sill pillar.
Primary-secondary is applied in the upper parts of the Southern Extension zone as it enables rapid ramp-up
of the underground mining rate to match the plant capacity but is limited to approximately 1,000 m depth
where the induced stress conditions have been assumed to prevent use further down. This aligns with the
bottom of Panel 6 at -30 mRL.
Figure 24-8 shows progression of the generic primary/secondary sequence:
- First stope is generally located centrally in the block and the mining front advances to north and
south, with primary stopes mined 4-lifts high (100 m).
- Secondary stopes follow the primary stope front with a lag distance of 120-140m along strike to
create sufficient buffer between active primary stopes, development of secondary crosscuts and
extraction of secondary stopes, a large distance (120-140m).
- Secondary stopes are constrained to two lifts per stope, to limit exposure dimensions of the paste
fill mass in stope walls.
- Extraction of the sill pillar commences when there is a sufficient distance from secondary stopes in
the blocks above and below. Each crosscut into the sill pillar is scheduled to be redeveloped in time
for the uphole stopes to be mined.
- This resulting sequence has primary stope extraction almost, if not fully, complete before the first
secondary stope is mined; it creates a production profile which is high in the early years of primary
stoping, slows as secondary stopes are mined and becomes low when the block is only producing
from stopes in the sill pillar.
Figure 24-8 Primary/secondary stope extraction sequence, transverse stopes
Page 276NI 43-101 Technical Report (March 2021) Wassa Gold Mine
24.3.2.2.1.2 Pillarless Retreat Sequence
The pillarless retreat sequence extracts all stopes in single-pass fronts to the north and south. No pillars
are left, with each stope mined directly alongside the fill mass of the stope before.
The pillarless retreat sequence has advantages:
- Reduced step-out distance and removal of pillars/secondaries, will improve redistribution of mining
induced stress.
- Not needing a second-pass mining front for secondary stopes, permits earlier extraction of the sill
pillar which creates a more consistent production profile over the life of the production block and
improves management of induced stress in the sill pillar.
The pillarless retreat sequence has disadvantages:
- Slower ramp-up of the production rate, although more consistent across the life of the block.
- Requires high-strength paste backfill in all stopes as they will all have sidewalls exposed.
Pillarless Retreat is applied in the deeper parts of the Southern Extension zone as it better manages mining
induced stress. In this assessment, the transition point is assumed to be approximately 1,000 m depth but
will require refining as the study progresses and the in-situ stress field and response to mining is better
understood. The change to pillarless retreat is at the top of Panel 7. Figure 24-9 shows the stages of the
pillarless retreat sequence used in the design:
- The two single-pass stoping fronts start roughly in the centre and retreat to the block peripheries.
- The downhole stopes are two lifts high (50 m).
- Extraction of the sill pillar commences when there is a sufficient distance from each of the active
stope fronts. Crosscut development in the top level of the block will then be re-developed or
rehabilitated after the risk of undercutting the block above has been eliminated.
Figure 24-9 Pillarless retreat stope extraction sequence, transverse stopes
Page 277NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 278
24.3.2.2.2 Longitudinal Stoping
Longitudinal stopes are applied for stopes less than 15 m. The narrower width enables each stope to be
mined from a single ore drive along the strike of the mineralization. Apart from the access direction,
extraction methodology will be consistent with that used for transverse stopes, with the exception that
trough will not be left for the bottom lifts, rather they will be silled out prior to blasting the downholes
above.
Longitudinal stopes will be sequenced such that the first stope will be up to 4 lifts high, and thereafter two
lifts, in the same arrangement as the Pillarless Retreat sequence for transverse stopes.
24.3.2.2.3 Wide Width Mining
In sections of the deposit wider than 30 m, multiple transverse stopes must be sequenced across the
deposit width. In these circumstances, a 10m thick pillar between parallel stopes is left insitu. This means
that primary stopes always contain four rock walls, and secondary stopes contain up to two paste filled
walls. Figure 24-10 shows a generic arrangement for wide width mining.
Figure 24-10 Generic wide-width mining (illustration not to scale)
24.3.2.3 Stope Design
Mine design for Panels 4-8 was completed by AMC Consultants in October 2020, under direction of the
Golden Star corporate technical services team.
Optimal stope shapes were developed from the Mineral Resource block model using MSO software
consistent to the same methods applied to Panels 1-3.
The MSO inputs were:
- Cut off Grade: 2.3 g/t Au in Panels 4 and 5, 2.9 g/t Au in Panels 6, 7 and 8
- Stoping width (minimum/maximum): 5 m – 30 m
- Minimum pillar between adjacent stopes: 10 m
- Minimum hanging/foot-wall dip angle: 80°
Optimization shapes were validated by manual checks to remove outliers.
“Split” 1
“Split” 2
“Split” 1
“Split” 2NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 279
24.3.2.4 Modifying Factors
The modifying factors applied to the in-situ stopes tonnes and grade are shown in Table 24-1 and are
reflected in the stope inventories contained in the PEA production plan.
Table 24-1 Stope Modifying Factors contained in the MSO settings
Modifying Factor
Panels 4 – 6
Panels 7 & 8
Dilution
7.5% at 0.0 g/t Au
13.0% at 0.0 g/t Au
Stope Recovery
95%
75%
Panels 4, 5 and 6 have had modifying factors applied which are approximate the operating mine’s
performance with increased dilution, which is considered appropriate to reduce scheduled stope grades
reported from the Inferred Mineral Resource.
Panels 7 and 8 have had more conservative modifying factors applied for the following reasons:
- Geotechnical conditions are not well assessed in the deeper panels and mining conditions may
negatively impact dilution and recovery; and
- Definition drill hole spacing in Panels 7 and 8 is wider than above and the application of more
conservative factors is considered prudent.
The conservative modifying factors applied to Panels 7 and 8 are a major mitigant of the resource risk
inherent to the PEA. Reducing stope recovery by 20%, compared to factors applied in the upper panels,
reduces planned gold production by approximately 500-550 koz.
Development in mineralization above the cut-off grade has been assigned 30% dilution in all Panels to
reflect a lower grade delivered to the ROM, consistent with the treatment of stopes.
Table 24-1 shows the conversion of the Inferred Mineral Resource in each panel after application of cut-off
grades and modifying factors. The proportion of contained metal converted to the PEA mining plan
appropriately considers geological risk, with 54% of metal included in the PEA inventory in Panels 4 and 5
where there is more definition drilling, which decreases to 48% for the deeper panels 7 and 8 where
definition drilling is widely spaced.
Table 24-2 Conversion of Inferred Mineral Resource to PEA inventory
Units
Panel 4
Panel 5
Panel 6
Panel 7
Panel 8
Total
Inferred Mineral
Resource,
in-situ
Mt
7.8
11.5
8.6
19.6
18.6
66
Au g/t
3.0
3.1
2.7
4.0
3.6
3.4
Moz
0.76
1.14
0.74
2.52
2.14
7.3
PEA Inventory
Mt
4.1
5.5
3.1
9.4
7.8
30
Au g/t
3.3
3.5
3.7
4.3
3.8
3.8
Moz
0.42
0.61
0.37
1.31
0.94
3.6
Conversion to PEA
Inventory
%Moz
54%
49%
48%
50%
Cut-off Grade
Au g/t
2.3 g/t
2.9 g/t
–
Modifying Factors,
Stopes
7.5% Dilution
95.0% Recovery
13.0% Dilution
75.0% Recovery
–
24.3.2.5 Development Design
The Southern Extension will be accessed from infrastructure in place for extraction of the Mineral Reserve.
Decline Ramps, ventilation airways and services (power, water, air) are assumed to be pre-existing and
available to use for the access and extraction of the Southern Extension zone.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
24.3.2.5.1 Main Accesses
The Southern Extension zone will be divided into East and West sides with independent decline access on
each. Mineralization has a large plan footprint (up to 850 m along and over 300 m across strike) and dual
access reduces lateral development required to access all of the large footprint and reduces interactions
between production blocks. Ramp grades are 1:7 and have connecting link drives at the bottom of each
block (nominally 125 m vertically). The twin decline approach either side of the deposit enables:
- Definition drilling platforms directly off the decline, rather than establishing large drill-drives into
the hanging-wall as would be the case for a single footwall decline;
- Greater independence between production blocks, maximizing productivity;
- Simplification of level layouts with greater consistency, particularly for Panels 4-6 where single
access levels would otherwise need to access up to 300 m across the deposit;
- Higher hauling capacity, enabled by establishment of a one-way hauling loop in the two ramps to
surface and the resulting efficiency improvements;
- Improved long term infrastructure stability by keeping ramps and shafts well distanced from
production areas, compared to a single decline position, if it were more centrally located; and
- Secondary egress from the mine.
Figure 24-11 shows the east decline and its mining areas and Figure 24-12 shows the west.
Figure 24-11 East decline, oblique looking north-west
Page 280NI 43-101 Technical Report (March 2021) Wassa Gold Mine
The east ramp will take-off from the main decline at the southern end of Panel 2 in the current mining
zone, and the west ramp will connect from the 570-DDD hanging-wall drill drive being developed for
definition drilling of Panels 4 and 5. Design of these connections will be optimized as the project progresses
and deposit knowledge increases.
Each ramp is positioned to cover the strike length of mineralization down to approximately 1,500 m depth.
Ramps will have long straights running roughly parallel the strike of the deposit, providing good coverage
for definition drilling platforms and improved mining efficiency with better traffic management, reduced
truck driveline wear and more efficient/effective road maintenance.
Figure 24-12 West decline, oblique view looking north-east
24.3.2.5.2 Production Blocks
Stopes will be grouped into production blocks. Each block is designed to be mined independently of
neighbouring blocks, separated with respect access, geotechnical and ventilation aspects.
The preliminary geotechnical assessment recommended that to be independent, blocks should be
separated by at least 40 metres horizontally and on level (25 m) vertically. Natural boundaries between
mineralized areas generally permit independence between blocks, but where mineralization is more
continuous, pillars are placed throughout the mining areas to create independence between blocks and for
managing stope heights.
Page 281NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Production blocks have been designed with independent infrastructure for ventilation and materials
handling, to support rapid stope turnover. The consistent layouts, facilitate mining and scheduling
repeatability, improving efficiency. The main features of production blocks include:
- Separable ventilation network, separated from the decline and other blocks, which delivers fresh
air to the working levels via intake raises connecting to footwall accesses at the end of the block.
This ensures the active stope headings, where most work outside of air-conditioned cabins occurs,
will receive first use of the fresh air. In contrast, if the decline is used to distribute fresh air, air
would be contaminated by equipment in the decline before reaching the stope headings, which
would reduce its cooling efficiency.
- Dual-purpose orepass/return ventilation raise:
o Exhaust point for each level, connecting to the return air network via the bottom level of
the block, facilitating removal of dust generated in the pass directly with return air flows
from the block. The dual-purpose system is designed to rationalize the number of airways
and will be achieved by through the use:
▪ Regulators on the bottom level to manage the total airflow through the block;
▪ Ore sizing rings on top of the finger raise at each tipping point, to regularize block
airflow shared between each level;
▪ Plug covers in orepass fingers to isolate level flow as required; and
o Decouples truck loading activities from stope loading on the levels above, specifically
remote loading and potential automation applications.
- Ore bin between the bottom level and the truck haulage level below, separate from the ore-pass
system, remove the constraint where the loading rate on the bottom level may be constrained if
the orepass is filled with material from levels above; and
- Footwall access drive, parallels the strike of mineralization for cross-cut access and grade-control
drilling. Footwall drives are stood-off from mineralization minimum 25 m.
The generic set-out of the production blocks has a significant benefit that it is modular and can be designed
to match the geometry of the defined mineralization. Similar concepts are applicable whether the stope
groups are anywhere from 150 m, up to 500 m along strike. This makes the layout particularly suitable to
represent future production layouts in Panels 6-8 where drilling density of the Inferred Mineral Resource is
low and there remains likelihood that with more drilling, interpretation of the mineralization geometry will
change. This is contrary to other design layouts which could have shown increased development and cost
efficiency but would have been reliant on large continuous zones of mineralization.
The consistent layout of production blocks means they will generally be developed in a consistent
sequence:
- Phase 1:
Capital development on top and bottom levels of the block are prioritized to access ventilation
positions and platforms for resource infill drilling (refer Section Geological Definition Drilling).
- Phase 2:
Remaining footwall and other level capital development is completed to access intake and exhaust
airways, including the orepass.
Concurrently, the main intake and exhaust airways are developed.
Haulage and truck loading development is completed below the block.
- Phase 3:
Grade control drilling is done from the footwall drives, targeting an inventory of three years stoping
to defined, ready for production.
Internal block ventilation airways (including dual-use orepass and fingers) are constructed to
prepare the block for operations.
Page 282NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Operating stope crosscuts and ore drives, will be mined just in time within the stope production
cycle. Opportunities to improve the crosscut layouts and “stubbing in” with footwall drive
development (to minimize interruptions during production phase) will be addressed in future work.
Figure 24-13 shows a generic longitudinal view of a production block, showing the ventilation connections
and infrastructure arrangement. Figure 24-14 shows an indicative production block level (295 mRL) and the
consistent layout features which are applicable, regardless of production tonnage in the block. It also
highlights the spread of mining areas in Panels 4 and 5 and suitability of access with two declines which
simplifies the level layouts.
Figure 24-13 Generic production block layout with primary/2ndary sequence and vent flows, longitudinal view
Page 283NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 24-14 Level layout (295 mRL) showing deposit width and twin decline arrangement, plan view
24.3.2.5.3 Truck Haulage and Connecting Link Drives
The east and west declines will be connected, nominally every 125 m vertical height with truck loading
infrastructure positioned on connecting levels. These levels, along with the two declines, are used to
create one-way haulage which results in efficient traffic management and haulage cycle times. The
connections will also create secondary means of egress, i.e. there are two directions to travel in to exit the
mine from any production block in production.
On each haulage level there is at least one truck loading position on each side of the deposit, where passes
will deliver material dumped by loaders on the levels above. The load out arrangement consists of a truck
loop mined around the bottom of the two ore bins which sit between the bottom level of the block above
and the truck haulage so that each bin has sufficient volume to facilitate process separation between stope
and truck loading. The truck-loading horizon is approximately one level below the bottom stoping horizon
of the block.
Truck loading at the bottom of passes will be amenable to the use of loading infrastructure (eg: feeder) but
this assessment simplistically assumes trucks are filled by loaders as this best represents current processes
in Panels 1 and 2 upon which the cost estimate is based. Loading bays are designed with an elevated
loading position, to maximize loading efficiency. Trade-off studies are required as the project progresses to
evaluate the automated loading infrastructure which where production block tonnages are sufficient to
justify the establishment cost.
Figure 24-15 shows a haulage level arrangement with the level connection between the two declines.
Page 284NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 24-15 Haulage level arrangement, 470 mRL
24.3.2.6 Geological Definition Drilling
Definition drilling of the Southern Extension Panels will be drilled progressively as the declines advance.
Drilling is planned in three different categories:
- Resource Development: intended to upgrade Inferred Mineral Resource to Indicated. Timing is to
be completed ahead of capital investment for mining panel (decline and access development) and
will occur as the western decline reaches the top of each new Panel. The intent is to mitigate
capital risk by providing at least an indicated confidence level in each Panel before committing to
progressing the decline.
- Resource Infill: increase drill density of Indicated Mineral Resource material to reduce spatial risk to
permit accurate development positioning. Timing is to provide a drilled inventory 2-3 years ahead
of stoping.
- Grade Control: final drilling before stope block is ready for production. Drilling will be from
footwall accesses on each level and timed to ensure that the following year’s production is drilled
to the highest confidence classification (1-1.5 years drilled inventory). The intent is enabling the
geological controls to be defined and minimize grade risk for the upcoming budget year.
Approximate locations of Resource development drilling platforms are shown in Figure 24-16. This drilling,
along with Resource infill drilling, will be done from diamond drilling platforms mined off the western
decline and will provide up to 50% of the total pierce points.
Page 285NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 286
The drilling profile and Panel stope timing is outlined in Table 24-3. Resource development drilling will be
done in time to allow the declines to advance continually.
Figure 24-16 Oblique view, approximate Resource development and infill drilling horizons, looking north west
Table 24-3 Proposed Resource diamond drilling quantities relative to stope timing by Panel
Activity
Quantity
Units
Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y8 Y9 Y10 Y11 Y12 Y13 Y14 Y15 Y16 Y17 Y18
Drilling
Resource Dev’t & Infill
749
‘000m
32 61 45 77 48 81 79 69 53 66 65 50 23
Grade Control
424
‘000m
2 5 17 31 34 36 36 38 38 37 36 35 30 12
Stopes in Production
Panel 4
3.8
Mt
Panel 5
5.2
Mt
Panel 6
2.9
Mt
Panel 7
8.6
Mt
Panel 8
7.2
MtNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 287
24.3.2.7 Design Quantities
The design quantities for Panels 4-8 for the Southern Extension Zone are summarized in Table 24-4.
Table 24-4 Wassa Panels 4-8 mine design quantities
24.3.3 Geotechnical
The approach to the geotechnical assessment for the Southern Extension is consistent with Panels 1-3.
The geotechnical data set is considered appropriate for this assessment. Data from drill hole logging, face
mapping and other sources, will continue to be collected as the Southern Extension potentially progresses
through the project development and production stages.
24.3.3.1 Geotechnical Data
24.3.3.1.1 Drill Hole Database
In the Southern Extension zone, the geotechnical drill hole database includes 89 holes and 60,196 m of
core.
- Rock Quality Designation (RQD) has been logged for all core; and
- Joint Set Number (Jn) has been logged for 57,141 m of core.
Figure 24-17 shows the drill holes with RQD values assigned. Colour range is from blue, showing good
quality or competent rock, through to red showing low quality or weak rock.
Southern Extension Zone
Panel 4
Panel 5
Panel 6
Panel 7
Panel 8
Mined to ROM, Stopes
‘000 t
3,797
5,212
2,914
8,623
7,151
g/t
3.32
3.51
3.73
4.38
3.83
‘000 oz
405
587
349
1215
881
share% oz
12%
17%
10%
35%
26%
Mined to ROM, Development
‘000 t
161
250
167
783
594
g/t
3.00
3.12
2.88
3.64
3.18
‘000 oz
15.5
25.0
15.5
91.8
60.6
Mined to ROM, Total
‘000 t
3,958
5,461
3,081
9,406
7,744
g/t
3.31
3.49
3.68
4.32
3.78
‘000 oz
421
612
365
1,307
942
Development, Total
m
25,522
34,351
19,955
51,854
36,161
Dev’t Capital
m
13,648
16,356
12,178
24,031
17,415
Dev’t Operating
m
11,874
17,996
7,777
27,824
18,746
Vertical Development
m
3,943
4,623
2,616
5,255
3,176
Mined to Waste
‘000 t
1,638
2,205
1,281
3,329
2,321
Paste Backfill
‘000 m3
1,059
1,454
813
2,405
1,995NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 24-17 Geotechnical drill hole data in Southern Extension, plan (left) and longitudinal (right) views
(OreTeck, 2020)
Spatial density of the geotechnical logging data set was measured by calculating the distance from each 5 m
grid point in the rock mass model to the nearest neighbouring point. Stope blocks were then classified by
the spatial density of material within the stope shape, with the results classified into four categories:
- Good: stope <=30 m from a geotechnically logged hole;
- Medium: stope 30-60 m from a geotechnically logged hole;
- Low: stope 60-90 m from a geotechnically logged hole; or
- Insufficient: stope >90 m from a geotechnically logged hole.
The data density is generally Good to Medium for the higher Panels 4 and 5. The deeper panels 6-8 have
Low to Insufficient data density, which is commensurate with the wider drill hole spacing at depth. The
density is acceptable for this assessment but further data will be required as the project progresses.
Additional drill hole logging will also require additional parameters to inform higher level geotechnical
assessments:
- Q values;
- Rock Mass Rating (RMR); and
- Geological Strength Index (GSI).
24.3.3.1.2 In-Situ Stress
In-situ stress measurements have been collected and are discussed in Section 16.3.2.2, along with the
interpreted in-situ stress gradient.
Figure 24-18 shows the Wassa in-situ stress gradient and reference lines for mines and regions which
experience various levels of in-situ stress damage.
The interpreted principal stress gradient is based on a single data point and, whilst suitable for this
assessment, it is considered indicative only. As the project progresses, additional in-situ stress
measurements will required to better inform the geotechnical interpretation.
Based on Figure 24-18, the onset of stress damage can be expected at depths around 800 m to 1000 m
below surface. The mine plan in this assessment includes a change from primary/secondary stope
sequencing to pillarless retreat sequencing at this depth to manage the impact of mining induced stress and
potential seismicity.
Page 288NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 289
Figure 24-18 Wassa preliminary principal stress gradient with reference mines and regions (OreTeck, 2020)
0
200
400
600
800
1000
1200
1400
1600
0
50
100
150
200
Magnitude (MPa)
Principal Stress with Depth
Mine A – Low stress damage
Mine B – High stress Damage
Mine C – Low stress Damage
Yilgarn (Westeran Australia)
Sudbury (Ontario Canada)
Wassa Mine Stress Gradient
Wassa 645 Site 1 Stress Measurement
Wassa 570 Site 2 Stress Measurement
Depth below Surface (m)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
24.3.3.2 Geotechnical Rock Mass Model
A geotechnical rock mass model was created for the Southern Extension using the geotechnical drill hole
database. The rock mass model includes data for RQD, field strength estimates and Joint Set Number (Jn)
with estimates of Barton’s Q values, Q’ (Barton et al, 1974), GSI and RMR rock mass characterization
systems. A plan view and cross section of the point model is shown in Figure 24-19.
Figure 24-19 Geotechnical rock mass model in Southern Extension, showing Q-prime in plan (left) and cross-section
(OreTeck, 2020)
24.3.3.3 Geotechnical Design, Stopes
The Modified Stability Graph (MSG) method (Matthews, 1981; Potvin, 1988) described in 16.3.2.5.1 was
used to assess the Southern Extension stope stability.
Observations from the site Ground Control Management Plan for Joint Roughness (Jr) and Joint Alteration
(Jw) were applied in the rock mass model to calculate Q-prime in the Matthews modified stope stability
assessment to determine stable, unsupported stope side-walls (hanging) and crowns. The RQD values were
used to estimate Barton Q values to calculate the stable stope dimension.
Modifying factors, B and C described in Section 16.3.2.5.1 were adopted for the Southern Extension.
Modifying factor, A, which accounts for induced mining stress and intact rock strength, was adjusted with
increasing depth, using the overburden weight and depth of stoping below surface. This approach will be
refined to include the in-situ stress gradient once additional in-situ stress measurements are available.
Numerical modelling will be required to determine the expected mining induced stress field at increasing
mining depths.
24.3.3.3.1 Panels 4 and 5
The preliminary stope stability parameters for transverse and longitudinal stopes in Panels 4 and 5 of the
southern extension are summarized in Table 24-5 and Table 24-6.
The unsupported stable design hydraulic radii are plotted on the stope stability curve shown in Figure 24-20
for expected rock mass conditions and current design stope hanging-wall geometries are summarized in
Table 24-7.
Page 290NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 291
Table 24-5 Modified Stability Number (N’) for Panels 4 and 5, transverse stopes (after Potvin, 1988)
Table 24-6 Modified Stability Number (N’) for Panels 4 and 5, longitudinal stopes (after Potvin, 1988)
Parameter
Stope Wall, Transverse
Comments
Back
Side (Hanging)
Q’
50
50
From Rock Mass Model values
UCS, Sigma C
Mpa
130
130
Depth
m
850
850
At 170 mRL
Max. Principal Stress, Sigma
1
Mpa
25
25
Estimated overburden stress,
subject to in-situ stress measures
Stress : Strength Ratio
1:
5.2
5.2
Factor A
0.6
0.6
Angle between Stope Face &
Daylighting Joint
15°
15°
Critical Joints, based on Panels 1-3
Factor B
0.2
0.2
Average dip of stopes is 70°
Potential Failure Mode
Gravity
Slabbing
Gravity or Slabbing
Dip of Stope Face
0°
75°
Hanging-wall dip angle from initial
MSO stope shapes
Factor C
2
6.4
N = Q’ x A x B x C
12
38
Expected Stable Hydraulic Radius
6.3
10.1
Parameter
Stope Wall, Longitudinal
Comments
Back
Side (Hanging)
Q’
50
50
From Rock Mass Model values
UCS, Sigma C
Mpa
130
130
Depth
m
850
850
At 170 mRL
Max. Principal Stress, Sigma
1
Mpa
25
25
Estimated overburden stress,
subject to in-situ stress measures
Stress : Strength Ratio
1:
5.2
5.2
Factor A
0.6
0.6
Angle between Stope Face &
Daylighting Joint
15°
15°
Critical Joints, based on Panels 1-3
Factor B
0.2
0.5
Average dip of stopes is 70°
Potential Failure Mode
Gravity
Slabbing
Gravity or Slabbing
Dip of Stope Face
0°
75°
Hanging-wall dip angle from initial
MSO stope shapes
Factor C
2
6.4
N = Q’ x A x B x C
12
96
Expected Stable Hydraulic Radius
6.3
13.8NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 292
Figure 24-20 Unsupported stable stope spans for expected rock mass conditions and current design hydraulic radii
(Mathews, 1981; Potvin, 1988)
Table 24-7 Stable stope dimensions, Panels 4 and 5
24.3.3.3.2 Panels 6-8
Insufficient geotechnical data is available in Panels 6-8 to conduct the assessment done for panels 4 and 5.
Geotechnical conditions have been assumed to be consistent with the panels above so similar design
criteria have been assumed, with additional consideration for in-situ stress conditions requiring a change in
mining method at depth.
Stopes in Panel 6 have been designed using the Panel 4 and 5 dimensions, recognizing that Panel 6 is lies
between 800 and 1,000m depth. Further studies may recommend that this panel use pillarless retreat
sequencing or shorter primary stope heights.
The vertical stable stope spans for Panels 7 and 8 have been reduced to 50 m based on the empirical stable
stope span assessment, which considers the increased maximum mining induced stress with depth.
Changing the stope sequence to Pillarless Retreat will also be required to manage mining induced stress.
Unsupport Stable Transverse HW
Unsupport Stable Longitudinal HW
Unsupport Stable Transverse Design (HW)
Unsupport Stable Longitudinal Design (HW)
Stope Dimension
Transverse Stope
Longitudinal Stope
MIN
MAX
Design
MIN
MAX
Design
Primary 2ndary
Height
m
25
100
100
50
25
50
25
Strike Length
m
20
20
20
20
<60
75
60
Width across Strike
m
15
30
30
25
<15
15
15
Dip, end/side-walls
75°
75°
75°
75°
75°
75°
75°NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 24-21 contains a heat map of the stope unsupported hydraulic radii determined by the geotechnical
assessment.
Figure 24-21 Unsupported hanging-wall stable hydraulic radii for Southern Extension, longitudinal view
(OreTeck, 2020)
24.3.3.4 Mining Induced Seismicity
As the Southern Extension is developed and the stoping progresses below 800 m, the risk of strain bursting
could emerge because of the estimated in-situ stress gradient and the competent rock mass conditions and
mining induced seismicity, which may occur. Further assessment and numerical modelling is required to
investigate the expected stress environment and response to mining.
A seismic network of approximately 5 geophones will be completed during mining of Panels 4 and 5 to
establish a seismicity and rock noise baseline. The system will be required prior to commencing below
800-1000 m threshold depth (200-0 mRL). The progression of mining induced seismicity will then be
measured and analysed to provide a better understanding of the rock mass response to ahead of mining in
Panels 6, 7 and 8.
24.3.4 Hydrogeology
In 2019, GSR undertook hydrogeological studies to test hydrogeological conditions in the Southern
Extension zone. Testing identified a fresh rock aquifer with low primary porosity and narrow, higher
permeability zones along discreet zones associated with fracturing/faulting/shearing. These are isolated
and will generally form a very small percentage of the overall rock mass and will only cause localized higher
inflow in the underground workings. Base case modelling indicated that the underground would likely
produce an average of 1,149 m3 /d (13.3 l/s) at the end of the 2021, increasing to 4,250 m3 /d (49.2 l/s) at
the end of 2024.
Page 293NI 43-101 Technical Report (March 2021) Wassa Gold Mine
24.3.5 Backfill
Backfill for stopes in Panels 4-8 will include both cemented paste and unconsolidated rock fill.
24.3.5.1 Paste Fill
Paste backfill is the primary fill system proposed for stopes in Panels 4-8.
Paste will be supplied from the recently constructed plant and properties are assumed to be consistent
with paste filling in Panels 1 and 2.
The increased mining rate is at the upper end of the benchmark capacity which can be supported by the
current paste plant and an allowance for capital expenditure to upgrade capacity is included. This is likely
to be achieved through establishment of new boreholes and distribution, but also may require additional
filtration capacity in the plant.
24.3.5.2 Rock Fill
Rock fill is also planned in Panels 4-8 primarily as a method of disposing development waste to avoid
hauling to and dumping at surface.
Waste rock can be dumped in the following stope void types, without the resulting fill mass negatively
impacting neighbouring stopes:
- Secondary stopes which are at least two lifts above a sill pillar;
- Secondary stopes with no planned stoping immediately below;
- End stopes in any sequence with no planned stoping alongside; or
- Where waste rock can be integrated into the fill mass by placement during the paste fill cycle
(eg: core and shell), although this results in extending duration of the fill cycle due to the relatively
slower rate of waste rock generation, compared to paste filling.
24.3.6 Ventilation
Initial development of the Southern Extension zone will utilize the Panel 2 ventilation circuit, which will
require the intake and exhaust shafts planned for construction in 2021/22 to be increased to 6.0 m
diameter.
The ventilation design for Panels 4-8 includes the following high level concepts:
- Duplicated infrastructure on the east and west sides of the mine.
- One each side of the mine, two intake/exhaust circuits:
o Decline circuit: intake via the decline ramp and exhaust via series of raises connected to the
decline. This circuit supports advancing the decline ramp face and ventilation of activity on
the decline itself; and
o Production circuit: intake raises will deliver fresh (possibly refrigerated, depending on
timing) air to the block for first use on the levels, and exhaust via a series of raises,
connected to the bottom level of the block.
These circuits will connect to the main ventilation infrastructure which will consist of 5.0-6.0 m diameter
shafts to surface for intake and exhaust, pending geotechnical assessment of unsupported diameters.
Ventilation quantities have been determined using 5.5 m diameter main infrastructure shafts.
Page 294NI 43-101 Technical Report (March 2021) Wassa Gold Mine
24.3.6.1 Main Infrastructure
The ultimate ventilation network has been designed to deliver 1,150 m3 /s airflow which is required in 2032.
It will include 3 exhaust shafts and 2 intake shafts, which modelling has assumed as unsupported 5.5 m
diameter shafts, although 6.0 m diameter would improve ventilation efficiency and operating cost, subject
to geotechnical assessment. Figure 24-22 shows the ventilation circuit with main fan installation timing.
The shafts parallel to the production blocks have been modelled at 3.5 m diameter which is considered
appropriate to this level of assessment. However, one of the priority opportunities for future optimization
is to increase these shafts to larger diameters and improve network efficiency.
Figure 24-22 Wassa Panels 4-8, ventilation stages, oblique view
24.3.6.2 Production Block Circuits
A generic production block ventilation set up is shown in Figure 24-23. Each production block will be
serviced by two 3.5 m diameter raises, one each for intake and exhaust which will connect to the main
airways. This diameter was selected to permit construction with a medium size-class raise drill and ensure
no geotechnical risk but requires further investigation to confirm diameter as there are benefits if these
shafts can be developed with larger profiles.
Page 295NI 43-101 Technical Report (March 2021) Wassa Gold Mine
- Intake: air is delivered directly from the intake raise to the working levels where the majority of
work done outside air-conditioned machine cabins is conducted.
This, along with the use of orepasses to remove trucks from the production levels, is a key element
to maximizing ventilation network efficiency. Separating the highest quality air from contaminants
and heat (ie: truck hauling) maximizes the benefit of that air and minimizes energy wasted on
airflow volumes and refrigeration, by moving it to a working area in a haulage decline.
- Exhaust: is via the dual-use orepass, which will connect at the bottom of the block, to the block’s
exhaust raise. A regulator at the base of the raise will control total volume through the block and
flow on the levels above will be controlled by covering the orepass fingers.
Temporary ventilation restrictions will be required to prevent open stope voids short-circuiting the
exhaust system which will likely result in low airflow and failure to remove dust and contaminants
on the level.
With the 3.5 m diameter raises, each block can sustain three simultaneous working levels with 30 m3 /s
(90 m3 /s total) where higher flow rates will require larger diameter, or duplicate, airways. 30 m3/s per
working level is lower than that needed in Panels 1-3 as trucks are not loaded on the level in Panels 4-8.
Reduction of diesel equipment, through full electrification or hybrid units, provides opportunities to further
reduce the airflow demand on each level.
Figure 24-23 Panels 4-8, production block ventilation flows
24.3.6.3 Decline Circuits
Each of the east and west declines will be ventilated with a separate circuit separate from the production
blocks. The decline circuits will be exhausted by a series of raises (either 3.5 m raisebore or 4 x 4 m long
hole raises, depending on length) which will pull up to 190 m3 /s through the decline ramps.
Twin 200 kW fans with 1400 mm low resistance duct will enable secondary vent runs of up to 500 m
between airway extensions (approx. 70 m vertical spacing), assuming 30 m3 /s airflow at the face.
The mine schedule places the highest development priority on the decline ventilation circuit, followed by
advancing the next leg of the decline ramp, then level development to establish the new production block
ventilation circuit.
Page 296NI 43-101 Technical Report (March 2021) Wassa Gold Mine
24.3.6.4 Surface Fans
The Southern Extension primary exhaust fans have been forecast to develop the applied pressures and
require the motor power shown in Figure 24-24, assuming 5.5 m diameter main shafts. Applied pressure
does not include fan losses. Intake fans have been selected to ensure that there is sufficient velocity
maintained in the ramps and across the production levels. Surface fan configurations were not assessed in
this study, however, GSR will seek to standardize its fan motor size across its main fans.
Figure 24-24 Primary fan applied pressure (air density 1.1 kg/m3 ) and motor power (75% efficiency)
24.3.6.5 Refrigeration
A basic climatic study was completed by SRK to estimate the potential for refrigeration, assuming a reject
temperature of 30.0°C as the design limit for acclimated workers.
The heat load associated with the rock mass was not considered in this assessment because of the low
projected virgin rock temperature through most of the mine. Measurements will be required as the
development deepens as the project progresses and a thermal model will be required.
Refrigeration requirements based on heat loads were estimated for:
- Auto compression;
- Electrical equipment (including fans); and
- Mobile equipment.
A psychrometric heat balance was developed to provide a basic comparison, or indication, of a refrigeration
requirement. The three components used for this initial analysis include auto compression, equipment
loads, and the natural cooling capacity of the unrefrigerated air. The calculations and assumptions are on
the mobile fleet schedule; Y13 has the highest refrigeration requirement, which is shown by heat source in
Figure 24-25. Figure 24-26 shows the refrigeration demand over the total scheduled life.
Figure 24-25 Heat loads and cooling summary for Y12 (SRK, 2021)
Page 297NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 24-26 Estimated refrigeration capacity over mine life (SRK, 2021)
24.3.7 Mining Schedule
Mining quantities for Panels 4-8 were scheduled using Deswik software, with spatial links between
development and stoping, and capacity constraints which reflect the methodology and sequence outlined
above.
The key scheduling assumptions applied were:
- Advance rates:
o Single heading: maximum 100 m/mth for decline heading group (face, stockpiles and vent
accesses);
o Multiple heading/Levels: maximum 180 m/mth for groups once primary ventilation is
established past the level;
- Maximum ROM material from a single stope: 2,300 tonnes per day; and
- Total Material Movement: up to 2.7 Mtpa to ROM and 1.0 Mtpa to waste.
Milestones assumed in the scheduling of Panels 4-8 are:
- Year 1: Definition drilling, targeting upgrade of the Inferred Mineral Resource in Panel 4 and 5,
feasibility study for Panels 4 and 5 commences;
- Year 2: Definition drilling and feasibility study for Panels 4 and 5 completed, project approved and
development initiated late in year;
- Year 3: Development commences with some development material to ROM;
- Year 5: Development ongoing, first stope production;
- Year 6: Ramp up of stoping rate;
- Year 7/8: Stoping ramped up and mining rate from Panels 4-8 matches processing capacity;
- Years 9-16: Mining rate to ROM maintained at processing capacity, with reducing development rate
from year 13 onwards; and
- Year 17: Mining complete.
The Southern Extension mining schedule is contained in Table 24-8.
Page 298NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Table 24-8 Wassa mining schedule quantities, Southern Extension PEA
Page 299NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 24-27 Lateral development schedule for Southern Extension PEA
Figure 24-28 ROM material mining schedule for Southern Extension PEA
24.3.8 Mobile Equipment
The mobile equipment fleet for Panels 4-8 is assumed to be the standardized machine types planned for
Panels 1-3. The planned higher mining rate and depth of Panels 4-8, particularly in later years, will require
truck haulage rates to increase well above what is currently required at Wassa – more than four times
higher in peak years.
The haulage plan in this assessment is validated by a haulage simulation completed by SRK in December
2020 (SRK,2020 a & b). Various scenarios were simulated:
- 2020 haulage quantities to calibrate model;
- Comparison of 40 t vs 60 t trucks;
- Limiting haulage capacity for single ramp, hybrid loop consisting of a single decline in the Southern
Extension and dual ramp system above 595 mRL and one-way loop decline configurations; and
- Truck fleet estimation for Panels 4-8 mining schedule.
Page 300NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 301
The results indicated:
- For 40 t trucks in a single decline configuration, the current production rate of 5,000 t/d (1.8 Mtpa)
is approaching the system’s limiting capacity, which supports the planned upgrade to 60 t units;
- Limiting capacity of 60 t trucks with a single decline, is in the order of 7,000 t/d (2.6 Mtpa),
indicating that increasing the mining rate to match installed processing capacity will require the
haulage system to operate at maximum capacity and will realize reduced efficiency due to traffic
interactions in the single ramp;
- Limiting capacity of 60 t trucks with two decline ramps through from the working levels through to
surface, creating a one-way haulage loop, creates a system which is limited only by loading unit
capacity and how many trucks can be supported by the ventilation system. Rates in excess of
10,000 t/d (3.6 Mtpa) should be achievable.
Truck fleet numbers in the mining schedule were calibrated to match the simulation numbers with <1%
variance of truck-years in the two estimates.
The fleet schedule for Panels 4-8 is shown in Table 24-9.
Table 24-9 Mobile fleet schedule, Southern Extension PEA
24.3.9 Mine Services
24.3.9.1 Dewatering
This study assumes pumping stations will be installed similar to the one recently constructed at the
620 mRL, which will pump approximately 400 m vertically to surface. Similar stations will be required
around the 220, -180 and -500 mRL levels. The base case simplistically assumes these stations pumping in
series, but more optimal solutions are likely to be developed as the project progresses.
24.3.9.2 Electrical
Panels 4-8 will connect into the 11 kV circuit at 570 level ring main unit, which is supplied 8.0 MVA from
surface. The 11 kV circuit will be extended throughout the Southern Extension using substations
(11 kV/1 kV 2.0MVA) placed every 5-6 levels which will result in approximately one substation per
production block. The Southern Extension will continue to use 1 kV distribution to electrical starter boxes
for equipment, fans and pumps.
The surface electrical infrastructure network is expandable to allow for increased loads in the mine
required for additional work areas or increased electrification (eg: electric trucks), defined as “Phase 2
expansion” in Figure 24-29. Phase 2 can incorporate an 11 kV ring main. Further work is required to define
and schedule electrical loads which will then define the requirement for the Phase 2 expansion.
–
–
2
2
6
6
6
6
6
6
6
6
5
3
2
2
2
–
–
–
–
1
2
4
4
4
4
4
4
4
4
4
4
2
–
–
1
1
3
3
6
6
6
6
6
5
5
5
4
4
3
–
–
1
1
5
7
12 13 15 15 16 18 19 17 17 18 10
–
–
1
2
7
8
14 14 14 14 14 14 13 12 11 11 6
Machine Type
Development Jumbo
Production Drill
UG Loader
UG Truck
ROM & Ancillary
Y1
Y2
Y3
Y4
Y5
Y6
Y7
Y8
Y9
Y10
Y11
Y12
Y13
Y14
Y15
Y16
Y17NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Abbreviations: kV: kilo-volt; kVA: kilo-volt
amperes; MVA: mega-volt amperes; Sub:
sub-station; RMU: ring main unit
Figure 24-29 Electrical distribution with Phase 2 expansion required to support Southern Extension
24.3.9.3 Other services
Compressed air and water supply for each decline will connect from Panel 2’s circuit. Additional
compressors for the air circuit and a pressure reduction strategy for the water supply will be determined in
future studies.
24.4 Metallurgical Testing
A test work program was completed in September 2018 characterizing the comminution and metallurgical
performance of samples selected from the Southern Extension. The test work was completed by the
Minerals Engineering Department of the University of Mines and Technology, Tarkwa.
24.4.1 Scope
The metallurgical evaluation test work program included the following investigations:
- Head Assays (gold only);
- Bond Ball Work Index (BBWi);
- Gravity Concentration;
- Leachability vs Grind test work;
- Preg-Robbing Characterization;
- Diagnostic Leaching; and
- Reagent Consumption test work.
Test work details and conclusions are taken from “Profiling of Mining Zones at Golden Star Resources,
Wassa Mine” September 2018.
24.4.2 Sampling and Head Assays
The seven composites were selected from drill core in Lower F Shoot (Pod 1), Upper F Shoot (Pod 2) and B
Shoot (Pod 3). A summary of the selected intervals is presented in Table 24-10 and locations in Figure
24-30.
Page 302NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 303
Table 24-10 Metallurgical Composite Sample Location
Met Sample ID
Hole ID
Interval (m)
Weight (kg)
Grade (Au g/t)
WUG-SLC-18MET001
(Lower F Shoot)
BS17DD385D2
539.0 – 554.2
19.46
1.10
BS17DD385D2
559.0 – 624.4
37.95
4.84
BS17DD385M
1046.0 – 1074.0
32.81
4.16
Total WUG-SLC-18MET001
90.22
3.79
WUG-SLC-18MET002
(Lower F Shoot)
BS17DD385D3
752.0 – 790.0
42.94
7.91
BS18DD388D1
544.3 – 591.0
59.55
2.17
Total WUG-SLC-18MET002
102.49
4.58
WUG-SLC-18MET003
(Lower F Shoot)
BS17DD385D3
790.0 – 885.0
107.35
3.88
Total WUG-SLC-18MET003
107.35
3.88
WUG-SLC-18MET004
(Upper F Shoot)
BS18DD388D2
279.6 – 330.2
57.18
2.96
BS18DD388M
1005.0 – 1042.1
41.92
5.44
Total WUG-SLC-18MET004
99.10
4.01
WUG-SLC-18MET005
(Upper F Shoot)
BS18DD388D2
337.2 – 346.2
10.17
3.13
BS18DD388M
1042.1 – 1077.4
39.89
3.87
Total WUG-SLC-18MET005
50.06
3.72
WUG-SLC-18MET006
(B Shoot)
BS18DD389M
722.0 – 396.1
30.71
4.00
BS18DD389M
766.0 – 351.6
25.59
3.10
Total WUG-SLC-18MET006
56.30
3.59
WUG-SLC-18MET007
(B Shoot)
BS17DD385D1
293.1 – 315.1
24.86
3.89
BS17DD385D1
345.1 – 367.1
24.86
2.71
BS17DD385M
869.2 – 886.0
18.98
2.60
BS17DD385M
915.0 – 929.9
20.23
3.42
Total WUG-SLC-18MET007
88.93
3.18NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 304
Figure 24-30 Metallurgical Sample Drillhole Location
Each composite was crushed and blended, then submitted for assay with results summarized in Table
24-11. There is significant variation in several of the composites between the assay head grade and the
calculated head grade based on weighted core assays. This typically suggests the presence of coarse free
gold within the sample which can cause variance in assay results both within a single blended sample and
between core splits as observed here. This is consistent with operating experience at Wassa underground
mine where there is significant variation in assay repeatability and high gravity recoverable gold content in
both geological and metallurgical samples.
Table 24-11 Metallurgical Composite Head Assay
Met Sample ID
Head Grade
Assay 1
Assay 2
Average
Weighted Avg.
of Intervals
Au g/t
Au g/t
Au g/t
Au g/t
WUG-SLC-18MET001
5.34
5.15
5.25
3.79
WUG-SLC-18MET002
5.09
5.16
5.13
4.58
WUG-SLC-18MET003
4.55
4.47
4.51
3.88
WUG-SLC-18MET004
4.75
5.09
4.92
4.01
WUG-SLC-18MET005
3.78
4.04
3.91
3.72
WUG-SLC-18MET006
4.24
4.01
4.13
3.59
WUG-SLC-18MET007
3.91
3.99
3.95
3.18NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 305
24.4.3 Comminution Tests
BBWi tests were undertaken on all composites at a closing screen size of 106 µm to give a mill product of
around 75-80% passing 75 µm. The results are summarized in Table 24-12.
Similar to the 2015 Feasibility Study test work on samples in the current mining areas, the BBWi results of
13.6-15.7 kWh/t indicate moderate hardness. There is no strong trend of increasing BBWi with depth
based on the current results, shown in Figure 24-31.
Table 24-12 Bond Ball Work Index Results
Met Sample ID
Bond Ball
Average
P80
BBWI
RL
kWh/t
m
WUG-SLC-18MET001
71
15.7
50
WUG-SLC-18MET002
72
14.4
-145
WUG-SLC-18MET003
72
14.8
-295
WUG-SLC-18MET004
65
13.8
50
WUG-SLC-18MET005
71
15.0
-35
WUG-SLC-18MET006
67
13.6
-350
WUG-SLC-18MET007
75
14.7
250
Figure 24-31
Ball Mill Bond Work Index against sample depth (mRL)
24.4.4 Gravity Recovery Tests
Gravity recovery test work was carried out on all seven composites at two different grind sizes (P80 700 µm
or P40 106 µm). The coarser grind represents a typical cyclone underflow feed to a centrifugal
concentrator after screening off the >1.0 mm fraction. The second, finer, feed was tested to establish what
additional liberation of free gold occurs that can be recovered by gravity concentration. All tests were
carried out on a laboratory scale Knelson concentrator.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 306
A summary of the results is presented in Table 24-13. There is some increase in gold recovered to
concentrate for finer ground samples but any consideration of feeding a more finely ground product would
need to assess the overall recovery/cost benefit to the flowsheet.
Table 24-13 Gravity Recovery Gold – Summary
Met Sample ID
Gravity Recovery (%)
P80 700µm
P40 106µm
WUG-SLC-18MET001
40.6
41.8
WUG-SLC-18MET002
29.1
42.3
WUG-SLC-18MET003
15.1
27.7
WUG-SLC-18MET004
19.1
28.0
WUG-SLC-18MET005
24.0
31.2
WUG-SLC-18MET006
16.5
21.6
WUG-SLC-18MET007
19.7
26.8
24.4.5 Leaching Tests
Leaching test work was carried out on all the composites to assess multiple variables including:
- Grind sensitivity;
- Preg-robbing characterization;
- Diagnostic Leaching; and
- Reagent Consumption.
24.4.5.1 Grind Sensitivity
Grind sensitivity cyanide leach tests were done on all composites at three different grinds (P40, P60 and
P80 106µm) for whole of ore feed with otherwise consistent leaching conditions (pH and NaCN
concentration). The grind sensitivity tests were carried out as direct leach only on whole of ore feed (not
gravity concentration tails) and as such, the leach extraction results can only be used for assessment of
relative grind sensitivity. A summary of the results is presented in Figure 24-32.
All composites showed some degree of grind sensitivity with the B-Shoot composites showing the least
variation across grind sizes. Tests utilizing lead nitrate as a leach additive indicated no improvement of
leach recovery or reducing cyanide addition to maintain leach extraction or cyanide concentration.
Figure 24-32 Direct Leach – Grind Sensitivity Summary NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 307
24.4.5.2 Preg-Robbing
Preg-robbing characterization tests were completed on all composites to test for any gold adsorption
potential from naturally occurring organic carbon in the samples. Any gold adsorbed by the naturally
occurring organic carbon presents as unleached gold in tailings. The characterization is achieved by
comparing direct leach gold extraction with carbon-in-leach (CIL) gold extraction as generally activated
carbon can adsorb leached gold-cyanide complexes faster than any naturally occurring organic carbon
resulting in limited ‘robbing’ of the leached gold in solution. The results are summarized in Figure 24-33.
Moderate preg-robbing is observed in the Lower F-Shoot composites, less in the Upper F-Shoot composites
and minimal in the B-Shoot composites. This suggests there may be lithological differences between the
deposit zones or potential for increasing preg-robbing with relative depth.
Figure 24-33 Preg-robbing Characterization Summary
24.4.5.3 Reagent Consumption
Reagent consumption tests were completed under standard leach conditions to establish baseline reagent
consumption data and any trends in consumption across the composites. Results are summarized in Table
24-14.
There was no observable variation in lime consumption across the composites although the natural pH is
trending in the F-Shoot composites compared against the B-Shoot composites. The cyanide consumption is
also relatively higher in the F-Shoot composites. This could be an indication of increased reactive sulphides
in the F-Shoot compared to the B-Shoot.
Table 24-14 Reagent Consumption Summary
Met Sample ID
Reagent Consumption
Natural
Ca (OH)2
CaO eq.
NaCN
pH
Kg/t
Kg/t
Kg/t
WUG-SLC-18MET001
9.1
1.0
0.8
0.17
WUG-SLC-18MET002
9.3
1.0
0.8
0.18
WUG-SLC-18MET003
9.3
1.0
0.8
0.15
WUG-SLC-18MET004
9.3
1.0
0.8
0.19
WUG-SLC-18MET005
9.6
1.0
0.8
0.13
WUG-SLC-18MET006
9.5
1.0
0.8
0.13
WUG-SLC-18MET007
9.6
1.0
0.8
0.14NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 308
24.4.5.4 Diagnostic Leach
A diagnostic leach was completed on the composites. Results are summarized in Table 24-15. Reasonable
variation can be seen in the free-milling component of the composites. As the work was completed on
whole ore and not gravity tailings, depending on the coarse gold component (which is typically difficult to
leach in any reasonable time frame), the ‘free milling’ component could be under-represented.
Table 24-15 Diagnostic Leach Summary
Met Sample ID
Distribution
Free-milling
Carbonates
Sulphides Carbonaceous Quartz Locked
WUG-SLC-18MET001
88.1%
2.4%
4.1%
3.1%
2.4
WUG-SLC-18MET002
84.5%
1.9%
6.3%
4.4%
2.8
WUG-SLC-18MET003
85.4%
1.4%
2.8%
3.8%
6.6
WUG-SLC-18MET004
93.8%
1.2%
2.4%
1.8%
0.9
WUG-SLC-18MET005
89.4%
1.2%
5.1%
2.7%
1.6
WUG-SLC-18MET006
92.2%
0.7%
3.7%
2.0%
1.4
WUG-SLC-18MET007
89.5%
1.1%
4.4%
2.9%
2.2
24.4.6 Test Work Findings
The level of detail, type of test work and sample representivity of the metallurgical tests completed for the
Inferred Mineral Resource which forms the Southern Extension, is sufficient to develop metallurgical
performance criteria to support generation of a plant feed schedule for this preliminary assessment.
Further test work is required to inform future studies and provide the requisite level of confidence as the
project progresses toward any potential development decision.
24.4.6.1 Comminution
The BBWi results for the Southern Extension composites tested are similar to those of the 2015 Feasibility
Study test work, suggesting that the Southern Extension will likely have a similar performance in any
moderate to fine grinding environment as material mined from underground to date.
24.4.6.2 Gravity Concentration and Leaching
Based on a limited number of test samples, the test work results indicate material from the Southern
Extension can potentially deliver similar recovery profiles to material currently processed.
There is some risk evident with all composites showing some level of preg-robbing (very mild to moderate),
although the observed degree of preg-robbing is considered manageable within the existing Wassa process
plant. Further work is required to characterize the issue and better understand the underlying controls
(lithology, depth, zonal). All future test work should be carried out on gravity tails to reduce head grade
variation and provide more definitive leach performance data.
The composites tested were amenable to gravity concentration at coarse feeds typical of cyclone underflow
in the Wassa processing plant. There is a potential opportunity increase gold recovery to concentrate by
changing the concentrator feed stream to cyclone feed rather than cyclone underflow. This can be
assessed in the next phase of work.
Some level of grind sensitivity was observed for the Southern Extension. Additional test work and
cost/benefit analysis is required to select the optimal grind size but tests indicate that material from the
Southern Extension will perform similarly to current material.
Reagent consumption data from the test work is generally aligned with that achieved in the 2015 Feasibility
Study suggesting similar performance to material currently being processed.
The diagnostic leach suggested minor amounts of gold is locked in quartz, carbonaceous material and
sulphides. The latter two can generally be addressed through pre-leach aeration, optimal grind size and NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 309
Carbon-in-leach. Future diagnostic work should be completed on gravity tails rather than whole of ore to
deliver more definitive/absolute performance data rather than relative performance data.
Future leach test work should consider finer grind leach conditions as well as optimizing reagents and
air/oxygen addition on gravity tails. Mineralogy of the gravity tails and leach tails is also required to
support the optimization and diagnostic leach test work.
24.5 Recovery Methods
It is proposed that the Southern Extension will use the same recovery methods as currently employed at
Wassa. No additions or alterations to the processing plant have been assumed in this preliminary
assessment.
Metal recovery calculations through the process plant are consistent with the approach for current
operations with the additional consideration that recoveries for higher grade material are capped at 95.0%.
Further metallurgical testing will seek to confirm and optimized plant configuration for processing material
from the Southern Extension.
The processing schedule is shown in Table 24-16.
Figure 24-34 Processing schedule for Southern Extension PEANI 43-101 Technical Report (March 2021) Wassa Gold Mine
Table 24-16 Processing Schedule, Southern Extension PEA
Page 310NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 24-35 Gold Production schedule for Southern Extension PEA
24.6 Infrastructure
Wassa is an operating site and its installed infrastructure will continue use during the development and
operation of the Southern Extension. Additional capital items for the Southern Extension include:
- Main ventilation fans, described in section 24.3.6.4
- Refrigeration plant, described in section 24.3.6.5
- Potential paste fill expansion, described in section 24.3.5.1
The requirement for an electrical expansion will be assessed during further studies. Section 24.3.9.2
outlines a possible surface and underground configuration. Electrical equipment is included in the scope of
general sustaining capital allowance.
24.7 Environmental, Permitting and Social and Community Impact
The following items are relevant to the PEA:
- Environmental and Permitting
o Permitting: The expansion of underground mining operations outlined in this assessment
are not anticipated to require additional permitting. Whilst this study does indicate a
material increase in production from current levels, it is within the current permitted limits.
o TSF: Planned tailings volumes are will be met by the approved TSF design capacity. The TSF
facility was designed for high tonnage open pit mining and will be sufficient to store the
balance of tailings calculated in the new plan, after accounting for tails solids used in paste
backfill.
o Hydrogeology: Additional modelling for the southern extension is in development and will
continue to inform mine dewatering and water management design.
o Biodiversity: The expansion of underground mining operations outlined in this assessment
are not anticipated to cause further impact to flora and fauna. All proposed surface
facilities lie within previously impacted areas.
- Social and Community Impact
o Resettlement and Compensation: The expansion of underground mining operations
outlined in this assessment is not anticipated to trigger the requirement to resettle people,
with plans for mining, tailings and waste rock storage accommodated by existing permits
and previously compensated lands.
Page 311NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 312
24.8 Closure Planning
Closure costs include all tenure associated with GSWL including Wassa, Hwini Butre and Benso concessions.
The PEA estimates $3.0 M for closure activities associated with the Southern Extension.
24.9 Capital and Operating Costs
Costs for this assessment were estimated using methodology and classification consistent with that applied
to Panels 1-3.
24.9.1 Capital Costs
24.9.1.1 Cost Estimation, Capital
24.9.1.1.1 Major Projects
Estimate basis and timing of major projects required for the Southern Extension are shown in Table 21-1.
Table 24-17 Cost estimate, Major Projects for Southern Extension PEA
24.9.1.1.2 Mine Development
Mine development cost allocations to capital were calculated consistent with the methodology for
Panels 1-3.
Table 24-18 Mine development capital allocation for Southern Extension PEA
Timing
Year
Vent, Fans RAR2
Y4
Vent, Fans RAR3
Y6
Vent, Refrigeration
Y5, 8
Paste Plant, Expansion
Y6
Technical Studies
Y1/2, 6, 10
7,500
Replicate of RAR1, timing from mine schedule
20,000
SRK Report guides 10MWR in 25 and 10WR in 28.
Benchmark estimate of $1M per MWR
7,500
Estimate for expansion of current plant and
distribution in first year of Sth-Ext stoping.
2,400
Technical Studies to progress Southern Extension.
Duplicated for each new phase in Y6 and Y10.
7,500
Replicate of RAR1, timing from mine schedule.
Cost is based on supplier budget quote.
Expenditure
Description
$ ‘000
Lat. Development
–
100% 85% 75% 65% 55% 50% 50% 50% 50% 40% 40% 40% 40% 40% 40% 38%
Cost $M
–
3.1 9.6 12.4 26.6 22.6 21.4 21.7 22.3 22.2 17.9 18.5 16.0 10.5 7.9 7.9 7.5
Vert. Development
–
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
Cost $M
–
0.7 2.5 3.6 9.0 7.8 8.1 8.1 8.1 8.1 8.1 8.1 6.7 4.0 2.7 2.7 2.7
Mine Overheads
–
100% 86% 73% 47% 29%
17%
17%
17%
17%
14%
14%
12%
9%
6%
6%
11%
Cost $M
–
0.1 0.2 0.3 0.7 0.5
1.0
1.0
1.0
1.0 0.8 0.8 0.7 0.5 0.3 0.3 0.4
Refrigeration
–
–
–
–
–
29%
17%
17%
17%
17%
14%
14%
12%
9%
6%
6%
11%
Cost $M
–
–
–
–
–
0.6 0.3 0.7 0.7 0.7 0.6 0.6 0.5 0.4 0.3 0.2 0.4
Total
–
88% 79% 66% 47% 32% 16% 16% 16% 16% 14% 14% 12% 9% 6% 6% 9%
Cost $M
–
3.8 12.3 16.4 36.3 31.5 30.8 31.5 32.0 31.9 27.4 28.0 24.0 15.3 11.1 11.1 11.0
90.8
9.5
6.0
15.8%*
354.5
Total
248.2
Y1
Y2
Y3
Y4
Y5
Y6
Y7
Y8
Y9
Y10
Y11
Y12
Y13
Y14
Y15
Y16
Y17NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 313
24.9.1.1.3 Minor Projects
Minor Projects costs are estimated consistent to methodology used for Panels 1-3 with lower unit costs
resulting from the fixed and variable costs being applied over increased annual production.
Table 24-19 Cost estimate, Minor Projects for Southern Extension PEA
24.9.1.1.4 Mobile Fleet
Mobile fleet categories and machine capacity assumptions are consistent to those applied for Panels 1-3.
Table 24-20 shows the purchases required to deliver the scheduled mining for the Southern Extension.
Table 24-20 Cost estimate, Mobile Fleet addition/replacement schedule for Southern Extension PEA
24.9.1.2 Capital Allocations, Growth and Sustaining
For this assessment of the Southern Extension zone all capital expenditure is allocated to growth until 5% of
the total production inventory is mined and the zone is considered to be in full production.
The allocation methodology of growth capital has an expected accuracy of +/-30%, where the error will
result in misallocation of capital to either of growth/sustaining.
UofM
Mining UG
ug.all.t
Geology UG
ug.ddm.cap
Processing
mill.t
G&A
mill.t
TSF
mill.t.tsf
23,035
Tails Solids to TSF
0.57
12,657
Tonnes Processed
0.31
39,256
Tonnes Processed
0.97
84,943
Total Material Mined, UG
2.10
60,366
Definition Drilling, UG
1.49
Expenditure
Driving Quantity
Resultant Rate
$ ‘000
Description
$/ROM.t mined
Dev Drill
–
–
2
–
–
–
–
1
2
2
1
–
–
–
–
–
–
Cost $M
–
–
2.80
–
–
–
–
1.40 2.80 2.80 1.40
–
–
–
–
–
–
LH Drill
–
–
–
–
1
–
–
–
–
1
1
2
–
–
–
–
–
Cost $M
–
–
–
–
1.40
–
–
–
–
1.40 1.40 2.80
–
–
–
–
–
UG Ldr
–
–
1
–
1
1
2
1
1
1
1
–
2
1
–
1
–
Cost $M
–
–
1.40
–
1.40 1.40 2.80 1.40 1.40 1.40 1.40
–
2.80 1.40
–
1.40
–
UG Truck
–
–
1
–
4
2
3
4
6
2
4
6
7
–
5
6
–
Cost $M
–
–
0.97
–
3.86 1.93 2.90 3.86 5.79 1.93 3.86 5.79 6.76
–
4.83 5.79
–
Ancillary
–
–
1
1
5
1
2
1
–
1
3
3
6
1
2
2
–
Cost $M
–
–
0.40 0.40 2.00 0.40 0.80 0.40
–
0.40 1.20 1.20 2.40 0.40 0.80 0.80
–
Total
–
–
5
1
1 1
4
7
7
9
7
1 0
1 1 1 5
2
7
9
–
Cost $M
–
–
5.6 0.4 8.7 3.7 6.5 7.1 10.0 7.9 9.3 9.8 12.0 1.8 5.6 8.0
–
Total
8
11.2
5
7.0
1 3
96.3
18.2
5 0
48.3
2 9
11.6
105
Y1
Y2
Y3
Y4
Y5
Y6
Y7
Y8
Y9
Y10
Y11
Y12
Y13
Y14
Y15
Y16
Y17NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 314
Table 24-21 Capital cost summary for Southern Extension PEA
24.9.2 Operating Costs
Operating costs are estimated consistent to methodology used for Panels 1-3 with the general trend that
lower unit costs resulting from the fixed and variable costs being applied over increased annual production.
Haulage allowances in the development and operating costs increase significantly over the project as
mining depth increases. Haulage costs start at $3.08 /t in year 2 with 3.3 km average haul, increases to
$5.36 /t in year 9 with 5.7 km average haul and peak in year 16 at $9.01 /t with 9.6 km average haul to the
portal bench.
Costs are added for refrigeration to allow for energy, consumables and maintenance for the refrigeration
plant. Cost estimate is based on indicative benchmark ratios provided by SRK with the ventilation study.
Assumes power cost calculated as 250 kW electrical power per MWR, 8,000 hours per year at a diversity
factor of 0.75 and the Genser supplied power rate of $0.135 /kWh. Allowance of 20% of the power cost is
added for refrigerants, consumables, and maintenance.
Growth
Mine Dev’t
–
3.9 12.8 17.1 40.4 24.2
–
–
–
–
–
–
–
–
–
–
–
Mining UG
–
0.2 0.6 0.9 3.0 6.7
–
–
–
–
–
–
–
–
–
–
–
Def’n Drill
4.5 8.4 6.0 10.3 7.6 8.8
–
–
–
–
–
–
–
–
–
–
–
Processing
–
–
0.0 0.0 0.2
1.0
–
–
–
–
–
–
–
–
–
–
–
G&A
–
–
0.0 0.0 0.2 2.9
–
–
–
–
–
–
–
–
–
–
–
TSF
–
0.1 0.2 0.9 3.5 2.1
–
–
–
–
–
–
–
–
–
–
–
Mob. Fleet
–
–
5.6 0.4 8.7 2.9
–
–
–
–
–
–
–
–
–
–
–
Proj. Vent
–
–
–
7.5 10.0 7.5
–
10.0
–
–
–
–
–
–
–
–
–
Proj. Other
0.4 0.4
–
–
–
8.3
–
–
–
0.8
–
–
–
–
–
–
–
Growth
4.9 12.9 25.2 37.1 73.5 64.4
–
10.0
–
0.8
–
–
–
–
–
–
–
$/ROM.t
–
897 475 343 98.3 61.0
–
3.7
–
0.3
–
–
–
–
–
–
–
$/rec.oz
–
8,896 4,723 3,617 1,004 485
–
34
–
3
–
–
–
–
–
–
–
Sustaining
Mine Dev’t
–
–
–
–
–
7.6 30.8 31.5 32.1 31.9 27.4 28.0 24.0 15.3 11.1 11.1 11.0
Mining UG
–
–
–
–
–
2.1 8.7 8.7 8.7 8.7 8.7 8.6 8.4 7.6 7.3 7.4
–
Def’n Drill
–
–
–
–
–
2.8 11.2 9.7 7.5 9.4 9.3 7.1 3.4 0.1
–
–
–
Processing
–
–
–
–
–
0.3
1.3
1.3
1.3
1.3
1.3
1.2
1.2
1.2
1.2
1.2
–
G&A
–
–
–
–
–
0.9 3.9 3.9 3.9 3.9 3.9 3.8 3.8 3.8 3.8 3.8
–
TSF
–
–
–
–
–
0.7 2.8 2.8 2.8 2.8 2.8 2.6 2.1 1.9
1.9
–
–
Mob. Fleet
–
–
–
–
–
0.8 6.5 7.1 10.0 7.9 9.3 9.8 12.0 1.8 5.6 8.0
–
Proj. Vent
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Proj. Other
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Sustaining
–
–
–
–
–
15.0 65.2 64.9 66.2 65.8 62.5 61.2 54.9 31.7 30.9 31.6 11.0
$/ROM.t
–
–
–
–
–
14.2 24.1 24.0 24.5 24.4 23.3 23.2 20.8 12.7 12.6 12.5 7.7
$/rec.oz
–
–
–
–
–
113 227 220 229 229 172 180 177 108 95
106 76
Total Capital
Grow th
4.9 12.9 25.2 37.1 73.5 64.4
–
10.0
–
0.8
–
–
–
–
–
–
–
Sustaining
–
–
–
–
–
15.0 65.2 64.9 66.2 65.8 62.5 61.2 54.9 31.7 30.9 31.6 11.0
Total
4.9 12.9 25.2 37.1 73.5 79.5 65.2 74.9 66.2 66.6 62.5 61.2 54.9 31.7 30.9 31.6 11.0
$/ROM.t
–
897 475 343 98.3 75.2 24.1 27.7 24.5 24.7 23.3 23.2 20.8 12.7 12.6 12.5 7.7
$/rec.oz
–
8,896 4,723 3,617 1,004 599 227 254 229 232 172 180 177 108 95
106 76
$98.3M
$11.2M
$45.7M
$1.2M
$3.2M
$6.8M
Total
$261.8M
$84.9M
$60.4M
$12.7M
$39.3M
$23.0M
$17.6M
$35.0M
$9.9M
$229M
7.72
66
$228.8M
$560.8M
$790M
26.65
228
$78.7M
–
–
$561M
18.93
162
Y1
Y2
Y3
Y4
Y5
Y6
Y7
Y8
Y9
Y10
Y11
Y12
Y13
Y14
Y15
Y16
Y17NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 315
Table 24-22 Cost estimate, Operating for Southern Extension PEA
Table 24-23 Operating cost summary for Southern Extension PEA
UofM
Mining, Development
m.adv
Mining, Production
stope.t
Mining, Backfill
fill.m3
Mining, Surface Haulage
ROM.t
Mining, Overheads
ug.all.t
Mining, Refrigeration
ug.all.t
Mining, Geology
ug.ddm.op
Processing
mill.t
G&A
mill.t
Refining
rec.oz
15,552
Au Produced
0.38
520,782
Tonnes Processed
12.87
203,111
Tonnes Processed
5.02
39,270
Total Material Mined, UG
1.43
73,430
Grade Control Drilling, UG
1.82
21,554
ROM Material
0.53
54,183
Total Material Mined, UG
1.34
601,928
Stope Material
14.88
123,984
Paste Backfill
3.07
Resultant Rate
$ ‘000
Description
$/ROM.t mined
256,770
Lateral Development
6.35
Expenditure
Driving Quantity
Mining
Dev’t
–
–
1.3 3.5 10.9 18.5 21.4 21.7 22.3 22.2 26.9 27.8 24.0 15.7 11.8 11.8 12.4
Production
–
0.1
–
0.3 8.0 16.7 48.7 50.0 52.7 51.9 52.8 55.3 57.5 56.3 58.0 60.1 33.6
Backfill
–
–
–
0.1 1.7 3.3 10.7 10.7 10.7 10.7 10.5 10.3 11.2 12.1 12.5 12.9 6.8
Surf. Haul
–
0.0 0.0 0.1 0.5 0.9 2.0 2.0 2.0 2.0 2.0
1.9
1.9
1.8
1.8
1.8 0.9
Overheads
–
–
–
–
0.1 0.7 4.8 4.8 4.8 4.8 4.9 4.9 4.9 4.8 4.8 4.9 3.7
Refrig’n
–
–
–
–
–
1.7
1.7 3.4 3.4 3.4 3.5 3.5 3.6 3.8 3.9 3.9 3.7
Geology
–
0.2 0.6
1.8 3.5 6.6 6.6 6.6 6.6 6.5 6.5 6.4 6.2 6.1 5.4 2.8
1.2
Mining
–
0
2
6
25
48
96
99
102 101 107 110 109 101 98
98
62
$/ROM.t
–
20.2 36.0 54.4 32.9 37.8 35.5 36.7 37.9 37.6 40.0 41.8 41.3 40.1 40.2 39.0 51.7
$/rec.oz
–
201 359 574 336 365 334 336 355 353 294 324 353 342 301 331 427
Processing
Processing
–
0.2 0.7
1.5 10.2 14.4 47.4 47.4 47.4 47.4 47.1 46.5 46.7 44.8 44.0 44.9 30.0
Process’g
–
0
1
1
10
14
47
47
47
47
47
47
47
45
44
45
30
$/ROM.t
–
14.0 13.6 13.7 13.7 13.7 17.6 17.6 17.6 17.6 17.6 17.7 17.6 17.9 18.0 17.8 21.0
$/rec.oz
–
138 135 144 140 109 165 161 164 165 129 137 151 152 135 151 206
G&A
Site G&A
–
0.0 0.1 0.3
1.7 2.5 18.5 18.5 18.5 18.5 18.4 18.3 18.4 18.0 17.9 18.1 15.5
Refining
–
0.0 0.0 0.1 0.3 0.6
1.3
1.3
1.3
1.3
1.6
1.5
1.4
1.3
1.5
1.3 0.7
G&A
–
0
0
0
2
3
20
20
20
20
20
20
20
19
19
19
16
$/ROM.t
–
2.8 2.6 2.8 2.8 2.9 7.3 7.3 7.3 7.3 7.5 7.5 7.5 7.7 7.9 7.7 11.3
$/rec.oz
–
28
26
29
28
23
69
67
69
69
55
58
64
66
59
65
111
Total Operating
Mining
–
0
2
6
25
48
96
99
102 101 107 110 109 101 98
98
62
Processing
–
0.2 0.7
1.5 10.2 14.4 47.4 47.4 47.4 47.4 47.1 46.5 46.7 44.8 44.0 44.9 30.0
G&A
–
0.0 0.1 0.3 2.1 3.1 19.8 19.8 19.8 19.8 20.1 19.9 19.7 19.4 19.4 19.4 16.2
Total
–
1
3
8
37
66
163 166 170 169 174 177 176 165 161 163 108
$/ROM.t
–
37.0 52.3 70.9 49.3 62.4 60.4 61.6 62.8 62.5 65.1 67.0 66.4 65.7 66.0 64.6 75.9
$/rec.oz
–
367 520 747 504 496 568 564 588 588 479 520 568 560 496 547 744
$52.8M
$39.5M
$73.4M
Total
$252.3M
$1,166M
$520.8M
$218.7M
$1,905M
64.29
551
151
$203.1M
$15.6M
$219M
7.38
63
$1,166M
39.33
337
$520.8M
$521M
17.58
$602.0M
$124.0M
$21.6M
Y1
Y2
Y3
Y4
Y5
Y6
Y7
Y8
Y9
Y10
Y11
Y12
Y13
Y14
Y15
Y16
Y17NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 316
24.9.3 Closure Costs
The closure cost allowance is the practical closure estimate for Wassa discussed in Section 20.6 plus $3.0 M
for the Southern Extension zone.
Closure costs for the satellite deposits at Benso and Hwini Butre are not included in this assessment.
Table 24-24 Closure cost summary for Southern Extension PEA
Y16
Y17
Y18
Y19
Y20
Y21
Y22
Y23
Y24
Y25
Wassa
–
2.2 3.7 3.7 2.2
1.5 0.7 0.7
–
–
Total
–
2.2 3.7 3.7 2.2
1.5 0.7 0.7
–
–
Total
$14.6M
$14.6M
Y1-15
–
–NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 317
24.10 Economic Analysis
The PEA inventory has been valued using discounted cash flows at an appropriate discount rate to
determine a Net Present Value. The effective date is 31 December 2020.
Sensitivity analyses were performed for variations in gold price, gold grade, gold recovery, operating costs,
capital costs and exchange rates to determine their relative importance as value drivers.
24.10.1 Cautionary Statements
- Certainty of Preliminary Economic Assessment:
The preliminary economic assessment is conceptual. It includes Inferred Mineral Resources that
are considered too speculative geologically to have the economic consideration applied to them to
enable their classification as Mineral Reserve. There is no certainty the preliminary economic
assessment will be realized.
- Mineral Resources Are Not Mineral Reserves:
Mineral Resources are not Mineral Reserves and do not have demonstrated economic viability.
24.10.2 Assumptions
Table 24-25 below shows the key inputs and assumptions used to develop the economic model.
Table 24-25 Key life of mine inputs and assumptions used in the economic model, PEA
Parameter
Unit
Mine Life
years
Underground Mining
ROM, Development
Mt
g/t
cont.koz
ROM, Stope
Mt
g/t
cont.koz
ROM, Total
Mt
g/t
cont.koz
Waste Mined, Total
Mt
Development, Capital
km.adv
Development, Operating
km.adv
Vertical Dev’t, Capital
‘000 vm
LG Stockpile
Mt
g/t
cont.koz
Processing
Throughput Capacity
Mtpa
Au Recovery, Average
%
Au Recovery, Minimum
%
Au Recovery, Maximum
%
Au Produced & Sold
koz
Au Sales
Au Price,Base Case
$/oz
Au Price, Consensus Case
$/oz
Price Escalation
Inflation
%
3,456
1,300
Value
16
–
29.6
3.83
3,644
10.7
83.6
82.5
1.9
3.30
205
27.7
3.86
3,439
2.70
94.8%
–
95.4%
–
–
1,585
166.2
0% (nil)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 318
24.10.3 Stream, Taxes and Royalty
24.10.3.1 Stream
Royal Gold holds a two tier gold stream over the Wassa LOM production:
- Tier 1: delivery of 10.5% of all production at 20% of gold price until 240,000 ounces have been
delivered; and
- Tier 2: delivery of 5.5% of all production at 30% of gold price for all ounces thereafter.
The economic assessment for the PEA assumes remaining balance of the Tier 1 stream is 12,435 oz.
24.10.3.2 Taxes and Royalty
The income tax rate in Ghana is 35% of taxable earnings. The royalty rate is 5% of gross revenue. The
government of Ghana holds a 10% free carried interest in the project. Taxation calculations have been
prepared by GSR based on current application and legislation which may be subject to change beyond the
scope of this assessment.
24.10.4 Economic Results, Base Case
The project is potentially economically viable at the Base Case gold price assumption ($1,300 /oz), with an
after-tax NPV at 5% discount rate, of $ 452.2M (100% Basis). Table 24-28 shows the projected cash flows
from the economic analysis and Table 24-27 presents the detailed results of the evaluation.
Table 24-26 Cash flows, PEA economic analysis – Base Case
Figure 24-36 Cash Flows by Year for Southern Extension – Base Case
Unit
Net Revenue (post Stream)
$M
Operating Costs & Royalties
$M
Cash Flow from Operations
$M
Tax
$M
Capital, Growth & Sustaining
$M
Cash Flow after Tax & Capital
$M
Pre-tax NPV (5%)
$M
Post-tax NPV (5%)
$M
Pre-tax IRR
%
Post-tax IRR
%
+46.7%
+36.8%
852.1
748.7
452.2
Value
4,313.2
1,920.6
852.1
527.2
789.5NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 319
Table 24-27 Economic Analysis – Base CaseNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 320
24.10.5 Economic Results, Consensus Case
The project is potentially economically viable at the Consensus Case long-term gold price assumption
($1,585 /oz), with an after-tax NPV at 5% discount rate, of $ 783.5M (100% Basis). Table 24-28 shows the
projected cash flows from the economic analysis and Table 24-29 presents the detailed results of the
evaluation.
Table 24-28 Cash flows, PEA economic analysis – Consensus Case
Figure 24-37 Cash Flows by Year for Southern Extension – Consensus Case
Unit
Net Revenue (post Stream)
$M
Operating Costs & Royalties
$M
Cash Flow from Operations
$M
Tax
$M
Capital, Growth & Sustaining
$M
Cash Flow after Tax & Capital
$M
Pre-tax NPV (5%)
$M
Post-tax NPV (5%)
$M
Pre-tax IRR
%
Post-tax IRR
%
+65.9%
+53.2%
1,421.0
1,268.8
783.5
Value
5,257.7
1,920.6
1,421.0
853.7
789.5NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Table 24-29 PEA Economic Analysis – Consensus Case
Page 321NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 322
24.10.6 Sensitivity Analysis of the PEA
Sensitivity analyses were completed for the PEA Base and Consensus cases. Results presented are NPV at
5% discount rate, after tax.
Table 24-30 Sensitivity results for the Southern Extension PEA at different gold prices and discount rates
Discount
Rate
1,200/oz
Base
1,300/oz
1,400/oz
1,500/oz
Consensus
1,585/oz
1,600/oz
1,700/oz
1,800/oz
1,900/oz
0%
$653 M
$852 M
$1,052 M $1,252 M $1,421 M $1,452 M $1,629 M $1,807 M $1,985 M
5%
$336 M
$452 M
$568 M
$685 M
$783 M
$801 M
$905 M
$1,008 M $1,111 M
7.5%
$242 M
$332 M
$423 M
$513 M
$590 M
$604 M
$684 M
$764 M
$845 M
10%
$174 M
$245 M
$316 M
$388 M
$448 M
$459 M
$522 M
$585 M
$648 M
24.10.6.1 Economic Sensitivity of PEA Base Case
Figure 24-38 Sensitivity analysis of the Southern Extension PEA base case ($1,300 /oz)
Table 24-31 Sensitivity results of the Southern Extension PEA base case ($1,300 /oz)
Sensitivity
-30%-
-25%-
-20%-
-15%-
-10%-
-5%-
+0%
+5%
+10%
+15%
+20%
+25%
+30%
Gold price
$ M
-9
7 1
149
225
301
377
452
528
603
679
755
830
906
Processed gold grade
$ M
-11
6 9
148
225
300
376
452
528
604
680
756
832
907
Growth capital cost
$ M
507
498
488
479
470
461
452
443
434
425
416
407
398
Sustaining capital cost
$ M
552
536
519
502
486
469
452
435
419
402
385
369
352
Operating cost: mining
$ M
655
622
588
554
520
486
452
418
384
351
317
283
249
Operating cost: processing
$ M
543
528
513
497
482
467
452
437
422
407
392
377
362
Operating cost: G&A
$ M
487
481
475
470
464
458
452
446
441
435
429
423
417
Sensitivity
-2.5%- -2.0%- -1.5%- -1.0%- -0.5%-
+0%
+0.5% +1.0% +1.5% +2.0% +2.5%
Gold Recovery
$ M
414
422
429
437
445
452
460
467
475
483
490NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 323
24.10.6.2 Economic Sensitivity of PEA Consensus Case
Figure 24-39 Sensitivity analysis of the Southern Extension PEA consensus case ($1,585 /oz)
Table 24-32 Sensitivity results of the Southern Extension PEA consensus case ($1,585 /oz)
24.11Conclusions and Interpretations
The following conclusions are made from the PEA:
- Resource and Definition Drilling:
The geometry of the Southern Extension mineralization supports a progressive definition drilling
strategy where panels are sequentially drilled.
o The PEA assumes panels are progressively drilled from underground workings as the
declines progressively access the top of each block.
o The drilling density for the Southern Extension currently supports its classification as an
Inferred Mineral Resource. Due to the wide drill spacing at depth there is a risk that the
geometry of mineralization in the Panels 7 and 8 may be more fragmented than currently
modelled and the mine design and modifying factors have been applied to reflect this risk.
- Mine Design:
The mine design, schedule and infrastructure proposed for the Southern Extension are based on
conceptual designs and locations.
o The geotechnical assessment of the Southern Extension has used one stress measurement
taken at the 570 level. The stress gradient determined from this one measurement can
only be interpreted as indicative.
Sensitivity
-30%-
-25%-
-20%-
-15%-
-10%-
-5%-
+0%
+5%
+10%
+15%
+20%
+25%
+30%
Gold price
$ M
199
297
394
491
589
686
783
881
978
1075
1172
1269
1366
Processed gold grade
$ M
197
295
393
490
588
686
783
881
978
1076
1173
1271
1368
Growth capital cost
$ M
838
829
820
811
802
793
783
774
765
756
747
738
729
Sustaining capital cost
$ M
884
867
850
834
817
800
783
767
750
733
717
700
683
Operating cost: mining
$ M
987
953
919
885
851
817
783
750
716
682
648
614
580
Operating cost: processing
$ M
874
859
844
829
814
799
783
768
753
738
723
708
693
Operating cost: G&A
$ M
818
812
807
801
795
789
783
778
772
766
760
755
749
Sensitivity
-2.5%- -2.0%- -1.5%- -1.0%- -0.5%-
+0%
+0.5% +1.0% +1.5% +2.0% +2.5%
Gold Recovery
$ M
735
745
754
764
774
783
793
803
813
822
832NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 324
o The change from primary/secondary to pillarless retreat stope sequencing is nominally
planned at 1,000 m depth but cannot be determined without further measurements and
modelling to determine the in-situ stress conditions and rock mass response to mining.
o The lateral development connections between the Southern Extension and Panel 2 are not
optimized.
o The locations of the Southern Extension main ventilation shafts are not considered final;
the proposed unsupported diameters of the shafts have not been confirmed by
geotechnical drilling.
o The refrigeration requirement estimated for the mine is based on a factored equipment
requirement plan and has not considered the in-situ rock temperature.
- Mine Operation:
The mining methods and techniques selected and discussed in the PEA can be implemented by the
Wassa operation.
o Development, production drilling, loading and hauling rates are based on current
productivities with minor improvements.
o The Southern Extension mining method uses downhole stope drilling which is a change
from Panel 2’s uphole drilling.
o The Southern Extension relies on paste fill to achieve the planned recovery and mining
rates. Wassa is yet to commission its paste fill plant (planned in Q1 2021).
- Metallurgy:
The metallurgical test work from the 2018 Southern Extension is based on a limited number of
holes. The assessment concludes that the 2018 test work returned similar results to the 2015
Feasibility Study metallurgical test work. It is reasonable to suggest, for this preliminary level of
study, that processing performance for the Southern Extension feed will be similar to material
currently treated.
- Economic Analysis:
The economic evaluation is based on a PEA level of study. The production schedule in based on
Inferred Mineral Resource that are not Mineral Reserves and do not have demonstrated economic
viability. There is no certainty that the results in the PEA will be realized.
The preliminary economic assessment of the Inferred Mineral Resource of the Southern Extension
zone shows production from this area is potential economically viable.
For the Inferred Mineral Resource (Southern Extension zone):
o Growth Capital:
$228.8 M;
o Development Duration: 6 years;
o Production Phase Life: 11 years;
o Production Phase Rate: 294 koz/yr;
o All-in Sustaining Cost: $778 /oz; and
o After-tax NPV5%:
▪ Base Case ($1,300 /oz):
$452.2 M (100% basis)
▪ Consensus Case ($1,585 /oz): $783.5 M (100% basis)
Further studies based on updated Mineral Resource estimates as definition drilling is completed will assist
in optimizing the project and clarifying the risk profile.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 325
24.11.1 Risks
The risks outlined in this section are specific the PEA and do not include risks outlined in Section 25.2 which
continue to exist for the Southern Extension.
24.11.1.1Geology, Mining and Processing
Table 24-33 contains the key risks for geology, mining and processing.
Table 24-33 Geology, Mining and Processing risks for Southern Extension
Risk
Description
Risk Management / Mitigation
Geological
continuity
Additional Definition Drilling and
geological models do not support PEA
mining method, adversely impacting the
production rate and project value.
Resource definition drilling to higher levels of
confidence will occur ahead of capital development and
project investment decisions.
Production Block layout is modular and is adaptable to
variable geometry.
More conservative modifying factors are applied to
panels where drill density is lowest.
Geotechnical
conditions
In-situ rock stress and rock mass
response to mining induced stresses
adversely impact the production rate
and project value.
Complete recommended geotechnical program to test
the parameters assumed in the mining method.
Limited geotechnical data indicates ground conditions
are consistent with current areas which are very good.
Pillarless sequence with paste fill is planned at depth
and can be applied higher up if required.
Gold grade
achieved
Grade and volume are overestimated
because the Mineral Resource is only
classified as Inferred, incorrectly
elevating the gold production profile
and project value
Assessment is described as a PEA with appropriate
disclosure regarding the Inferred Mineral Resource and
is presented separately to Mineral Reserves.
Further definition drilling will be completed to increase
resource confidence and will be incorporated in future
studies ahead of capital investment decisions.
Development
advance rate
Development advance rates assumed in
the PEA are not met, adversely
impacting schedule adherence,
production profile and project value
Development advance rates are higher than current
rates achieved on site, but improvement assumptions
are reasonable.
Fleet numbers, ventilation quantities and refrigeration
planning support the development schedule.
Stope turnover
Stope turnover rate is lower than
scheduled, adversely impacting annual
production rates and project value.
Design and methodology applies extra infrastructure
and access to allow consistent stope layouts and
blasting sequences.
25 m level spacing permits good drilling accuracy.
Plant feed
variability
Plant feed metallurgical variability
increases with material from the
Southern Extension, leading to lower
gold recovery (eg: mild preg robbing
which increases with depth).
Limited test work to date has not identified any fatal
flaws.
GSR will undertake a metallurgical testing program in
parallel with Resource definition and infill drilling of
Panels 4 and 5.
24.11.1.2 Capital and Operating Costs
The majority of the required growth capital is for mine development to access and establish the production
blocks. Wassa is an operating site and has already installed most of the infrastructure for the increased
underground production rate, including site power upgrades and the paste fill plant.
Operating cost estimates for mining activities have a high level of confidence as they based on actual costs
in 2020. However, the low geological confidence retains the risk that the mine design and activity
quantities and subsequent operating cost, are exposed to change as more drilling information is collected,
as outlined in Table 24-34.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 326
Table 24-34 Economic risks for Southern Extension
Risk
Description
Risk Management / Mitigation
Capital Costs
Capital costs significantly increase,
adversely impacting project value
Capital development costs are progressively incurred
rather than lump sum.
Future studies with increased resource confidence will
determine economic viability ahead of capital
investment decisions.
Operating Costs
Unit operating costs significantly
increase due to productivity
assumptions not being met, adversely
impacting project value
Operating costs reflect current actual costs for mining
activities which are calculated from a spatial mine
design, rather than generic factors.
GSR is undertaking organization and operating system
re-design, and mining modernization to increase labour
productivity.
24.11.2 Opportunities
24.11.2.1Geological Drilling
Geological definition drilling in this assessment is scheduled to deliver the associated mine plan and Panels
are progressively drilled as the declines access the top of each new panel.
Additional drilling to target increasing the Inferred Mineral Resource and expediting drilling to bring
forward knowledge about the deeper panels should be considered as opportunities, as outlined in Table
24-35.
Table 24-35 Geological Drilling opportunities for Southern Extension
Opportunity
Description
Realization
Additional drilling to grow
the Inferred Resource
The Southern Extension zone is open to the
South, North (below Panels 1/2) and up-dip.
Larger Mineral Resource could extend
project life and could enable higher
production rate and subsequent economies
of scale.
Additional definition drilling outside
the defined Inferred Mineral Resource
to increase it.
Expedite drilling of deeper
Panels 6-8
Mineral Resource at depth shows materially
higher grades and continuity of
mineralization but is based on wide spaced
drilling and is not scheduled for drilling until
year 10.
Conservative modifying factors have been
applied in deeper panels to mitigate the risk
of geological continuity fragmenting.
Bringing forward expenditure to
expedite drilling of Panels 6-8 would
confirm good grade and continuity in
current geological model.
Modifying factors could be adjusted to
be consistent with other panels and
increase recovered grade and ounces.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 327
24.11.2.2 Productivity and Mine Design
Mine design optimization and productivity improvements are the main opportunities to be assessed in
future work. Table 24-36 contains the opportunities identified.
Table 24-36 Mine design and productivity opportunities for Southern Extension
Opportunity
Description
Realization
Increase level spacing
25 m level spacing is based on current
operating methods, equipment and low
geological confidence.
Level spacing could potentially be increased
to 30-50 m which would reduce lateral
development per ROM tonne mined,
reducing costs and potentially increasing
production rates.
Definition drilling will increase
confidence of the Inferred Mineral
Resource and further technical work is
required to confirm viability of
increased level spacing in terms of
both selectivity and operability.
Increase stope size
Geotechnical conditions may be favourable
for increasing the strike length of stopes (to
reduce number of cross-cuts) and/or height
(more lifts per stope/bigger blocks) which
would increase dev’t yield (ROM t/m.adv) ad
reduce cost.
Future geotechnical assessment and
modelling to challenge/validate design
assumptions, along with definition
drilling and design review.
Refine ventilation design
An alternative option was identified to
exhaust part of the Southern Extension via
sealed off workings in the existing mine.
This would negate the need to develop one
or more new shafts to surface.
Further ventilation studies.
Optimize design between
Panel 2 and Southern
Extension
Optimize design between Panel 2 and 4 to
reduce duplicated development and
potentially bring forward mining of Panel 4
stopes by extracting with the Panel 2
sequence.
Future studies based on increased
geological confidence.
Combine PEA and Panels 1-3 into
single mine design (currently designed
as two separate zones).
Increase machine
productivity through
technology
Semi/full automation to increase shift
operating time and remove operators from
hazardous areas.
Highest likelihood applications are
production drilling and drawpoint loading.
Progress GSR technology roadmap
which is being established.
Current projects are introduction of
tele-remote loading and digitalization
of production data.
Haulage Infrastructure
Replacement of truck haulage with
infrastructure system (eg: shaft hoisting,
conveyor, Rail-Veyor).
Capital demand would be offset by large
reduction in operating costs with automated
systems, reduced diesel consumption and
reduced ventilation demand.
Haulage options study to design
different systems, estimate capital
and operating costs, then complete
trade-off analysis,
Truck loading systems
Current design assumes loaders digging from
open passes to load trucks.
Feeder systems could be installed to
automate loading, increasing efficiency and
reducing operating cost.
Trade-off analyses in further technical
studies (capital vs operating,
operational flexibility vs efficiency).NI 43-101 Technical Report (March 2021) Wassa Gold Mine
25 CONCLUSIONS AND INTERPRETATIONS
25.1 Conclusions
Based on the data in this report, the Qualified Persons conclude that the information has been interpreted
appropriately and that it supports the economic analysis.
The following interpretations and conclusions are made by the Qualified Persons in their respective areas of
expertise, based on the review of data contained in this Technical Report.
25.1.1 Mineral Titles and Agreements, Surface Rights and Royalties and Encumbrances
- The mineral rights for the Wassa concession granted to GSWL under the Minerals and Mining Act
2006 (Act 703) are in good standing, supporting the declaration of a Mineral Resource and Mineral
Reserve for the Wassa operation. GWSL holds the necessary mining leases, surface rights, major
approvals and permits required for its operations.
- GWSL’s Wassa Mining Lease contains a 5% royalty on gross revenue payable quarterly to the
Government of Ghana. GSWL also pays a gold stream to Royal Gold Inc. and its wholly owned
subsidiary RGLD Gold AG (RLGD). The royalty payments and tax to government are payable prior to
the RGI and RGLD stream payments.
25.1.2 Exploration, Drilling and Analytical Data Collection
- The Wassa mineralization is classified as an Eoeburnean folded vein system and is the only such
deposit recognized to date within the Ashanti belt.
- The understanding of the geological setting, lithologies and structural and alteration controls on
the mineralization is sufficient to support estimation of Mineral Resources and Mineral Reserves.
- The understanding of the mineralization style and setting are well understood and can support a
declaration of Mineral Resources.
- The exploration programs completed to date are appropriate for the style of deposits reported on.
There is significant potential for the discovery of additional mineralization, particularly around the
Wassa underground deposit where the Mineral Resource is open to the south and at depth.
- The sampling methods used to collect the raw data are acceptable for Mineral Resource
estimation.
- Sample preparation, analysis and security are performed to a standard that is fit for use in Mineral
Resource and Mineral Reserve estimation.
- The quantity and quality of the lithological, structural, collar and down-hole survey data collected
during the exploration and delineation drilling programs are sufficient to support Mineral Resource
and Mineral Reserve estimates.
- QA/QC programs adequately address issues of precision and accuracy. Duplicates, CRMs and
blanks are routinely submitted with batches to monitor laboratory quality. Umpire analysis has
been completed and is planned when further exploration drilling is completed in 2021.
25.1.3 Metallurgical Test Work
- The 2015 metallurgical test work program for the Wassa Underground Feasibility Study remains
relevant to, and reflective of, the processing plant’s metallurgical performance.
- The locations of the test work samples reasonably represent the blend of mineralization in the
plant feed scheduled in the Mineral Reserve estimate.
- The 2015 metallurgical test work did not identify any significant issues for processing plant
performance, which has been validated by the plant’s performance in the years since the test work
program.
Page 328NI 43-101 Technical Report (March 2021) Wassa Gold Mine
25.1.4 Mineral Resource Estimates
- Mineral Resources are estimated as:
o Measured and Indicated Mineral Resource: 29.3 Mt at 3.76 g/t, containing 3.54 Moz; and
o Inferred Mineral Resource: 74.0 Mt at 3.44 g/t, containing 8.18 Moz.
- The Mineral Resources have been prepared in accordance with the 2014 CIM Definition Standards
and 2019 Best Practice Guidelines. Mining is assumed by underground methods at Wassa and
Hwini Butre, and open pit methods at all other locations.
- Mineral Resources have a reasonable expectation of economic extraction, with estimates
constrained as follows, assuming $1,500 /oz gold selling price:
o Open Pit: constrained by open pit optimization shell and cut-off grade; and
o Underground: constrained by cut-off grade.
- Factors which may impact the Mineral Resource estimate include changes in the following
parameters:
o Economic: gold price assumed, cut-off grade assumptions;
o Geological: interpretations of mineralization geometry and continuity, grade continuity,
density and domain assignments; and
o Mining and Processing: geotechnical, mining method and metallurgy recovery assumptions.
25.1.5 Mineral Reserve Estimates
- Proven and Probable Mineral Reserves are estimated as 11.5 Mt at 2.94 g/t, containing 1.09 Moz.
- The Mineral Reserves have been prepared in accordance with the 2014 CIM Definition Standards
and 2019 Best Practice Guidelines. Mining will be by underground long hole open stoping. The
former open pit component of the Mineral Reserve has been replaced by underground extraction.
- Mineral Reserves are supported by a positive economic test assuming $1,300 /oz gold selling price.
- Factors which may impact the Mineral Reserve estimate include changes to the following
parameters:
o Economic: gold price assumed; capital and operating cost input assumptions;
o Geological: interpretations of mineralization geometry, continuity and other aspects which
may influence estimation of the Mineral Resource;
o Technical: geotechnical assumptions; dilution and stope recovery performance;
o Operational: development advance rates, stope turnover rates and infrastructure
performance and duties required, availability of skilled personnel;
o Regulatory: maintaining the good standing of mining leases, rights and permits; and
o Environmental and social: maintaining social license to operate;
- The cut-off grade selected for the Mineral Reserve is appropriate and facilitates the company’s
objectives;
- The Mineral Reserve assumes that the paste plant is commissioned in Q1-2021 and achieves its
designed performance. Stope cycle activities will now incorporate paste fill preparation, filling and
curing activities.
25.1.6 Mining Methods
- The geotechnical conditions support the stoping methods and dimensions selected.
- The mine plan and schedule use:
o Conventional underground mining practices and equipment to carry out long hole open
stoping, consistent with currently employed techniques;
o Demonstrated mining rates based on recent development and stoping performance;
Page 329NI 43-101 Technical Report (March 2021) Wassa Gold Mine
- The introduction of paste fill will require integrating into the stope cycle sequence to enable
secondary stoping to commence.
- The ventilation quantity increases to 590 m3 /s to support 9 working areas independently.
- The mobile equipment plan will introduce 60 t trucks from 2021, phasing out the 40 t trucks as
their useful life comes to an end.
25.1.7 Recovery Methods
- Recovery methods in the processing plant and forward recovery assumptions (average 94.1%) and
are supported by test work and plant history.
- The processing plant capacity exceeds mine production in all years for the Mineral Reserve plan.
- No plant upgrades are required to process the mine production plan.
25.1.8 Environmental, Permitting and Social Considerations
- GSWL has submitted, received approval for, and remains in compliance of, all of its environmental
and social regulatory requirements. Its Environmental and Social Management System has been
developed in-line with an ISO 14001 system.
- GSR complies with international requirements on environmental and conservation, human rights,
and anti-corruption. It has adopted voluntary international codes on corporate responsibility:
o Cyanide management;
o TSF design;
o Responsible Gold Standard and Responsible Gold Mining Principles; and
o IFC’s Performance Standard 5 on Land Acquisition and Involuntary Resettlement.
GSR has corporate assurance processes which include independent review, audit and/or validation
to ensure conformance of the principles ascribed in these codes and standards.
- GSWL has posted and periodically updates its reclamation bond. At the end of 2020 the GSWL
bond was $13,672,231.
- GSWL has installed water diversion infrastructure to limit the amount of water making contact with
the operation.
- Hydrogeological studies have informed GSWL’s groundwater model, which has determined:
o Water drawdown from operations is not expected to have a significant impact on
community groundwater boreholes; and
o The receiving environment will not receive underground mine leachate in the recovered
state and no decant is expected to occur. Additionally, leachate from mine waste rock
dumps is controlled by the cone of depression and is not expected to impact on the
receiving environment.
- Periodic geochemistry studies have consistently shown that the rock lithologies, ore and waste, are
not acid generating (NAG) and is validated by over two decades of mining.
- Water quality has been routinely sampled since 2003 and externally analyzed since 2012.
Groundwater quality study results indicate that measured constituents will not exceed water
quality guidelines in the underground mine drainage.
- GSR demonstrates its corporate commitment to environmental and social responsibilities through
provision of dedicated and skilled staff in environment, safety, health, community affairs,
resettlement and security disciplines.
- The company supports a number of community and social initiatives, including:
o Golden Star Development Foundation for community and social development projects;
o Golden Star Oil Palm Plantation, a sustainable agribusiness sponsored by GSR as part of its
local economic development program, which aims to become self-supporting; and
Page 330NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 331
o Capacity building and livelihood enhancement, which provides practical and technical skills
training to young people in sectors unrelated to mining. The local procurement supply
chain capacity is further strengthened through GSR’s and GSWL’s partnership programs.
These initiatives proactively aim to build capacity and diversify the economy of local communities
as well as reduce uptake of small-scale illegal mining.
25.1.9 Capital and Operating Costs
- Capital costs: Wassa is a steady state operation in which:
o Capital costs include capitalized mine development, equipment replacements, fixed plant
maintenance projects, TSF capacity increases and other minor projects;
o Capital costs are split between growth to expand production, and sustaining capital to
support the existing capacity;
o The growth capital cost for the life of mine is $47.7 M; and
o The sustaining capital cost for the life of mine is $136.5 M.
- Operating costs: the operating costs used are based on actual 2020 costs and are projected through
the mine plan.
o The average unit activity costs for extraction of the Mineral Reserve are:
▪ UG Mining: $34.57 /t;
▪ Processing: $20.37 /t; and
▪ Site G&A: $9.24 /t (excluding refining).
- Unit production costs estimated for the Mineral Reserve are:
o Direct operating cost: $682 /oz;
o All-in sustaining cost: $881 /oz; and
o All-in cost: $964 /oz.
25.1.10 Economic Analysis of the Mineral Reserve
An economic analysis to support the declared Mineral Reserve was prepared. Using the assumptions
outlined in this Technical Report, the operations show a positive cash flow at the $1300 /oz reserve selling
price and support the declaration of a Mineral Reserve.
For the Mineral Reserve:
- Growth Capital:
$47.7 M;
- Development Duration: nil (in production);
- Production Phase Life: 6 years (2021-2026);
- Production Phase Rate: 171 koz/yr;
- All-in Sustaining Cost: $881 /oz; and
- After-tax NPV5%:
o Base Case ($1,300 /oz):
$121.2 M (100% basis)
o Consensus Case (av $1,751 /oz):$335.6 M (100% basis)NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 332
25.2 Risks
The risks outlined in this section are project specific and do not include external risks such as gold price
fluctuations or exchange rate risks.
25.2.1 Geology, Mining and Processing
Table 25-1 Geology, Mining and Processing risks contains the key risks for geology, mining and processing.
Table 25-1 Geology, Mining and Processing risks for the Mineral Reserve
Risk
Description
Risk Management / Mitigation
Geological
complexity
Delays to completing requisite tightly
spaced drill programs for de-risking stope
designs cause production delays or
unexpected grade outcomes, impacting
cash flow.
Ensure definition drilling is integrated to the
mining schedule to bring forward geological
knowledge ahead of the production to mitigate
grade risk profile in the mine plan.
Development
advance rate
Development advance rates assumed in
the plan are not met, adversely impacting
schedule adherence and cash flows.
Development advance rates are reflective of rates
being achieved on site. Fleet numbers, ventilation
quantities support the development schedule.
Stope turnover
Stope turnover rate is lower than
scheduled, adversely impacting annual
production rates and cash flow.
Commission and implement paste filling to stope
operations, including methods for working on
paste filled floors when mining secondary stopes.
Geotechnical
conditions
In-situ rock stress and rock mass
response to mining induced stresses
adversely impact the production rate and
cash flows.
Undertake an external review of the site’s Ground
Control Management Plan, including assessment
of activities to prepare for future mining areas.
Underground
mining around
open pits
Underground mining around open pits
changes the geotechnical,
hydrogeological and hydrological
conditions, which adversely impact
production rates and cash flows.
Risk assess the underground designs around the
open pits and prepare a risk management plan,
including a change management plan, prior to
commencing mining.
Mining sill pillars
under fill
Sill pillar recovery mining encounters
difficulty, adversely impacting production
rates and cash flow.
Develop a risk management plan for sill pillar
recovery.
25.2.2 Infrastructure
The site’s infrastructure risks are outlined in Table 25-2. Commissioning the paste plant and achieving its
designed steady state, and executing the ventilation upgrade are the key risk areas for the mine plan.
Table 25-2 Infrastructure risks for the Mineral Reserve
Risk
Description
Risk Management / Mitigation
Paste plant
commissioning and
operation
Delays to commissioning and/or not
achieving design capacity adversely
impacts production rates and cash flow.
Identify alternative production plans reflective of
the paste plant timing and output not achieving
the rates assumed in the mine plan.
Ventilation upgrade
The surface to underground exhaust and
intake shafts are not able to be mined at
the desired un-supported diameter;
project execution is delayed, impacting
production rates and cash flow.
Undertake shaft geotechnical drilling as soon as
practicable.
Review ventilation system requirements for
smaller diameter shaft scenarios.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 333
25.2.3 Economic
Wassa is an operating site and has already installed enabling capital to support the mine plan, including site
power upgrades and the paste fill plant. The established operations provide reliable operating cost data.
Table 25-3 Capital and Operating Cost risks for the Mineral Reserve
Risk
Description
Risk Management / Mitigation
Capital costs
Capital costs significantly increase,
adversely impacting cash flow, with
potential inability to fund growth
projects to completion.
Capital development costs are progressively
incurred rather than lump sum.
Baseline production rate already established.
Operating costs
Unit operating costs significantly increase
due to productivity assumptions not
being met or adverse movements of
major cost components (eg: labour,
energy), adversely impacting cash flow.
Unit operating costs reflect current costs and
productivity.
GSR is undertaking organization and operating
system re-design, and mining modernization to
increase labour productivity.
25.2.4 Environmental and Social
GWSL has a demonstrable environmental track record. The key social risks are outlined in Table 25-4.
Table 25-4 Environmental and Social Risks
Risk
Description
Risk Management / Mitigation
Access to personnel
with required skills
Sufficient personnel with skills required
to development and operate Wassa are
not available in the local area. Skilled
personnel are brought to site from across
Ghana (mostly) and some internationally.
Availability of personnel can be
compromised by both regional
(eg: competition, security) and global
(eg: pandemic, transport) factors
Turnover of current workforce is low and whilst
issues such as the Covid-19 pandemic did cause
disruption during 2020, it did not cause a material
disruption to site operations.
Continue with vocational skills programs,
recruitment, training and development of local
people.
Modernization and
community
employment
expectations
Modernization of mining practices and
application of technology decreases
reliance on un/semi-skilled labour.
Future potential of Mineral Resources
increases the local community
expectations for employment.
Continue vocational skills programs and local
procurement strategy.
Develop and implement change management
plans alongside implementation of new
technology and techniques.
Unauthorized
small-scale mining
Artisanal mining around Wassa and the
district increases over the life of mine
impacting GSR’s environmental and social
plans, closure planning costs, and its
corporate reputation.
Continue with vocational skills programs and local
procurement strategy.
Continue to identify and assess new avenues for
local procurement of goods and services.
Continue tenure assessment and relinquishment
of mineral concessions deemed non-prospective.
Maintain dialogue with the Minerals Commission
and legal small-scale mining associations.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 334
25.3 Opportunities
25.3.1 Mineral Resource upside
The significant size of the Inferred Mineral Resource, together with untested in-mine and near-mine targets
create the main Mineral Resource opportunities outlined in Table 25-5.
Table 25-5 Mineral Resource Opportunities
Opportunity
Description
Realization
Definition drilling to
upgrade classification of
Inferred Mineral Resource
The large Inferred Mineral Resource to the
south of the mine creates mine life
extension and possible expansion
opportunities.
Continue with the drilling program to
increase geological knowledge of the
resource in this area.
Various targets to extend
the defined mineralisation
are not yet tested
Drill test targets which can leverage the
mine’s installed capital for incremental
production opportunities. Targets exist
around the main Wassa orebody, plus
anomalies defined in soil sampling within
10 km from the Wassa plant and the regional
package including the Mineral Resource at
Father Brown/Adoikrom UG.
Continue with in-mine and near-mine
exploration target assessment and
drilling programs.
25.3.2 Productivity and Mine Design
Productivity improvements are the main opportunities to be assessed in future work. Table 24-36 contains
the opportunities identified.
Table 25-6 Mine design and productivity opportunities for the Mineral Reserve
Opportunity
Description
Realization
Increase productivity
through technology
Semi/full automation to increase shift
operating time and remove operators from
hazardous areas.
Highest likelihood applications are
production drilling and drawpoint loading.
Assess mechanized options for improving
stope slotting activity rates.
Progress GSR technology roadmap
which is being established.
Current projects are introduction of
tele-remote loading and digitalization
of production data.
Expedite commencement
of stoping in Panel 3
Mineral Reserve schedule commences
development in Panel 3 (242 and B-Shoot) in
2022 but stoping does not commence until
Review mine schedule to potentially
bring stope extraction forward to
2023 or 2024 and increase production
in those years.
Geotechnical
Migrate toward numerical modelling of
geotechnical conditions to simulate
increased stope dimension scenarios.
Identify data requirements to support
dynamic modelling of the rock mass
conditions and response to mining
Paste Backfill
Optimize paste filling to increase production
rates and reduce binder cost.
Once steady state operations are
achieved, conduct de-bottle-necking
of plant.
Optimization program including
excavation/sequence design, test
work and assessment of alternative
pozzolan binders. NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 335
25.3.3 Sustainability
The PEA outlines a conventional approach to operating Wassa, consistent with proven methodology in key
aspects such as level spacing, truck haulage and utilization of installed processing capacity.
This approach has excluded assessment of a number of sustainability opportunities which could be included
to the project scope with further work. If implemented, the opportunities outlined in Table 25-7 could
reduce carbon emissions, improve energy efficiency and reduce water demand.
Table 25-7 Sustainability Opportunities
Opportunity
Description
Realization
CARBON EMISSIONS
Mobile equipment
electrification
Assess options for clean energy technology
applications, particularly battery electric
equipment.
Assess available systems and develop
fleet selection criteria.
Haulage electrification
Assess alternatives to diesel truck haulage,
including installation of infrastructure (shaft,
conveyor, Rail-Veyor) and electric trucks.
Haulage options study.
Renewable energy supply
Increase renewable energy component in
site energy supply. Leverages well with
equipment electrification projects.
Assess options, potentially in
partnership similar to recently
installed Genser gas power station.
AIR & WATER
Water efficient operations
Complete water balance model for the site’s
future state and
assess opportunities to
reduce consumption and/or increase
recycling.
Complete water balance and identify
opportunities.
Water quality
preservation
Assess water balance model to identify and
remove contamination of clean streams with
contaminated streams.
Commission 620 mRL pump station
which removes contaminants before
pumping to surface and continue
similar projects over time.
ENERGY SAVINGS & OPERATIONAL EFFICIENCY
Comminution
optimization
Once haulage study complete (outcome may
include crushing), review crushing and
grinding circuit options (eg: consolidate 4-
stage crushing, SAG milling, ore sorting).
Current configuration was optimized
for each investment point (eg: 4-stage
crush is legacy of original heap leach)
and projected life is now longer than
at previous investment point.NI 43-101 Technical Report (March 2021) Wassa Gold Mine
26 RECOMMENDATIONS
Recommendations are provided separately for the current operations at Wassa and for the Southern
Extension zone which was the subject of the PEA.
26.1 Current Operations
Based on the positive results of the technical and economic analysis of the Mineral Reserve of the Wassa
gold mine, the following actions are recommended:
- Geology and Drilling:
Continue with the definition drilling of the following areas:
o Panels 1 and 2: resource infill and grade control drilling to increase confidence in the
Mineral Resource to support ongoing production.
o Panel 3: resource infill drilling to increase confidence in local geometry of the Mineral
Resource to finalize development designs.
Complete the drilling programs to test targets with potential to increase the defined mineralization,
both around the main Wassa orebody, local anomalies around Wassa defined by soil sampling and
the regional tenement package, including the Mineral Resource at Father Brown/Adoikrom.
- Mining:
Continue extraction of the Mineral Reserve by underground methods:
o Reduce cut-off grade from 2.4 to 1.9 g/t to deliver the optimal economic return at the
reserve selling price assumption.
o Extraction of Panels 1 and 2 to continue with current stoping methodology.
o Upper mine areas (B-Shoot, F-Shoot and 242), which were previously planned for open pit
mining, to be changed to more selective underground mining to improve margins and bring
forward production.
Continue and proceed capital projects:
o Paste plant commissioning and implementation of steady-state paste filling operations.
o Ventilation upgrade to construct two ventilation shafts (intake and exhaust) and fans to
support production from Panel 2.
o Design finalization and execution planning to commence development of Panel 3 in 2022.
Investigate potential to expedite stoping from the Panel 3 (242 and B-Shoot) areas, to potentially
increase production in 2023-2025.
- Processing:
Continue processing of the Mineral Reserve using CIL treatment in the Wassa processing plant.
- Sustainability:
Continue current governance practices to ensure ongoing statutory compliance and license to
operate is maintained, including:
o Heath, Safety, Environmental and Social management systems for monitoring and
reporting;
o Social investment programs for community development, capacity building and livelihood
enhancement; and
o Corporate responsibility programs.
Page 336NI 43-101 Technical Report (March 2021) Wassa Gold Mine
26.2 Southern Extension Zone
For the Inferred Mineral Resource in the Southern Extension Zone, based on the positive results of the
preliminary economic assessment, the risks and opportunities identified, and conclusions made, the
following actions are recommended to progress the project.
- Geology and Drilling:
Continue with the resource development drilling of Panels 4 and 5 to increase geological
confidence.
Continue to update Mineral Resource models with new drilling results to support future technical
studies.
- Technical Studies:
Metallurgical:
o Collect appropriate samples from definition drilling conduct test work on composites to
test comminution, grindability and ore density variability.
o Complete gravity concentrate and leach recovery testing to determine optimal grind size.
o Undertake test work to characterize the level of preg-robbing in the Southern Extension
zone and determine variability and plant operational controls to mitigate.
o Complete diagnostic leach test work on gravity tails samples to establish gold deportment
and lock-up mechanisms.
Geotechnical:
o Collect additional rock mass characterization data from geotechnical core logging and
conduct laboratory rock strength testing on core samples.
o Conduct acoustic emission testing of orientated drill core to complement the existing
Hi-cell measurements to confirm the in-situ stress field.
o Complete numerical modelling using the larger data-set to assess the likely rock mass
response and associated risk arising from different mining sequences and stope
dimensions.
Ventilation:
o Evaluate various network design configurations, including shaft diameters.
o Refine ventilation network design in the production blocks (hybrid exhaust/orepass) and
decline ventilation circuits (secondary ventilation distances).
Mine Design:
o Consolidate mine designs for Panels 1-3 and the Southern Extension so that design
synergies are incorporated into the plan.
o Assess opportunity to increase level intervals and/or stope dimensions based on updated
geological and geotechnical data.
Page 337NI 43-101 Technical Report (March 2021) Wassa Gold Mine
- Optimization & Operations Readiness:
o Complete option and trade-off studies to optimize the project plan:
▪ Alternative haulage methods to current diesel trucking – shaft hoisting, conveyor,
electric trucks and Rail-Veyor;
▪ Equipment selection, including application of battery electric equipment and
semi/full-automation; and
o Continue implementation of the management operating system and technology roadmap,
which includes assessment of real-time data applications, drilling accuracy for increased
level spacing, personnel and equipment tracking.
o Conduct trials in the current underground operation to validate operability of proposed
stoping methodology in Panels 4-8 (eg: lateral development, mechanical slotting, downhole
blasting, stope loading on paste fill, sill pillar extraction).
- Sustainability:
o Investigate electrification and renewable energy options to reduce greenhouse gas
emissions.
o Complete site water balance model and assess opportunities to reduce water consumption,
increase recycling and reduce discharged contaminants.
o Review crushing and grinding circuit to optimize comminution efficiency.
26.2.1 Project Execution Plan
The progressive development plan proposed for the Southern Extension zone has the project being
developed in three major phases of definition drilling and capital investment.
- Panels 4 and 5: Resource development drilling in progress and studies planned to inform an
investment decision at the end of project year 2 (Y2) and full production by Y6.
- Panels 6 and 7: Resource development drilling in Y6-7, decline development starting Y6 and stope
production in Y8.
- Panel 8: Resource development drilling in Y10, decline development starting Y10 and stope
production in Y12.
The project execution plan for progressing to production from the Southern Extension zone outlines the
activities for only the first phase (Panels 4 and 5) to reach an investment decision and the potential
timeframe to production.
The timing of project activities and production milestones are the best estimate at this point in time.
Whilst the project activities have funding committed in the 2021 budget, there is no guarantee that funds
will be available to deliver the scheduled dates. Progressing the project to execution will be subject to a
positive feasibility study and investment approval.
The schedule of activities to progress the later phases are not detailed due the current level of geological
confidence (Inferred Mineral Resource), level of study (PEA) and timeframe (+5 years).
The activities outlined in the plan are based on the risks and opportunities identified in Section 25 and will
provide the required geological, technical and economic evaluations to inform and investment decision
with a feasibility level study. Figure 26-1 shows the activity timing and the expected regulatory reporting,
decision making and approval.
Page 338NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Page 339
26.2.2 Activity Cost Estimate
The cost estimates in Table 26-1 are the external costs required to progress Panels 4 and 5 to an
investment decision. Outside this cost estimate, a share of the GSR corporate overhead is directed to this
work.
The external costs are included in the economic analysis in Section 24.10.
- Definition drilling costs are as detailed in Section 24.9.1.1.3.
- Geotechnical and metallurgical costs are based on consultant estimates.
- The haulage study and other consultant costs are calculated from indicative consulting rates and
time estimates by GSR.
The 2021 share of these costs are allowed for in the 2021 company budget.
Figure 26-1 shows the required activity to progress the project toward execution and preliminary estimates
of milestone dates.
Table 26-1 Cost estimate for 2021 – 2022 Resource definition drilling and technical studies
Activity
2021-22 Cost
Definition Drilling, Total
$13.2 M
Technical Studies, Total
$0.8 M
Geotechnical
$0.2 M
Metallurgical Testing
$0.2 M
Haulage Study
$0.3 M
Mine Design and Ventilation
$0.1 M
Total
$14.0 MNI 43-101 Technical Report (March 2021) Wassa Gold Mine
Figure 26-1 Project Execution Plan, Southern Extension Panels 4 and 5
Page 340NI 43-101 Technical Report (March 2021) Wassa Gold Mine
27 REFERENCES
Adadey, K., Clarke, B., Theveniaut, H., Urien, P., Delor, C., Roig, J.Y., Feybesse, J.L., 2009: Geological Map
Explanation – Map Sheet 0503B (1:100 000): CGS/BRGM/Geoman, Geological Survey Department of Ghana
(GSD).
Allibone, A., McCuaig T.C., Harris D., Etheridge M., Munroe S., Byrne D.; 2002a; Structural Controls on Gold
Mineralization at the Ashanti Gold Deposit, Obuasi, Ghana: Society of Economic Geologists, Special
Publication, Vol. 9, pp. 65–93.
Allibone A., Teasdale J., Cameron G., Etheridge M., Uttley P., Soboh A., Appiah-Kubi J., Adanu A., Arthur R.,
Mamphey J., Odoom B., Zuta J., Tsikata A., Pataye F., Famiyeh S., Lamb E., 2002b: Timing and Structural
Controls on Gold Mineralization at the Bogoso Gold Mine, Ghana, West Africa: Economic Geology, Vol. 97,
- 949-969.
Barton, N., Lien, R., and Lunde, J., 1974: Engineering classification of rock masses for the design of tunnel
support: Rock Mechanics and Rock Engineering 6(4): 189-236. Also published in: Norges Geotekniske
Institutt, Publikasjon 106.
Barton, N. and Grimstad, E., 1993: Updating of the Q-System for NMT: Proceedings of the International
Symposium on Sprayed Concrete, Fagernes, 22-26 October 1993, 46-66.
Bourassa Y., 2003: Geology of the Wassa Mine Report: Golden Star Resources Ltd, 32p (Unpublished).
Dansgaard, W., 1964: Stable Isotopes in Precipitation: Tellus Vol. 16, No. 4, pp 436-469
Davis D.W., Hirdes W., Schaltegger U., Nunoo E.A., 1994: U-Pb age constraints on deposition and
provenance of Birimian and gold-bearing Tarkwaian sediments in Ghana, West Africa: Precambrian
Research, Vol. 67, pp. 89-107.
Eisenlohr B.N., 1992b: Conflicting evidence on the timing of mesothermal and paleoplacer gold
mineralization in early Proterozoic rocks from southwest Ghana, West Africa: Mineralium Deposita, Vol. 27,
- 23-29.
Eisenlohr B.N., Hirdes W., 1992a: The structural development of the early Proterozoic Birimian and
Tarkwaian rocks of southwest Ghana, West Africa: Journal of African Earth Sciences, Vol. 14, No. 3, pp.
313-325.
Feybesse J.L., Billa M., Guerrot C., Duguey E., Lescuyer J.L., Milési J.P., Bouchot V., 2006: The
paleoproterozoic Ghanaian province: Geodynamic model and ore controls, including regional stress
modelling: Precambrian Research, Vol. 149, pp. 149-196.
Fortescue, J.A.C., 1992: Landscape geochemistry—Retrospect and prospect—1990: Applied Geochemistry,
- 7, pp. 1–53.
Geosystems Consulting, 2013: Golden Star (Wassa) Limited; Tailings Storage Facility (TSF) 2 Project
Environmental Impact Statement: February 2013.
Geosystems Consulting, 2015: Golden Star (Wassa) Limited; Updated Tailings Storage Facility (TSF) 2 Project
Environmental Impact Statement: September 2015.
Golden Star Resources, 2015: Wassa Expansion Project Environmental Scoping Report.
Golder Associates, 2016: Wassa Expansion Project Environmental Impact Statement. November 2016.
Hirdes W., Davis D.W., 1998: First U-Pb zircon age of extrusive volcanism in the Birimian Supergroup of
Ghana/West Africa: Journal of African Earth Sciences, Vol. 27, No. 2, pp. 291-294.
Hirdes W., Davis D.W., Eisenlohr B.N., 1992: Reassessment of Proterozoic granitoid ages in Ghana on the
basis of U/Pb zircon and monazite dating: Precambrian Research, Vol. 56, pp. 89-96.
Page 341NI 43-101 Technical Report (March 2021) Wassa Gold Mine
ICI Australia, 1990: ‘Environmental Effects of Blasting’ in Handbook of Blasting Tables: pp 33-35.
INAP, 2010: Global Acid Rock Drainage Guide (the GARD Guide), Version 0.8: The International Network for
Acid Prevention, http://www.gardguide.com.
International Union for Conservation of Nature and Natural Resources, 2016: www.iucnredlist.org (IUCN,
2016).
Isaaks E., 2013: Grade Estimation for the Wassa Resource Model: Independent Mineral Consultant, 21p
(Unpublished).
John T., Klemb R., Hirdes W., Loh G., 1999: The metamorphic evolution of the Paleoproterozoic (Birimian)
volcanic Ashanti belt (Ghana, West Africa): Precambrian Research, Vol. 98, pp. 11-30.
Junner N.R., 1940: Geology of the Gold Coast and Western Togoland: Gold Coast Geological Survey, Memoir
No. 11, 40 p.
Kitson, A.E., 1928: Provisional geological map of the Gold Coast and Western Togoland, with brief
descriptive notes thereon: Gold Coast Geological Survey, Bulletin No. 2.
Knight Piésold, 2011: Wassa Tailings Storage Facility 2, Site Investigation Factual Report: December 2011.
Knight Piésold, 2012: Golden Star Wassa Limited, Wassa Gold Mine, TSF Detailed Design Report.
Knight Piésold, 2015: Golden Star Wassa Limited, Wassa Gold Mine, TSF Detailed Design Report.
Knight Piésold, 2017: Conceptual Level Alternative Staging Design of TSF 2, for Annualized Construction with
Compacted Soil Liner (CSL): Memorandum; October 2017.
Kumapley N.K., 1996: Seismicity of southern Ghana: causes, engineering implications and mitigation
strategies: Ghana Min J 2(1):33–41
Marinos P., Marinos V., Hoek E., 2007: Geological Strength Index (GSI). A characterization tool for assessing
engineering properties for rock masses: Underground works under special conditions, eds. Romana,
Perucho & Olalla, 13-21. Lisbon: Taylor and Francis.
Mathews, K.E., Hoek, E., Wyllie, D.C., Stewart, S.B.V., 1981: Prediction of stable excavation spans at depths
below 1000m in hard rock mines: (Tech Report DSS Serial No. OSQ80-00081), Ottawa: Canada Centre for
Mineral and Energy Technology.
MEL, 1996 a: Satellite Goldfields Limited, Wassa Hydrogeological Assessment, Progress Report for Work
During First Quarter 1996: MEL Report 1031R087.
MEL, 1996 b: Reinterpretation of VLF Data to Locate Zones of Preferential Groundwater Flow: MEL Report
1031R138.
MEL, 1996 c: Satellite Goldfields Limited, Wassa Hydrogeological Assessment, Progress Report for Work
During Third Quarter 1996: Minerex Environmental Limited, December 1996. MEL Report 1031R156.
MEND, 2009: Prediction Manual for Drainage Chemistry from Sulphidic Geologic Materials: Report prepared
by W.A. Price, CANMET, British Columbia, for the MEND Program.
Milési JP., Ledru P., Feybesse JL., Dommanget A., Marcoux E., 1992: Early Proterozoic ore deposits and
tectonics of the Birimian orogenic belt, West Africa: Precambrian Research, Vol. 58, pp. 305-344.
Morin, K., Hutt, N., 2007: Morrison Project – Prediction of Metal Leaching and Acid Rock Drainage, Phase 1:
Minesite Drainage Assessment Group, 588p.
NDPC & UNDP, 2010: 2008 Ghana Millenium Development Goals Report. April 2010: National Development
Planning Commission (NDPC) / Government of Ghana and the United Nations Development Program
(UNDP) Ghana.
Page 342NI 43-101 Technical Report (March 2021) Wassa Gold Mine
Oberthür T., Vetter U., Davis D.W., Amanor J.A., 1998: Age constraints on gold mineralization and
Paleoproterozoic crustal evolution in the Ashanti belt of southern Ghana: Precambrian Research, Vol. 89,
- 129-143.
Oberthür T., Vetter U., Schmidt Mumm A., Weiser T., Amanor J.A., Gyapong W.A., Kumi R., Blenkinsop T.G.,
1994: The Ashanti Gold Mine at Obuasi, Ghana: Mineralogical, Geochemical, Stable Isotope and Fluid
Inclusion Studies on the Metallogenesis of the Deposit: Geologisches Jahrbuch, D 100, pp. 31-129.
Oberthür T., Weiser T., Amanor J.A., Chryssoulis S.L., 1997: Mineralogical siting and distribution of gold in
quartz veins and sulfide ores of the Ashanti mine and other deposits in the Ashanti belt of Ghana: genetic
implications: Mineralium Deposita, Vol. 32, pp. 2-15.
Perrouty S., Aillères L., Jessell M.W., Baratoux L., Bourassa Y., Crawford B., 2012: Revised Eburnean
geodynamic evolution of the gold-rich southern Ashanti Belt, Ghana, with new field and geophysical
evidence of pre-Tarkwaian deformations Precambrian Research, Vol. 204-205, pp. 12-39.
Perrouty S., Jessell M.W., Aillères L., Apau D., Velasquez G., Siebenaller L., Miller J., Bourassa Y., Beziat d.,
Baratoux L., 2012: Tectonic Context of Eoeburnean Gold Mineralization in Wassa mine, Southwest Ghana:
(unpublished).
Pigois JP., Groves D.I., Fletcher I.R., McNaughton N.J., Snee L.W.; 2003; Age constraints on Tarkwaian
palaeoplacer and lode-gold formation in the Tarkwa-Damang district, SW Ghana; Mineralium Deposita, Vol.
38, pp. 695-714.
Potvin, Y., 1988: Empirical open stope design in Canada: Ph.D. thesis, University of British Columbia,
Vancouver, B.C.
Price W.A., Morin K., Hutt N., 1997: Guidelines for prediction of acid rock drainage and metal leaching for
mines in British Columbia: Part II. Recommended procedures for static and kinetic tests: Proceedings of the
Fourth International Conference on Acid Rock Drainage. Vancouver, B.C. Canada, 1, pp. 15–30.
Wexford Goldfields Limited, 2004: Reclamation Security Agreement between Wexford Goldfields Limited
and Environmental Protection Agency: 14 November 2004.
Scott Wilson, 2004: Wexford Goldfields Limited, The Wassa Project Environmental Impact Statement
SGS, 1996: Satellite Goldfields Limited, Wassa Gold Project, Environmental Baseline Study: SGS Laboratory
Services (Ghana) Limited, November 1996.
SGS Laboratory Services Ghana Limited, 1998: Wassa Project Environmental Impact Statement for Satellite
Goldfields Limited.
SGS, 2002 : Wassa Environmental due diligence audit : SGS Laboratory Services (Ghana) Limited.
Soregaroli, B.A., Lawrence, R.W., 1997: Waste Rock Characterization at Dublin Gulch: A Case Study:
Proceedings of the Fourth International Conference on Acid Rock Drainage, Vancouver, B.C. Canada, p631-
SRK Consulting (Canada) Limited, 2020 a: Wassa Truck Haulage Simulation, Preliminary Results:
(unpublished)
SRK Consulting (Canada) Limited, 2020 b: Wassa Truck Haulage Simulation, Revised Production Schedule –
60 T Trucks Dual Ramp: (unpublished)
SRK Consulting (UK) Limited, 2013: NI 43-101 Technical Report on Mineral Resources and Mineral Reserves
Golden Star Resources Ltd, Wassa Gold Mine, Ghana Effective Date 31st December 2012.
SRK Consulting (UK) Limited, 2015: NI 43-101 Technical Report on a Feasibility Study of the Wassa Open Pit
Mine and Underground Project in Ghana, Effective Date 31st December 2014.
Page 343NI 43-101 Technical Report (March 2021) Wassa Gold Mine
SRK Consulting (U.S.), Inc., 2021: PEA Ventilation Design for Golden Star’s Wassa Mine, Ghana:
(unpublished)
Tunks A.J., Selley D., Rogers J.R., Brabham G., 2004: Vein mineralization at the Damang Gold Mine, Ghana:
controls on mineralization: Journal of Structural Geology, Vol. 26, pp. 1257-1273.
United States Bureau of Mining, 1980: RI 8507 Structure Response and Damage Produced by Ground
Vibration from Surface Mine Blasting: DE Siskind, M.S. Stagg, J. W. Kopp and C. H. Dowding.
University of Mines and Technology (UMT), Tarkwa, Minerals Engineering Department, 2018: Final Report
on Profiling of Mining Zones at Golden Star Resources, Wassa Mine: (unpublished)
Wexford Goldfields Limited (WGL), 2004: Environmental Impact Statement for the Wassa Project.
Whitelaw O.A.L., 1929: The Geological and Mining Features of the Tarkwa-Abosso Goldfield; Gold Coast
Geological Survey: Memoir No. 1, 46 p.
Page 344NI 43-101 Technical Report (March 2021)
Wassa Gold Mine
Page 345
28 DATE AND SIGNATURES
The effective date of this Technical Report titled “NI 43-101 Technical Report on the Wassa Gold Mine” is
31 December 2020.
______________
______________________________
Matthew Varvari, FAusIMM
Date
_______________________________
______________
- Mitchel Wasel, MAusIMM CP(Geo)
Date
_______________________________
______________
Philipa Varris, MAusIMM CP(Env)
Date
1 March 2021
1 March 2021
1 March 2021
“Matthew Varvari“
“S. Mitch Wasel”
“Philipa Varris”