Technical report summary: Sibanye-Stillwater US PGM operations

TECHNICAL REPORT SUMMARY OF

THE SIBANYE-STILLWATER US PGM OPERATIONS

SITUATED IN THE

MONTANA, UNITED STATES

Report Date: 13 December 2023

Effective Date: 31 December 2021

Prepared by:

Qualified Persons at Sibanye-Stillwater US PGM Operations

Important Notices

Description of Amendments to Previously Filed Technical Report Summary

This Technical Report Summary (TRS) for the US PGM Operations of Sibanye-Stillwater Limited (Sibanye- Stillwater) (the Sibanye-StillwaterUS PGM Operations), dated 13 December 2023, serves as an amendment to the TRS prepared by the Qualified Persons at Sibanye-Stillwater for the fiscal year ended 31 December 2021, effective 31 December 2021, which was filed as Exhibit 96.1 to Sibanye- Stillwater's 2021 annual report filed on Form 20-F on 22 April 2022 (the Original 2021 Sibanye-StillwaterUS PGM Operations TRS) and incorporated by reference into Sibanye-Stillwater's 2022 annual report filed on Form 20-F on 24 April 2023.

This TRS was prepared by the Qualified Persons at Sibanye-Stillwater following the receipt of comment letters by Sibanye-Stillwater and associated dialogue with the staff (the Staff) of the United States Securities and Exchange Commission (the SEC) regarding information in the Original 2021 Sibanye- Stillwater US PGM Operations TRS. While this TRS incorporates certain changes to the Original 2021 Sibanye-Stillwater US PGM Operations TRS, it maintains an effective date of 31 December 2021 with regard to assumptions and the knowledge of the Qualified Persons at Sibanye-Stillwater. This TRS revises the following information in the Original 2021 Sibanye-Stillwater US PGM Operations TRS as a result of the comments received from the Staff:

• Revisions to the abridged cash flow results table on page [253] (Table 63) to include the particularized disclosure requirements of Item 601(b)(96)(iii)(B)(19) of Regulation S-K in one table, including annual production for the life of the project and the associated revenue, operating and capital costs, taxes, and royalties.

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Table of Contents
EXECUTIVE SUMMARY	1
Introduction	1
Property Description, Mineral Rights and Ownership	1
Geology and Mineralisation	2
Exploration Status, Development and Operations and Mineral Resource Estimates	2
Mining Methods, Ore Processing, Infrastructure and Mineral Reserve Estimates	4
Capital and Operating Cost Estimates and Economic Analysis	7
Permitting Requirements	8
Conclusions and Recommendations	8
INTRODUCTION	9
Registrant	9
Compliance	9
Terms of Reference and Purpose of the Technical Report	9
Sources of Information	10
Site Inspection by Qualified Persons	11
Units, Currencies and Survey Coordinate System	11
RELIANCE ON INFORMATION PROVIDED BY REGISTRANT	12
PROPERTY DESCRIPTION	14
Location and Operations Overview	14
Mineral Title	15
Title Overview	15
Title and Tenure Held	15
Title and Tenure Conditions and Compliance	17
Surface Rights and Servitudes	18
Royalties	20
Legal Proceedings and Significant Encumbrances to the Property	20
ACCESSIBILITY, CLIMATE, LOCAL RESOURCES, INFRASTRUCTURE AND PHYSIOGRAPHY	22
Topography and Elevation	22
Stillwater Mine and the Hertzler Tailing Storage Facility	22
East Boulder Mine	22
Fauna and Flora	22
Access, Towns and Regional Infrastructure	23
Climate	23
Infrastructure and Bulk Service Supplies	24

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Personnel Sources	25
HISTORY	26
Ownership History	26
Previous Exploration and Mine Development	27
Previous Exploration	27
Mine Development	28
Plant, Property and Equipment	29
ADJACENT PROPERTIES	31
GEOLOGICAL SETTING, MINERALISATION AND DEPOSIT	32
Regional Geology	32
Local and Property Geology	35
Local Stratigraphy	35
J-M Reef Mineralisation	37
EXPLORATION	44
Data Acquisition Overview	44
Gravity Surveys	44
Aeromagnetic Surveys	44
Topographic Surveys	45
Exploration and Mineral Resource Evaluation Drilling	45
Drilling	45
Core Logging and Reef Delineation	50
Survey Data	50
Density Determination	52
Underground Mapping	52
Hydrogeological Drilling and Testwork	53
Stillwater Mine	53
East Boulder Mine	56
Geotechnical Data, Testing and Analysis	58
Geotechnical Characterisation	58
Geotechnical Testwork and Data Collection	58
Geotechnical Results and Interpretation	60
SAMPLE PREPARATION, ANALYSES AND SECURITY	62
Sampling Governance and Quality Assurance	62
Reef Sampling	63
Sample Preparation and Analysis	63
Laboratory	63

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Sample Preparation and Analysis	64
Analytical Quality Control	65
Nature and Extent of Quality Control Procedures	65
Quality Control Results	66
DATA VERIFICATION	71
Data Storage and Database Management	71
Database Verification	71
MINERAL PROCESSING AND METALLURGICAL TESTING	73
Metallurgical Testwork and Amenability	73
Deleterious Elements	73
MINERAL RESOURCE ESTIMATES	74
Background	74
Geological Modelling and Interpretation	74
Zone Picking and Evaluation Cut Determination	74
Data Processing and Analysis	75
Structural Modelling and Geological Loss Determination	81
Geological Interpretation and Wireframe Modelling	81
Block Modelling	86
Grade and Tonnage Estimation	86
Grade and Thickness Estimation	86
Block Model Validation	90
Tonnage Estimation	92
Mineral Resource Classification	92
Cut-off Grades, Technical Factors and Reasonable Prospects for Economic Extraction	93
Prospects for Eventual Economic Extraction Assessment	93
Cut-off Grades and Minimum Mining Width	94
Mineral Resource Estimates	96
MINERAL RESERVE ESTIMATES	98
Mineral Resource to Mine Reserve Conversion Methodology	98
Mineral Resources Available for Conversion	98
Mineral Reserve Estimation Methodology	98
Point of Reference	100
Cut-off Grades	100
Mineral Reserve Classification Criteria	101
Mineral Reserve Estimates	104
Risk Assessments	105

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MINING METHODS	107
Introduction	107
Mine Design	107
Mining Method Rationale	107
Ramp and Fill Method	108
Captive Cut and Fill Method	109
Sub-level Extraction and Sub-level Development	109
Transverse Long Hole Stoping	110
Stope Extraction Ratios	111
Hydrogeological Model	111
Stillwater Mine	111
East Boulder Mine	112
Geotechnical Model	112
Geotechnical Characterisation	112
Support Design	113
Surface and Subsidence Control	114
Backfill	114
Stillwater Mine Operations	115
Background	115
Key Operational Infrastructure	116
Mine Layout	116
East Boulder Mine Operations	117
Background	117
Key Operational Infrastructure	117
Mine Layout	118
Life of Mine Planning and Budgeting	120
Introduction	120
Mine Planning Criteria	120
Modifying Factors	122
Indicated Mineral Resources to Probable Mineral Reserves Conversion Factors	124
Life of Mine Production Scheduling and Budgeting	125
Process Overview	125
LoM Production Schedule for Stillwater Mine	126
Life of Mine Production Schedule for East Boulder Mine	128
Mining Equipment	129
Stillwater Mine	129
East Boulder Mine	130
Logistics	131
Stillwater Mine	131
East Boulder Mine	132
Underground Mine Services	133
Stillwater Mine	133

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East Boulder Mine	136
Manpower	140
PROCESSING AND RECOVERY	143
Mineral Processing Methods	143
Background	143
Ore Processing	143
Stillwater Concentrator	143
East Boulder Concentrator	147
Concentrator Process Control Sampling	151
Smelting and Refining	152
Background	152
Smelter	152
Base Metal Refinery	157
PGM Prill Splits	161
Processing Logistics	161
INFRASTRUCTURE	163
Stillwater Mine Complex	163
Concentrator Infrastructure	163
Tailings Storage Facilities	163
Power	166
Bulk Water	167
Roads	168
Equipment Maintenance	168
Buildings	169
Transportation	171
East Boulder Mine Complex	172
Concentrator Infrastructure	172
Tailings Storage Facilities	172
Power	174
Bulk Water	174
Roads	176
Buildings	176
Equipment Maintenance	177
Transportation	178
Dry Fork Waste Rock Storage Area	178
Columbus Metallurgical Facility	178
MARKET STUDIES	180
Introduction	180

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PGM Market Overview	180
Platinum and Palladium Demand and Supply	181
Demand Drivers	181
Platinum	181
Palladium	181
Palladium and Platinum Pricing Outlook	181
Metals Marketing Agreements	182
The Columbus Metallurgical Complex	182
Precious Metals Refining	182
Wheaton International Streaming Agreement	182
The 2020 Palladium Hedge	183
ENVIRONMENTAL STUDIES, PERMITTING, PLANS, NEGOTIATIONS/AGREEMENTS	184
Social and Community Agreements	184
Environmental Studies, Permitting and Plans	185
Overview of Environmental Legislation and Regulation	185
Environmental Setting and Factors	190
Environmental Studies	190
Permitting Status and Compliance	194
Requirements for Environmental Monitoring, Closure and Post Closure, and Management
Plans	220
Reclamation Plans and Costs	229
CAPITAL AND OPERATING COSTS	235
Overview	235
Capital Costs	235
Background	235
Stillwater Mine	235
East Boulder Mine	239
Columbus Metallurgical Complex	242
Operating Costs	244
Background	244
Stillwater Mine	244
East Boulder Mine	245
Columbus Metallurgical Complex	246
ECONOMIC ANALYSIS	251
Background	251
Economic Viability Testing Method	251
Economic Assumptions and Forecasts	252
Taxation	252
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	Metal Price Forecast	252
	Discount Rate	252
DCF Results and Sensitivity Analysis	252
	DCF Model	252
	Net Present Values	256
	Internal Rate of Return	256
	Sensitivity Analysis	256
OTHER RELEVANT DATA AND INFORMATION	258
Catalytic Converter Recycling Business	258
	Background	258
	Recycle Processing	258
	Recycling Operations	259
INTEPRETATION AND CONCLUSIONS	260
RECOMMENDATIONS	264
QUALIFIED PERSONS' CONSENT AND SIGN-OFF	265
REFERENCES	266
List of Figures
Figure 1:	Location of Sibanye-Stillwater US PGM Operations in Montana	14
Figure 2:	Sibanye-Stillwater US PGM Operations Mineral Title and Tenure Map	19
Figure 3:	Regional Geology of the Stillwater Complex and Surrounds	33
Figure 4:	South to North Sections Through Stillwater Mine Showing Subsurface Geology	34
Figure 5:	A Schematic Section through Stillwater Mine Depicting the Horseman Thrust
	System	34
Figure 6:	General Stratigraphy of the Stillwater Complex	36
Figure 7:	Typical Stratigraphic Sequence and Pd-Pt Grade Profiles of the J-M Reef	39
Figure 8:	West to East Schematic Section Showing Variability in Stratigraphy and Impact
	on the J-M Reef at Stillwater Mine	41
Figure 9:	West to East Section Showing Geological Blocks of the J-M Reef at Stillwater Mine
	........................................................................................................................................	42
Figure 10: West to East Section Showing Geological Blocks of the J-M Reef at East Boulder
	Mine	43
Figure 11: Underground Definition Diamond Drilling Pattern	46
Figure 12: Drillhole Layout for Stillwater Mine	48
Figure 13: Drillhole Layout for East Boulder Mine	49

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Figure 14: Sub-surface Water Basin in the Stillwater East Mine Area	54
Figure 15: Hydrogeological Drillhole Locations along Adits in the Stillwater East Section	55
Figure 16: Average Water Inflow at East Boulder Mine	57
Figure 17: Test Sites for In Situ stress Measurements at Stillwater Mine	59
Figure 18: Test Sites for In Situ Stress Measurements at East Boulder Mine	60
Figure 19: Repeat Data Analysis for Stillwater Mine	67
Figure 20: Repeat Sample Data Analysis for East Boulder Mine	67
Figure 21: Blank Sample Data Analysis for Stillwater and East Boulder Mines	68
Figure 22: Laboratory Standard MF-14 Data Analysis	69
Figure 23: Laboratory Standard MF-15 Data Analysis	69
Figure 24: Laboratory Standard MF-16 Data Analysis	69
Figure 25: Laboratory Standard MF-18 Data Analysis	70
Figure 26: Laboratory Standard MF-20 Data Analysis	70
Figure 27: Laboratory Standard MF-21 Data Analysis	70
Figure 28: Scatter plot of Composite UHW vs. 2E Grade for Stillwater Mine	77
Figure 29: Scatter plot of Composite UHW vs. 2E Grade for East Boulder Mine	77
Figure 30: Histogram Plot of Composite 2E Grades for Stillwater Mine	78
Figure 31: Histogram Plot of Composite 2E Grades for East Boulder Mine	78
Figure 32: Spatial Analysis of FCW Continuity	80
Figure 33: Illustration of Reef Channel Wireframe Model Terminated at a Fault at Stillwater
Mine	82
Figure 34: Illustration of Reef Channel Wireframe Model Terminated at Dykes at East Boulder
Mine	83
Figure 35: J-M Reef Geological and Structural Models for Stillwater Mine	84
Figure 36: J-M Reef Geological and Structural Models for East Boulder Mine	85
Figure 37: Modelled 2E Grades and Classification for Stillwater Mine	88
Figure 38: Modelled 2E Grades and Classification for East Boulder Mine	89
Figure 39: Blitz Mean 2E Grade (opt) by Easting	91
Figure 40: Frog Pond East Mean 2E Grade (opt) by Easting	91
Figure 41: Mineral Reserve classification for Stillwater Mine	102
Figure 42: Mineral Reserve classification for East Boulder Mine	103
Figure 43: Overhand and Underhand Ramp and Fill Mining Methods	108
Figure 44: Sub-level Extraction (Longitudinal) Long Hole Open Stoping	109
Figure 45: Transverse Long Hole Open Stoping	110
Figure 46: Generalized Underground Layouts for Stillwater and East Boulder Mines	119
Figure 47: Typical Ramp and Fill Stope Design	122
Figure 48: LoM RoM ore production schedule for Stillwater Mine	127
Figure 49: LoM Production Schedule for East Boulder Mine	129
Figure 50: Stillwater Mine Compressed Air Service Map	135

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