Document

Exhibit 99.61

NI 43-101 Technical Report

Haile Gold Mine

Lancaster County, South Carolina

Effective Date: December 31, 2025

Report Date: March 27, 2026

Report Prepared by:

OCEANAGOLD

Suite 1020, 400 Burrard Street

Vancouver, BC V6C 3A6

Canada

Signed by Qualified Persons:

David Carr, Beng Metallurgical (Hons), MAusIMM (CP), (OceanaGold Head of Metallurgy)

Gregory Hollett, BEng (Mining Engineering), P.Eng (EGBC), (OceanaGold Head of Mine Engineering)

Brianna Drury, BSc Mining Engineering, RM-SME (OceanaGold Underground Engineering Superintendent)

Jonathan Moore, BSc Geology (Hons), MAusIMM (CP), (OceanaGold Head of Resource Development)

Douglas Corley, BSc Geology (Hons), MAIG (RPGeo), (OceanaGold Principal Geologist, Resource Development)

Larry Standridge, PE, MSE Geotechnical, (Call & Nicholas Principal Engineer, Geotechnical Engineer)

Robert Cook, PE, RM-SME, (Call & Nicholas Principal II Geological Engineer)

Jay Newton Janney-Moore, PE, RM-SME (NewFields Senior Project Manager I)

William Lucas Kingston, MSc, PG, RM-SME, Hydrogeology & Groundwater Management, (NewFields Senior Hydrogeologist)

Brooke J. Miller, MSc., CPG (SRK Principal Consultant, Geology)


NI 43-101 Technical Report – Haile Gold Mine, South Carolina, United States

Cautionary Note Regarding Forward-Looking Statements

This report contains certain “forward-looking statements” and “forward-looking information” (collectively, “forward-looking statements”) within the meaning of applicable Canadian securities laws which may include, but is not limited to, statements with respect to: future financial and operating performance; cash flow forecasts; projected capital, operating and exploration expenditures; targeted cost reductions; mine life and production rates; potential mineralization and metal or mineral recoveries; information pertaining to potential improvements to financial and operating performance and mine life at the Haile Gold Mine; future metals prices; the estimation of Mineral Reserves and Mineral Resources; the realization of Mineral Reserves and Mineral Resources estimates; costs of production; costs and timing of the development of new deposits; costs and timing of future exploration and drilling programs; timing of filing of updated technical information; requirements for additional capital; governmental regulation of mining operations and exploration operations; timing and receipt of approvals; consents and permits under applicable legislation; environmental risks; title disputes or claims; and the timing and possible outcome of current and pending litigation and regulatory matters. All statements in this report that address events or developments that OceanaGold Corporation (“OceanaGold”) expects to occur in the future are forward-looking statements. Forward-looking statements are statements that are not historical facts and are generally, although not always, identified by words such as “may”, “plans”, “expects”, “projects”, “is expected”, “scheduled”, “potential”, “estimates”, “forecasts”, “intends”, “targets”, “aims”, “anticipates” or “believes” or variations (including negative variations) of such words and phrases, or may be identified by statements to the effect that certain actions, events or results “may”, “could”, “would”, “should”, “might” or “will” be taken, occur or be achieved.

Forward-looking statements involve known and unknown risks, uncertainties and other factors which may cause OceanaGold’s actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements. Such risks include, among others: the risk of not achieving OceanaGold’s production estimates, forecasts or Guidance; inaccuracy of Mineral Reserves, Mineral Resources and operating and capital cost estimates; the actual results of current and future production, development and/or exploration activities; possible variations of ore grade, metallurgy or recovery rates; changes in mine plans, project parameters or assumptions as plans continue to be refined; delays in, or inability to complete, development or construction or expansion activities or to re-commence or sustain operations as planned; failures or underperformance of plant, equipment, infrastructure or processes; geotechnical risks or events, including open pit wall stability, crown pillar failure, land subsidence and tailings dam failures; challenges associated with effective water management; environmental, health and safety and climate-related risks; risks related to community acceptance, stakeholder engagement and social licence to operate; competition for mineral properties and other growth opportunities; legal and regulatory challenges to current and future permits, certifications, approvals or licences; adverse judicial, regulatory or governmental decisions; delays in, or inability to obtain, financing or governmental approvals on acceptable terms; changes in laws, regulations, taxation regimes, regulated accounting standards or their interpretation or application; the risks associated with operating in foreign jurisdictions, including political instability, changes in policy or law, civil unrest or conflict; fluctuations in the prices of gold, copper and silver; general business, economic and market conditions (including changes in global, national or regional financial, credit, currency or


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securities markets); changes or developments in global, national or regional political and social conditions; fluctuations in foreign exchange rates, including the value of the U.S. dollar relative to the Canadian dollar, the New Zealand dollar or the Philippine peso; inflationary pressure; labour availability, retention and turnover; accidents, labour disputes and other operational risks of the mining industry; limitations of insurance coverage or uninsured risks; the conclusions of economic evaluations, studies and models; and those other factors identified and described in more detail in the section entitled “Risk Factors” contained in OceanaGold’s most recent Annual Information Form and OceanaGold’s other filings with Canadian securities regulators, which are available under OceanaGold’s profile on SEDAR+ at sedarplus.com and on OceanaGold’s website at oceanagold.com. The list is not exhaustive of the factors that may affect OceanaGold’s forward-looking statements.

OceanaGold’s forward-looking statements are based on the applicable assumptions and factors Management considers reasonable as of the date hereof, based on the information available to Management at such time. These assumptions and factors include, but are not limited to, assumptions and factors related to our ability to carry on current and future operations, including: exploration and development activities; the timing, extent, duration and economic viability of such operations; the accuracy and reliability of estimates, projections, forecasts, studies and assessments; our ability to meet or achieve guidance, estimates, projections and forecasts; the availability and cost of inputs; the price and market for outputs, including gold, copper and silver; foreign exchange rates; taxation levels; the timely receipt of necessary approvals, permits or certifications; the ability to meet current and future obligations; the ability to obtain timely financing on reasonable terms when required; the current and future social, economic and political conditions; and other assumptions and factors generally associated with the mining industry.

OceanaGold’s forward-looking statements are based on the opinions and estimates of OceanaGold management and reflect their current expectations regarding future events and operating performance and speak only as of the date hereof. OceanaGold does not assume any obligation to update forward-looking statements if circumstances or management’s beliefs, expectations or opinions should change other than as required by applicable law. There can be no assurance that forward-looking statements will prove to be accurate, and actual results, performance or achievements could differ materially from those expressed in, or implied by, these forward-looking statements. Accordingly, no assurance can be given that any events anticipated by the forward-looking statements will transpire or occur, or if any of them do, what benefits or liabilities OceanaGold will derive therefrom. For the reasons set forth above, undue reliance should not be placed on forward-looking statements.


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Table of Contents


1	Summary		19
	1.1	Property Description, Location, Access and Ownership	19
	1.2	History	19
	1.3	Geological Setting, Mineralization and Deposit Types	20
	1.3.1	Geology	20
	1.3.2	Mineralization and Deposit Types	20
	1.4	Mineral Permits and Regulatory Matters	21
	1.5	Exploration	22
	1.6	Drilling	22
	1.7	Sampling, Analysis and Data Verification	22
	1.8	Mineral Processing and Metallurgical Testing	23
	1.9	Mineral Resources Estimate	24
	1.9.1	Combined Open Pit and Underground Resource Estimate	25
	1.10	Mineral Reserve Estimate	27
	1.10.1	Open Pit Mineral Reserves Estimate	27
	1.10.2	Underground Mineral Reserves Estimate	28
	1.10.3	Combined Open Pit and Underground Reserves Estimate	30
	1.11	Mining Methods	32
	1.11.1	Open Pit Mining Methods	32
	1.11.2	Underground Mining Methods	34
	1.11.3	Combined OP and UG Production Schedule	34
	1.12	Processing and Recovery Methods	36
	1.13	Infrastructure	37
	1.14	Environment Studies and Permitting	38
	1.15	Capital and Operating Costs	38
	1.16	Economic Analysis	40
	1.17	Conclusions and Recommendations	41
	1.17.1	Conclusions	41
	1.17.2	Recommendations	42


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2	Introduction		43
	2.1	Sources of Information and Data	43
	2.2	Qualifications of Consultants	43
	2.3	Site Visits and Scope of Personal Inspection	44
	2.4	Units of Measure	45
	2.5	Effective Date	45
3	Reliance on Other Experts		46
4	Property Description and Location		47
	4.1	Property Location	47
	4.2	Ownership	49
5	Accessibility, Climate, Local Resources, Infrastructure and Physiography		50
	5.1	Accessibility	50
	5.2	Climate	50
	5.3	Local Resources and Infrastructure	50
	5.4	Physiography	50
	5.5	Infrastructure Availability and Sources	51
6	History		52
7	Geological Setting and Mineralization		54
	7.1	Regional Geology	54
	7.2	Local Geology	56
	7.2.1	Lithology	56
	7.2.2	Structure	61
	7.2.3	Mineralization and Alteration	63
8	Deposit Types		65
	8.1	Haile Genetic Model	65
	8.2	Haile Geological Model	66
9	Exploration		67
	9.1	Pre-Romarco	67
	9.2	Romarco	67
	9.3	OceanaGold	67
	9.3.1	Geologic Mapping and Surface Sampling	68


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	9.3.2	Geophysics	68
10	Drilling		70
	10.1	Type and Extent	70
	10.2	Sample Collection	71
	10.3	Collar Locations and Downhole Surveys	72
11	Sample Preparation, Analyses and Security		74
	11.1	Sample Preparation for Analysis	74
	11.1.1	Off-Site Sample Preparation	75
	11.2	Sample Analysis	76
	11.3	Check Assays	76
	11.4	Quality Assurance/Quality Control Procedures	76
	11.4.1	Certified Reference Material	76
	11.4.2	Blanks	77
	11.4.3	Duplicates	77
	11.4.4	Actions and Results	77
	11.5	Opinion on Adequacy (Security, Sample Preparation, Analysis)	77
12	Data Verification		79
	12.1	Data Validation of Pre-Romarco Holes	79
	12.2	Verification of Romarco and OceanaGold Data	79
	12.2.1	Romarco Data Verification	80
	12.2.2	Horseshoe Data Verification 2016	80
	12.3	Haile QA/QC ALS July 2017- December 2025	81
	12.3.1	July 2017 to December 2025 CRM Performance	81
	12.3.2	Contamination Monitoring	85
	12.3.3	Statement of Data Adequacy	85
13	Mineral Processing and Metallurgical Testing		86
	13.1	Testing and Procedures	87
	13.1.1	Comminution	87
	13.1.2	Throughput Estimate Assumptions	93
	13.1.3	Flotation and Cyanidation	94
	13.1.4	Sample Representativeness	105


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	13.2	Palomino Deposit	106
	13.3	Ledbetter Underground Deposit	112
	13.4	Recovery Estimate Assumptions	120
14	Mineral Resource Estimates		122
	14.1	Drillhole Database	122
	14.1.1	Data Cut-Off Date – Mineral Resource Models	123
	14.2	Geologic Model Concepts	123
	14.3	Lithology	124
	14.3.1	Silicification	125
	14.3.2	Pyrite	125
	14.4	Domaining	125
	14.4.1	Gold	125
	14.4.2	Silver	126
	14.5	Compositing	127
	14.6	Top-Capping	128
	14.7	Bulk Density	128
	14.8	Mineral Resource – Open Pit	128
	14.8.1	Block Model	130
	14.8.2	Estimation Methodology	131
	14.8.3	Open Pit Geometallurgical Model	131
	14.9	Mineral Resource - Horseshoe Underground	132
	14.9.1	Block Model	133
	14.9.2	Estimation Methodology	134
	14.10	Mineral Resource - Palomino Underground	134
	14.10.1	Block Model	135
	14.10.2	Estimation Methodology	136
	14.11	Mineral Resource – Ledbetter Underground	137
	14.11.1	Block Model	139
	14.11.2	Estimation Methodology	140
	14.11.3	Ledbetter Underground Geometallurgical Model	140
	14.12	Open Pit and Underground Resource Classification	141


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	14.13	Open Pit and Underground Model Validation	141
	14.13.1	Open Pit and Underground Model Reconciliation	145
	14.13.2	Open Pit and Underground Model Reviews	146
	14.13.3	Open Pit and Underground Combined Mineral Resource Statement	148
	14.14	Relevant Factors	149
15	Mineral Reserve Estimates		150
	15.1	Open Pit Mineral Reserve Estimate	150
	15.1.1	Introduction	150
	15.1.2	Conversion Assumptions, Parameters and Methods	150
	15.1.3	Reserve Estimate	151
	15.2	Underground Mineral Reserve Estimate	153
	15.2.1	Introduction	153
	15.2.2	Conversion Assumptions, Parameters and Methods	154
	15.2.3	Reserve Estimate	155
	15.3	Open Pit and Underground Combined Reserves Statement	156
16	Mining Methods		158
	16.1	Open Pit Mining Methods	158
	16.1.1	Current or Proposed Mining Methods	158
	16.1.2	Geotechnical	159
	16.1.3	Optimization	165
	16.1.4	Ledbetter Open pit vs Underground Study	169
	16.1.5	Mine Design	171
	16.1.6	Overburden/Geochemical	172
	16.1.7	Mine Production Schedule	177
	16.1.8	Mining Fleet and Requirements	182
	16.1.9	Open Pit Mine Dewatering	183
	16.2	Underground Mining Methods	184
	16.2.1	Cut-off Grade Calculations	184
	16.2.2	Underground Geotechnical	185
	16.2.3	Mine Design	199
	16.2.4	Geochemical Classification	201


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	16.2.5	Mining Operations	202
	16.2.6	LOM Production Schedule	204
	16.2.7	Mine Equipment	207
	16.2.8	Hydrogeology and Mine Dewatering	207
	16.3	Combined Production Schedule	208
17	Recovery Methods		210
	17.1	Processing Methods	210
	17.2	Processing Flowsheet	213
	17.3	Operational Results	213
	17.4	Processing Schedule and Unit Costs	217
	17.5	Contact Water Treatment Plant	219
	17.6	Concentrate Leach Circuit Upgrade	219
18	Project Infrastructure		221
	18.1	Tailing Storage Facility	221
	18.2	Overburden Storage	224
	18.3	Potential Acid Generating (PAG) Overburden Storage Areas	224
	18.4	Site Wide Water Management	226
	18.5	Site Wide Water Balance	228
	18.6	Water Supply	229
	18.7	Surface roads and Bridges	229
	18.8	Underground Surface Infrastructure	229
	18.9	Power Supply	231
19	Market Studies and Contracts		232
20	Environmental Studies, Permitting, and Social or Community Impact		234
	20.1	Required Permits and Status	237
	20.2	Environmental Studies	237
	20.3	Environmental Bond	237
21	Capital and Operating Costs		238
	21.1	Capital Expenditure Estimates	238
	21.2	Operating Cost Estimates	238


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22	Economic Analysis		240
	22.1	Principal Assumptions and Input Parameters	240
	22.2	Taxes, Royalties and Other Interests	241
	22.2.1	Taxation	241
	22.2.2	Royalties	241
	22.2.3	Financing Costs	242
	22.3	Pricing Model Results – Reserves Case	242
	22.4	Sensitivity Analysis	244
	22.4.1	Operational Sensitivity	244
	22.4.2	Gold Price Sensitivity	244
	22.4.3	Discount Rate Sensitivity	245
	22.4.4	Alternative Pricing Model Result	246
23	Adjacent Properties		247
	23.1	Ridgeway Mine	248
	23.2	Brewer Mine	248
	23.3	Barite Hill Mine	249
24	Other Relevant Data and Information		250
25	Interpretation and Conclusions		251
	25.1	Geology and Mineralization	251
	25.2	Resource Estimation	251
	25.2.1	Open Pit	251
	25.2.2	Underground	252
	25.3	Status of Exploration, Development and Operations	252
	25.4	Mining Reserves	252
	25.4.1	Open Pit	253
	25.4.2	Underground	253
	25.5	Mineral Processing and Metallurgical Testing	254
	25.6	Recovery Methods	254
	25.7	Project Infrastructure	255
	25.8	Environmental Studies and Permitting	255
	25.9	Economic Analysis	255


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26	Recommendations		257
	26.1	Recommended Work Programs	257
	26.1.1	Exploration	257
	26.1.2	Resource Estimation	257
	26.1.3	Status of Exploration; Development and Operations	257
	26.1.4	Mining and Reserves	258
	26.1.5	Mineral Processing and Metallurgical Testing	258
	26.1.6	Project Infrastructure	258
	26.1.7	Environmental Study Results	259
	26.1.8	Economic Analysis	259
	26.2	Recommended Work Program Costs	259
27	References		261
28	Glossary		266
	28.1	Mineral Resources	266
	28.2	Mineral Reserves	266
	28.3	Definition of Terms	267
	28.4	Abbreviations	269

Tables


Table 1-1:	Haile Open Pit and Underground Resource Statement as of December 31, 2025	26
Table 1-2:	Haile Open Pit Mineral Reserves Estimate as of December 31, 2025	28
Table 1-3:	Haile Underground Reserves Estimate as of December 31, 2025	30
Table 1-4:	OP and UG Reserve Statement for Haile Gold Mine as of December 31, 2025	31
Table 1-5:	Major Equipment Required to Achieve the Mine Schedule	33
Table 1-6:	Haile Underground Annual Production	34
Table 1-7:	Combined OP and UG Mining Production and Processing Schedule	35
Table 1-8:	Total Capital Expenditure Summary (US$000’s)	39
Table 1-9:	LoM Operating Cost Summary	39
Table 1-10:	LoM Indirect Costs Summary	40
Table 1-11:	Indicative Economic Results	41


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Table 2-1:	Site Visit Participants	45
Table 7-1:	Geological Summary of Major Gold Deposits of SE USA	56
Table 10-1:	Haile Drilling Campaigns by Year, Owner and Lab	71
Table 13-1:	Bond Ball Mill Work Indices for Haile Samples	87
Table 13-2:	Bond Rod and Ball Mill Work Indices for Haile Composite	88
Table 13-3:	Rod and Ball Mill Work Indices for Ledbetter Extension Samples	88
Table 13-4:	Rod and Ball Mill Work and Abrasion Indices for Horseshoe Samples	88
Table 13-5:	ALS Comminution Tests on Horseshoe Samples	89
Table 13-6:	ALS Comminution Tests on Mill Zone Pit Samples	89
Table 13-7:	ALS Comminution Test Results for 2018 Infill Sample Program	90
Table 13-8:	SGS Comminution Test Results for 2022 Variability Program	91
Table 13-9:	Geopyora Competency Test Results	93
Table 13-10:	RDi Whole-Ore Leach Test Results	95
Table 13-11:	Flotation Test Results – Averages by Grind	95
Table 13-12:	Flotation Test Results Average by Grade and Grind	96
Table 13-13:	Flotation Tailing Leach Test Results Average by Grade and Grind	97
Table 13-14:	Leaching Tests Conducted on the Flotation Concentrates and Flotation Tailings .100 Table 13-15: Gold Recovery by Ore Zone and Ore Grade	99
Table 13-16:	CIL Test Results for Fine Ground Flotation Concentrate	101
Table 13-17:	Tests Results for Composites from Mill Zone and Snake Areas	102
Table 13-18:	Test Results for Horseshoe Samples	103
Table 13-19	Test Results for Horseshoe Samples	104
Table 13-20:	Palomino Metallurgical Composite Plan	106
Table 13-21:	Palomino Competency Testing Results	107
Table 13-22:	Geochemical Analysis of Palomino Composites	109
Table 13-23:	Palomino Leach Test Results	111
Table 13-24:	Ledbetter Underground Lobe 1 Sample Distribution	113
Table 13-25:	Ledbetter Underground Prefeasibility Program Sample Source Summary	114
Table 13-26:	Geochemical Analysis of Ledbetter Underground Composites	115
Table 13-27:	Ledbetter Underground First Round Recovery Results	116
Table 13-28:	Ledbetter Underground Second Round Recovery Results	117


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Table 13-29:	Ledbetter Underground Third Round Recovery Results	118
Table 14-1:	Data Cut-Off Dates for Resource Models	123
Table 14-2:	Hard Boundaries Au Domain Thresholds	125
Table 14-3:	Assigned Lithological Bulk Density Values	128
Table 14-4:	Haile Open Pit Indicator Gold Class Thresholds and Means	130
Table 14-5:	HA0725OLM_V6 Block Model Dimensions	131
Table 14-6:	Horseshoe UG 3m composite Statistics Comparison by Domain	133
Table 14-7:	Block Model Dimensions and Origin	133
Table 14-8:	Palomino UG Basic Statistics for 3 m Composites by Domain	135
Table 14-9:	Palomino Block Model Dimensions and Origin	136
Table 14-10:	Ledbetter UG Basic Statistics for 3 m Au Composites by Domain	139
Table 14-11:	Ledbetter UG Basic Statistics for 3 m Ag Composites (Based Only on Actual Ag Data) by Ag Domains	139
Table 14-12:	Ledbetter UG Basic Statistics for 3 m Ag Composites (Based on Actual and Simulated Ag Data) by Ag Domains	139
Table 14-13:	Block Model Dimensions and Origin Setup	140
Table 14-14:	Haile Open Pit and Underground Resource classification Criteria	141
Table 14-15:	Open Pit Resource Model Reconciliation	146
Table 14-16:	Underground Resource Model Reconciliation	146
Table 14-17:	Haile Open Pit and Underground Resource Statement as of December 31, 2025 .145 Table 15-1: Pit Optimization Parameters	148
Table 15-2:	Haile Open Pit Mineral Reserves Estimate as of December 31, 2025	152
Table 15-3:	Dilution ELOS Assumptions	154
Table 15-4:	Mine Design Dilution Factors	155
Table 15-5:	Haile Underground Reserves Estimate as of December 31, 2025	156
Table 15-6:	Combined Reserve Statement for OceanaGold’s Haile Gold Mine as of December 31, 2025	157
Table 16-1:	ISA Recommendations for Near Surface Materials	162
Table 16-2:	Mill Zone ISA Recommendations for Metasediments and Diabase Dikes	162
Table 16-3:	Mill Zone ISA Recommendations for Metavolcanics	163
Table 16-4:	ISA Recommendations for Metasediments and Diabase Dikes – Snake, Haile, and Ledbetter Pits	163
Table 16-5:	ISA Recommendations for Metavolcanics – Snake, Haile, and Ledbetter Pits	164


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Table 16-6:	Summary of Rock Mass Properties	164
Table 16-7:	Pit Optimization Parameters	166
Table 16-8:	Optimization Results for Selected Shell on US$44 Gold Price Increments	168
Table 16-9:	Overburden Classification at Haile	175
Table 16-10:	Cut-off Grade Calculation	177
Table 16-11:	Tonnage and Grade Multipliers for Application of Mining Dilution and Ore Recovery	178
Table 16-12:	Phase Inventory (1/1/2026 to End of Mine Life)	179
Table 16-13:	Open Pit Production Summary	180
Table 16-14:	LoM Yearly Bench Sinking Rates (10 m bench equivalents)	181
Table 16-15:	Factors in Estimation of Potential Operating Hours for a Typical Year	182
Table 16-16:	Major Equipment Required to Achieve the Mine Schedule	183
Table 16-17:	Underground Cut-off Grade Calculation	184
Table 16-18:	Drillhole Data Used in Underground Geotechnical Block Models	185
Table 16-19:	In Situ Stress Measurement Summary	188
Table 16-20:	Summary of the Laboratory Testing	188
Table 16-21:	Summary of Strength Properties (mi and σci)	192
Table 16-22:	Summary of Permanent Support Categories for Palomino and Ledbetter	198
Table 16-23:	Summary of Production Support Categories for Palomino and Ledbetter	199
Table 16-24:	Underground Stope Design Dimensions	199
Table 16-25:	Underground Production Summary	205
Table 16-26:	Horseshoe Underground Production Summary	206
Table 16-27:	Palomino Underground Production Summary	206
Table 16-28:	Ledbetter Underground Production Summary	206
Table 16-29:	Mobile Equipment Fleet	207
Table 16-30:	Combined Open Pit and Underground Mining Schedule and Processing Schedule	209
Table 17-1:	Key Consumable Consumption Rates	218
Table 19-1:	Key Contracts and Status Requirements	233
Table 20-1:	Mine Permits	236
Table 21-1:	Total Capital Expenditure Summary (US$000’s)	238
Table 21-2:	LoM Operating Cost Summary	239


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Table 21-3:	LoM Indirect Costs Summary	239
Table 22-1:	Basic Model Parameters	240
Table 22-2:	Haile Tax Deductions (US$000’s)	241
Table 22-3:	Financial Performance Summary (Reserve Case)	243
Table 22-4:	Indicative Economic Results at Alternative Price Profile	247
Table 26-1:	Summary of Costs for Recommended Work	260
Table 28-1:	Definition of Terms	267
Table 28-2:	Abbreviations	269

Figures


Figure 1-1:	Final Pit Design and Site Layout	32
Figure 1-2:	LoM Production Schedule	33
Figure 1-3:	Combined OP and UG Ore Production Schedule	36
Figure 1-4:	Annual Processing Schedule	37
Figure 4-1:	General Location Map of the Haile Gold Mine	47
Figure 4-2:	Site Map of the Haile Gold Mine	48
Figure 4-3:	Land Tenure Map	49
Figure 7-1:	Time Distribution of Major Geological Events in the Carolinas	55
Figure 7-2:	District Geology of North-Central South Carolina (UTM NAD83 Z17N)	58
Figure 7-3:	Geologic Map of the Haile Area with Gold Zones (UTM NAD83 Z17N)	59
Figure 7-4:	Haile Stratigraphic Column	60
Figure 7-5:	High Strain Fabrics in Core Samples	62
Figure 12-1:	Horseshoe AuFA_grav KML vs. ALS 0-53 g/t (n=253)	81
Figure 12-2:	July 2017- December 2025 CRM Analyses vs. Expected Value	82
Figure 12-3:	July 2017 to December 2025 CRM Analyses vs. Expected Value <4 g/t	82
Figure 12-4:	July 2017- December 2022 CRMs: OxF125 (Au=0.806), OxG124 (Au=0.918), and OxH122 (Au=1.247)	83
Figure 12-5:	January 2024 - December 2025 CRMs: OXE150 (Au=0.658), OXI177 (Au=1.811), OXI121 (Au=1.834), and OXJ176 (Au=2.385)	84
Figure 12-6:	October 2019 to December 2025 CRMs: SC127 (Au=0.225) and SF85 (Au=0.848)	84


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Figure 12-7:	October 2017 to December 2025 CRMs: HiSilK2 (Au=3.474) and HiSilP3 (Au=12.240)	85
Figure 13-1:	Updated Modeled vs. Measured SAG Specific Energy Values	92
Figure 13-2:	Overall Percent Recovery vs. Head Grade	105
Figure 13-3:	Haile Global Recovery Database Results by Source	112
Figure 13-4:	Relationship Between Gold Deportment and Concentrate Leach Recovery at 24 hours	119
Figure 13-5:	Overall Gold Recovery Estimation from Gold Telluride Deportment at Varying Concentrate Leach Residence Times	120
Figure 14-1:	Schematic Cross-Section Looking NE – Showing Relationship of UG deposits to MS/MV contact (Blue line) and Regional Foliation (Orange Line)	124
Figure 14-2:	Ledbetter UG deposit log-scale scatter plot of Ag (Original / Simulated) vs Au	127
Figure 14-3:	Haile Open Pit	129
Figure 14-4:	Plan View showing Horseshoe (Red) Relative to Open Pit Areas	132
Figure 14-5:	Long-Section Looking NNW, showing Palomino Mineralization, Horseshoe, HEX and, Entire Haile Drilling Intercept Dataset Shown (colored by Au g/t)	134
Figure 14-6:	Ledbetter UG Lithology Slice View, along Strike of Mineralization (striking NW), looking NE	137
Figure 14-7:	Looking South – Ledbetter UG deposit, relative to the final Ledbetter open pit	138
Figure 14-8	Swath Plot Open Pit (Domain 1) Block Model Grade (vol weighted) vs. 2.5 m Top Capped Composite (Declustered Weighting)	142
Figure 14-9	Swath Plot Horseshoe UG (Domain 1) Block Model Grade (vol weighted) vs. 3 m Top Capped Composite (length Weighted)	143
Figure 14-10	Swath Plot Ledbetter UG (Lobe 1) Block Model Grade (vol weighted) vs. 3 m Top Capped Composite	144
Figure 14-11	Swath Plots Palomino UG (Easting only) Domain 1 Block Model Grade (vol. weighted) vs. 3 m Top Capped Composite (Length and declustered weighting)	145
Figure 15-1:	General Site Layout and Location of the UG Reserve Area (in blue)	153
Figure 16-1:	Haile Open Pit Naming Convention	158
Figure 16-2:	Pit Optimization Results by Gold Price	167
Figure 16-3:	Cross-Section, Ledbetter optimization shell showing revenue factor step change and resource model block >0.5 g/t Au	169
Figure 16-4:	Cross-Section, Footprint of Ledbetter Phase 4 Open Pit vs Ledbetter Underground	170
Figure 16-5:	Incremental Value – Relative valuation of Ledbetter Phase 4 OP vs UG	171


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Figure 16-6:	LoM Ultimate Pit Design	172
Figure 16-7:	Final Pit Design and Ultimate Overburden Storage Site Plan	176
Figure 16-8:	Open Pit Annual Production Schedule	180
Figure 16-9:	OP Mined Material Type Annual Schedule	181
Figure 16-10:	Rock Quality Distributions within the HUG, PUG, and LUG MSO Shapes	186
Figure 16-11:	Horseshoe, Palomino, and Ledbetter UG Stereonets	187
Figure 16-12:	HUG, PUG, and LUG Rock Qualities by Rock Type	189
Figure 16-13:	Generalized Geotechnical Cross Section – Horseshoe (Looking NE)	190
Figure 16-14:	Generalized Geotechnical Cross Section – Palomino (Looking NE)	191
Figure 16-15.	Generalized Geotechnical Cross Section - Ledbetter (Looking NE)	192
Figure 16-16:	Stability Graph Results – Horseshoe	194
Figure 16-17:	Stability Graph Results – Palomino	195
Figure 16-18:	Stability Graph Results – Ledbetter	195
Figure 16-19:	Long Hole Stoping Method Schematic	200
Figure 16-20:	Typical Stoping Sequence	200
Figure 16-21:	Typical Secondary Stope Line Backfill	201
Figure 16-22:	Typical Level Ventilation Overview	203
Figure 16-23:	Underground Life of Mine Ventilation Model	204
Figure 16-24:	Annual Underground Ore Production Schedule	205
Figure 16-25:	Annual Open Pit and Underground Production	208
Figure 17-1:	Haile Process Flow Sheet	213
Figure 17-2:	Mill Throughput Performance Since Startup	214
Figure 17-3:	SAG Mill Utilization Since Startup	215
Figure 17-4:	Flotation Circuit Recovery	216
Figure 17-5:	Gold Recovery Performance 2021-2025	217
Figure 17-6:	Process and Gold Production Schedule	217
Figure 17-7	Proposed new Concentrate Leach CIP circuit location	220
Figure 18-1:	Tailing Storage Facility Layout	222
Figure 18-2:	Tailing Storage Facility Typical Section	223
Figure 18-3:	West PAG Overburden Storage Area	225
Figure 18-4:	As Built Fresh Water Storage Dam	227


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Figure 18-5:	Underground Surface Infrastructure Detail	230
Figure 18-6:	Proposed Ledbetter Underground Surface Infrastructure	230
Figure 22-1:	Project After-Tax Metrics Summary	242
Figure 22-2:	Operational Sensitivity Analysis	244
Figure 22-3:	Gold Price Sensitivity Analysis	245
Figure 22-4:	Discount Rate Sensitivity Analysis	246

Appendices


Appendix A: Certificates of Qualified Persons			246


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NI 43-101 Technical Report – Haile Gold Mine, South Carolina, United States

1Summary

OceanaGold Corporation (OceanaGold) has prepared this National Instrument 43-101 (NI 43-101) Technical Report (Technical Report) on the Haile Gold Mine (Haile or Project) to support disclosures in OceanaGold’s Annual Information Form for the year (Y) ended December 31, 2025.

This report includes both open pit (OP) and underground (UG) mining components and a single economic analysis based on Mineral Reserves. Underground mining components include previously reported Horseshoe Underground (HUG) and Palomino Underground (PUG). This report also includes technical data from a Feasibility Study (FS) to support the initial Mineral Reserve for the Ledbetter Underground (LUG), first reported in the OceanaGold Mineral Reserve Statement for End of Year 2025.

1.1Property Description, Location, Access and Ownership

The Haile Gold Mine is located 5 kilometres (km) northeast of Kershaw in southern Lancaster County, South Carolina. It is 30 km southeast of Lancaster, the county seat, and 80 km northeast of Columbia, the state capital of South Carolina. As of December 31, 2025, Haile Gold Mine Inc. (HGM) owns a total of 10,978 acres in South Carolina. Of this total, 5,469 acres are within the mine permit boundary.

The Haile property is accessible by U.S. Highway 601, with the main access via Snowy Owl Road.

The Haile Gold Mine, (HGM), is 100% (percent) owned and operated by OceanaGold through its wholly owned subsidiary. HGM owns or controls all land associated with Haile and within the mining permit boundary. Its interest in the properties includes surface, water and mineral rights with no associated royalties, and is free of all claims and access restrictions.

1.2History

Haile is situated in the Carolina Terrane, which was the location of the first gold (Au) rush in the U.S. in the early 1800’s. Gold was first discovered in 1827 near Haile in the gravels of Ledbetter Creek (now the Haile Gold Mine Creek (HGMC)), which led to placer mining and prospecting until 1829.

In 1882, a sixty-five-stamp mill was constructed and operated continuously until 1908. From mid-1937 to 1942, larger scale mining was undertaken on site by the Haile Gold Mines Company and was shut down in 1942 because of World War II. By this time, the Haile Gold Mine had produced over US$6.4 million worth of gold (in 1940 U.S. dollars).

Between 1981 and 1985, Piedmont Land and Exploration Company (later Piedmont Mining Company (Piedmont)) explored the historic Haile Gold Mine and surrounding properties. Piedmont mined the Haile deposits from 1985 to 1992, producing 85,000 ounces (oz) of gold from open pit heap leach operations that processed oxide and transitional ores.

In May 1992, Amax Gold Inc. (Amax) and Piedmont entered into a joint venture agreement and established the Haile Mining Company (HMC). At the end of the Amax / HMC program in 1994, a gold reserve estimate was prepared, but due to unfavourable economic conditions at the time, Amax did not proceed with mining.


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Kinross Gold Corporation (Kinross) acquired Amax in 1998, assumed Amax’s portion of the HMC joint venture and later purchased Piedmont’s interest. Kinross decided not to reopen the mine.

Romarco Minerals, Inc. (Romarco or RMI) acquired the Haile property from Kinross in October 2007. It completed a confirmation drilling program and began infill and exploration drilling programs during its ownership.

OceanaGold acquired Haile through the acquisition of Romarco in 2015 and commenced commercial production in early 2017.

1.3Geological Setting, Mineralization and Deposit Types

1.3.1Geology

Haile is the largest operating gold mine in the eastern U.S. It is situated within the northeast-trending Carolina Terrane, also known as the Carolina Slate Belt, which hosts the past-producing Ridgeway, Brewer, and Barite Hill gold mines in South Carolina. Mineralization at Haile is currently interpreted as a structurally modified, low-sulfidation, disseminated gold deposit. The Haile property consists of eleven gold deposits within a 4 km x 1 km area. The deposits occur within a variably deformed ENE-trending structural zone at or near the contact between metamorphosed Neoproterozoic volcanic and sedimentary rocks. The deposits are hosted in metamorphosed laminated siltstones and volcanic rocks of the Upper Persimmon Fork Formation and are dissected by barren NNW striking diabase dikes. Deformation includes brittle and ductile styles with ENE trending foliation, faults, brecciation, and isoclinal folds. Sedimentary rocks are folded within an ENE trending anticlinorium with a steep SE limb and a gentle NW limb. Foliation dips to NW.

1.3.2Mineralization and Deposit Types

The age of gold mineralization is assumed at ~ (approximately) 549 Ma (mega-annum), based on closely associated molybdenite dated using Rhenium-Osmium (Re-Os) isotopes (Mobley et al., 2014), which postdates peak volcanism. Pressure shadows around pyrite grains, stretched pyrite and pyrrhotite grains, and flattened hydrothermal breccia (brecciated rocks) clasts indicate that some deformation has occurred subsequent to sulphide mineralization whereas the bulk geometry and orientation of the deposits is difficult to reconcile with pre-folding emplacement. The Re-Os date coincides with a major tectonostratigraphic change from intermediate volcanism and tuffaceous to epiclastic sedimentation to basinal turbiditic sedimentation. Quartz-sericite-pyrite (QSP) alteration is overprinted by regional greenschist facies metamorphism with carbonate-chlorite-pyrite alteration.

Haile gold mineralization occurs as an en-echelon 4 km long x 1 km wide cluster of northeast-striking moderately to steeply dipping ore lenses. Ore body geometry, depth, size, grade, mineralogy and alteration vary between deposits and is strongly controlled by post-mineral shearing and rotation. Some of the deposits coalesce, especially in the central part of the district around the large Ledbetter deposit. Ore lenses are typically 50 to 300 metres (m) long, 20 to 100 metres wide, and 5 to 30 m thick. Gold mineralization is mostly hosted by laminated siltstone and intermediate volcanics of the upper Persimmon Fork Formation and is overlain by volcanic rocks. Mineralization is typically within 100 m of the main sediment volcanic contact. Haile is currently interpreted as a tectonically modified, low-sulfidation, disseminated gold deposit.


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1.4Mineral Permits and Regulatory Matters

Haile is subject to the Haile Mine Operating Permit, SCDES 401 Water Quality Certification, National Pollutant Discharge Elimination System (NPDES) permit, Title V Air Quality permit, and the permit under Section 404 of the Clean Water Act (404 Permit). The current permits for Haile expire in December 2039.

HGM owns or controls all land associated with Haile and within the mining permit boundary. Its interest in the properties includes surface, water and mineral rights with no associated royalties, and is free of all claims and access restrictions.

Haile is relatively unique in that mining occurs wholly on private land owned by HGM and does not impact federal or public (United States Department of the Interior Bureau of Land Management (USBLM) or United States Forest Service (USFS)) lands that would be subject to modifications from these surface management agencies.

In May 2018, HGM applied to the United States Army Corps of Engineers (USACE) to initiate the National Environmental Policy Act (NEPA) process and launch a Supplemental Environment Impact Statement (SEIS). The USACE has jurisdictional responsibility for all waters of the U.S. and works cooperatively with the U.S. Environmental Protection Agency (EPA) and South Carolina Department of Environmental Services (formerly the South Carolina Department of Health and Environmental Control) (SCDES) for modifications that have impacts to wetlands, groundwater and surface water conditions, and air emissions. HGM submitted a Project Description, Alternatives Analysis, and additional technical reports in support of this application. These technical reports covered a wide range of matters, including impact assessments to the wetlands, air, land, vegetation, groundwater, surface water, flora and fauna, cultural heritage sites, socioeconomic conditions, and reclamation plans.

To adjust current and supplemental mine plans, a modified application of the 404 Permit under the Clean Water Act of 1972 was submitted in the Q4 2020. The final SEIS was published in August 2022. The Supplemental Environmental Impact Statement Record of Decision (SEIS ROD) and modified 404 Permit were received in December 2022. Various permitting approvals and certifications were also required from SCDES, including modification of the Haile Mine Operating Permit, which was received in December 2022, and 401 Water Quality Certification which was received in November 2022. Other federal and state agencies included in the review process during the SEIS included EPA, United States Fish and Wildlife Service, South Carolina Department of Natural Resources, South Carolina State Historic Preservation Office, South Carolina Department of Transportation and Catawba Indian Nation. The NEPA process also allows non-government or civil society groups (NGOs) and other interested parties an opportunity for review and comment on the anticipated impacts.

Since December 2022, SCDES has approved two additional modifications to the Haile Mine Operating Permit. An expansion of the Horseshoe Underground operation was approved on February 21, 2024, and the Palomino Underground operation was approved on March 15, 2024. The permit modification for the method of mining change for Ledbetter Phase 4 to an underground is classed as a minor modification and is expected to be completed in 2027 before mining takes place in 2028.


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1.5Exploration

Geologic mapping and surface sampling are key tools for exploration at Haile despite the fact that mapping is challenged by poor bedrock exposure due to extensive saprolitic weathering, Coastal Plains Sands (CPS) cover, and dense vegetation.

Historical mapping has been scanned and loaded into three-dimensional (3D) software for structural interpretation, exploration planning, and geologic modeling. The use of the structural dataset in conjunction with the drilling dataset has provided the foundation for a 3D digital geologic model. Over 5,000 surface samples have been compiled based on location, sample type (rock chip, saprolite (Sap), soil, stream sediment), rock type, alteration, and assay to further the geological knowledge. However, quality analysis / quality control (QA/QC) data were generally lacking for these surface samples, and most were assayed only for gold.

In 2016, HGM conducted proprietary inversion modeling to depths of 1,500 m using airborne magnetic and electromagnetic (EM) data. In 2023, HGM engaged a third party to reprocess previous surface induced polarization (IP) / resistivity data and to perform additional downhole IP surveys.

1.6Drilling

Resource definition drilling at Haile by Romarco and subsequently OceanaGold has significantly increased the resources since 2007. Reserve growth has resulted from continued drilling, project development, and higher gold prices. Initial Mineral Reserves for Horseshoe and Palomino undergrounds were declared in 2017 and 2023, respectively. This Technical Report includes an initial Mineral Reserve for Ledbetter Underground which replaces Ledbetter Phase 04 open pit.

The Haile database includes 3,754 holes in the Haile district which are securely stored in an acQuire database. Drillhole collar locations, downhole surveys, geological logs, geotechnical logs, density values and assays have been verified and used to build 3D geological models and are used for grade and tonnage interpolations. Geologic interpretation is based on structure, lithology, and alteration as logged in the drillholes. Robust geological models enable better prediction of the nature and behaviour of the disseminated style of gold mineralization at Haile. Resource drilling at Haile has predominantly been conducted by core and RC drilling, with drillhole spacing typically ranging from 25 to 40 m. Hole depths have ranged from 50 to 700 m. Sample interval lengths average 1.5 m and can vary based on geological logging. QA/QC results were validated from assay labs and showed excellent precision and accuracy relative to certified reference materials (CRMs).

1.7Sampling, Analysis and Data Verification

Drill core is cleaned, measured, and photographed at HGM’s on-site core shed. Geotechnical and geologic logging are completed on the whole core. All logging and sampling handling is conducted by HGM personnel. Data collecting during core logging includes structure, rock type, alteration, mineralogy, Rock Quality Designation (RQD), core recovery, hardness, and joint condition. Standardized templates are used for logging consistency. HGM’s geologists routinely review core together and compare notes to ensure accuracy and continuous improvement.

Density samples are collected every ten metres and use the water immersion method to measure specific gravity. Competent core at Haile does not require plastic or wax coatings for density measurements. Sample collection, preparation, and analysis are according to industry standards.


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Core is primarily prepared and assayed at the independent ALS Limited (ALS) laboratory in Tucson, Arizona and Reno, Nevada, U.S., both of which are ISO-9001 certified and 17025 accredited. At times, samples have been prepared and assayed by HGM’s Kershaw Mineral Lab (KML) facility in Kershaw, South Carolina and the independent Alfred H. Knight (AHK) Geochem preparation facility in Spartanburg, South Carolina.

Certified Standards are routinely inserted at a rate of one in 20 samples (5%). Standards used are purchased from and certified by Rocklabs. Blanks are routinely inserted at a rate of one in 20 samples (5%). Such blanks include commercially available marble, sand, and quartz pebble.

Core, pulp, and reverse circulation (RC) samples are stored securely. Sample transport is by HGM personnel between secure facilities and by approved couriers to external labs. No significant risks have been identified for sample contamination or sample exchange.

All Haile drillhole data (assays, logs, surveys) are stored in a secure acQuire database which is managed by HGM’s senior database geologist. Assay data are imported by HGM’s exploration and geology personnel and checked by HGM’s senior database geologist. Strict data importing and verification protocols are followed to avoid, for example, overlapping or missing intervals, mismatched hole depths in different fields, duplicate hole IDs, or sample numbers and invalid logging codes.

1.8Mineral Processing and Metallurgical Testing

Samples of ore have been collected by HGM for metallurgical testing since 2010, which indicates that the ore will respond to flotation and direct agitated cyanide leaching technology to extract gold.

Comminution testwork on mineralized samples was performed by the independent Resource Development, Inc. (RDi), ALS Global, and Société Générale de Surveillance (SGS) laboratories. Tests included Bond work indices (Wi), SAG Mill Comminution (SMC), and JK Drop Weight impact testing. The results of the test work were used for additional power modeling to predict circuit throughputs with a modified SAG–Ball Mill-Pebble Crusher (SABC) grinding circuit that was subsequently commissioned in 2018. Testwork on core samples of the remaining open pit reserve indicate an increase in competency and hardness at depth to levels similar to that observed in the Horseshoe, Palomino, and Ledbetter UG deposit testwork.

The relative low variability of test work indicates that the different mineralized zones are similar in terms of ore grindability, mineral composition, and flotation and cyanide leaching response. Overall gold recovery will be in the range of 65% to 92% dependent primarily on head grade to the mill and less related to which zone the ore is mined from.

The data developed in the test programs has been used to establish a relationship between overall gold recovery and head grade. Operating experience and metallurgical development programs have indicated this relationship is valid over the life-of-mine (LoM).


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Testing of core samples from the Horseshoe and Palomino deposits has been undertaken using the same laboratory flowsheet that correlates well with plant performance. Overall results suggest these deposits will respond well to processing in the existing process plant without modification.

Testwork undertaken on the Ledbetter UG Resource has indicated that the Intrusive Breccia domain has a significantly different deportment of gold which is present in a number of telluride minerals rather than native gold inclusions. The testwork program has indicated an increase in leach residence time from the current 36 hours to 96 hours can significantly offset the impact of the telluride leach kinetics and return acceptable leach recoveries compared to the performance of metasediment (MS) hosted ore domains. Detailed design for the plant modification will be completed in 2026 and construction and commissioning completed in early 2028 with the capital costs incorporated into the LoM capital costs used in the economic analysis.

1.9Mineral Resources Estimate

The Mineral Resources and their classification have been prepared in accordance with the Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Standards on Mineral Resources and Reserves: Definitions and Guidelines, May 10, 2014 (CIM, 2014). Mineral Resources, which are inclusive of Mineral Reserves, are reported in accordance with NI 43-101 – Standards of Disclosure for Mineral Projects. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. It is reasonably expected that the majority of Inferred Mineral Resources could be upgraded to Indicated Mineral Resources with continued exploration; however, there is no certainty that Mineral Resources that are not Mineral Reserves will be converted into Mineral Reserves.

OceanaGold has a comprehensive Resource governance process in place, including model validation, peer review, external review, and model to mine to mill reconciliation. OceanaGold continues to develop and improve these processes.

The Resource estimates are based on drilling up to October 2025, interpreted lithologies, and geologic controls. Assays for gold supporting Resource drilling are comprehensive. However, the collection of silver, carbon, and sulfur (S) assay data has largely been retrospective and is significantly sparser than for gold. Sulfur and carbon data are primarily used for the prediction of overburden classification types. Sulfur grades are also used for mill feed sulfur estimates. Silver grade estimates are provided for metallurgical considerations (carbon stripping and electro-winning) as well as for revenue estimation, albeit silver is a minor contributor to revenue. Gold estimation was constrained within implicitly modeled grade shells. Model block estimates for post mineralization dikes were assigned zero gold grades post estimation. Metasediment / metavolcanic (MV) contacts were not used to constrain gold estimation. These approaches are supported by relationships between mineralization, bedding, and dikes observed in open pit grade control sample data. In situ dry densities are based upon lithologically grouped immersion determinations from core samples.

For the open pit estimate, grades were estimated into 10 m E x 10 m N x 5 m RL (reduced level) blocks using 2.5 m composites within the implicit grade domain. Grade estimation was completed in VulcanTM software, using Multiple Indicator Kriging (MIK) to produce E-Type estimates for gold. Top caps of 50 g/t (grams per tonne) Au were used to temper mean grades for the top indicator class threshold.


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Ordinary Kriging (OK) was used for silver, sulfur and carbon estimates, given the sparser data coverage.

For the underground estimates gold grades were estimated with VulcanTM modeling software into parent 10 m E x 10 m N x 10 m RL blocks (all sub-blocked for better volumetric determination) using OK with 3 m domained composites.

The reported open pit and underground Mineral Resources are classified as Indicated and Inferred Mineral Resources, based primarily on drillhole spacing but also considering kriging variance, slope regression, and geological complexity.

1.9.1Combined Open Pit and Underground Resource Estimate

Table 1-1 presents the combined open pit, stockpiles, and underground Resource statement for the Haile Property.


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Table 1-1: Haile Open Pit and Underground Resource Statement as of December 31, 2025


Gold	Measured			Indicated			Measured & Indicated			Inferred
	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Au (g/t)	Contained Oz (Moz)	Tonnes (Mt)	Au (g/t)	Contained Oz (Moz)	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)
Haile
Horseshoe Underground	1.98	5.11	0.33	2.76	5.11	0.45	4.74	5.11	0.78	0.5	2.7	0.0
Palomino Underground	-	-	-	4.19	3.38	0.45	4.19	3.38	0.45	0.8	2.5	0.1
Ledbetter Underground	-	-	-	4.07	4.12	0.54	4.07	4.12	0.54	1.2	2.9	0.1
Open Pits	2.58	1.21	0.10	16.1	1.64	0.85	18.7	1.58	0.95	0.6	0.9	0.0
Haile Total	4.56	2.91	0.43	27.1	2.63	2.30	31.7	2.67	2.72	3.1	2.4	0.2
Silver	Measured			Indicated			Measured & Indicated			Inferred
	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)
Haile
Horseshoe Underground	1.98	1.9	0.1	2.8	2.1	0.2	4.7	2.0	0.3	0.5	1.0	0.0
Palomino Underground	-	-	-	4.2	2.8	0.4	4.2	2.8	0.4	0.8	2.1	0.1
Ledbetter Underground	-	-	-	4.1	12	1.6	4.1	12	1.6	1.2	7.5	0.3
Open Pits	2.58	2.2	0.2	16 .1	2.5	1.3	18.7	2.5	1.5	0.6	2.4	0.0
Haile Total	4.56	2.0	0.3	27.1	4.0	3.5	31.7	3.7	3.8	3.1	4.0	0.4

Source: OceanaGold, 2025

•Mineral Resources are reported inclusive of Mineral Reserves and are reported on an in situ basis. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability.

•All Mineral Resources are based on metal prices of US$ (United States Dollar) 2,450/oz gold, US$4.50/lb copper and US$28.50/oz silver.

•It is reasonably expected that most of the Inferred Mineral Resources could be upgraded to Indicated Mineral Resources with continued exploration.

•Open Pit Mineral Resources reported within the Mineral Reserve design pit.

•Open Pit primary cut-off grade (CoG) is 0.50 g/t Au, while oxide CoG is 0.60 g/t Au.

•Underground Mineral Resources are reported within volumes guided by conceptual stope designs which are based upon economic assumptions above and exclude dilution.

•Horseshoe, Ledbetter, and Palomino Underground Mineral Resources at 1.70 g/t Au cut-off.

•All figures are rounded to reflect the relative accuracy and confidence of the estimates and totals may not add correctly.

•The Mineral Resources for the open pits and Horseshoe Underground were estimated under the supervision of Jonathan Moore, MAusIMM CP(Geo) of OceanaGold, a Qualified Person. The Mineral Resources for Palomino Underground and Ledbetter Underground were estimated under the supervision of Douglas Corley, MAIG RPGeo, a QP.


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1.10Mineral Reserve Estimate

1.10.1Open Pit Mineral Reserves Estimate

Dilution and ore recovery have been applied to the resource block model to account for a portion of mineralized material expected to be mined by face shovel excavators. The resource block model was then used for open pit optimization without further modification, as the block size in the model matched the selective mining unit (SMU) size of 10 m x 10 m x 5 m considered appropriate for the backhoe excavator loading units operating at Haile.

The open pit Mineral Reserves are reported within a pit design based on open pit optimization results (Lerchs-Grossmann algorithm) with a gold price of US$2,200/oz Au and silver price of US$25/oz Ag. Subsequent to pit optimization, inferred material within the final pit design was assigned as waste and given a zero-gold grade. The overall pit slopes (inter-ramp angle slopes) used for the design are based on operational level geotechnical studies and range from 30° to 45° (degrees). This includes a 5° allowance for ramps and geotechnical catch benches.

The open pit area referred to as Ledbetter Phase 4 has been removed from the open pit Mineral Reserve and added to the underground Mineral Reserve based on a trade-off study completed in 2025, which showed that project economics were improved by mining the deposit by underground methods, as well as other improvements including a smoother production profile, reduced waste and tailings storage requirements, and lower total carbon emissions.

Measured Mineral Resources were converted to Proven Mineral Reserves and Indicated Mineral Resources were converted to Probable Mineral Reserves by applying the appropriate modifying factors, as described herein, to potential mining pit shapes created during the mine design process.

The open pit mine design process results in open pit mining Mineral Reserves, including existing stockpiles, of 18.6 million tonnes (Mt) with an average grade of 1.57 g/t Au. The Mineral Reserve statement, as of December 31, 2025, for the Haile Open Pit is presented in Table 1-2.


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Table 1-2: Haile Open Pit Mineral Reserves Estimate as of December 31, 2025


Gold	Proven (1)			Probable			Proven & Probable
	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)
Haile
Open Pits	2.47	1.23	0.10	16.1	1.62	0.84	18.6	1.57	0.94
Haile OP Total	2.47	1.23	0.10	16.1	1.62	0.84	18.6	1.57	0.94
Silver	Proven (1)			Probable			Proven & Probable
	Tonnes (Mt)	Ag (g/t)	Contained Oz (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Oz (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Oz (Moz)
Haile
Open Pits	2.47	2.1	0.2	16.1	2.3	1.2	18.6	2.2	1.3
Haile OP Total	2.47	2.1	0.2	16.1	2.3	1.2	18.6	2.2	1.3

Source: OceanaGold, 2025

(1)Includes 0.8 Mt of stockpile material grading 1.0 g/t Au and 1.0 g/t Ag

•Mineral Reserves are based on a US$2,200/oz Au gold price and US$25/oz Ag silver price.

•Open pit Mineral Reserves are stated using a 0.5 g/t Au cut-off for primary and 0.6 g/t Au cut-off for oxide material.

•Open pit Mineral Reserves include variable dilution and mining recovery that has been applied in the mine schedule to the upper benches of each pit stage to account for assumed mining by face shovel excavator in these areas.

•Metallurgical recoveries for gold are based on a recovery curve for primary material of (1-(0.2152*Au grade^-0.3696)). with +2.5% uplift applied to material > 1.7 g/t Au. Recovery for oxide material is applied at 67%.

•Metallurgical recovery for silver is applied at 70%.

•Mineral Reserves are converted from resources through the process of pit optimization, pit design, production schedule and supported by a positive cash flow model.

•All figures are rounded to reflect the relative accuracy of the estimates. Totals may not sum due to rounding.

•The open pit Mineral Reserves were estimated under the supervision of Gregory Hollett of OceanaGold, a Qualified Person.

Technical risks to the Mineral Reserve have been reviewed and there are two relevant risk areas that have been identified.

A geotechnical risk associated with the south wall of Ledbetter Phase 3 is currently under evaluation and management due to a localized area of instability. Management plans are in the process of being developed for remediation of this area, which will potentially impact the short-term mine schedule and costs. However, this will have relatively minor impact on the long-term mine plan. Therefore, this is not considered to be a material risk to the Mineral Reserve.

The depleted Mill Zone open pit is currently being used for excess water storage. This has the potential to slow or limit access to the Haile Phase 2 open pit, due to the planned mining of the saddle between Haile Phase 1 and Mill Zone. Management plans are in place to remove the water in Mill Zone prior to the planned schedule for mining Haile Phase 2 and is therefore not considered to be a material risk to the Mineral Reserve.

OceanaGold knows of no existing environmental, permitting, legal, socio-economic, marketing, political, or other factors that might materially affect the open pit Mineral Reserve estimate.

1.10.2Underground Mineral Reserves Estimate

The current underground Mineral Reserves consist of three deposits: HUG; LUG; and PUG. These deposits are separated by ~1 km of development and encompass mineralization that extends down at depth and outside the pit extents.


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Based on the orientation, depth, and geotechnical characteristics of the mineralization, a transverse sublevel open-stoping method (long hole) with ramp access is used for all deposits. The stopes are 15 to 20 m wide at HUG and 15 m wide for LUG and PUG and stope lengths vary based on mineralization grade and geotechnical considerations. A spacing of 25 m between levels is used. Cemented rock fill (CRF), Unconsolidated Rock Fill (URF), and a mixture of the two is planned to be used to backfill the stopes. The CRF has sufficient strength to allow for mining adjacent to backfilled stopes.

The underground mine design process resulted in combined underground mining Mineral Reserves of 7.9 Mt (diluted) with an average grade of 3.56 g/t Au for Horseshoe, Ledbetter, and Palomino. The Mineral Reserve statement, as of December 31, 2025, for the combined underground mines are presented in Table 1-3.

This estimate is based on a mine design cut-off of 1.86 g/t Au. The numbers include a 94% to 100% mining recovery based on type of opening (e.g., stope, development) to the designed wireframes in addition to a 2% to 10% unplanned dilution where the additional material uses a value of zero for the grade of both Au and Ag.


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Table 1-3: Haile Underground Reserves Estimate as of December 31, 2025


Gold	Proven			Probable			Proven & Probable
	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)
Haile
Horseshoe Underground	1.52	4.39	0.21	2.63	4.24	0.36	4.14	4.29	0.57
Palomino Underground	-	-	-	3.62	2.96	0.34	3.62	2.96	0.34
Ledbetter Underground	-	-	-	4.00	3.39	0.44	4.00	3.39	0.44
Haile UG Total	1.52	4.39	0.21	10.2	3.45	1.14	11.8	3.57	1.35
Silver	Proven			Probable			Proven & Probable
	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)
Haile
Horseshoe Underground	1.52	1.5	0.1	2.6	1.8	0.2	4.1	1.7	0.2
Palomino Underground	-	-	-	3.6	2.7	0.3	3.6	2.7	0.3
Ledbetter Underground	-	-	-	4.0	11	1.3	4.0	11	1.3
Haile UG Total	1.52	1.5	0.1	10.2	5.5	1.8	11.8	5.0	1.9

Source: OceanaGold, 2025

•Mineral Reserves are based on a gold price of US$2,200/oz.

•Metallurgical recoveries for Ledbetter Underground are based on a geometallurgical model that correlates recovery with gold mineralogical association.

•The Mineral Reserve estimate is based on a mine design using an elevated cut-off grade of 1.86 Au g/t, with adjacent lower grade stopes included in the design. Incremental material is included in the Mineral Reserves based on an incremental stope cut-off grade of 1.74 g/t Au and an incremental development cut-off grade of 0.59 g/t Au.

•Mining recovery ranges from 94% to 100% depending on activity type. Sill levels use a 75% recovery. Mining dilution is applied using zero grade. The dilution ranges from 2% to 10% unplanned dilution where the additional material uses a value of zero for the grade of both Au and Ag.

•All figures are rounded to reflect the relative accuracy of the estimates. Totals may not sum due to rounding.

•Mineral Reserves have been stated on the basis of a mine design, mine plan, and cash-flow model.

•The Mineral Reserves were estimated under the supervision of by Brianna Drury of OceanaGold, a Qualified Person.

OceanaGold knows of no existing environmental, permitting, legal, socio-economic, marketing, political, or other factors that might materially affect the underground Mineral Reserve estimate.

1.10.3Combined Open Pit and Underground Reserves Estimate

Table 1-4 presents the combined open pit and underground Mineral Reserves statement for Haile.


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Table 1-4: OP and UG Reserve Statement for Haile Gold Mine as of December 31, 2025


Gold	Proven (1)			Probable			Proven & Probable
	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)
Haile
Underground	1.52	4.39	0.21	10.2	3.45	1.14	11.8	3.57	1.35
Open Pits	2.47	1.23	0.1	16.1	1.62	0.84	18.6	1.57	0.94
Haile Total	3.99	2.43	0.31	26.3	2.33	1.98	30.3	2.35	2.29
Silver	Proven (1)			Probable			Proven & Probable
	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)
Haile
Underground	1.52	1.5	0.1	10.2	5.5	1.8	11.8	5.0	1.9
Open Pits	2.47	2.1	0.2	16.1	2.3	1.2	18.6	2.2	1.3
Haile Total	3.99	1.9	0.2	26.3	3.5	3.0	30.3	3.3	3.2

Source: OceanaGold

(1) Includes 0.8 Mt of stockpile material grading 1.0 g/t Au and 1.0 g/t Ag

•Mineral Reserves are based on a gold price of US$ 2,200/oz Au and silver price of US$25/oz Ag.

•Metallurgical recoveries are based on a recovery curve for primary material of (1-(0.2152*Au grade^-0.3696)) with +0.025% uplift applied to material > 1.7 g/t Au. Recovery for oxide material is applied at 67%. .

•Metallurgical recoveries for Ledbetter Underground are based on a geometallurgical model that correlates recovery with gold mineralogical association.

•Overall metallurgical recovery for gold equates to 82.7%.

•Metallurgical recovery for silver is applied at 70%.

•Open pit Mineral Reserves are stated using a 0.5 g/t Au cut-off for primary and 0.6 g/t Au cut-off for oxide material. Open pit Mineral Reserves include variable dilution and mining recovery that has been applied in the mine schedule to the upper benches of each pit stage to account for assumed mining by face shovel excavator in these areas.

•Underground Mineral Reserves are based on a mine design using an elevated cut-off grade of 1.86 Au g/t, with adjacent lower grade stopes included in the design. Incremental material is included in the Mineral Reserves based on an incremental stope cut-off grade of 1.74 g/t Au and an incremental development CoG of 0.59 g/t Au. Mining recovery ranges from 94% to 100% depending on activity type. Sill levels use a 75% recovery. Mining dilution is applied using zero grade. The dilution ranges from 2% to 10% depending on activity type.

•All figures are rounded to reflect the relative accuracy of the estimates. Totals may not sum due to rounding.

•Mineral Reserves have been stated on the basis of a mine design, mine plan, and supported by a positive cash-flow model.

•The open pit Mineral Reserves were estimated under the supervision of Gregory Hollett of OceanaGold, a QP. The underground Mineral Reserves were estimated under the supervision of by Brianna Drury of OceanaGold, a QP.

An underground vs. open pit trade-off study has been completed specifically targeting the mineralization within, and in close proximity to, Ledbetter Phase 4. Results of this study showed that changing the mining method for Ledbetter Phase 4 from an open pit to an underground is economically preferable and delivers increased overall project value. This change is reflected in the overall Mineral Reserves.


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1.11Mining Methods

1.11.1Open Pit Mining Methods

The open pit at Haile is currently being mined using conventional truck and excavator methods.

The open pit that forms the basis of open pit Mineral Reserves and the Life of Mine, (LoM), production schedule is approximately 2.5 km from east to west, 1.25 km north to south with a maximum depth of 300 m. The design consists of multiple pushbacks with ramp locations targeting saddle points between the pit bottoms and also acting as catch benches for geotechnical purposes. Each bench has at least one ramp for scheduling. Generally, the number of benches mined within a pit phase within a given year fall below the target bench sinking rate of one 10 m bench per month.

Overburden and waste material are classified using blasthole sulfur and carbon assays that inform the routing and placement of materials. “Red” potentially acid generating (PAG) material is sent to geomembrane-lined facilities where the material is placed in lifts and compacted by haulage trucks. “Yellow” PAG can be stored in a lined facility or below a prescribed water table level within pits. “Yellow” material in-pit will be mixed with lime during placement in the pit void. “Green” non-PAG material can be placed in unlined facilities or used for construction. Figure 1-1 illustrates the site layout and final pit design.

Source: OceanaGold, 2025

•Current Phases (Blue), in-pit waste storage (yellow) and Final LOM Ex-Pit Facilities – PAG cell (red) and green waste OSA (green)

Figure 1-1: Final Pit Design and Site Layout

Open pit ore production rates are targeted to balance processing rates with underground production and stockpile balance. Processed tonnes average approximately 2.9 million metric


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tonnes per year (Mt/yr) over LoM. Total open pit fleet material movement, including rehandle, peaks at 38 Mt/yr in 2027 before reducing through to the end of the open pit mine life as underground production becomes the primary feed source for the processing plant. The mine production schedule (Mined + Rehandle) is summarized in the note section in Figure 1-2.

Source: OceanaGold, 2025

•Rehandle includes open pit ore (stockpile to ROM), open pit waste (temporary in-pit to final destination), Underground ore, and waste (portal to final destination)

Figure 1-2: LoM Production Schedule

Typical ancillary equipment, including small hydraulic excavators, track dozers, wheel dozers, motor graders, water trucks, and small rigid dump trucks (Caterpillar (Cat) 785) for rehandle support the mining operation. Table 1-5 shows the major equipment required annually to achieve the mine schedule.

Table 1-5: Major Equipment Required to Achieve the Mine Schedule


Machine Type	2026	2027	2028	2029	2030	2031	2032	2033
PC4000 Excavator	2	2	2	1	1	1	1	1
PC3000 Excavator	1	1	1	1	1	1	1	1
Cat 6020B Excavator	1	1	1	1	1	1	1	1
Komatsu 730E Trucks	19	19	17	11	8	8	7	5
Sandvik Leopard DI650i	7	7	6	6	6	6	6	2
Sandvik DR410i Drill	4	3	1

Source: OceanaGold, 2025


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1.11.2Underground Mining Methods

Underground mining at Haile is currently being performed via the transverse sublevel open stoping (long hole) method. The Haile underground consists of three deposits that are extensions of the open pit and are named, respectively, Horseshoe, Ledbetter, and Palomino Underground. Access to the three mines will be via portals within the open pits, with Horseshoe via Snake Pit already established, and future Ledbetter via Ledbetter Pit. Palomino will be accessible via a twin decline from Horseshoe and a single decline from Ledbetter Underground.

Stopes are planned to be backfilled with cemented rockfill, unconsolidated rockfill, or a mixture of the two.

The LoM plan uses internal company standards and historic mining rates for the site to establish the schedule and sequence of mining. The latest LoM schedule has underground mining planned to finish in 2035, producing on average 1,600 thousand tonnes (kt) total tonnes per year with two peak years in 2030 and 2031 at just under 2,000 kt total tonnes when all three undergrounds are in full production. Reference Table 1-6 for Haile Underground Annual Production.

All material, both ore and waste, from the underground is hauled out via underground 50 tonne articulated trucks to a surface stockpile where it is then rehandled to its destination via the open pit haulage fleet.

Table 1-6: Haile Underground Annual Production


Year	Ore Tonnes (kt)	Au (g/t)	Waste Tonnes (kt)	Total Tonnes (kt)
2026	734	4.37	466	1,199
2027	714	4.18	462	1,176
2028	1,046	3.30	545	1,591
2029	1,156	4.29	447	1,603
2030	1,444	3.54	517	1,961
2031	1,583	3.31	377	1,960
2032	1,476	3.45	69	1,545
2033	1,500	3.60	126	1,626
2034	1,403	3.33	133	1,536
2035	703	2.70	9	713
LOM Total	11,757	3.57	3,152	14,909

Source: OceanaGold, 2025

1.11.3Combined OP and UG Production Schedule

Table 1-7 shows the combined annual open pit and underground ore production and processing schedule, with the ore mined production profile shown in Figure 1-3.


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Table 1-7: Combined OP and UG Mining Production and Processing Schedule


Description	Description	Unit	2026	2027	2028	2029	2030	2031	2032	2033	2034	2035	2036	LoM Total
Underground Mining	Ore	Mt	0.73	0.71	1.05	1.16	1.44	1.58	1.48	1.50	1.40	0.70	-	11.8
	Au Grade	g/t	4.37	4.18	3.30	4.29	3.54	3.31	3.45	3.60	3.33	2.70	-	3.57
	Contained Au	Moz	0.10	0.10	0.11	0.16	0.16	0.17	0.16	0.17	0.15	0.06	-	1.35
	Ag Grade	g/t	1.6	1.4	1.5	1.9	4.4	4.9	7.6	8.3	6.8	7.6	-	5.0
	Contained Ag	Moz	0.04	0.03	0.05	0.07	0.20	0.25	0.36	0.40	0.31	0.17	-	1.9
Open-pit Mining(1)	Ore	Mt	4.38	4.79	1.59	1.03	1.37	2.32	1.18	1.10	-	-	-	17.8
	Au Grade	g/t	2.01	1.91	1.06	1.16	1.16	1.38	1.30	1.06	-	-	-	1.59
	Contained Au	Moz	0.28	0.29	0.05	0.04	0.05	0.10	0.05	0.04	-	-	-	0.91
	Ag Grade	g/t	2.0	2.7	1.9	2.3	2.0	2.1	2.1	3.4	-	-	-	2.3
	Contained Ag	Moz	0.28	0.42	0.10	0.08	0.09	0.16	0.08	0.12	-	-	-	1.3
	Strip Ratio	w t:o t	5.7	5.0	12.0	5.4	2.9	2.4	4.5	2.3	-	-	-	5.1
	Waste	Mt	25.1	23.8	19.2	5.6	3.9	5.6	5.3	2.6	-	-	-	91.0
Total Mining	Ore	Mt	5.11	5.50	2.64	2.19	2.81	3.90	2.66	2.60	1.40	0.70	-	29.5
	Au Grade	g/t	2.35	2.20	1.95	2.82	2.38	2.16	2.50	2.52	3.33	2.70	-	2.38
	Contained Au	Moz	0.39	0.39	0.17	0.20	0.22	0.27	0.21	0.21	0.15	0.06	-	2.26
	Ag Grade	g/t	1.9	2.5	1.7	2.1	3.2	3.2	5.1	6.2	6.8	7.6	-	3.4
	Contained Ag	Moz	0.32	0.45	0.15	0.15	0.29	0.41	0.44	0.52	0.31	0.17	-	3.2
Mill Feed	Ore Feed (Mt)	Mt	2.91	2.90	2.83	2.86	2.96	2.95	2.78	2.72	2.83	2.70	1.91	30.3
	Ore Feed Au (g/t)	g/t	3.04	2.86	2.67	2.53	2.45	2.67	2.52	2.46	2.11	1.25	0.61	2.35
	Ore Feed Ag (g/t)	g/t	2.1	2.3	2.0	2.1	3.2	3.7	5.1	5.7	4.4	3.6	2.0	3.3
	Gold Recovery	% Au	87.8	86.7	85.5	86.4	86.6	83.8	77.4	77.3	75.7	74.6	69.2	82.7
	Silver Recovery	% Ag	70	70	70	70	70	70	70	70	70	70	70	70
	Gold (Au) Produced	Moz	0.25	0.23	0.21	0.20	0.20	0.21	0.17	0.17	0.15	0.08	0.03	1.90
	Silver (Ag) Produced	Moz	0.14	0.15	0.13	0.13	0.21	0.24	0.32	0.35	0.28	0.22	0.09	2.26

Source: OceanaGold, 2025

(1) Does not include stockpile material


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Source: OceanaGold, 2025

Figure 1-3: Combined OP and UG Ore Production Schedule

1.12Processing and Recovery Methods

The processing plant continues to utilize the conventional flowsheet developed comprising:

•Primary Jaw Crushing

•Conventional SABC grinding circuit incorporating flash flotation on the cyclone underflow

•Rougher flotation

•Two stage concentrate regrind with a tower mill followed by an Isamill

•Carbon-in-leach (CIL) leaching of reground concentrate and flotation tailings

•Carbon stripping, electrowinning and smelting of bullion

•Cyanide destruction

Additional equipment was installed in some areas of the plant between 2018 and 2020 to achieve the expanded capacity above the original design of 2.35 Mt/yr with annual rates up to 3.5 Mt achieved and to ensure required concentrate regrind performance to maximize gold recovery at higher throughput rates. The production plan sees annual milling rates between 2.8 and 3.0 Mt/yr being processed with approximately 40% from underground operations and 60% from open pit. Upside potential exists from plant utilization improvement initiatives currently being pursued.

The existing flowsheet has proved to be very successful in recovery of gold from the ore with rates 2.5% above the original feasibility study model at head grades above 1.7 g/t gold. With the presence of gold hosted in tellurides in part of the Ledbetter Underground Resource, a modification to the leach circuit is proceeding to increase residence time to overcome slower leach kinetics in this material.

The annual processing schedule is shown in Table 1-7 and Figure 1-4.


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Source: OceanaGold, 2025

Figure 1-4: Annual Processing Schedule

Contact water treatment capacity has been expanded on site to account for increased PAG storage and open pit catchment area. The expanded plant has been augmented with the addition of a reverse osmosis stage to ensure compliance with discharge permits across a wider range of contact water hardness. Additional capital costs have been incorporated into the LoM plan to further enhance water treatment capacity.

1.13Infrastructure

Power is available in the area via an existing 44 kilovolt (kV) transmission grid with Duke Energy and a 69 kV transmission grid with Lynches River Electric Cooperative. All incoming power demand for the site is met by the local grid and supplied by Lynches River Electric Cooperative. The total power demand for the site (including underground operations) is estimated to be 23 Mega Volt-Ampere (MVA). The HGM owns and maintains the transmission infrastructure within the operation.

The permitted Duckwood Tailings Storage Facility (TSF) will be progressively expanded, to a total capacity of 63 Mt, to store plant tailings by raising the crest height using downstream construction methods. The existing permitted PAG facility is currently being expanded to store additional PAG material.

The underground infrastructure required to support underground mining includes extension of the ventilation, dewatering, power lines, air, and water supplies. The surface facilities that support the underground mining include a run-of-mine (RoM) stockpile area for underground ore, a batch plant, maintenance shop and warehouse, offices, laydown storage areas, and will host the future metal removal plant. The current facilities utilized for Horseshoe will support Palomino with nominal upgrades required. Mining of Palomino Underground requires an upgrade and extension of a high voltage power line along with a ventilation shaft to the 800 level. Ledbetter Underground is planned


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to have its own surface facilities consisting of RoM stockpile area with metal removal plant, maintenance shop and warehouse, laydown storage areas, offices and a batch plant.

All other infrastructure that is required for the LoM plan is in place.

1.14Environment Studies and Permitting

In late 2022, HGM received all of the major permits required to begin construction and operation of the mine including: Clean Water Act 404 Dredge and Fill Permit, Mine Operation Permit, 401 Water Quality Certification, TSF Dam Permit, North Fork Dam Permit, Air Permit (to construct), and various NPDES Permits (wastewater treatment and storm water).

In Q1 2024, South Carolina Department of Health and Environmental Control approved mine operating permit modifications for additional Horseshoe underground levels and Palomino. This minor modification took less than three months to complete. The permit modification for the method of mining change for Ledbetter Phase 4 to an underground is classed as a minor modification and is expected to be completed in 2027 before mining takes place in 2028.

1.15Capital and Operating Costs

Capital Cost

The total LoM capital is US$1,113 million as summarized in Table 1-8.

LoM Sustaining capital is US$574 million, the majority of which includes open pit capitalized pre-strip, underground operating capital development, underground project expansion (PUG & LUG), Process Plant Concentrate Leach Circuit Upgrade project and Contact Water Treatment Plant (CWTP). The remaining balance covers surface infrastructure, open pit mine equipment replacements and Social Performance projects.

LoM non-sustaining capital is US$539 million. Major projects in non-sustaining capital include the development of the PUG and LUG mines, process plant upgrades to support processing of LUG ore, plus estimated reclamation costs at closure.

Capital expenditures have been estimated referencing same or similar works at Haile, quotations from suppliers, and estimates provided by consultants with appropriate expertise.

Capital expenditure estimation is consistent with proposed development programs and ongoing requirements and has been undertaken to an appropriate level of estimation accuracy. Actual expenditures are likely to vary over the LoM due to inflation, modifications, upgrades, introduction of new technology and other unforeseen factors.


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Table 1-8: Total Capital Expenditure Summary (US$000’s)


Description	Non-Sustaining Capex	Sustaining Capex	Total
OP Capitalized Pre-Strip		147,541	147,541
OP Mining Property, Plant, & Equipment (PP&E)		103,320	103,320
UG Mining PP&E		66,296	66,296
UG Mine Development Capitalized	57,372	98,363	155,735
UG PUG – Development Phase	135,538		135,538
UG LUG – Development Phase	152,929		152,929
Processing	67,107	66,143	133,250
Infrastructure(1)	126	92,515	92,641
External Affairs and Social Performance (EA&SP)	2,000		2,000
Total Net Capex	415,072	574,178	989,250
Reclamation/Closure (2)	123,465	-	123,465
Total LoM Net Capex	538,537	574,178	1,112,715

Source: OceanaGold, 2025

1General site infrastructure. Additional infrastructure costs are captured within specific project totals i.e. PUG & LUG Development Phases and Processing

2 Captured as Capex in Cashflow

Operating Cost

The total LoM operating cost (excluding capitalized operating cost) is US$2,455 million. Operating costs have been estimated based on historical performance at Haile, supplier quotations, estimates from consultants with appropriate expertise and otherwise estimated internally by appropriately credentialled HGM staff.

Total LoM unit rate operating cost of US$80.93/ore tonne processed is summarized in Table 1-9.

Table 1-9: LoM Operating Cost Summary


Description	US$000’s	US$/t Mined
OP Mining ($/t rock mined (ore and waste)) - All Material	727,076	6.68
OP Mining ($/t rock mined (ore and waste)) - (excl. capitalized cost)	579,535	5.33
UG Mining ($/t rock mined (ore and waste)) – All Material	913,855	61.29
UG Mining ($/t rock mined (ore and waste)) - (excl. capitalized cost)	758,120	50.85
US$000’s		US$/t Ore Processed
Subtotal Mining (Operational Material Only)	1,337,655	44.11
Processing	706,105	23.28
G&A Cost	402,627	13.28
Refining/Freight Costs	8,209	0.27
Total Operating Costs	$2,454,596	$80.93

Source: OceanaGold, 2026

There are cost items excluded from the operating cost, as detailed in Table 1-10, which OceanaGold does not consider to be direct operating costs, but is considered under the Indirect


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costs for the operation and these costs are included in the economic analysis. These include payments related to leasing arrangements of the open pit and underground mobile equipment fleets and other social commitments.

Table 1-10: LoM Indirect Costs Summary


Description	US$000’s	US$/tonne Ore Processed
Reclamation Trust Agreement - Remaining Contributions	10,080	0.33
Reclamation Trust Agreement - Release	-20,000	-0.66
Community Contributions	9,200	0.3
Interest Expense - Capital Leases	3,562	0.12
Principal Payment - Capital Leases: Sustaining	25,877	0.85
Principal Payment - Capital Leases: Non-Sustaining	13,086	0.43
Total Non-Operating Costs	41,805	1.38

Source: OceanaGold, 2025

1.16Economic Analysis

The Project consists of operating surface and underground mines with a mill. The milling facility is fed by the open pit mine directly and then through stockpiles in later years. The mill feed is supplemented with ore from underground mines at a 1.6 Mt/yr max annual capacity operation.

Haile is expected to produce 1.9 million ounces (Moz) of payable gold over a 11-year mine life at an average rate of 172 koz Au per year during full production years with a LoM all-in sustaining cost (AISC) of US$1,592/oz Au.

The Project is expected to incur sustaining capital in the amount of US$574 million over the modeled life and a non-sustaining capital spend, including rehabilitation costs, of US$539 million for total capital expenditure of US$1,113 million.

The project cash flow using the Mineral Reserve price of US$2,200/oz Au flat over the LoM and a 5% discount rate results in a pre-tax net present value (NPV) of US$462 million and after-tax NPV of US$414 million. As a result of significant depreciation and depletion, the operation is expected to incur limited income tax liability ($51 million) at the Mineral Reserve price. Existing loss carry-forwards have not been included in the economic model. Inclusion of these items may further reduce the income tax liability of the operation.

An alternative price profile more reflective of current market conditions (refer to section 22.4.2) which consists of a flat US$4,000/oz Au price and US$45.00/oz Ag price over the life of the operation was also evaluated. At these prices and a 5% discount rate, the project is estimated to produce pre-tax and after-tax NPV values of US$3,266 million and US$2,583 million, respectively. In this scenario, income tax liabilities of around $814 million would arise and are included in the above analysis.

As summary of the model results for both the reserve case and the alternative price case is presented in Table 1-11.


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Table 1-11: Indicative Economic Results


Scenario	Reserve Case Price	Alternative Price
Description	US$000’s	US$000’s
Market Prices
Gold (US$/oz)	2,200	4,000
Silver (US$/oz	25	45
Payable Gold (Moz)	1.9	1.9
Revenue
Gross Gold Revenue	4,169,596	7,581,084
Silver By-Product Credit	55,899	100,618
Total Gross Revenue	4,225,495	7,681,702
Operating Costs
Total Operating Costs	(2,496,401)	(2,496,401)
Operating Margin (EBITDA)	1,729,094	5,185,301
Taxes
Income Tax	(50,932)	(814,474)
Operating Cash Flow	1,678,163	4,370,827
Capital
Total Capital	(1,112,715)	(1,112,715)
Metrics
Pre-Tax Free Cash Flow	616,379	4,072,586
After-Tax Free Cash Flow	565,447	3,258,112
Pre-Tax NPV at 5%	461,753	3,265,974
After-Tax NPV at 5%	414,307	2,583,459

Source: OceanaGold, 2026

Because the Project is operational and is valued on a total project basis and not by an incremental analysis, an initial rate of return (IRR) value is not relevant in this analysis. In terms of sensitivity, the Project is most sensitive to gold grade and price, followed by operating costs and capital costs.

1.17Conclusions and Recommendations

1.17.1Conclusions

The following conclusions have been drawn from this Technical Report:

•The Mineral Resources and Mineral Reserves have been estimated in accordance with the Canadian Institute of Mining, Metallurgy and Petroleum Standard Definitions for Mineral Resources and Mineral Reserves dated May 10, 2014, (CIM definitions) and provide a reasonable basis for medium to long term planning.

•The trade-off study for the Ledbetter Phase 4 open pit versus underground has been finalized and the mining method change resulting in improved economics for the site.

•Risks to the open pit plan include geotechnical highwall stability and water management. These are not considered material risks to the Mineral Reserve; however, might present risk to schedule and costs.


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•Future ores testing programs on new sources has confirmed the ability to recovery gold at current rates from the Horseshoe and Palomino sources and has highlighted the change in gold deportment in a portion of the Ledbetter Underground that would lead to lower recoveries without extending leach residence time.

•Mill throughput rates required in the production plan have been influenced from ore hardness testing and are at rates that have been achieved in recent years.

•Gold recovery from the current process flowsheet has proved effective in achieving rates at or above that predicted from the original feasibility study.

•Horseshoe Underground is ramped up to full production, and the Palomino Underground is starting initial decline development.

•Exploration drilling continues to investigate near-mine targets.

•All permits are up to date, with only a minor modification required for Ledbetter Underground.

•Project is cashflow positive at Mineral Reserve Gold Price of US$2,200/oz Au.

1.17.2Recommendations

•Continued regional and near mine exploration.

•Continued infill drilling programs for both open pit and underground deposits with focus on risk mitigation and conversion drilling to Measured and Indicated Mineral Resources.

•High focus on quality mining and schedule discipline to increase underground mining horizons allowing for de-risking and flexibility.

•The collection of additional metallurgical samples from drilling core to confirm recovery estimates for both Palomino and Ledbetter Underground deposits.

•Continue to develop geometallurgical models for open pit, underground and stockpiles to predict throughput and recovery rates for mine planning.

•Continue to develop and implement mitigation plans for geotechnical anomaly in the South Wall of the Ledbetter open pit.

•Continue to develop and implement management plans for the water currently stored in Mill Zone to mitigate the risk to mining in the Haile open pit.

•Continued focus on active water treatment to achieve at a minimum a neutral water balance year over year.

•Progress the concentrate leach circuit upgrade through detailed design and construction prior to Ledbetter Underground ore production arriving at the plant.

•Complete underground haulage study to further de-risk though identification of bottlenecks to LoM Plan.

•Complete study of utilization of paste versus CRF for backfilling of the underground stopes.


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2Introduction

This report has been prepared to support disclosures in OceanaGold’s Annual Information Form for the year ended December 31, 2025.

This report provides updated information on the Haile Gold Mine, including an updated Mineral Resources and Mineral Reserves estimate.

References in this report to OceanaGold include OceanaGold Corporation and its wholly owned subsidiary, HGM.

This report uses Mineral Reserve and Mineral Resource classification terms that comply with reporting standards in Canada and the Mineral Reserve and Mineral Resource estimates are made in accordance with the CIM Council – Definition Standards for Mineral Resources & Mineral Reserves adopted by the CIM Council on May 19, 2014, which were adopted by the Canadian Securities Administrators’ NI 43-101 – Standards of Disclosure for Mineral Projects.

This report includes scientific and technical data from a feasibility study to support the initial Mineral Reserves estimate for Ledbetter Underground included herein.

2.1Sources of Information and Data

Reports and documents listed in Section 27 of this report were used to support preparation of the report. Additional information was provided by HGM Staff as requested. Supplemental information was also provided to the QPs by third party consultants retained by OceanaGold in their areas of expertise.

2.2Qualifications of Consultants

The following individuals, by virtue of their education, experience and professional association, are considered QPs as defined in the NI 43-101 standard and are members in good standing of appropriate professional institutions. QP certificates of authors are provided in Appendix A. The QPs are responsible for specific sections as follows:

•David Carr, BEng Metallurgical (Hons), MAusIMM (CP) (OceanaGold Head of Metallurgy) is the QP responsible for mineral processing, all of Sections 13, 17, Section 18.9, and the process plant capital and operating costs of section 21, and portions of Sections 1, 25 and 26 summarized therefrom, of this Technical Report.

•Gregory Hollett, BEng (Mining Engineering), MBA, P.Eng (EGBC), (OceanaGold Head of Mine Engineering) is the QP responsible for environmental and open pit Mineral Reserves, Sections 2, 3, the open pit portions of Section 15 and 16.3, Section 16 opening statements, Sections 16.1, 16.1.1, 16.1.3, 16.1.4, 16.1.5, 16.1.7, 16.1.8, 18.7, 19, 20, the open pit operating costs portion of section 21, the other/G&A portions of the operating costs in section 21, 22, 24, 27, 28, and portions of Sections 1, 25, and 26 summarized therefrom, of this Technical Report.

•Brianna Drury, BSc Mining Engineering, RM-SME (OceanaGold Underground Engineering Superintendent), is the QP responsible for underground Mineral Reserves, the underground portions of Section 15 and 16.3, Sections 16.2, 16.2.1, 16.2.3, 16.2.5, 16.2.6, 16.2.7, 18.8, the capital costs portion of Section 21 with the exception of processing capital, the


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underground mining operating costs portion of Section 21, and portion of Sections 1, 25, and 26 summarized therefrom, of this Technical Report.

•Jonathan Moore, BSc Geology (Hons), MAusIMM (CP), (OceanaGold Group Manager, Resource Development), is the QP responsible for the open pit and Horseshoe underground Mineral Resources, Sections 4 through 12, the open pit and Horseshoe underground portions of section 14, 23, and portions of Sections 1, 25, and 26 summarized therefrom, of this Technical Report.

•Douglas Corley, BSc Geology (Hons), MAIG (RPGeo), (OceanaGold Principal Geologist, Resource Development), is the QP responsible for the Ledbetter and Palomino underground Mineral Resources, the Palomino and Ledbetter underground portions of Section 14 and portions of Sections 1, 25, and 26 summarized therefrom, of this Technical Report.

•Larry Standridge, PE, MSE Geotechnical, (Call & Nicholas Principal II Geotechnical Engineer) is the QP responsible for open pit geotechnical work, Section 16.1.2 and portions of Sections 1, 25, and 26 summarized therefrom, of this Technical Report.

•Robert Cook, PE, RM-SME, (Call & Nicholas Principal II Geological Engineer), is the QP responsible for underground geotechnical information, Section 16.2.2 and portions of Sections 1, 25, and 26 summarized therefrom, of this Technical Report.

•Jay Newton Janney-Moore, PE, RM-SME, (NewFields Senior Project Manager I), is the QP responsible for tailing and overburden storage, Sections 18.1, 18.2, 18.3, 18.4, 18.5, and portions of Sections 1, 25, and 26 summarized therefrom, of this Technical Report.

•William Lucas Kingston, MSc, P.G., RM-SME, Hydrogeology and Groundwater Management, (NewFields Senior Hydrogeologist) is the QP responsible for hydrogeology, Sections 16.1.9, 16.2.8, 18.6, and portions of Sections 1, 25, and 26 summarized therefrom, of this Technical Report.

•Brooke J. Miller, MSc, C.P.G. (SRK Principal Consultant, Geology), is the QP responsible for geochemistry, Section 16.1.6 and 16.2.4 and portions of Sections 1, 25, and 26 summarized therefrom, of this Technical Report.

2.3Site Visits and Scope of Personal Inspection

Site visits conducted by QPs are summarized in Table 2-1.


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Table 2-1: Site Visit Participants

Personnel

Company

Expertise

Date(s) of Visit

Details of Inspection

Robert Cook

Call & Nicholas

Geotechnical

November 29-30, 2017

July 27-28, 2021

January 16-19, 2023

January 22- 24, 2024

July 15-16, 2025

January 13-15, 2026

Inspect open pit and underground mining conditions.

Larry Standridge

Call & Nicholas

Geotechnical

November 29-30, 2017

October 10-11, 2018

January 14-16, 2020

May 18-20, 2021

January 24, 2024

January 20-21, 2026

General site inspection with a focus on pit slope conditions.

David Carr

OceanaGold

Metallurgy

Various visits in 2017, 2018, 2019, 2020, 2022, February 17-March 22, 2025, June 16-August 8, 2025

Plant Commissioning support and plant investigations. Plant Commissioning and ramp-up of operations, investigations, benchmarking and study support.

Gregory Hollett

OceanaGold

Open pit mining and Mineral Reserves

Various visits in 2018-2023.

July 8-19, 2024

November 11-14, 2024

November 10-14, 2025

General site inspection, open pit inspection, mine planning and reporting reviews.

Jay Newton Janney-Moore

NewFields

Geotechnical/

Infrastructure

Sept. 24-26, 2019

Aug 31-Sept 2, 2021

Oct 18, 2022

Sept. 26-27, 2023

Oct. 21-31, 2024

Oct 29-30, 2025

Inspection of the Duckwood TSF, PAG OSA, and geomembrane lined ponds. ITRB meeting

Brooke J. Miller

SRK

Geochemistry

November 2023

Visited Overburden Storage Areas and open pit mine, tour of surface facilities on site.

William Lucas Kingston

NewFields

Hydrogeology and Groundwater Management

December 4-5, 2019

August 31 - September 2, 2021

General site inspection, including dewatering system.

Douglas Corley

OceanaGold

Geology/Resources

10 June to 3 July 2024

Resources. Drill core, open pit and underground visits.

Jonathan Moore

OceanaGold

Geology/Resources

Annually since 2015. Most recently, November 20 to December 8, 2025

Review of Resource and Reconciliation. Drill core, open pit and underground visits.

•Brianna Drury is based in South Carolina and is on-site regularly.

2.4Units of Measure

The Metric System for weights and units has been used throughout this report unless otherwise noted. Tonnes are reported in metric tonnes of 1,000 kilogram (kg). Gold is reported in grams (G) and troy ounces (Koz), where applicable (1 Troy ounce = 31.1035 grams). All currency is in U.S. dollars (US$) unless otherwise stated.

2.5Effective Date

The effective date of this report is December 31, 2025.


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3Reliance on Other Experts

The QPs opinions contained herein are based on information provided by OceanaGold throughout the course of the investigations. The QPs have relied upon OceanaGold and the work of other consultants in various project areas in support of this Technical Report.

The QPs have used their experience to determine if the information from previous reports was suitable for inclusion in this Technical Report and adjusted information that required amending. This report includes scientific and technical information, which required subsequent calculations to derive subtotals, totals, and weighted averages. Such calculations inherently involve a degree of rounding and consequently introduce a margin of error. Where these occur, the Consultants do not consider them to be material.

For reporting of environmental and other matters in Section 20, the QP has relied upon the internal memo:

“Taxation and Related Assumptions”, dated March 23, 2026, by OceanaGold’s Environmental EA&SP Manager (Haile)

For reporting of tax calculations and related matters in Section 22, the QP has relied upon the internal memo:

“Haile tax, depreciation, royalty, and related matters”, dated December 31, 2025, by OceanaGold’s Commercial Manager (Haile)

The QPs have relied upon OceanaGold for information regarding the surface land ownership / agreements as well as the mineral titles and their validity. Land titles and mineral rights for the Project have not been independently reviewed by the QP, who has have relied on OceanaGold legal counsel and a titles and mineral rights due diligence report from the time of OceanaGold’s acquisition of HGM by Womble Carlyle Sandridge & Rice dated July 24, 2015.


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4Property Description and Location

4.1Property Location

The Haile gold mine is located 5 km northeast of Kershaw in southern Lancaster County, South Carolina, United States of America (USA), in the north-central part of the state, as shown in
Figure 4-1. Haile is 27 km southeast of Lancaster, the county seat, and is 80 km northeast of Columbia, the state capital. The geographic centre of the mine is at 34° 34’ 46” N latitude and 80° 32’ 37” W longitude. Mineralized zones at Haile lie within an area extending from UTM NAD83 zone 17N coordinates 540000E to 544000E and 3825500N to 3827500N. Figure 4-2 shows a site map of the Haile Gold Mine.

Source: State-Maps.org and Google Maps, 2014

Figure 4-1: General Location Map of the Haile Gold Mine


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Source: OceanaGold, 2023

Figure 4-2: Site Map of the Haile Gold Mine


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4.2Ownership

HGM is a wholly owned subsidiary of OceanaGold. References in this document to OceanaGold refer to the parent company together with its subsidiaries, including HGM. As of December 31, 2025, HGM owns a total of 10,978 acres in South Carolina. Of this total, 5,469 acres are within the mine permit boundary. Figure 4-3 shows the Land Tenure map as of December 31, 2025, with Fee Simple (OceanaGold owned) and leased properties, almost entirely in Lancaster County.

Source: OceanaGold, 2025

Figure 4-3: Land Tenure Map


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5Accessibility, Climate, Local Resources, Infrastructure and Physiography

5.1Accessibility

The Haile property is easily accessible on paved roads and highways from U.S. Highway 601 to the mine entrance on Snowy Owl Road, located 5 km northeast of Kershaw, South Carolina. The major international airport at Charlotte, North Carolina, is an 80-minute (min) drive from the mine property.

5.2Climate

The Haile area of South Carolina has a subtropical climate. Summers are hot and humid with maximum daytime temperatures averaging 31°C to 33°C (degrees Celsius). Winters are mild and temperatures range from -1°C to 14°C. Average annual precipitation is 1,220 millimetres (mm) while annual evaporation is estimated at 760 mm (US Climate Data). Rain is abundant throughout the year with January, March, and July being the wettest months. Snowfall is insignificant and averages less than 80 mm per year. South Carolina averages 50 days of thunderstorm activity and 14 tornadoes per year. The mine operating season is year-round.

5.3Local Resources and Infrastructure

Local resources (labor force, manufacturing, supplies, housing, utilities, emergency services, etc.) and infrastructure are in place and are widely utilized at Haile. Numerous small communities exist around the Haile mine with populations ranging from 700 to 10,000 people. Power is available in the area via an existing 44 kV transmission grid with Duke Energy and a 69 kV transmission grid with Lynches River. The Haile Gold Mine utilizes both grids. Surrounding nearby land use is dominantly for agriculture and timber.

5.4Physiography

The Haile Gold Mine and its surroundings occur within the Sand Hills sub-province of the Piedmont physiographic province of the Southeastern United States. This province trends from southwest to northeast and is bound by the Coastal Plain to the southeast and the southern Appalachian Mountains to the northwest. Gentle topography and rolling hills, dense networks of stream drainages, and white sand to red brown saprolitic soils characterize the province. The mine elevation ranges from 120 to 170 m above mean sea level (amsl). Topography is dissected by the perennial, southwest-flowing Haile Gold Mine Creek and by its intermittent tributaries. HGMC enters the southeast-flowing Little Lynches River 1.6 km southwest of the mine site. Gradients within the drainages are gentle to moderate (9% to 13%) and slopes above the drainages are gentle to nearly flat (less than 1%). The property is heavily wooded by pine and hardwood forests.


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5.5Infrastructure Availability and Sources

There are large industrial centres near the mine property. Equipment and sources of logistical and professional expertise can be obtained from the major cities of Charlotte, N.C., and Columbia, S.C., which are both within one hour travel of the mine. Multiple contractors provide skilled workers for the Project and there is adequate labor available for operation of the mine.


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6History

Gold was discovered in 1827 by Colonel Benjamin Haile, Jr. in gravels of Ledbetter Creek (now HGMC). This led to placer mining and prospecting until 1829, when lode deposits at the Haile-Bumalo pit site were found. Surface pit and underground work continued at the Haile-Bumalo site for many years. In 1837, a five-stamp mill was built (Newton et al., 1940). Gold production and pyrite-sulfur mining for gunpowder continued through the Civil War from 1861 to 1865. General Sherman’s Union troops invaded the area and burned down the operations near the war’s end.

In 1882 a sixty-five-stamp mill was constructed by E.G. Spilsbury and operated continuously until a fatal boiler explosion killed the mine manager in 1908. During that time, Adolph Thies developed the Thies barrel chlorination extraction process and improved gold recovery from Haile sulfide ores (Pardee and Park, 1948). During the 26-year operation period, mining grew to include the Blauvelt, Bequelin, New Bequelin, and Chase Hill areas. From 1907 to 1913, an attempt to operate a cyanide plant to extract gold from mine tailings was unsuccessful. Pyrite used to produce sulfuric acid was mined at Haile from 1914 to 1918 (Newton et al., 1940).

From mid-1937 to 1942, larger scale mining was undertaken by the Haile Gold Mine Company. The property then consisted of owned or leased ground totaling about 1,335 hectares (Ha) (Newton et al., 1940). Most of the main pits were mined to the 46 m level with some underground operations at Haile-Bumalo reaching the 106 m level (Pardee and Park, 1948). The Red Hill Deposit was discovered by crude induced polarization techniques next to the Friday pyrite diggings (Newton et al., 1940). This fairly large operation was shut down by presidential decree in 1942 because of World War II. By this time, Haile had produced over US$6.4 million worth of gold (in 1940 US$) (Newton et al., 1940).

Starting in 1951, the Mineral Mining Company (Kershaw, South Carolina) mined mineralite from sericite-rich pits around Haile. This industrial product is a mixture of sericite, kaolinite, quartz, and feldspar and is used in manufacturing insulators and as a paint base. Mineralite mining ended
in 1991.

In 1966, Earl Jones conducted exploration work in the area and eventually interested Cyprus Exploration Company (Cyprus) in the Project. Cyprus worked Haile from 1973 to 1977. Numerous companies explored the Haile regional area in the 1970’s and 1980’s, including Amselco, Amax, Nicor, Callaghan Mining, Westmont, Asarco, Newmont, Superior Oil, Corona, Cominco, American Copper and Nickel, Kennecott, and Hemlo.

The 1980’s heralded the first successful modern exploration and production at Haile. Piedmont Land and Exploration Company (later Piedmont Mining Company) explored Haile and surrounding properties from 1981 to 1985. Piedmont drilled 67 core holes and 1,215 RC holes on the property and greatly expanded the footprint of the Haile deposits. Piedmont mined the Haile deposits from 1985 to 1992 and produced 85,000 oz of gold from open pit heap leach operations in oxide and transitional ores. New areas mined by Piedmont included the Gault Pit (next to Blauvelt), the 601 pits (by the US 601 highway), and the Champion Pit. Piedmont expanded the Chase Hill and Red Hill pits and combined the Haile-Bumalo zone into one pit. Piedmont also discovered the large Snake sulfide gold resource and mined its small oxide cap. Piedmont extracted gold ores from a mineralized trend 1.6 km long, from east to west. Historical gold production at Haile is estimated at 360,000 Oz (Speer and Madry, 1993, Maddry and Kilbey, 1995).


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In June 1991, Amax signed an agreement to evaluate Haile to determine if it should enter a joint venture. During the evaluation period, core drilling stepped north of the Haile-Bumalo area and discovered the new sulfide resource of Mill Zone under the old 1940’s mill. Amax and Piedmont entered into a joint venture agreement and established the HMC in May 1992.

From 1992 to 1994, HMC completed a program of exploration and development drilling, property evaluation, Mineral Resource estimation, and technical report preparation. During this period, the large Ledbetter resource zone was discovered under a mine haul road. At the end of the HMC program in 1994, the gold reserve was stated as 780,000 oz of contained gold within 7.9 Mt at an average gold grade of 3.05 g/t. A QP has not done sufficient work to classify the historical estimate as Mineral Resources or Mineral Reserves. HGM is not treating the historical estimate as Mineral Reserves. Because of unfavorable economic conditions at the time, Amax did not proceed with mining and began a reclamation program to mitigate acid rock drainage (ARD) conditions at the site.

Kinross acquired Amax in 1998, assuming Amax’s portion of the Haile joint venture and later purchased Piedmont’s interest. Because Haile was a low priority compared to larger and more profitable projects, Kinross decided not to reopen the mine and continued the reclamation and closure program. Reclamation and closure proceeded through to 2007 when Haile operations commenced again under Romarco Minerals Inc.

Romarco acquired Haile from Kinross in October 2007 and began a confirmation drilling program in late 2007. Romarco completed the confirmation drill program in early 2008 and began infill and exploration drilling focused around the Ledbetter resource. Drilling accelerated in early 2009 with a major RC infill drilling program that continued through 2012. Condemnation drilling by Romarco for mine facilities commenced in September 2009. Drilling east of the Snake deposit discovered the high-grade Horseshoe deposit in 2010 and required the planned TSF to be relocated 3 to 4 km northwest of the mine. Geotechnical drilling was initiated in September 2009 for pit slope designs. The final hole at Ledbetter discovered a deeper northwest extension in 2010 that was named Mustang. Drilling between the Red Hill and Horseshoe areas had identified large zones of lower grade material that led to the late 2011 discovery of the deep Palomino prospect. Due to low gold prices and mine permitting, Haile exploration drilling was suspended during 2013 and 2014.

Romarco submitted a FS for Haile in February 2011. Drillhole data available as of November 17, 2011, were used in the March 2012 Mineral Resource estimate. Romarco completed a large portion of detailed engineering and permitting for the Project in 2011 and 2012. In November 2014, an updated FS was completed after receiving the necessary permits. In April 2015, construction of the Project began by Romarco and mining commenced in the Mill Zone pit.

OceanaGold acquired Romarco Minerals Inc. in October 2015 and became owner and operator of Haile. Project construction during 2015 and 2016 included a new CIL flotation process plant, power upgrades, a lined PAG overburden storage area (OSA), and a TSF. The first gold pour at the new process plant was in January 2017.


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7Geological Setting and Mineralization

7.1Regional Geology

Gold endowment in the southern Appalachian piedmont is predominantly from the Carolina Slate Belt (CSB), also known as the Carolina Terrane (Hibbard et al., 2010). The 700 km long belt is characterized by a strong northeast structural grain (stratigraphy, faults, foliation, and fold axes) extending from Alabama to Virginia that is up to 140 km wide in North Carolina. Volcanic arcs formed adjacent to the African continent and were accreted to the North American craton during the Late Proterozoic to Silurian (Hibbard et al., 2010).

The CSB is a northeast-trending, late Proterozoic to early Cambrian belt of intermediate to felsic volcanic flows and pyroclastic rocks mixed with fine-grained epiclastic and turbiditic sediments. At Haile, sedimentary rocks were deposited under calm, subaqueous anoxic slope conditions as evidenced by laminated, laterally extensive siltstones and subordinate turbidite flows. Volcanic and sedimentary facies are interfingered in the Haile region and are cut by post-metamorphic mafic dikes.

The CSB has a prominent flexure in central South Carolina near Haile. Structural trends southwest of this area are east–northeasterly, whereas trends northeast of the flexure are mostly northeasterly (Hibbard et al., 2002). The CSB was intruded by dominantly granite plutons approximately 595 to 520 Ma and by post-metamorphic Carboniferous granite plutons approximately 300 Ma (Fullagar and Butler, 1979). Hydrothermal activity prior to regional metamorphism is indicated by folded and recrystallized quartz veins and by pressure shadows with fringes of chlorite and quartz on pyrite. At least four tectono-thermal periods are recorded in the Carolina Terrane (Hibbard et al., 2002), including:

•Late Neoproterozoic to Early Cambrian Virgilina events (578 to 535 Ma): folding, foliation, and faulting with granite plutonism.

•Late Ordovician to Silurian Cherokee orogeny (457 to 425 Ma): greenschist facies metamorphism accompanied by a steep, generally northwest-dipping slaty cleavage that is axial planar to regional-scale folds that are commonly overturned to the southeast

•Devonian events of the Gold Hill-Silver Hill dextral shear zone (393 to 381 Ma) reactivation of Cherokee structures that juxtaposes the Carolina and Charlotte Terranes (west over east reverse motion).

•Late Paleozoic Alleghanian events (333 to 260 Ma): ductile, often mylonitic (e.g., Hyco and Modoc shears) (Hibbard et al., 1998) reactivation of older structures. Deformation is generally constrained to areas immediately proximal to such structures and focused along the southeast margin of the CSB.

See Figure 7-1 as a geologic timeline of major events shaping Haile’s geology.


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Source: OceanaGold, 2021

Figure 7-1: Time Distribution of Major Geological Events in the Carolinas


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The largest known gold deposits in the southeastern United States are in the north-central portion of South Carolina. They are oriented SW-NE and occur at or near the contact between metamorphosed volcanic and sedimentary rocks of Neoproterozoic to Early Cambrian age. In descending order, the largest deposits are Haile, Ridgeway, and Brewer (Foley and Ayuso, 2012) as shown in Table 7-1. Haile is classified as a structurally modified low sulfidation, sediment-hosted, disseminated, gold deposit with proximal quartz-sericite-pyrite alteration and distal carbonate-chlorite alteration. Ridgeway is geologically similar to Haile in that it is predominantly sediment-hosted and lies proximal to a major volcanic-sedimentary transition. East-west to ENE structural controls and local folding characterize the Haile and Ridgeway deposits. By contrast, Brewer is a high sulfidation, pyrite-enargite-chalcopyrite-topaz-rich, volcanic-hosted, breccia pipe characterized by advanced argillic alteration (pyrophyllite-andalusite).

Table 7-1: Geological Summary of Major Gold Deposits of SE USA

Deposit

Type

Host Rocks

Alteration

Au Age

(Ma)

Haile

Sediment / volcanic-hosted

Persimmon Fork

quartz-pyrite-sericite

549

Low Sulfidation

Ridgeway

Sediment / volcanic-hosted

Persimmon Fork

quartz-pyrite-sericite

553

Low Sulfidation

Brewer

Breccia Pipe

Persimmon Fork

pyrite-enargite-chalcopyrite

550

High Sulfidation

Source: OceanaGold and Foley and Ayuso, 2012

7.2Local Geology

Haile geological history includes several major events, as listed below from oldest to youngest. Regional and local geologic maps are presented in Figure 7-2 and Figure 7-3. A schematic stratigraphic column is presented in Figure 7-4.

7.2.1Lithology

The following rock units are described in chronostratigraphic order from oldest to youngest. Haile stratigraphy is described from mapping and core drilling over a thickness of about 1 km.

Neoproterozoic Rocks

About 555 to 551 Ma (Hibbard et al., 2002) igneous and interbedded epiclastic rocks were deposited that form the approximately 3 km thick Persimmon Fork Formation. This comprises laminated siltstone with minor sandstone and conglomerate overlain and interfingered with lapilli and ash flow tuffs. Tuffaceous rocks mostly occur in north-central areas of the Haile district at Ledbetter and Snake. They have irregular, hackly joints in contrast to the harder, well-jointed dacites. Grey laminated, pyritic siltstones are the dominant host rocks the middle and lower portions of the mine stratigraphy.

This is conformably overlain by the Richtex Formation siltstones along the southeast edge of Haile. The Richtex consists of ENE-striking, 40° to 60° SE-dipping, thin-bedded siltstone and mudstone with sandstone. The lower portion of the Richtex Formation contains mafic tuff and amygdaloidal


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basalt flows near Ridgeway (Secor and Wagener, 1968). Thickness near Haile is unknown but the Richtex is greater than 3 km thick near Ridgeway.

Paleozoic Rocks

Lamprophyre Dikes

Lamprophyre dikes intrude rocks of the Persimmon Fork and Richtex Formations. These dark green fine-grained dikes contain biotite, hornblende and plagioclase with chlorite and calcite and display spherulitic textures. The near-vertical to moderately dipping dikes commonly strike NE-SW or E-W and range in thickness from 1 cm to 2 m. Lamprophyre volume at Haile is estimated at about 1%. Lamprophyres are not foliated or pyritic and were likely emplaced during the waning stages of the Alleghanian Orogeny. Dates (40Ar/39Ar) in biotite yielded Pennsylvanian ages at approximately 311 Ma, coincident with the Dutchman Creek Gabbro (Fullagar and Butler, 1979).

Granites

The northeast-elongated Liberty Hill and Pageland plutons are exposed 8 km west and 5 km north respectively of the Haile mine. These fresh, medium-grained granites have less than 5% biotite and hornblende and are weakly foliated. The large (30 km x 20 km) Liberty Hill granite is dated at 293 ± 15 Ma. The Pageland granite (25 km x 10 km) is dated at 296 ± 5 Ma (Fullagar and Butler, 1979). Granite has not been observed in drillholes at Haile. Metamorphic aureoles around the plutons are less than 0.5 km wide and do not impact rocks at Haile.

Mesozoic Rocks

Diabase Dikes

Diabase dikes mapped at Haile are dark gray, dense, medium-grained, sub-ophitic and magnetic in character. These dikes cut all other units except the CPS. Dominant minerals are plagioclase and pyroxene with minor olivine. The diabase dikes margins are often chilled and / or spherulitic. The dikes strike NW with near-vertical dips and range in thickness from 1 to 30 m. Diabase dikes at Haile occur as both discrete dikes and as swarms (at Mill Zone and Horseshoe) tens of metres wide with a spacing of 300 to 400 m. Diabase dikes have horsetail, anastomosing, and sigmoidal geometries. The dikes weather to dark brown, earthy colors with chlorite and serpentine commonly observed along fractures. Dike emplacement post dates gold mineralization and occurred during the Late Triassic to Early Jurassic and accounts for about 5% by volume of rocks at Haile and often truncate ore zones.

Saprolite

Most of South Carolina is covered by Saprolite; a thick, structureless, unconsolidated, kaolin-rich, red orange to white residuum derived from intense acidic bedrock weathering in sub-tropical climates. Saprolite thickness ranges from 10 to 40 m at Haile and is thickest in metavolcanic rocks and along faults. Saprolite is rarely mineralized at Haile.

Coastal Plain Sand

The Cretaceous Middendorf Formation (Nystrom et al., 1991) is a south-eastward-thickening apron of unconsolidated sand. Its northwest limit conceals much of the Haile property and unconformably overlies the Richtex Formation in the southeast of Haile. The sands postdate gold mineralization and is the youngest unit in the region. The sands are up to 30 m thick at Haile and hundreds of metres thick south of Haile. The basal portion contains 10 to 60 cm thick layers of red


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brown ferricrete and quartz pebbles in a sandy matrix. The middle unit is white to red sand with a kaolinite matrix with frequent cross bedding. The upper unit is a clean tan to white quartz sand.

Source: OceanaGold, 2021

Figure 7-2: District Geology of North-Central South Carolina (UTM NAD83 Z17N)


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Source: OceanaGold, 2021

Figure 7-3: Geologic Map of the Haile Area with Gold Zones (UTM NAD83 Z17N)


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NI 43-101 Technical Report – Haile Gold Mine, South Carolina, United States

Source: OceanaGold, 2021

Figure 7-4: Haile Stratigraphic Column


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7.2.2Structure

The structural history of Haile is complex and is affected by four deformational / hydrothermal episodes, as summarized in Section 7.1 and depicted in Figure 7-1. The timing of mineralization in relation to major orogenic events is also unclear but has traditionally been interpreted as pre-deformation. Recent structural analysis incorporating pit mapping data and high resolution blasthole sampling suggests syn- or post-deformational mineralization and investigations are ongoing. Consequently, the relative timing of the D1 and D2 events listed below is currently unclear.

Four deformation events are observed at Haile; the D1 and D2 events provide the dominant geometric constraints on the Haile ore deposits.

•D1 is defined by syn-mineral hydrothermal flooding and replacement of sedimentary rocks by silica and pyrite with Au, Ag, As, and Mo precipitation. Mineralization was focused at the volcanic-sedimentary contact with the overlying volcanics acting as a cap and at the base of sedimentary rocks as veins, breccias, and wall rock flooding.

•D2 regional metamorphism and deformation is characterized by folding, shearing, pervasive foliation, quartz veins and greenschist facies mineral assemblage. This is the dominant event that overprints the Haile region. Pervasive foliation strikes east-northeast and dips 40 to 600 northwest and increases in intensity along the volcanic-sedimentary contact and weaker laminated siltstones. Rocks were folded into an asymmetric anticlinorium with a steep southeast limb and moderate northwest limb.

•D3 is manifest as minor brittle reactivation of foliation along NW-dipping normal faults and displaces some ore zones.

•D4 is defined by diabase dike intrusions and minor dextral faults that step down the district geology from west to east.

Figure 7-5 highlights the intense ductile and brittle strain fabrics that overprint and deform ore zones at Haile. The top photo shows a pressure solution cleavage (S1) imposed on folded bedding (S0) flanked by a shear zone of completely transposed bedding. The lower photo shows axial planar cleavage (S1) in folded and bedded (S0) siltstone with folded pyrite lenses. At the ore deposit scale, the pyrite lenses are similar to irregular ore zone shapes. Compositional layering subparallel to the foliation is generally transposed bedding and represents S1 and S2 fabrics (Hayward, 1992). The S1 foliation is formed by both pressure solution parallel to axial planes of folds and ductile shear strain (Tosdal, 2020).


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Source: OceanaGold, 2021

Figure 7-5: High Strain Fabrics in Core Samples

Many contacts between volcanic and sedimentary rocks have undergone grain size reduction and thus represent high strain zones recording ductile slip. Greenschist facies metamorphism produced significant volume loss due to dehydration reactions at temperatures of 250°C to 300°C and developed pressure solution cleavage. Primary feldspars and biotite have been converted to sericite and chlorite.

The Haile gold deposits are exposed within a metasediment (MS) window flanked and overlain by MV. The ENE-trending window is about 4 km long x 0.5 to 1 km wide (Figure 7-3). Sedimentary rocks are folded within an ENE-trending anticlinorium with a steep SE limb and a moderate NW limb. The MV / MS contact is conformable with bedding. High strain fabrics overprint all MV and MS units in the mine area. The ENE-striking MV / MS contact dips 60 to 80 SE along the southeast margin of the district and generally constrains gold mineralization at Red Hill East, Palomino, Deep Snake, and Horseshoe. The MV / MS contact dips 30 to 50 NW in north-central portions of district and caps gold mineralization at Ledbetter, Upper Snake, Mill Zone, and Red Hill West.


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The district is dissected by several ENE-striking, 30° to 60° NW-dipping dip- and oblique-slip shears that appear to both focus gold mineralization and displace mineralized zones. The Mill Zone orebody is faulted into two segments with about 100 m of normal displacement. Brittle deformation is characterized by anastomosing fault zones with discrete thin slip planes, commonly filled with ribbon quartz or gouge. Fold axes observed in drilling and mapping mostly occur in the southeast portion of the district in the Red Hill, Palomino, and Snake deposits. Portions of the Ledbetter deposit contain chaotic folds with variable orientations. Fold axes strike N40° E to N70° E and plunge gently east.

7.2.3Mineralization and Alteration

Gold mineralization at Haile is hosted by laminated siltstone and felsic volcanics in the Upper Persimmon Fork Formation. Within the laminated siltstone, gold is found at two primary horizons. The primary ore zone is located at upper siltstone / dacite contact where it is capped by less permeable coherent dacite flows. A secondary ore zone is found at the basal siltstone / felsic volcanics contact. The primary mineralization is typically within 100 m of the dacite-siltstone contacts.

The mineralization is disseminated in silicified, pyritic rocks with local K-feldspar and molybdenite and occurs as en echelon clusters of moderately to steeply dipping ore lenses within a 4 km x 1 km area. Eleven named gold deposits are recognized at Haile. From west to east, these deposits include Champion, Small, Mill Zone, Haile, Ledbetter, Red Hill, Palomino, Snake, Horseshoe, Pisces, and Clydesdale that often show ‘pearls on a string’ alignment. Ledbetter is by far the largest orebody (approximately 1 Moz) and includes the shallow Chase and Ledbetter UG deposits. Orebody geometry, depth, size, grade, mineralogy, and alteration are variable. The orientation of gold mineralization generally parallels the regional NW moderate dipping foliation but is primarily concentrated along the metavolcanic metasediment contact with local concentrations deeper in the stratigraphy at the base of metasediment. Orebody geometry is partly controlled by the variable orientation of volcanic sediment contacts and the location of barren dacite sills. Ore lenses are typically 50 to 300 m long, 20 to 100 m wide, and 5 to 30 m thick. Ore zones are separated by barren siltstone, dacite sills, and diabase dikes. The MV / MS contact and gold mineralization gradually deepen from west to east across the Haile district. The MV / MS contact at Champion has been partly removed by erosion in the west portion of the district while is over 500 m deep at the Horseshoe deposit, 4 km east of Champion. Depth and position of the contact are further complicated by faulting and folding. Drilling in southeast areas around Palomino has encountered gold mineralization up to 1 km deep.

Small, mineralized zones at Ledbetter, Red Hill, Mill Zone, and Snake are hosted in the overlying dacite along fault zones within 15 m of the MV / MS contact. Gold grades in mineralized dacite are typically lower than in the underlying rocks while sericite alteration is more intense in the dacite. Hydrothermal brecciation is common in portions of the Ledbetter, Horseshoe, Small, and Champion deposits where milled, silicified siltstone clasts occur in a fine-grained quartz-pyrite matrix intruded by fingers of quartz feldspar porphyry with quartz stockwork veinlets. The secondary mineralization zone shares many characteristics with the upper zone and includes some classic epithermal features such as banded veining, colloform / crustiform quartz adularia veins with local quartz after bladed calcite, indicative of boiling. Gold grades can be elevated (circa 18 g/t) within these veins but quickly drops off to more typical Haile grades in disseminated mineralization within the surrounding wall rock.


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Mineral zonation grades outward from quartz-pyrite ± K-feldspar + gold (QS) / QSP ± gold / sericite + pyrite ± pyrrhotite / chlorite-calcite ± epidote (propylitic). QS and QSP mineralized zones are tens of metres thick. Sericite envelopes range in thickness from tens to hundreds of metres and are controlled by protolith, permeability, and weathering. Within the mineralized zones, quartz is dominant (60% to 80%), pyrite is moderate (1% to 10%), and sericite is variable at 5% to 40%. Semi-massive pyrite zones are locally observed over thicknesses of 0.5 to 5 m, especially in the Mill Zone, Red Hill and Haile pits.

Early pervasive, replacement-style sulfidation and silicification is overprinted locally by hydrothermal brecciation, quartz stockwork veining, and cm-scale quartz-pyrite veining. These secondary features generally define the high-grade zones within an ore body. Pyritized and sericitized envelopes extend beyond the silicified ore zones, are elongated parallel to foliation, and broadly define the 0.1 g/t Au shell. Pyrite grain size is typically less than 20 microns (µm) in ore zones. A late phase of barren, coarse, cubic, undeformed pyrite that formed during regional greenschist metamorphism is present outside of mineralized zones. Pyrite cubes in chloritic metamorphosed rocks are 0.5 to 1 mm in size but can be as large as 1 to 2 cm. Pyrrhotite commonly occurs in 5 to 25 m thick halos around and on the edges of ore zones but is sometimes present within the deeper, underground deposits. Its ductile nature produces length; width ratios more than 5:1 in foliated rocks. Pyrrhotite formation is interpreted to be coeval with early, fine-grained pyrite precipitation.

Gold spatially correlates with silver, arsenic, molybdenum, and tellurium. Base metals are rare at Haile. Thin section petrography and scanning electron microscopy show that the gold occurs as native gold, gold-pyrite, gold-pyrite-pyrrhotite clusters in fine-grained silicified zones, and in Au tellurides. Gold tellurides are more common deeper in the system at the Clydesdale and Ledbetter Underground zones. Smeared molybdenite occurs primarily on foliation surfaces and as fine-grained aggregates in silicified zones. Molybdenite at Haile has been dated by Re-Os isotopes at 553.8 ± 9 Ma (Stein et al., 1997), which is coeval with the zircon crystallization age of 553 ± 2 Ma reported by Ayuso et al. (2005). This age correlation indicates that molybdenite mineralization was concurrent with Persimmon Fork volcanism. Seven Re-Os molybdenite ages from Haile (Mobley et al., 2014) yielded ages ranging from 529 to 564 Ma. Four of these samples produced an average age date of 548.7 ± 2 Ma (Mobley et al., 2014).


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8Deposit Types

Hundreds of gold occurrences in the southeast USA are located along a 700 km long SW-NE trend that extends from Alabama to Virginia (McCauley and Butler, 1966, Butler and Secor, 1991). Most of these deposits are small prospects worked and explored along narrow quartz veins. The larger gold deposits are located at or near the contact between volcanic and sedimentary rocks, including the Haile, Brewer, Barite Hill, and Ridgeway mines. Brewer is unique in the region and is classified as a high-sulfidation epithermal gold system with volcanic and breccia-hosted gold accompanied by quartz, pyrite, topaz, enargite, and chalcopyrite. Gold mineralization at Barite Hill contains the assemblage of pyrite-chalcopyrite-galena-sphalerite and is characteristic of a submarine, high-sulfidation volcanogenic massive sulfide deposit. Haile and Ridgeway are similar in that gold mineralization is hosted by silicified, sheared and foliated siltstone.

8.1Haile Genetic Model

The origin of the Carolina slate belt gold deposits is controversial. Contributing theories include:

•Worthington and Kiff (1970) concluded that a genetic link must exist between ore genesis and volcanism in the Carolina Terrane due to the intimate association with volcanic host rocks.

•Spence et al. (1980) found a genetic link between gold mineralization hosted within siliceous and pyritic zones and intense alumina alteration which produced kaolinite and sericite-rich zones stratigraphically above mineralized zones and interpreted these as analogous to features observed in modern hot springs based on geochemical signatures, stratiform nature, stratigraphic position, and geochronology.

•Feiss et al. (1993) built on the model of Spence et al. (1980) by proposing that hot spring type mineralization must have occurred under extension in a back-arc setting based on oxygen isotope data, which they interpreted to mark a shift from a subaerial to submarine environment. Feiss et al. classified Haile as a syngenetic hot spring system formed as the volcano-sedimentary pile accumulated with subsequent metamorphic overprints.

•Maddry and Speer (1993) proposed an exhalative model for mineralization at Haile whereby gold deposition resulted from hydrothermal fluids venting to the seafloor to produce stratabound ore bodies in marine volcaniclastic rocks. They interpreted intense alumina alteration noted by Spence et al. (1980) to be the effects of saprolitic weathering in warm, humid climates. Strong ductile deformation and structural dismemberment, mineral paragenesis, and mineral textures suggest ore deposition within shear zones or fold axes and that the fluid source was from metamorphic devolatilization reactions and pressure solutions related to Precambrian collisional events (e.g., Tomkinson, 1988; Hayward, 1992). Hayward (1992) emphasized the importance of folds in controlling the location of ore formation in anticlinal fold hinges. Hayward also noted that alteration zones at Haile are generally discordant to bedding and commonly display symmetrical patterns around ore bodies. Tomkinson (1988) proposed that Haile was an orogenic deposit based on textural and structural connections between gold mineralization and shear zones.

•Bierlein & Crowe (2000) discussed evidence for epigenetic (i.e., orogenic) vs. syngenetic gold mineralization for CSB gold deposits and concluded the evidence strongly favored syngenetic mineralization with local gold remobilization.


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•Hardy (1989) and Worthington (1993) interpreted the features observed by Hayward (1992) and Tomkinson (1988) as evidence for the remobilization of pre-existing mineralized horizons, causing gold enrichment along structurally controlled pathways during deformation which postdated the primary phase of mineralization at Haile. Hardy also concluded that fluids deposited silica, K-feldspar, pyrite, and gold in breccia zones. Gillon et al. (1995) proposed a model at Ridgeway that invoked early gold mineralization and remobilization during Neoproterozoic deformation.

•Foley et al. (2001) observed multiple generations of pyrite in Haile ores and concluded that disseminated pyrite and gold mineralization were contemporaneous with host volcanic rocks and volcaniclastic sediments.

Pressure shadows around pyrite grains, stretched pyrite and pyrrhotite grains, and flattened hydrothermal breccia clasts indicate that there has been deformation subsequent to sulfide mineralization. These observations are consistent with either pre- or syn-tectonic gold mineralization. Mineralized zones were subsequently foliated and sheared accompanied by regional greenschist facies metamorphism. Similar timing for gold mineralization and peak magmatism in the Haile and Ridgeway areas suggests that the hydrothermal systems that produced these deposits were related to magmatism. The geological understanding of the Haile deposit is increasing as exploration and mining continue. Haile is currently interpreted as a low sulfidation, disseminated, sediment-hosted, gold system with some local epithermal veining based on tectonic setting, low sulfide content, host rock lithology, and geochemistry.

8.2Haile Geological Model

The Haile geological model was constructed using Seequent’s Leapfrog Geo software (Leapfrog). The model box is approximately 4 km EW x 2 km NS x 800 m deep. The geological understanding of the Haile mineralization continues to evolve and is documented by mapping and drilling. Low grade mineralization is typically continuous, albeit exhibits local complexity, and concentration into economic mineralization pods. The 3D geological interpretations provide a good basis for 3D modeling and gold estimation. The Haile geological models are updated as needed with ongoing drilling.

The model consists of 3D solids for the following five geological units: dacitic metavolcanics, rhyodacitic metavolcanics, metasediments, basement undifferentiated rocks, and dikes. Surfaces that represent faults and shears, the base of CPS, base of surface clay alteration, base of saprolite, and the base of surface oxidation have also been modeled. Consistency of the geologic model has been improved by relogging of several hundred core holes and incorporation of Portable X-ray Fluorescence (pXRF) and other geochemical data.


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9Exploration

9.1Pre-Romarco

Modern exploration, development, and mining activity on the Haile property began with mapping in 1970 (Worthington and Kiff, 1970). Between 1973 and 1977, Cyprus conducted an extensive exploration program consisting of surface geophysical surveys, trenching, geologic mapping, auger drilling, core drilling, air-track drilling, and metallurgical testing. Cyprus calculated the Haile Mineral Resources at 186,000 oz (5,785 kg) of gold with an average grade of 2.13 g/t. Resources reported in this section do not conform to the standards of NI 43-101 and are included only as part of the historic record.

Between 1981 and 1985, Piedmont explored the historic Haile Mine and surrounding properties with core and RC drilling, surface geophysics, soil sampling, trenching, and rock-chip sampling. Piedmont’s total drilling was 69,647 m, much of which was for mine development. Piedmont mined several deposits on the Haile property from 1985 to 1992, producing about 86,000 oz (2,675 kg) of gold.

In 1991, Amax performed an extensive exploration program on the Haile property under an exploration option with Piedmont. In 1992, Amax and Piedmont formed Haile Mine Venture (HMV) as a joint venture, and from 1992 to 1994 HMC (the operating company) completed a program of exploration / development drilling using core and RC drilling, mineral resource estimation, and technical report preparation. The Ledbetter deposit was discovered, and the Mill and Snake areas were expanded.

Kinross acquired Amax in 1998, assumed Amax’s portion of the HMC joint venture, and later purchased Piedmont’s interest. Kinross performed no exploration activities on the property and limited their operations to a highly successful reclamation program from 1998 to 2007.

9.2Romarco

Romarco completed the Haile property acquisition in October 2007. By February 2008 Romarco had reviewed the quality of historical drilling and assay data and turned their effort to exploration and resource expansion drilling. During its ownership, Romarco significantly expanded the resource and reserve of the property. This report documents the results of the drill program achieved to date with Romarco assay data available through November 17, 2011 (i.e., data cut-off for previous Independent Mining Consultants, Inc (IMC) 15 Mineral Resource estimate), and subsequently by OceanaGold, as described below.

9.3OceanaGold

OceanaGold purchased Romarco in October 2015 and continued the drilling programs to expand and derisk resources and reserves at Haile. Both brownfields exploration and mine development drilling is ongoing, with particular focus on underground growth opportunities.


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9.3.1Geologic Mapping and Surface Sampling

Numerous workers have performed geologic mapping and surface sampling in and around the Haile Mine area. Mapping is challenged by poor bedrock exposure due to extensive saprolitic weathering, CPS cover, and dense vegetation. Outcrop is estimated at only 1% to 2% in the Haile area. Detailed mapping is generally restricted to mining excavations. The United States Geological Survey (USGS) published a geologic map for the Kershaw quadrangle in 1980 (Bell, 1980). More detailed mapping was conducted at Haile by Spence, Kiff, and Maye, who constructed a detailed geologic map for the mine site in 1975. Subsequent detailed geologic mapping was done by Taylor (1985) and Cochrane (1986). Ph. D. dissertations by Tomkinson (1985) and by Hayward (1991) included detailed geologic mapping in open pits. Geologic mapping by OceanaGold geologists at the Mill Zone pit resumed with mining in 2016.

Historical mapping has been scanned and loaded into the VulcanTM software for structural interpretation, exploration planning, and geologic modeling. The use of the structural dataset in conjunction with the drilling dataset has provided the foundation for a 3D digital geologic model. This model continues to be used successfully to expand the Mineral Resources and Mineral Reserves at the Haile property. Surface samples have been compiled into an Access database and evaluated by OceanaGold. Over 5,000 samples have been compiled based on location, sample type (rock chip, saprolite, soil, stream sediment), rock type, alteration and assay. QA/QC data are generally lacking for these surface samples, and most were assayed only for gold.

9.3.2Geophysics

Numerous geophysical surveys have been conducted at Haile since the 1970’s. The following geophysical methods have been applied at Haile:

•Gravity

•Airborne and Ground Magnetics

•Airborne Electromagnetics

•Ground-based Induced Polarization

•Ground-based Electrical Resistivity

•Self-Potential

•Down-hole Induced Polarization

Numerous IP / Resistivity surveys have been conducted at Haile, including surveys by Piedmont in 1975 and 1989, by Romarco in 2015 at Champion, Mill Zone, Ledbetter, and Horseshoe, and by OceanaGold in 2016 adjacent to Haile. Geophysical surveys conducted by Piedmont in the late 1980’s include ground magnetics and dipole-dipole IP / resistivity methods that led to discovery of the Snake deposit (Larson and Worthington, 1989). The ground magnetic data were acquired in a patchwork fashion and were not corrected for diurnal changes. The dipole-dipole IP / resistivity data were reprocessed by OceanaGold in 2016 (Weis, 2016).

In 2023, OceanaGold contracted Zonge International Geophysical Services and Equipment to reprocess previous surface IP / resistivity data and to perform additional downhole IP surveys. Downhole IP / resistivity was able to successfully identify known mineralization in a test hole, but five additional holes did not reveal any priority targets. Re-processed surface IP / resistivity data yielded new potential target areas.


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Regional gravity survey and aeromagnetic data have been downloaded from the South Carolina data repository (Daniels, 2005). These were supplemented by more detailed gravity stations in 2009 and 2010 by Romarco along roads in the Haile area and as transects over Haile deposits.

Airborne EM and magnetic surveys were flown by Aeroquest for Romarco in 2010 over the Haile-Brewer area on 50 m and 100 m spaced flight lines with a bearing of 150° to 330°. The magnetic data can map the diabase dikes and granite plutons but do not differentiate the older units. Proprietary 3D inversion modeling was conducted by OceanaGold in 2016 to depths of 1,500 m using airborne magnetic and EM data.


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10 Drilling

During 2016, the Romarco Minerals drilling database was translated to OceanaGold’s standard acQuire database platform. Where available, original source assay and survey data were used for the acQuire translation and database validation. There was a further internal database review in late 2018 / early 2019. No material errors were identified.

10.1Type and Extent

Drilling at the Haile property commenced in the 1970’s and has continued intermittently to the present by several companies. The database used for this latest Mineral Resource estimate was extracted from the acQuire database on October 29, 2025. It contains 4,057 drillholes including 1,614 core holes for 432,249 m (representing 50% of the metres drilled), 209 hybrid (RC with diamond tail) holes for 124,333 m (14%), and 2,184 RC holes for 311,031 m (36%). Some of the historical drilling (i.e., shallow exploration auger or air track drilling) was judged insufficiently reliable and was excluded from the Mineral Resource estimation database. RC and core drilling by Romarco continued from 2008 to 2012 and then resumed in 2015 after a two-year hiatus due to permitting and lower gold prices. Drilling at Haile since early 2015 has almost been entirely core drilling, besides targeted RC grade control campaigns. Drill campaigns by company and year are summarized in Table 10-1.


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Table 10-1: Haile Drilling Campaigns by Year, Owner and Lab

Start Hole

End Hole

Hole

Type

Start Yr.

End Yr.

Owner

Lab

DDH0001

DDH0031

core

1975

1977

Cyprus

CMS, Cyprus, Union

WW0600

WW0673

1975

1990

Piedmont

NE Geochemical

DDH0032

DDH0098

core

1985

1990

Piedmont

Piedmont, NE Geochemical

NDH0001

NDH0037

core

1985

1988

Nicor

Cone Geochemical

RC0001

RC0031

1985

1986

Piedmont

Union

RC0032

RC0183

1986

1987

Piedmont

NE Geochemical

NRH0001

NRH0054

1987

1988

Nicor

Cone Geochemical

RC0184

RC1230

1987

1990

Piedmont

Bondar Clegg, NE Geochemical

RC1231

RC1303

1990

1992

Piedmont

Bondar Clegg

DDH0099

DDH0288

core

1991

AMAX

Bondar Clegg

RC1304

RC1501

1992

1994

AMAX

Bondar Clegg

DDH0289

DDH0341

core

2008

Aug-15

Romarco

Inspectorate

DDH0342

DDH0431

core

2008

2009

Romarco

Alaska

RC1502

RC1527

2008

2009

Romarco

Inspectorate

DDH0432

DDH511

core

2009

Sep-11

Romarco

KML

RC1528

RC2083

Jan-10

Jan-11

Romarco

Alaska

RCT0001

RCT0157

RC/core

Apr-10

Jan-11

Romarco

Alaska

RC2084

RC2122

Jan-11

Sep-11

Romarco

Acme, Chemex, KML

RCT0158

RCT0178

RC/core

Jan-11

Sep-11

Romarco

Acme

DDH512

DDH596

core

Oct-11

Jun-17

OceanaGold

KML

RC2123

RC2205

Oct-11

Jun-15

Romarco

KML

RCT0179

RCT0211

RC/core

Oct-11

Dec-12

Romarco

KML

DDH0597

DDH1305

core

Jul-17

ongoing

OceanaGold

ALS

RC2219

RC2396

Feb-20

ongoing

OceanaGold

ALS, SGS

UGD0001

UGD0121

core

2023

ongoing

OceanaGold

ALS, SGS

UGC0004

UGC0194

core

2023

ongoing

OceanaGold

SGS

Source: OceanaGold, 2025

10.2Sample Collection

Both RC and Diamond Drilling (DDH, UGD, UGC) have been used for the Resource estimates at Haile. This section describes the sampling procedures applied to both data collection techniques. Historical drilling prior to Romarco (pre-2007) accounts for approximately 16% of the data. The sample procedures applied to the historic drilling (i.e., drilling prior to Romarco) at Haile are not well documented. Having said this, approximately ten years of mining have tested the veracity of the Resource estimates, which are based on this data. No material flaws have been identified.

The techniques described in this section reflect the procedures applied by Romarco and OceanaGold during the period 2007 to October 29, 2025.


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Reverse Circulation Drilling

The RC drilling at Haile typically used 16 cm drill bits. RC drills are equipped with a cyclone and a rotary splitter. Most RC drilling at Haile was under wet conditions. Water injection was typically 15 to 19 litres per minute (L/min) above the water table and decreases to 4 L/min when groundwater is encountered. Sample sizes were between 3 to 7 kg (20 and 30 lbs) with a minimum requirement of 3 kg (15 lbs). The standard size reflected a 15% to 20% split of the total drilled volume. Drill intervals were generally 1.5 m (5 ft) intervals and were collected in bags, to which flocculant was added to settle fine particles. Sampling during advancement of each twenty-foot (6.1 m) rod was a continuous process. Chip samples were collected from the waste discharge and stored in plastic chip trays for geologic logging. The wet samples were bagged, drained, and allowed to settle (aided by flocculent). Sample bags were collected at the end of each shift and transferred to the Haile sample storage area for initial drying.

Diamond Drilling

Diamond core drilling is by wireline methods and generally utilizes HQ and NQ size core with
63.5 mm and 48.3 mm diameters, respectively. Drill rods are 10 ft (3.1 m) or 5 ft (1.5 m) long. Core is transferred from the core barrels into plastic core boxes at the drill rig by the driller.

Each core box can hold up to 10 ft (3.1 m) of core stored in five rows, each 2 ft (0.6 m) long. Core is gently broken by hammer as required to completely fill the boxes and marked on core as a mechanical break. Hole numbers and drill depths are marked on the outside of the core boxes and interval marker blocks are labeled and placed in the core box. Boxed whole core is covered with plastic lids and is transported to the core shed for logging and sampling by HGM staff or contractors.

Sample Recovery

Reverse Circulation: No primary RC sample weights were recorded for RC drilling, so RC recoveries cannot be directly calculated. However, 34,000 rotary split RC subsamples were weighed by Romarco. Splitter ratio settings ranged from 8% to 17%, based on back calculating the range of likely total sample weights. RC recoveries appear to have been largely acceptable.

Diamond Core: Core recoveries average 92% and are rarely less than 90%. There is no observed grade relationship between core recovery and grade. Core recovery in saprolite ranges from 10% to 50%. Minimal ore has been identified in saprolite.

10.3Collar Locations and Downhole Surveys

Drillhole numbers are assigned and maintained by company geologists via an Excel tracking spreadsheet that records location, depth, azimuth, dip, start, and end dates. Historical drillhole collar surveys by Piedmont and Cyprus were surveyed by theodolite and recorded on paper. Drill set ups in the field were by traditional Brunton compass methods to establish azimuths within 2° accuracy. Since February 2019, the Reflex Aziliner tool or Stockholm Precision Tools POLESTAR have been used for drillhole set ups within 0.3° accuracy.

Haile drillhole collars from 2007 to October 2017 were surveyed by Romarco and OceanaGold surveyors using digital GPS methods.


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Collar surveys are named by hole number, downloaded as .csv files, and saved on a network drive. Collar coordinates are verified against planned coordinates by the geologist overseeing the drilling and then imported into the acQuire database.

Historical drillholes prior to Romarco in 2007 were not surveyed for downhole deviation. The majority of these holes intersected mineralization less than 75 m down hole, so the locational uncertainty is unlikely to be large.

Since 2007, all surface angle holes have been surveyed using the Reflex Sprint-IQ and EZ-Gyro survey tools. Multishot surveys are recorded down hole for azimuth and dip every 6.1 m (20 ft). Upon verification, the data are saved to a local drive and imported into the acQuire database.

Survey data are also stored digitally in the acQuire database. As part of a company-wide metrification process, OceanaGold transformed all surface and drillhole data from the South Carolina NAD27 coordinate system to the UTM NAD83 zone 17N system in November 2016. Coordinate transfer was verified by both geologists and engineers; no issues were identified. Additionally, collar coordinate elevations have been adjusted by +1000 metres to avoid negative reduced level values.

All underground holes are surveyed using Stockholm Precision Tool’s GYROMASTER or Boart Longyear’s TRUCORE. Survey data is downloaded from the tool and verified by HGM staff, stored on a local network, and uploaded to the acQuire database.


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11Sample Preparation, Analyses and Security

11.1Sample Preparation for Analysis

Reverse Circulation Drilling

The RC sample bags were transferred by HGM staff to the sample handling facility where they are prepared for shipment to a lab. RC samples were prepared at either the KML in Kershaw, South Carolina, the AHK preparation facility in Spartanburg, South Carolina, or the ALS preparation facility in Tucson, Arizona.

Lithological chip samples are retained in chip trays, labeled with the drillhole number and depth intervals in permanent marker.

The RC sample bags from the truck were transferred to the Haile sample handling facility where they are prepared for shipment to a lab. RC samples were prepared at either the KML in Kershaw, South Carolina, the AHK preparation facility in Spartanburg, South Carolina, or the ALS preparation facility in Tucson, Arizona.

Samples follow one of two paths:

•Some samples are weighed, and sample number tags added to the bags. The samples are poured through a Jones splitter to reduce the size to roughly 2.7 kg (6 lbs) for shipment to the sample lab. Coarse rejects are kept in their original sample bags and stored on site on pallets.

•Alternatively, samples are staged at Haile and placed in containers for direct shipment to KML, AHK, or ALS.

Diamond Drilling

At the exploration office, the core is cleaned, measured, and photographed. Geotechnical and geologic logging are completed on the whole core. All logging and sampling handling are conducted by HGM staff. Data collecting during core logging include structure, rock type, alteration, mineralogy, RQD, core recovery, hardness and joint condition. Alteration is logged as relative intensity and includes weak, moderate and strong categories. Standardized templates are used for all logging with drop down menus. Geologists routinely review core together and compare notes to ensure accuracy and consistency. Density samples are collected every 12 m (40 ft) and use the water immersion method to measure specific gravity. Competent core at Haile does not require plastic or wax coatings for density measurements. Pre 2017, paper logs were entered into an Excel spreadsheet and then imported into the acQuire database by the admin assistant. Logs are periodically checked by geologists for accuracy and completeness. Tablet-based geology logging in Excel was initiated in 2017 and enables logs to be directly uploaded into acQuire. Logging is conducted in the Imperial system using feet due to the 10 foot drill rods. Data are converted to metric units as part of being imported into the acQuire database. The logging geologist assigns the sample intervals and sample numbers prior to core sawing. Sample ID tags are placed in the core boxes. Sample lengths are typically 5 ft (1.5 m) and can range in length from 1 ft (0.3 m) to 10 ft (3.1 m). Geologic sample breaks may be selected by the geologists based on contacts or structural boundaries. ‘No sample’ intervals are marked by orange flagging tape in surficial fill or rubble zones and in massive barren diabase dikes exceeding 50 ft (15 m) in thickness. Most core is sawed in half along the core axis using circular masonry blades and then placed into sample bags labelled with


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the sample ID. An exception is underground grade control core (UGC) holes which are sampled without splitting. Paper ID tags are also placed into the bags. Saprolite zones are manually cut with a putty knife. The saw or knife are cleaned between each sample. The cooling water for the saw is not recycled and is discharged into a permitted pond.

Core samples are delivered to the sample preparation facilities. Core is prepared primarily at the ALS facility in Tucson, Arizona but has also been prepared at the company-owned KML facility in Kershaw, South Carolina and the AHK preparation facility in Spartanburg, South Carolina. Since 2018, KML has been operated and managed by SGS Testing Laboratory Services (SGS).

11.1.1Off-Site Sample Preparation

AHK, Spartanburg, South Carolina (ISO/IEC 17025 accredited)

Once the samples arrive at AHK in Spartanburg, South Carolina the following procedures were applied:

•Dry samples at 65°C (150°F (degrees Fahrenheit))

•Jaw crush samples to 80% passing 2 mm

•Split sample with a riffle splitter to prepare the sample for pulverizing

•Pulverize a 250 g sample to 90% passing 150-mesh (0.106 mm)

•Ship about 125 g of sample pulp for assay

Sample pulps were shipped to the AHK Laboratory in Fairbanks, Alaska for analysis.

KML, Kershaw, South Carolina (ISO/IEC 17025 accredited)

•Dry samples at 93°C (200°F)

•Jaw crush samples to 70% passing 10-mesh (2 mm)

•Split sample with a riffle splitter to prepare the sample for pulverizing

•Pulverize a 450 g sample (± 50 g) to 85% passing 140-mesh (0.106 mm)

•Approximately 225 g of pulp sample is sent for fire assay (FA)

Sample pulps from KML were either analyzed at KML or shipped to the AHK Laboratory in Fairbanks, Alaska for analysis.

ALS, Tucson, Arizona (ISO/IEC 17025 accredited)

•Dry samples, if excessively wet, at up to 120°C (248°F)

•Jaw crush samples to 70% passing 10-mesh (2 mm)

•Split sample with a Boyd rotary splitter to prepare the sample for pulverizing

•Pulverize a 250 g sample to 85% passing 75 microns

•Approximately 225 g of pulp sample is sent for fire assay

•Fire assay performed on a 30 g sample with an Atomic Absorption Spectroscopy finish

•For samples over 10 g/t Au, fire assay is performed on an additional 30 g sample with a gravimetric finish


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11.2Sample Analysis

Generally, all Mineral Resource samples are processed at ALS and grade control samples are processed at KML. But in some instances, this may be switched due the Laboratory capacity or time constraints.

The procedures currently applied at ALS for assay are as follows:

•Fire assay 30 g of pulp sample for gold, with Atomic Absorption finish

•If the gold assay results greater than or equal to 3 g/t Au, an additional 30 g of pulp sample is cyanide leached for gold using Atomic Absorption finish. Where it equals or exceeds 10 g/t an additional 30 g of pulp sample is fire assayed for gold using gravimetric finish

•Multi-element ICP analysis is performed as requested, normally testing specific areas

•Carbon and sulfur determinations are performed as requested, normally testing areas

ALS is ISO 9001 certified and ISO/IEC 17025 accredited. Coarse rejects and returned samples are stored at Haile under the control of HGM staff.

The procedures currently applied at KML for assays are as follows:

•Inventory the samples and create worksheets

•Insert quality control samples at prescribed rates (see Section 11.4)

•Fire assay 30 g of pulp sample for gold, with Atomic Absorption finish

•If the gold assay result is greater than or equal to 3 g/t Au, an additional 30 g of pulp sample is fire assayed for gold using gravimetric finish, and 0.5 g of pulp sample is analyzed for silver using a four-acid digestion with Atomic Absorption finish

•Multi-element ICP analysis is performed as requested, such as testing specific areas

•Carbon and sulfur determinations are performed as requested, such as testing waste mining areas.

KML is ISO/IEC 17025:2005 accredited for gold and silver assays through the Standards Council of Canada.

11.3Check Assays

Early in the Romarco drill program, samples were sent to the Inspectorate Lab in Reno, Nevada for preparation and assay. Inspectorate is an ISO 9001 certified laboratory. Check assays were sent to ALS-Chemex in Reno, Nevada. Beginning in late 2024, crush duplicates have been assayed for UG Grade Control drilling at KML and to date there has been good correlation with the original assay.

11.4Quality Assurance / Quality Control Procedures

11.4.1Certified Reference Material

CRM is routinely inserted at a rate of one in twenty samples (5%) per industry guidelines. CRMs used by Romarco were purchased from and certified by Rocklabs. OceanaGold currently uses CRMs from Rocklabs and OREAS.


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11.4.2Blanks

Blanks are routinely inserted at a rate of one in twenty samples (5%). Blanks used by Romarco and OceanaGold include commercially available marble, sand, quartz pebble.

11.4.3Duplicates

Starting in late 2024, crush duplicates have been assayed for UG grade control samples. Good comparisons have been reported against the original samples (within 20% variance of original sample).

11.4.4Actions and Results

QA/QC data and graphs are generated from the acQuire database. CRMs returning values outside of 20% variance from the expected value are re-assayed for failed batches. Blanks returning values greater than 0.05 parts per million (ppm) are also re-assayed. Reruns have been acceptable, and those values were imported into and accepted in the acQuire database.

Security Measures

RC coarse rejects and returned samples are stored and secured at Haile where they are under the control of HGM staff. Pulps, RC chips, and coarse rejects are stored at the exploration office. Boxed core is palletized and stored in a grass lot on the east side of the mine property. Pallets are covered by tarps and aluminum tags with hole IDs attached to each pallet.

11.5Opinion on Adequacy (Security, Sample Preparation, Analysis)

Historical holes drilled before 2007 comprise 15% of total drill metres and were not documented to the same standard as current OceanaGold practices. However, there is no evidence of material problems with the pre-2007 drilling, sampling and analyses. Furthermore, over ten years of mining has tested the veracity of the Mineral Resource estimates which are based on this data. No material flaws have been identified.

Sample collection, preparation, and analysis are according to industry standards. All labs used by Romarco and OceanaGold are certified to ISO-9001 standard or 17025 accredited for gold and silver through the Standards Council of Canada. The primary external lab used for check assays at ALS Reno is both ISO-9001 certified and 17025 accredited.

Core, pulp, and RC sample storage are considered secure. Sample transport is by HGM staff between secure facilities and by approved couriers to external labs. No significant risks have been identified for sample contamination or sample exchange. No samples have been reported as missing or tampered during transportation upon receipt at the lab.

All Haile drillhole data (assays, logs, surveys) are stored in the secure acQuire database, which is managed by the Principal Database Geologist in New Zealand. The database geologist has no direct reporting relationships to the Haile geologists or to the Director of Exploration. The acQuire database is an industry certified database. Database changes are tracked and verified. Strict data importing and verification protocols must be followed to avoid, for example, overlapping or missing intervals, mismatched hole depths in different fields, duplicate hole IDs or sample numbers, and invalid logging codes.


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In the opinion of the QP, the sample security, preparation and analyses are adequate for the purposes of Mineral Resource estimation.


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12 Data Verification

Verification of drilling, sampling and analyses is discussed as Pre-Romarco, Romarco and OceanaGold data groups in the sections below.

12.1Data Validation of Pre-Romarco Holes

Data validation was conducted by OceanaGold geologists in 2019 for pre-Romarco (pre-2008) RC and core holes. A total of 1,775 holes representing 54% of the resource database were validated using Au best values stored in the acQuire database. This includes drillholes RC0001-1501 (n=1403), DDH0001-0288 (n=288), NDH0001-0037 and NRH0001-0054 (n=84) drilled between 1975 and 1994. The data were compiled, sorted, filed from source data using original logs and assay certificates from dozens of binders and hard copy files for each drillhole. Differences between assays, depths, dips, azimuths, downhole surveys and collar coordinates were recorded and evaluated in spreadsheets. All paper files and logs are securely stored in exploration office at Haile.

No major or systematic errors were identified and there is no material impact to Reserves or Resources based on validation of pre-2008 drillhole data (Jory, 2019). Legacy drillhole data from 1975 to 1994 stored in acQuire are regarded as reliable and accurate. Romarco and OceanaGold data are also reliable and accurate. Minor data corrections were made for some legacy gold assays, collar coordinates, hole depths, and interval depths. Data validation showed that 0.77% of DDH holes and 5.4% of RC holes required corrections based on differences >0.007 ppm Au between acQuire Au best values and assay certificates or assay sheets. Many of the RC holes had negligible errors <1% of the acQuire assay vs. original assay. Most of the suspect holes are from the early Cyprus and Piedmont drill campaigns. Amax holes are of high confidence and include certified assays by Bondar Clegg with fire and gravimetric assays.

As a precautionary measure, extra diamond core drilling targeted within open pit designs has been completed in areas with large numbers of legacy (pre-Romarco) RC holes, including Snake, Red Hill and Haile. The Mill Zone, Ledbetter, Horseshoe and Small pits are largely drilled with core holes and have no RC grade bias risk. Extra diamond core drilling at Ledbetter UG resulted in the removal of legacy (pre-Romarco) RC holes for the Mineral Resource estimate.

12.2Verification of Romarco and OceanaGold Data

There are 24,794 CRM samples recorded in the OceanaGold acQuire database. There are an additional 20,148 blank samples. The number of CRM samples submitted by year varies and largely reflects the drilling activity in that year. The performance of these CRMs revealed no material problems with laboratory performance. Blanks and CRMs are inserted at industry normal frequencies of 1 in 20 samples.


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12.2.1Romarco Data Verification

In addition to the checks done by OceanaGold during database translation and the 2018 / 2019 review, the following checks have been made by IMC for drilling completed by Romarco (2008 to 2014).

•A comparison of certificates of assay from the laboratory vs. the Romarco computerized data base to check the reliability of data entry

•Statistical analysis of the CRMs that were inserted by Romarco for analysis by the assay lab

•Statistical analysis of the blank samples that were inserted by Romarco for analysis by the assay lab

•Statistical analysis of the check samples that were submitted by Romarco to a third-party laboratory

The QP has reviewed the checks and believes that the data are of acceptable quality for the purposes of Mineral Resource estimation.

12.2.2Horseshoe Data Verification 2016

In 2016, OceanaGold undertook a program of database verification for drilling at the Horseshoe Underground deposit:

•Assay Verification – 5% check of assay values

•Collar Verification – 100% check of collar locations

•Downhole Survey Verification – 100% check on downhole surveys

•CRM and Blank QA/QC

•KML vs. ALS Horseshoe assay comparison

The review identified no material flaws. The Horseshoe data is considered of acceptable quality for the purposes of Mineral Resource estimation. The KML vs. ALS check assay comparison study for Horseshoe concluded that “statistical variance from these studies for AuAA vs. AuFA comparisons (n=512) between KML and ALS Tucson indicate that the KML lab is 5% to 10% low, or conversely that the ALS lab is 5% to 10% high. KML adjusted their AA dilution process in late October 2016 to achieve better fit with expected values”. The KML assay data were validated and used in the Mineral Resource model.

All Horseshoe drilling was core using OceanaGold LF90 drills and company drillers. Sample preparation and assays were conducted by OceanaGold’s KML at Haile. Check assays on sample pulps were performed by ALS in Tucson, AZ. No significant errors were identified by the study as seen in Figure 12-1.


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Source: OceanaGold, 2021

Figure 12-1: Horseshoe AuFA_grav KML vs. ALS 0-53 g/t (n=253)

12.3Haile QA / QC ALS July 2017- December 2025

During the period July 2017 to December 2025, nearly all exploration and Resource definition samples were submitted to ALS laboratories. Samples were prepared at the Tucson, Arizona lab and certified assays were done in Reno, Nevada or Vancouver, British Columbia.

12.3.1July 2017 to December 2025 CRM Performance

ALS Reno laboratory accuracy was monitored by insertion of commercially CRMs into the sample stream. A total of 32 different CRMs sourced from Rocklabs and OREAS were submitted in sample batches for a total of 3,722 CRM analyses during the eight and a half-year period. Twenty nine of the 32 CRMs had more than 30 insertions into the sample stream. CRMs include oxide, sulfide, and high silica standards. Figure 12-2 shows CRM values plotted against the expected values. Figure 12-3 shows a zoomed in view of the most commonly inserted CRMs. No obvious bias was observed within the CRM expected vs. actual data. Relative standard deviation of all CRMs was good, averaging 4.3% of expected values over the period. Results confirm excellent precision and accuracy of assays provided by ALS Reno for Haile Mineral Resource calculations that are within industry guidelines. Results from blanks showed no contamination of samples used for Mineral Resource calculations.


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Source: OceanaGold, 2025

Figure 12-2: July 2017- December 2025 CRM Analyses vs. Expected Value

Source: OceanaGold, 2025

Figure 12-3: July 2017 to December 2025 CRM Analyses vs. Expected Value <4 g/t


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Standard control charts were plotted for commonly used CRMs. Examples of oxide (OxF125, OxG124, OxH122, OxE150, OxI177, OxI121, and OxI176), sulfide (SF85 and SC127), and high silica (HiSilK2 and HiSilP3) CRMs are shown in Figure 12-4 through Figure 12-7. No obvious trends in the process mean are apparent in the longer run CRM results. CRM OxF125 and OxG124 showed a consistent slight under call, compared to the CRM reported mean, but within two standard deviations (SD) of the reported CRM mean (see Figure 12-4). CRM SF85 showed a slight under call, compared to the CRM reported mean from Feb 2020 to Oct 2020, and preformed better after October 2020 (see Figure 12-6)

If a CRM returned a value greater than 20% above or below the expected value, and no sample swap was evident, all intervals within the failed batch and the nearest passing CRM or Blank were rerun.

Source: OceanaGold, 2025

Figure 12-4: July 2017- December 2022 CRMs: OxF125 (Au=0.806), OxG124 (Au=0.918), and OxH122 (Au=1.247)


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Source: OceanaGold, 2025

Figure 12-5: January 2024 - December 2025 CRMs: OXE150 (Au=0.658), OXI177 (Au=1.811), OXI121 (Au=1.834), and OXJ176 (Au=2.385)

Source: OceanaGold, 2025

Figure 12-6: October 2019 to December 2025 CRMs: SC127 (Au=0.225) and SF85 (Au=0.848)


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Source: OceanaGold, 2025

Figure 12-7: October 2017 to December 2025 CRMs: HiSilK2 (Au=3.474) and HiSilP3 (Au=12.240)

12.3.2Contamination Monitoring

Contamination is monitored by insertion of blank materials. From July 2017 to December 2025, a total of 3,526 blank samples of four different materials were inserted: Marble, Sand, Gravel, and Quartz Pebble. Lab detection limit (LDL) is 0.005 ppm Au and control limit used is 10 times the LDL (i.e., 0.050 ppm Au). Haile’s trigger threshold for a blank is 0.05ppm, only 11 out of the 3,526 were significantly above this threshold and were not proceeded by high grade samples. No action was taken. Overall, there is no indication of significant contamination during sample preparation.

The QP has reviewed the July 2017 to current data and believes it to be of acceptable quality for the purposes of Mineral Resource estimation.

12.3.3Statement of Data Adequacy

The QP believes that the data reviewed above, including drilling prior to 2007 and subsequent drilling by Romarco and OceanaGold, is adequate for the purposes of Resource estimation.


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13 Mineral Processing and Metallurgical Testing

Sample preparation and characterization, grinding studies, gravity concentration tests, whole ore leach tests, flotation tests and leaching of flotation tailings, and flotation concentrate tests were completed to determine the metallurgical response of the ore.

Samples of ore were collected by HGM for metallurgical testing. A series of metallurgical testing programs have been completed by independent commercial metallurgical laboratories. The test work indicated that the ore responds well to flotation and direct agitated cyanide leaching technology to extract gold. The results of the test programs are available in the following reports:

•Phillips Enterprises, LLC (Phillips) 17 September 2008, Progress Report #2 Process and Metallurgical Testing on Haile Gold Mine Ore Project No. 082003i

•Pocock Industrial Inc. (Pocock) Salt Lake City, Utah, May 2009, Flocculant Screening, Gravity Sedimentation, Pulp Rheology, Vacuum Filtration and Pressure Filtration Studies Conducted for Romarco Minerals Haile Gold Project

•Resource Development Inc. (RDi), Wheat Ridge, Colorado, September 16, 2009, Romarco Minerals, Inc. Haile Gold Project, Metallurgical Report

•Metso Minerals Industries Inc. (Metso), York, Pennsylvania, December 7, 2009, Test Plant Report No. 20000134-135

•Resource Development Inc. (RDi), Wheat Ridge, Colorado, March 31, 2010, Romarco Minerals, Inc. Work Index Data for Haile Composite Sample

•Resource Development Inc. (RDi), Wheat Ridge, Colorado, March 31, 2010, Romarco Minerals, Inc. Metallurgical Testing of Ledbetter Extension Samples

•Resource Development Inc. (RDi), Wheat Ridge, Colorado, May 27, 2010, Romarco Minerals, Inc. Flash Flotation, Cyanide Destruction & Leaching of Concentrate and Tailing for Haile Composites

•Resource Development Inc. (RDi), Wheat Ridge, Colorado, September 27, 2010, Romarco Minerals, Inc. Optimization of Leaching of Flotation Concentrate

•Resource Development Inc. (RDi), Wheat Ridge, Colorado, August 2010, Metallurgical Testing of Horseshoe Zone Samples

•Metso Minerals Industries, Inc. (Metso), York, Pennsylvania, February 2011, Stirred Media Detritor and Jar Mill Grindability Test on Bulk Flotation Concentrate T11-04

•KML Metallurgical Services, (KML), Kershaw, South Carolina, December 27, 2012, HGM Years 1 – 3 Silver Characterization Project Test Report

•Resource Development Inc. (RDi), Wheat Ridge, Colorado, June 6, 2011, Production of Flotation Concentrate and Confirmation Testing of Flowsheet

•G&T Metallurgical Services Ltd (G&T), Kamloops, Canada November 24, 2011, Flotation & Cyanidation Testing on Samples from the Horseshoe Deposit, Haile Gold Mine KM3076;

•Gekko Global Cyanide Detox Group (Gekko), Ballarat, Australia, July 18, 2016, OceanaGold Haile Gold Mine Cyanide Detox Test Work DTXSC021

•ALS Metallurgy Kamloops, BC, Canada, December 2016, Comminution Testing on Samples from the Haile Gold Mine KM 5180

•ALS Metallurgy Kamloops, BC, Canada, Comminution and Thickening Testing for Haile Gold Mine KM 5293


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The metallurgical test results were used to develop process design criteria and the flow sheet for processing the ore in the existing plant and the basis for progressive upgrades since commissioning.

In addition to the testwork undertaken in developing the plant flowsheet and design-criteria, ongoing future ores testwork has been undertaken to support additional Reserves utilizing the same laboratory flowsheet to allow direct comparison with historical testwork.

The following sections contain some information in short tons (st) and others in metric tonnes (t).

13.1Testing and Procedures

13.1.1Comminution

Comminution test work on mineralized samples was performed by RDi (using Phillips Enterprises, LLC) and by ALS Kamloops.

Bond ball mill work index (BMWi) values were determined by RDi for various Haile samples. Bond impact and abrasion tests were also completed. The BMWi results for selected composites from this work are presented in Table 13-1.

Table 13-1: Bond Ball Mill Work Indices for Haile Samples


Composite Number	Area	BMWi at 100-mesh (kWh/st)
1	Mill Zone	8.42
2	Mill Zone	8.07
3	Mill Zone	7.95
4	Mill Zone	8.03
5	Mill Zone	7.88
6	Haile	8.55
7	Haile	9.78
8	Ledbetter	7.49
26	Snake	10.34
27	Snake	10.39
31	Snake	5.13

Source: OceanaGold, 2025

Further testing, including Bond rod mill index testing as completed on Mill Zone, Haile, Ledbetter, and Red Hill ore zone samples. The Bond ball mill work index for each composite was also determined at both 100- and 200-mesh for these samples.

The results for selected composites from this work are presented in Table 13-2.


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Table 13-2: Bond Rod and Ball Mill Work Indices for Haile Composite


Composite Number	Sample Description	Rod Mill Wi (kWh/st)	Ball Mill Wi at 100-mesh (kWh/st)	Ball Mill Wi at 200-mesh (kWh/st)
2	Mill Zone-Average Grade	11.08	8.21	7.78
6	Mill Zone-High Grade	11.30	8.21	8.17
8	Haile-Average Grade	12.49	9.47	8.92
20	Ledbetter-Average Grade	12.18	8.95	8.42
24	Ledbetter-High Grade	12.56	9.47	9.03
34	Red Hill-Average Grade	-	8.73	9.47
54	Red Hill-Low Grade	-	8.83	9.50

Source: OceanaGold, 2025

RDi also performed comminution tests on samples from the Ledbetter Extension zone. The Bond rod and ball mill indices and an abrasion index for an ore composite (83) was determined. The results of this work are presented in Table 13-3.

Table 13-3: Rod and Ball Mill Work Indices for Ledbetter Extension Samples


Abrasion Index			Value (kWh/st)
Rod Mill Work Index			12.71
Ball Mill Work Index at 100-mesh			10.21
Ball Mill Work Index at 200-mesh			9.81

Source: OceanaGold, 2025

RDi also performed comminution studies on samples from Horseshoe. The Bond rod, ball mill, and abrasion indices for four different composites were determined. The samples were relatively abrasive and moderately hard. The results are presented in Table 13-4.

Table 13-4: Rod and Ball Mill Work and Abrasion Indices for Horseshoe Samples


Composite Number	Sample Description (Hole ID / intercepts / lithology)	RM Wi (kWh/st)	BMWi at 200-mesh (kWh/st)	Abrasion Index
83	RCT-03 / 1412 to 1460 ft / Silicified Metasediment (Ms)	-	12.29	0.2167
84	RCT-04 / 1460 to 1510 ft / Silicified Metasediment	-	11.29	0.2691
85	RCT-04 / 1510 to 1585 ft / Silicified Breccia	14.93	12.95	0.3786
86	RCT-04 / 1585 to 1655 ft / Silicified Breccia	13.56	13.77	0.8330

Source: OceanaGold, 2025


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ALS performed comminution tests on samples from Horseshoe and Ledbetter. The A x b parameter from the SMC test, SAG Circuit Specific Energy (SCSE) and Bond ball mill indices for composites were determined. The results of this work are presented in Table 13-5.

Table 13-5: ALS Comminution Tests on Horseshoe Samples


Composite Number	A x b	SCSE (kWh/st)	BMWi at 200-mesh (kWh/st)
Horseshoe 1	28.9	11.4	13.5
Horseshoe 2	29.9	11.3	13.6
Horseshoe 3	30.7	11.2	9.3
Horseshoe 4	29.4	11.6	10.9
Horseshoe 5	28.0	11.6	14.4
Horseshoe 6	27.1	12.4	10.6
Ledbetter 1	27.3	12.0	11.6
Ledbetter 2	25.6	12.2	13.5
Ledbetter 3	27.8	11.9	11.8
Ledbetter 4	30.8	11.3	8.9

Source: OceanaGold, 2025

ALS performed JK Drop Weight and Bond ball mill index tests on samples from mineralized material exposed in Mill Zone Pit. The results of this work are presented in Table 13-6.

Table 13-6: ALS Comminution Tests on Mill Zone Pit Samples


Composite Number	A x b	SCSE (kWh/st)	BMWi at 200-mesh (kWh/st)
1a	93.6	7.15	9.4
1b			9.1
2a	52.8	8.85	6.8
2b			6.6

Source: OceanaGold, 2025

The comminution circuit design developed for the expansion project incorporated the additional competency test work and power modeling for the overall circuit was developed with the assistance of external consultants. A series of plant grinding circuit surveys were completed in 2017 and 2018 to validate the predictions of the modeling work. The survey data indicated the Haile Semi-Autogenous Grinding (SAG) specific energy requirement was significantly lower than that predicted from the SMC test results on all surveys. Additional modeling work developed a Haile site specific model for SAG specific energy as a function of the drop weight index (DWI) from the SMC test and Bond ball mill work index.

Updated throughput modeling, using the site-specific model, indicated an increase in throughput averaging 70 tonnes per hour (t/h) higher than the original work. Based on the outcome of the power


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modeling work, the confidence of achieving 3.5 to 4.0 Mt/yr throughput rates for the majority of the ore sources was sufficient to proceed with the installation of the pebble crushing circuit but not to proceed with the detailed design of the secondary crushing circuit.

ALS performed SMC, Bond rod mill and Bond ball mill index tests on a further 17 composite samples taken from the Ledbettter, Snake, Haile, and Red Hill pits from infill drilling in 2018. These allowed additional variability analysis on expected ore competency across these pits based on the power modeling work that represented mill feed from 2019 to 2024. The results of the program are summarized in Table 13-7 and indicate similar values to the previous programs.

Table 13-7: ALS Comminution Test Results for 2018 Infill Sample Program


Sample ID (DDH/Deposit)	A x b	SCSE (kWh/tonne)	BMWi at 200-Mesh (kWh/tonne)
672A Ledbetter	25.4	12.6	11.0
693A Snake	39.8	10.1	8.6
698A Snake West	27.9	11.8	11.3
726A Snake West	24.8	10.6	10.9
726B Snake West	28.9	11.7	8.9
746A Snake	40.5	10.0	9.8
746B Snake	31.0	11.3	11.6
746C Snake	36.2	10.5	10.0
752A Ledbetter	28.3	11.9	9.9
752B Ledbetter	33.0	10.9	10.2
773A Ledbetter	28.9	11.8	10.1
802A Haile	31.7	11.2	8.8
802C Haile	35.7	10.5	10.1
802C Haile	31.1	11.2	9.4
802D Haile	38.4	10.1	9.1
803A Red Hill	31.8	11.2	10.5
806A Red Hill	46.6	9.4	7.5

Source: OceanaGold, 2025

In 2022 SGS Burnaby was sent 30 core composite samples from ore zones from the Haile, Ledbetter, and Mill Zone pits as part of a competency variability program to quantify variability expectations in the LoM plan from these pit stages. SMC, Bond rod mill, and Bond ball mill index tests were conducted on these samples providing a larger data set confirming the increased hardness expected in the Ledbetter pit compared to the upper areas of the Haile pit and Mill Zone pits. The results of the program are summarized in Table 13-8 and has increased the data set of competency data to allow development of hardness proxy measurements for the block model.


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Table 13-8: SGS Comminution Test Results for 2022 Variability Program


Sample ID (DDH/Deposit)	A x b	SCSE (kWh/tonne)	BMWi at 200-Mesh (kWh/tonne)
MET-MZ-88	128.5	6.31	4.7
MET-MZ-89	37.1	10.47	8.9
MET-MZ-90	59.0	8.34	4.9
MET-MZ-91	94.8	6.97	5.3
MET-HL-92	49.8	8.99	9.1
MET-HL-93	39.7	9.92	9.7
MET-HL-94	58.5	8.34	7.5
MET-HL-95	45.1	9.33	8.3
MET-HL-96	37.0	10.23	8.7
MET-HL-97	40.0	9.91	8.6
MET-HL-98	39.2	10.20	8.7
MET-HL-99	44.8	9.45	9.2
MET-HL-100	40.8	9.92	9.4
MET-LB-101	30.3	11.28	11.9
MET-LB-102	44.3	9.45	9.7
MET-LB-103	30.0	11.49	11.1
MET-LB-104	39.9	9.96	10.0
MET-LB-105	34.6	10.61	11.4
MET-LB-106	38.0	10.33	9.3
MET-LB-107	31.8	10.98	10.2
MET-MZ-108	32.9	10.98	11.5
MET-LB-109	41.8	9.79	10.8
MET-LB-110	37.8	10.26	9.4
MET-LB-111	30.8	11.77	9.6
MET-LB-112	47.9	9.22	10.3
MET-LB-113	37.0	10.26	8.9
MET-MZ-114	46.8	9.40	6.9
MET-MZ-115	48.4	9.37	9.0
MET-MZ-116	38.3	10.17	7.9
MET-MZ-117	53.7	8.80	8.7

Source: OceanaGold, 2025

In 2022 as part of a program of blast optimization trials to evaluate the impact on mill throughput a series of full grinding surveys were undertaken to validate the previously developed site-specific comminution model to allow conversion of competency parameters into throughput rates for the current circuit. Four additional surveys were completed and provided to Ausenco to balance and model fit with the additional points displayed below in Figure 13-1 with a good correlation between the measured and predicted SAG specific energy.


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Source: OceanaGold, 2025

Figure 13-1: Updated Modeled vs. Measured SAG Specific Energy Values

In May 2024 ore from the Ledbetter Phase 2A pit became the predominate feed source for the mill, with Horseshoe underground joining the blend later in the year. Increases in drill bit wear and a drop in penetration rates indicated an increase in ore competency along with poorer blast fragmentation. Milling rates were impacted in the mill with throughput rates dropping to 360 to 420 t/h on a 100% basis leading to investigating alternative blasting patterns and use of a mobile jaw crusher to test partial secondary crushing a portion of the mill feed to -75 mm to determine the impact on throughput.

As a result of the noticeable impact on mill throughput and to address ongoing throughput planning a Geomet program was undertaken submitting a series of 5 m core samples from the remaining three deeper sourced open pits for competency testing. These samples were submitted to SGS Lakefield using the Geopyora method to determine the DWi and Bond ball mill work index to increase the number of data points in the future pit phases for modeling. A summary of the results is presented below in Table 13-9 with the Bond BWi noticeably higher than results of larger composites from higher up in the pit phase previously tested.


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Table 13-9: Geopyora Competency Test Results


Pit Phase	Sample Count	DWi		BMWi at 150 micron (kWh/tonne)
		Range	Mean	Range	Mean
Ledbetter Phase 3	51	6.7 - 13.2	9.9	13.9 - 22.4	16.7
Snake Phase 3	12	8.1 - 11.0	9.8	14.9 - 17.8	16.4
Haile Phase 2	9	6.7 - 10.9	9.6	15.3 - 17.9	16.5

Source: OceanaGold, 2025

13.1.2Throughput Estimate Assumptions

The following approach was used to generate a throughput estimate for the block model to allow mine schedules to incorporate mill throughput estimation during the planning process. The existing DWi and BBWi data was supplemented with recent Geopyora DWi and BBWi core measurements for the three main remaining open pit ore sources. This data was used to calculate SAG circuit specific energy for each data point using the previously derived regression and mill throughput estimates assuming a 3100 kW available mill power draw. The throughput estimates were then assigned to the block model. With this information added to the block model, open pit schedules were then used to predict mill throughput for each period from the mine schedule.

For underground ore sources from Horseshoe and Palomino, deposits based on a similar approach from core testing results the 85th percentile of the hardest ore was used to determine a throughput rate equivalent to 3.2 Mt/yr on a 100% mill feed basis. Applying this approach to the Ledbetter Underground deposit a throughput rate equivalent to 2.8 Mt/yr was calculated.

For the current LoM plan this approach to modeling throughput was used rather than the previously used rates for open pit and underground and has led to a planned throughput rate in the range of 2.7 to 3.0 Mt/yr over the remaining project life. Whilst lower than previous methods used it reflects actual plant achieved rates and more up to date information on the remaining open pit Reserves, along with a change in mill feed blend from deeper competent underground sources from 25% of mill feed to over 50% from 2030 to 2034 with three deposits contributing over the LoM to open pit sourced ore.

It should be noted that the mill survey data used to generate the site-specific comminution model was based on ore source from the Snake Phase 2 and Ledbetter Phase 1 open pits with coarse fragmentation than that experienced with the underground produced ore and may tend to under estimate throughput expected in the long term. Secondary crushing trials in late 2024 with 20% of mill feed pre-crushed to -75 mm indicated a modest throughput increase of 15 to 20 tph on Ledbetter Phase 2A feed, and short trials with -50 mm material was more beneficial.

There is scope to conduct further work on partial secondary crushing trials to evaluate the
cost / benefit of increasing mill throughput above the current LoM with mobile crushing equipment on site and the current forecast is now considered a conservative estimate compared to that used in scheduling in previous years.

Additional short interval core samples are being sought from both open pit and underground sources to increase the data set available to improve the confidence in the block model prediction.


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13.1.3Flotation and Cyanidation

The Philips test work described in the September 2008 report was performed on composite ore samples of average grade material from the Haile and Mill Zone pit areas.

The testing was conducted to substantiate metal recoveries from sulfide flotation and cyanide leaching of flotation tailings and investigate oxidation methods for enhancing gold extraction from sulfide concentrate. Additional work was executed on tailings samples to assess thickening and filtration response, neutralization requirements, and provide material for environmental and tailing disposal engineering studies by others.

The work confirmed the sulfides carry the majority of the metal values in Haile deposits and this allows their concentration into a smaller fraction for processing. Previous operations at the site recognized this and sulfide concentration was practiced. However, the sulfides do not easily release the metal values and limited extraction was experienced by simple cyanidation. The sulfides contained in the ore composites tested by Phillips showed the same characteristics.

Flotation tests on the Haile composite indicated 66% of the gold was separated into a concentrate that represented 6.7% of the flotation feed mass. Tests on the Mill Zone composite indicated 89% of the gold was separated into a flotation concentrate that represented 13.6% of the feed. The Mill Zone composite test had a finer flotation feed particle size distribution and extended residence time which may explain the difference in recovery.

Leach tests on flotation tail indicated 82% (leach stage) extraction for gold for both composites. Leach tests on a blend of Haile and Mill Zone flotation concentrate revealed gold extraction of only 67% of the gold with the as-floated particle size. Applying a test procedure entailing a regrind in cyanide solution to 80% passing 15 µm, followed by an agitated cyanidation step, raised extraction to 80%.

The subsequent phase of work from 2009 was carried out by RDi on samples from the five areas within the Haile mineralized zone; Mill Zone, Haile, Red Hill, Ledbetter, and Snake. These discrete areas were provisionally derived from initial distinct open pits, but later design work and optimization may make the designation merely a legacy naming convention.

The methodology of compositing samples was to prepare composites from each hole’s intervals based on their assays as follows:

•Less than 0.5 g/t Au was considered waste

•Less than 1 g/t but greater than 0.5 g/t Au were combined as low-grade composites

•Between 1 g/t Au and 4 g/t Au were combined as average grade

•Over 4 g/t Au were combined as high-grade

Almost all the samples assayed over 0.3% sulfur and sulfide sulfur accounted for over 95% of the total sulfur (ST).

RDi performed gravity concentration testing using a laboratory centrifugal concentrator with cleaner gravity concentration using a shaking Gemini table. The results indicate that the cleaner stage recovered about 20% of the feed gold but into a concentrate with a mass pull of 1% to 2% of the feed, assaying 11 to 75 g/t Au. The concentrate grade was too low-grade to treat separately and there appears to be no coarse gold in the deposit, thus a gravity circuit was not considered to be applicable.


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RDi performed whole-ore cyanide leach tests to examine the effect of ore grind size and leach time on gold recovery. The test work indicated that direct leaching gold extraction from the samples was generally poor and variable, ranging from 40% to 79%.

Most of the gold that leached was in the initial six hours of leach time and extraction generally increased with increasing fineness of grind. The refractoriness of the gold is partially due to size dependence but predominantly due to gold association with sulfides. A summary of the test work is presented in Table 13-10.

Table 13-10: RDi Whole-Ore Leach Test Results


Composite Number	Grind Size (P80, mesh)	% Gold Extraction, Leach Time			NaCN Consumption at 48 hr. (lbs/st)
		6 hr.	24 hr.	48 hr.
Mill Zone Average	100	57.0	65.0	64.7	0.50
Mill Zone Average	200	64.7	65.7	65.9	0.42
Mill Zone Average	325	68.0	69.2	68.4	0.84
Haile Average	200	67.5	71.3	71.5	0.52
Haile Average	325	69.0	73.7	75.3	0.96
Ledbetter Average	200	72.2	75.60	75.8	0.24
Ledbetter Average	325	70.4	80.3	79.1	1.40

Source: OceanaGold, 2022

RDi performed flotation test work to investigate the recovery of gold and silver to a sulfide mineral concentrate. The tests indicated that a reagent suite of potassium amyl xanthate (PAX), AERO 404 (or equivalent), and methyl isobutyl carbinol (MIBC) frother, along with a laboratory flotation time of six minutes and a grind size of 200-mesh or finer will result in the highest gold recovery values.

A summary of the RDi flotation test work is presented in Table 13-11 and Table 13-12.

Table 13-11: Flotation Test Results – Averages by Grind


Sample Description	Primary Grind (P80, mesh)	Flotation Concentrate 6-minute Flotation Time Recovery %			Concentrate Grade (oz/st)
		% wt	Au	Ag	Au	Ag
Mill Zone Average	100	18.2	92.7	50.9	0.516	0.341
Mill Zone Average	200	14.2	91.7	58.7	0.630	0.679
Mill Zone Average	325	12.6	90.8	61.6	0.779	0.846
Red Hill Average	200	16.8	82.6	75.2	0.493	1.420
Red Hill Average	325	15.6	82.3	73.1	0.557	1.053
Ledbetter Average	200	10.3	91.8	57.7	1.234	0.749
Ledbetter Average	325	10.5	88.6	42.8	1.301	0.674
Haile Average	200	12.8	86.7	59.9	0.519	0.752
Haile Average	325	11.3	86.4	65.6	0.618	0.834
Snake Average	200	15.4	90.2	50.4	0.665	0.475
Snake Average	325	15.0	91.6	49.0	0.636	0.446

Source: OceanaGold, 2022


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Table 13-12: Flotation Test Results Average by Grade and Grind


Sample Description	Primary Grind (P80, mesh)	Flotation Concentrate 6-minute Flotation Time Recovery %			Concentrate Grade (oz/st)
		% wt	Au	Ag	Au	Ag
Mill Zone Average-Grade	200	13.5	93.4	77.1	0.674	1.012
Mill Zone Average-Grade	325	12.9	90.7	70.8	0.697	0.992
Mill Zone High-Grade	200	13.3	92.1	83.5	1.374	1.274
Mill Zone High-Grade	325	12.7	94.8	60.4	1.461	1.015
Red Hill Average-Grade	200	16.6	76.6	83.1	0.338	1.409
Red Hill Average-Grade	325	15.2	82.1	77.8	0.347	0.662
Red Hill High-Grade	200	20.0	93.9	94.3	1.569	3.228
Red Hill High-Grade	325	18.2	93.2	80.5	1.496	2.633
Ledbetter Average-Grade	200	12.2	90.7	68.9	0.703	0.624
Ledbetter Average-Grade	325	14.1	89.5	44.2	0.563	0.271
Ledbetter High-Grade	200	8.0	95.7	57.5	3.071	1.534
Ledbetter High-Grade	325	7.9	87.5	53.3	2.033	1.175
Haile Average-Grade	200	12.2	84.9	65.1	0.365	0.726
Haile Average-Grade	325	11.2	86.5	64.0	0.402	0.682
Haile High-Grade	200	14.8	91.8	86.0	1.595	1.858
Haile High-Grade	325	12.5	87.6	67.3	1.423	1.371
Snake Average-Grade	200	16.4	96.1	53.5	0.472	0.432
Snake Average-Grade	325	17.1	89.1	38.4	0.382	0.350
Snake High-Grade	200	19.0	96.2	69.9	1.575	0.962
Snake High-Grade	325	17.1	95.3	65.6	1.560	0.688

Source: OceanaGold, 2022

RDi performed flotation tailing cyanide leach tests to investigate the extraction of gold from the flotation tailing. The test results indicate that gold can be extracted from the flotation tails. A summary of the test work is presented in Table 13-13.


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Table 13-13: Flotation Tailing Leach Test Results Average by Grade and Grind


Sample Description	Primary Grind (P80, mesh)	Gold Extraction Leach Time – 24 hr. (%)	NaCN Consumption (lbs/st)	Lime Addition Ca(OH)2 (lbs/st)
Mill Zone Average-Grade	200	52.9	0.14	3.08
Mill Zone Average-Grade	325	63.0	0.50	3.08
Mill Zone High-Grade	200	71.7	0.16	3.08
Mill Zone High-Grade	325	71.9	0.44	3.08
Red Hill Average-Grade	200	68.5	0.74	13.19
Red Hill Average-Grade	325	67.5	1.22	12.83
Red Hill High-Grade	200	74.1	2.56	15.76
Red Hill High-Grade	325	81.1	1.40	15.30
Ledbetter Average-Grade	200	68.6	0.44	6.35
Ledbetter Average-Grade	325	70.7	0.24	5.65
Ledbetter High-Grade	200	72.0	0.20	n.r.
Ledbetter High-Grade	325	76.5	0.16	n.r.
Haile Average-Grade	200	62.7	0.16	13.68
Haile Average-Grade	325	62.2	0.26	13.70
Haile High-Grade	200	75.6	0.22	6.71
Haile High-Grade	325	77.1	0.18	6.31
Snake Average-Grade	200	62.38	0.02	8.53
Snake Average-Grade	325	66.34	0.16	8.45
Snake High-Grade	200	70.00	0.20	6.39
Snake High-Grade	325	70.90	0.24	6.29

Source: OceanaGold, 2022

Larger scale flotation test results achieved 91% gold recovery into a concentrate representing 8.8% weight of the flotation feed in 13.5 minutes of flotation time. Subsequent leach tests of flotation tail gave results that indicated 50% gold extraction in 16 hours of leaching.

Regrind test work on concentrate samples generated was performed by Metso Minerals Industries, Inc. (Metso 2009) to predict specific energy requirements for concentrate regrind.

RDi performed flotation test work on 23 drill core composite samples from the Ledbetter Extension zone. The methodology for compositing samples by grade was the same as used earlier.

Gold recovery by flotation averaged 86% for the 100-mesh grind samples, averaged 87% for the 150- mesh grind samples, and ranged from 81% to 95% but averaged 89% for the 200-mesh grind samples.

The flotation tailing samples were leached for 24 hours at 40% solids and gold extractions averaged 66% for 100-mesh grind samples, from 52% to 85% and averaged 68% for 150-mesh grind samples, and from 44% to 87% and averaged 69% for 200-mesh grind samples.

In 2010, RDi performed additional metallurgical testing on duplicate ore samples from the earlier testing. Additional composite samples were made to evaluate carbon loading, cyanide destruction, flash flotation, conventional flotation time, and leaching of concentrate and tailing samples.


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A procedure was developed and used to evaluate “flash flotation”. Flash flotation was shown to recover 62% to 66% of the gold in two minutes of flotation time. Conventional flotation improves the total flotation gold recovery to about 80% and leaching of flotation tailing extracts 76% to 80% of the gold from the flotation tailing sample.

Fifteen samples were selected for the generation of flotation concentrate in one cubic foot flotation cell tests. The fifteen samples were low, average and high grade from different ore zones (Red Hill, Snake, Ledbetter, and Mill Zone).

Five samples were selected for the generation of flotation concentrate in small-scale laboratory flotation cell tests. The five samples were identified as average grade material from the different ore zones.

The flotation tests were followed by leaching tests conducted on the flotation concentrates and flotation tailings. The results of these tests are presented in Table 13-14.


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Table 13-14: Leaching Tests Conducted on the Flotation Concentrates and Flotation Tailings


Test No.	Zone	Grade	Comp. No.	Flotation			Conc. Leaching			Tails Leaching			Total Recovery Au (%)
				Head Grade Au (oz/st)		Au Recovery (%)	Head Grade Au (oz/st)		Au Extraction (%)	Head Grade Au (oz/st)		Au Extraction (%)
				Assay	Calc		Assay	Calc		Assay	Calc
1/2	RH	L	49	0.027	0.033	91.5	0.172	0.140	62.7	0.003	0.005	83.8	64.5
7/8	H	L	47	0.010	0.011	64.7	0.093	0.190	82.6	0.004	0.006	85.9	83.8
17/18	S	L	51	0.015	0.015	84.0	0.230	0.245	79.8	0.003	0.003	66.0	77.6
19/20	L	L	43	0.021	0.020	86.7	0.248	0.207	71.9	0.003	0.005	61.3	70.5
25/26	MZ	L	H290	0.024	0.035	95.4	0.152	0.190	77.4	0.002	0.004	72.5	77.2
15/16	RH	A	34	0.080	0.095	92.0	0.589	0.513	83.3	0.009	0.010	67.2	82.0
11/12	H	A	8	0.085	0.064	85.5	0.455	0.467	74.8	0.010	0.012	60.3	72.7
9/10	S	A	39	0.056	0.052	89.6	0.735	0.583	64.2	0.006	0.006	77.7	65.8
3/4	L	A	23	0.059	0.073	89.6	1.009	0.752	80.4	0.008	0.013	71.8	79.5
13/14	MZ	A	2	0.057	0.059	92.6	0.423	0.382	69.3	0.005	0.006	69.2	69.3
C34	RH	A	-	0.073	0.072	86.0	-	0.370	80.0	0.012	0.012	80.2	80.0
C28	H	A	-	0.086	0.085	68.1	-	0.580	59.7	0.030	0.029	79.6	66.0
C31	S	A	-	0.051	0.056	93.7	-	0.166	58.5	0.005	0.005	45.1	57.7
C61	L	A	-	0.048	0.047	86.1	-	0.341	80.7	0.007	0.008	81.4	80.4
C5	MZ	A	-	0.073	0.078	92.2	-	0.292	69.5	0.008	0.008	67.0	69.3
27	RH	H	35	-	0.429	94.1	2.601	2.094	73.6	0.030	0.038	77.5	73.8
28	H	H	9	0.180	0.194	90.5	1.394	1.321	88.5	0.021	0.024	64.5	86.2
5/6	S	H	53	0.304	0.312	95.2	2.365	1.875	75.2	0.017	0.020	68.3	74.9
23/24	L	H	71	0.240	0.274	94.7	2.622	2.222	74.0	0.015	0.034	81.5	74.4
21/22	MZ	H	12/3	0.168	0.199	96.0	1.563	1.155	79.7	0.009	0.020	73.3	79.4

Source: OceanaGold, 2025


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The overall extraction, sorted by sampled zones, is presented in Table 13-15.

Table 13-15: Gold Recovery by Ore Zone and Ore Grade


Ore Zone	Au Extraction – Combined %				Average Au Extraction (%)
	Low Grade	Average Grade		High Grade
Red Hill	64.5	82.0	80.0	73.8	75.1
Haile	83.8	72.7	66.0	86.2	77.2
Snake	77.6	65.6	57.5	74.9	68.9
Ledbetter	70.5	79.5	80.8	74.4	76.3
Mill Zone	77.2	69.3	69.3	79.4	73.0
Average	74.7	72.3		77.8	74.3

Source: OceanaGold, 2022

RDi performed additional leach tests on flotation concentrates to ascertain if better results could be obtained. The results of performing leach tests on larger concentrate samples (i.e., twice the size used in previous tests) demonstrated a significant improvement in gold and silver extraction. Concentrate samples were ground to a size distribution of 80% passing 15 to 18 µm. The slurry was then pre-aerated for four hours and lead nitrate was added for the final three hours of pre-aeration and then leached for 48 hours with carbon present. A summary of the larger scale leach test results is presented in Table 13-16.


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Table 13-16: CIL Test Results for Fine Ground Flotation Concentrate


Test No.	Pit	Grade	Composite Number	Grind Size (P80, μm)	48 hr. Leach Time % Extraction		NaCN Consumption (lbs/st)
					Au	Ag
37	Red Hill	L	49	17	80.9	71.1	2.00
36	Haile	L	47	14	77.2	49.5	4.99
38	Snake	L	51	16	81.0	94.4	10.83
35	Ledbetter	L	43	16	88.3	91.9	5.09
21	Mill Zone	L	Hole 290	-	79.8	91.0	5.59
26	Mill Zone	L	Hole 290	-	85.0	82.3	4.75
33	Red Hill	A	34	16	85.8	77.2	4.60
31	Haile	A	28	18	95.6	97.4	4.36
22	Haile	A	8	-	81.6	93.2	3.62
32	Snake	A	31	18	58.8	18.2	4.26
24	Snake	A	39	-	84.7	96.4	5.25
40	Ledbetter Ext	A	61	14	89.8	98.3	1.96
27	Mill Zone	A	2	16	81.5	96.2	4.77
28	Mill Zone	A	5	17	79.2	50.0	4.72
41	Ledbetter Ext	A	73	16	83.7	93.4	3.30
23	Ledbetter	A	23	-	88.3	79.9	4.72
34	Red Hill	H	35	16	92.6	95.9	3.66
29	Haile	H	9	20	93.7	97.7	3.46
39	Snake	H	53	16	83.4	97.4	5.03
30	Mill Zone	H	12/3	19	88.7	95.9	4.00
25	Ledbetter Ext	H	71	-	94.9	95.6	12.3

Source: OceanaGold, 2025

KML was commissioned in 2012 to perform additional flotation and leach tests on 29 composites from Mill Zone and Snake areas. The samples selected were chosen to represent the initial three years of the operation’s mine schedule anticipated at the time.

Each composite was subjected to bulk flotation. The flotation concentrate was reground to a P80 of approximately 13 µm and leached for 48 hours. The flotation tailing was also leached for 48 hours. The overall gold recoveries ranged from 71.6% to 91% and overall silver recoveries ranged from 32.9% to 81.9%. A summary of the results is presented in Table 13-17.


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Table 13-17: Tests Results for Composites from Mill Zone and Snake Areas


Composite	Au Head Grade (oz/st)	Au Recovery (%)	Ag Head Grade (oz/st)	Ag Recovery (%)
1	0.224	90.6	0.07	75.8
2	0.028	74.7	0.05	74.2
3	0.127	89.8	0.06	73.1
4	0.101	82.6	0.05	73.8
5	0.128	88.6	0.06	81.4
6	0.037	71.6	0.04	68.4
7	0.320	90.7	0.08	77.7
8	0.071	83.7	0.06	77.5
9	0.077	87.9	0.13	81.1
10	0.142	88.7	0.17	81.9
12	0.038	77.5	0.05	64.5
13	0.064	81.3	0.06	78.5
14	0.047	84.0	0.11	80.6
15	0.079	85.1	0.11	75.0
16	0.114	82.6	0.15	75.3
17	0.056	82.9	0.06	78.7
18	0.054	76.0	0.09	75.5
19	0.061	77.7	0.03	70.7
20	0.036	75.8	0.04	76.7
21	0.065	76.6	0.08	71.8
22	0.148	87.5	0.12	71.6
23	0.245	91.0	0.10	74.4
24	0.055	86.5	0.03	52.8
25	0.029	87.6	0.02	43.6
26	0.013	76.3	0.02	62.3
27	0.010	80.8	0.01	58.0
28	0.016	76.8	0.02	35.5
29	0.027	80.9	0.01	32.9
30	0.107	88.8	0.04	46.0

Source: OceanaGold, 2022

RDi undertook additional test work on the composite samples from the Horseshoe Zone to determine the response to the process flowsheet selected. Visible gold was reported in some core intercepts used for Horseshoe test work. Test work included comminution (described above) and flotation and leaching of concentrate and flotation tailing.

The flotation process utilizing a simple reagent suite (PAX, AP404 and MIBC) developed for the deposit in earlier studies recovered 85% to 90% of the gold into the concentrate for most of the composites. Cyanide leaching consistently extracted about 70% of the gold in the flotation tailings. The composite concentrate samples were reground and subjected to a preparation step and a CIL


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test, which showed gold and silver extractions of over 90% for most composites. Lower recoveries were achieved for the low-grade composite 83. A summary of the test results is presented in Table 13-18.

Table 13-18: Test Results for Horseshoe Samples


Composite Number	Assay Head Au (g/t)	Primary Grind Size (P80, mesh)	Flotation Recovery (%)		Tailing Leach (%) Extraction		Concentrate Leach Extraction (%)		Overall Extraction (%)
			Au	Ag	Au	Ag	Au	Ag	Au	Ag
83	1.8	100	86.5	63.0	70.2	3.7	69.3	64.9	69.4	42.3
83		150	89.0	57.1	70.4	9.6			69.4	41.2
83		200	87.6	54.1	73.9	5.5			69.9	37.6
84	9.1	100	88.4	74.4	69.4	5.3	96.2	94.6	93.1	71.7
84		150	90.2	77.3	71.3	22.0			93.8	78.1
84		200	90.1	77.7	71.0	7.1			93.7	75.1
85	10.4	100	83.3	70.7	66.5	39.4	96.0	91.9	91.1	76.5
85		150	89.2	81.4	71.7	19.1			93.4	78.4
85		200	87.4	80.7	76.3	37.5			93.5	81.4
86	12.1	100	86.4	74.5	67.2	8.9	94.9	92.1	91.1	70.9
86		150	85.8	73.8	72.5	45.8			91.7	80.0
86		200	90.4	75.2	76.6	40.7			93.1	79.4
87	10.6	100	69.7	57.7	59.5	53.4	95.2	95.0	84.4	77.4
87		150	77.8	64.8	66.1	54.1			88.7	80.6
87		200	75.9	69.0	70.8	54.1			89.3	82.3

Source: OceanaGold, 2022

In late 2011, G&T Metallurgical Services was selected to perform the metallurgical test program on additional Horseshoe samples. The metallurgical test program involved testing of twelve variability samples to evaluate recoveries by flotation and cyanidation of concentrate and flotation tails.

The Horseshoe samples responded very well to the Haile flowsheet. A summary of the test results compiled by HGM staff is provided in Table 13-19.


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Table 13-19 Test Results for Horseshoe Samples


Composite Number	Gold Head Grade (oz/st)	Flotation P80 (μm)	Kinetic Flotation Recovery (%)	Bulk Flotation Recovery (%)	Regrind P80 (μm)	Concentrate Leach Extraction (%)	Tailings Leach Extraction (%)	Overall Gold Recovery (%)
1	0.199	81	93.9	86.5	15	90.4	81.1	89.2
2	0.339	70	92.5	90.7	13	99.5	67.3	96.6
3	0.043	78	96.5	94.0	14	86.1	87.6	89.8
4	0.060	73	93.3	97.0	16	98.5	74.1	86.1
5	0.076	81	90.2	83.4	10	94.9	85.5	94.4
6	0.168	84	88.4	86.0	11	93.0	90.2	94.9
7	0.082	82	85.2	88.0	15	94.9	75.6	93.8
8	0.094	66	89.0	84.4	12	98.6	83.3	92.6
9	0.057	69	86.2	89.2	11	97.1	81.7	96.0
10	0.121	75	75.1	77.6	15	90.3	82.1	90.6
11	0.349	88	86.2	87.5	14	97.4	88.4	95.8
12	0.129	77	85.3	83.6	10	97.4	84.2	96.1

Source: OceanaGold, 2022

Laboratory testing on ore composite samples demonstrated that the mineralization was readily amenable to flotation and cyanide leaching process treatment. A conventional flotation and cyanide leaching flow sheet can be used as the basis of process design. The relative low variability of flotation test work indicates that the mineralized zones are relatively similar in terms of mineral composition, and flotation and cyanide leaching response.

The samples tested responded favorably at a moderately-fine feed size range of 80% passing 200-mesh (74 µm). Therefore, a primary grind size of 80% passing 200-mesh was recommended for process circuit design development. Operational experience and minerology may allow this criterion to be relaxed, reducing comminution requirements and increasing plant capacity.

The flotation testing indicated that gold can be recovered in a flotation concentrate that will also contain the majority of the silver in the ore. The tailing from the flotation circuit can then be processed by cyanide leaching to recover gold onto activated carbon.

The test work indicated that the circuit should include regrinding of the flotation concentrate before slurry pre-aeration, and a leach time of 24 hours. A regrind circuit product size of 80% passing 15 µm is an appropriate target for regrind circuit design

Leaching of the flotation concentrate can extract 82% to 91% of the gold and 80% to 96% of the silver. Leaching of the flotation tailing can extract 45% to 86% of the gold in the flotation tailings. It appears that overall gold recovery will be in the range of 65% to 92% dependent primarily on head grade to the mill and less dependent on from which zone the ore is mined.

The unit operations that determine the amount of gold extraction are flotation, flotation concentrate regrind and leaching, and flotation tailing leaching.


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The data developed in the test programs has been used to establish a relationship between overall gold recovery and head grade as shown in the graph in Figure 13-2. The algorithm for the “best-fit” line that describes the head grade to recovery relationship is used to estimate gold recovery from a predicted mill head grade for example, at a mill head grade of 2.3 g/t, the recovery equation graph predicts a gold recovery of 84.2%. The results of grade and recovery data analysis are shown in Figure 13-2.

Source: OceanaGold, 2022

Figure 13-2: Overall Percent Recovery vs. Head Grade

Overall, the results from Horseshoe tests were in line with or exceeded the recovery model. The cyanide destruction test results indicated that the sulfur dioxide (SO2)/air cyanide destruction process destroys weak acid dissociable (WAD) cyanide very effectively, as well as free cyanide. Operations to date have achieved target levels of cyanide removal from the TSF and reagent usage is being optimized to further reduce costs.

13.1.4Sample Representativeness

Samples were collected from a range of locations across the main area of the Resources that is planned to be fed to the processing plant over the LoM. The minimal variability of test work indicates that the different mineralized zones are relatively similar in terms of chemical and mineral compositions, and flotation and cyanide leaching response. Given the uniform geological setting and mineralization, this is not surprising.


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It is evident from the comminution testing that ore competency is increased in the deeper resources (e.g., Horseshoe underground). This is confirmed by the trend of increased Bond Ball Milling Work indices for samples sourced from lower levels.

13.2Palomino Deposit

The Palomino deposit is currently under development at Haile. It is expected to be similar in nature to the other deposits at Haile that have been encountered to date. Gold is present both in silicates and as fine inclusions within pyrite requiring a fine grind to achieve economic liberation. Within the Palomino deposit two key lithologies have been identified as carrying the majority of the gold values, classified as Rhyodacite and Siltstone, the latter the equivalent of the metasediment domain previously used to describe the highly-silicified mineralization hosting much of the gold mineralization. Metavolcanics occur but are lesser in abundance.

Based on the geological and lithological model, a bingo chart was constructed for the deposit based on the total Measured, Indicated and Inferred Resource (MI&I) available at the conclusion of the scoping study encompassing the largest expected mineral inventory and allowing for any further conversion drilling success to be accommodated as part of the Prefeasibility Study program. The bingo chart considered nine bins based on the three core lithologies and the following three grade bins:

•1.4 to 1.7 g/t Au to cover development ore below CoG

•1.7 to 3 g/t Au for medium-grade ore

•>3 g/t Au for high-grade ore

From the bingo chart the distribution of composite samples targeted for testing was reviewed and discussed with the exploration team to locate mineralized intercepts targeting a single lithology and grade bin. The distribution of composites required is shown below in Table 13-20 with a total of 22 composites required. Intercepts of individual drillholes were then identified from the infill drilling program to match the lithology and target grade bin across the deposit.

Table 13-20: Palomino Metallurgical Composite Plan


Ore Class	Tonnes (kt) for each Lithology and Domain				Representative Samples (no.) for each Lithology and Domain
	LG Au (1.3-1.7)	MG Au (1.7-3)	HG Au (>3)	Total	LG Au (1.3-1.7)	MG Au (1.7-3)	HG Au (>3)	Total
Rhyodacite	245,145	1,617,891	1,126,338	2,99,374	1	5	4	10
Siltstone	715,763	2,031,615	877,742	3,625,120	2	6	3	11
Metavolcanics	6,792	201,108	88,763	296,663	0	1	0	1
Total	971,700	3,850,614	2,092,843	6,915,157	3	12	7	22

Source: OceanaGold, 2025

From the 22 composites, six were selected from quarter core to allow for competency and ore hardness characterization with the remaining composites sourced from coarse crushed rejects from the initial exploration core submitted for assay to preserve core for future testing. The samples were shipped to SGS Burnaby to conduct the test program designed to characterize the hardness of future Palomino ores and to estimate overall gold and silver recoveries by replicating the existing process flowsheet in the laboratory.


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The program consisted of two phases. Ore competency testing was carried out on six composites (three Rhyodacite and three Siltstone) sourced from intact quarter core incorporating SMC Testing for competency and Bond ball mill work index and Abrasion index for a measure of hardness.

The second phase on all 21 composites involved:

•Stage crushing and homogenization to -10 mesh followed by head assay analysis

•Batch flotation testing to produce a bulk concentrate on standard flotation conditions provided by OceanaGold based on prior programs to assess flotation response for sulfur and gold recovery

•Fine grinding of the flotation concentrates to a P80 of 13 µm

•Cyanide leach tests on both flotation tailings and reground flotation concentrate streams to assess gold recovery in the leach circuit

•Mass balance of results to estimate overall gold and silver recovery for each composite

Subsequent to the Prefeasibility study, a program was developed to support the internal Feasibility Study with an updated bingo chart from the updated Resource model focusing on the Measured and Indicated Resources. An additional 13 samples were identified for testing based on the targeted conditions to support the Feasibility Study criteria along with three additional samples to bracket around two samples in the original program that showed lower recovery than expected to quantify potential affected volumes.

The comminution testing results from both programs are summarized in Table 13-21 and are comparable to that observed in the Haile and Mill zone pits rather than the harder deep deposits in Horseshoe and Ledbetter Phase 3 and 4 open pit designs that are representative of the current grinding circuit performance.

Table 13-21: Palomino Competency Testing Results


Sample ID (DDH/Deposit)	Domain	A x b	ta	RM Wi at 14-Mesh (kWh/tonne)	BMWi at 200-Mesh (kWh/tonne)
MET_PAL_119	Rhyodacite	51.9	0.49	12.3	9.3
MET_PAL_124	Rhyodacite	42.6	0.38	12.0	11.2
MET_PAL_127	Rhyodacite	42.7	0.39	12.0	10.1
MET_PAL_137	Siltstone	46.4	0.43	13.1	10.1
MET_PAL_138	Siltstone	47.2	0.44	12.4	9.7
MET_PAL_139	Siltstone	40.6	0.39	13.7	11.3
MET_PAL_158	Rhyodacite	48.1	0.45	10.8	9.4
MET_PAL_160	Rhyodacite	36.8	0.35	13.0	11.3
MET_PAL_161	Rhyodacite	49.7	0.46	12.0	10.0
MET_PAL_163	Rhyodacite	41.9	0.39	11.3	11.7
MET_PAL_165	Rhyodacite	42.6	0.38	11.5	11.7
MET_PAL_167	Rhyodacite	47.4	0.44	12.1	11.2
MET_PAL_169	Rhyodacite	41.5	0.37	11.1	10.9
MET_PAL_171	Siltstone	33.5	0.31	13.7	9.1
MET_PAL_172	Siltstone	44.8	0.41	12.8	9.6
MET_PAL_173	Siltstone	32.8	0.30	12.2	9.1

Source: OceanaGold, 2025


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All samples were subjected to a suite of chemical analysis as per Table 13-22. The gold grades of the composites ranged from 1.39 to 11.1 g/t, with an average gold grade of 4.1 g/t. Silver grades varied from 0.7 to 14.0 g/t, with an average of 4.3 g/t with gold to silver ratios similar to other areas of the Haile deposit.

The total sulfur grade ranged from 0.3% to 13.1%, with an average of 4.1%; sulfur was present mainly as sulfide (S2-) with a low sulfate (SO4) content. This indicates low sample oxidation which gives confidence that laboratory test results will mirror plant performance.

All other analytes were at low levels and not considered to be a risk for processing. Tellurium was included in the 2024 program due to its addition to the standard geochemical suite from the presence of visible tellurides in the Ledbetter Underground drilling program. Mineralogical analysis of these samples by Tescan Automated Mineral Analysis (TIMA) indicated the tellurium present in the form of Hessite.


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Table 13-22: Geochemical Analysis of Palomino Composites


Composite	Au (g/t)	Ag (g/t)	Cu (%)	Fe (%)	As (%)	Hg (g/t)	S (%)	S2 (%)	TIC (%)	TOC (%)	Te (g/t)
MET_PAL_119	5.90	1.0	< 0.01	1.8	0.0	< 0.3	1.2	1.1	< 0.05	0.2
MET_PAL_120	1.83	4.0	< 0.01	11.3	0.0	< 0.3	11.4	11.3	0.1	< 0.05
MET_PAL_121	2.66	5.0	< 0.01	3.7	0.0	< 0.3	3.3	3.2	0.0	< 0.05
MET_PAL_122	5.36	11.0	0.0	11.7	0.0	< 0.3	10.7	10.4	0.1	< 0.05
MET_PAL_123	11.11	13.5	< 0.01	5.2	0.0	< 0.3	3.2	3.1	0.1	< 0.05
MET_PAL_124	2.16	3.2	< 0.01	6.5	0.0	< 0.3	6.2	5.8	< 0.05	0.1
MET_PAL_125	2.21	3.5	< 0.01	3.8	0.0	< 0.3	3.5	3.3	0.1	< 0.05
MET_PAL_126	3.00	6.0	< 0.01	12.3	0.0	< 0.3	13.1	12.9	0.0	< 0.05
MET_PAL_127	2.86	3.0	< 0.01	5.8	0.0	< 0.3	4.9	4.4	< 0.05	0.4
MET_PAL_128	4.71	3.0	< 0.01	7.4	0.0	< 0.3	6.1	5.9	0.1	< 0.05
MET_PAL_129	5.27	3.0	< 0.01	7.2	0.0	< 0.3	6.2	5.9	0.1	< 0.05
MET_PAL_130	1.39	4.5	< 0.01	2.6	0.0	< 0.3	1.6	1.5	0.1	< 0.05
MET_PAL_131	2.06	4.0	< 0.01	4.4	0.0	< 0.3	3.9	3.9	0.2	< 0.05
MET_PAL_132	2.31	5.0	< 0.01	9.1	0.0	< 0.3	10.0	9.8	0.1	< 0.05
MET_PAL_133	1.65	3.0	< 0.01	6.7	0.0	< 0.3	5.5	5.3	0.2	< 0.05
MET_PAL_134	2.68	<2	< 0.01	1.8	0.0	< 0.3	0.3	0.3	0.1	< 0.05
MET_PAL_135	2.88	12.5	< 0.01	4.3	0.0	< 0.3	3.7	3.5	0.1	< 0.05
MET_PAL_136	1.65	4.0	< 0.01	3.4	0.0	< 0.3	3.2	3.1	0.2	< 0.05
MET_PAL_137	2.22	1.5	< 0.01	3.1	0.0	< 0.3	1.2	1.1	< 0.05	0.5
MET_PAL_138	6.80	4.3	< 0.01	3.2	0.0	< 0.3	2.4	2.1	< 0.05	0.2
MET_PAL_139	3.63	3.7	< 0.01	2.2	0.0	< 0.3	1.1	1.2	< 0.05	0.2
MET_PAL_158	1.65	< 0.5	< 0.01	3.3	0.0	< 0.3	1.5	1.5	< 0.05	0.2	1.0
MET_PAL_159	2.39	0.8	< 0.01	1.5	0.0	< 0.3	0.7	0.6	< 0.05	0.3	0.7
MET_PAL_160	2.47	4.7	< 0.01	3.6	0.0	< 0.3	1.5	1.4	< 0.05	0.5	4.2
MET_PAL_161	2.00	0.8	< 0.01	4.1	0.0	< 0.3	3.3	3.2	< 0.05	0.4	0.9
MET_PAL_162	5.02	1.5	< 0.01	2.3	0.0	< 0.3	1.2	1.1	< 0.05	0.4	1.1
MET_PAL_163	4.28	3.2	< 0.01	4.2	0.0	< 0.3	3.7	3.7	< 0.05	0.4	2.8
MET_PAL_164	8.66	4.2	< 0.01	4.2	0.0	< 0.3	3.7	3.2	< 0.05	0.3	3.5
MET_PAL_165	7.64	9.5	0.0	8.3	0.0	< 0.3	6.8	6.6	< 0.05	0.2	8.2
MET_PAL_166	7.76	8.7	< 0.01	6.1	0.0	< 0.3	5.7	5.0	< 0.05	0.1	6.8
MET_PAL_167	2.58	0.7	< 0.01	2.5	0.0	< 0.3	1.5	1.4	< 0.05	0.1	0.7
MET_PAL_168	3.87	1.7	< 0.01	3.9	0.0	< 0.3	1.9	1.7	< 0.05	0.4	1.2
MET_PAL_169	4.69	3.2	0.0	7.5	0.0	< 0.3	6.2	5.9	< 0.05	0.1	2.7
MET_PAL_170	5.66	1.3	< 0.01	1.3	0.0	< 0.3	0.6	0.5	< 0.05	0.3	0.9
MET_PAL_171	5.21	3.3	< 0.01	4.0	0.0	< 0.3	2.7	2.6	< 0.05	0.2	4.5
MET_PAL_172	2.43	2.8	< 0.01	3.6	0.0	< 0.3	3.2	3.2	< 0.05	0.2	4.5
MET_PAL_173	10.8	4.2	< 0.01	4.9	0.0	< 0.3	4.2	4.1	< 0.05	0.1	4.7

Source: OceanaGold, 2025


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All of the composites responded well to flotation under the standard conditions for the bulk rougher test with 82.8% to 98.4% of the gold present reporting to the flotation concentrate across the two test programs. Mass pull was in line with the expectations from the given sulfur grade. With the expected strategy of Palomino representing 20% of mill feed, it is not expected to be an issue for the regrind circuit capacity.

The overall gold extractions from the flotation products (concentrates and tailings) corresponding to gold extractions by cyanidation from the head samples varied from 69.9% to 94.7%, with an average value of 84.5%. Full results are summarized in Table 13-23.


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Table 13-23: Palomino Leach Test Results


Composite	Au Recovery	Float Con %	Float Tail %	Overall %
MET_PAL_120	96	82.3	51	81.0
MET_PAL_121	93.7	82.5	55.4	80.8
MET_PAL_122	93	80.5	65.8	79.5
MET_PAL_123	89	90.6	71.1	88.4
MET_PAL_125	93.8	83.8	55.3	82.0
MET_PAL_126	96.7	87.5	71.3	86.9
MET_PAL_128	82.7	90.8	70	89.3
MET_PAL_129	98.4	70.1	58.1	69.9
MET_PAL_130	91.1	88	69.4	86.4
MET_PAL_131	96.9	82.8	68.8	82.3
MET_PAL_132	95.6	76.6	471	75.3
MET_PAL_133	94.3	82.5	54.9	80.9
MET_PAL_134	93.2	97.6	64.7	92.1
MET_PAL_135	91.7	86.3	74.7	85.3
MET_PAL_136	94.9	80.5	62.3	79.6
MET_PAL_119	82.8	92.4	68.2	88.3
MET_PAL_124	95.8	87.3	69	86.5
MET_PAL_127	93.2	93.3	68.7	91.7
MET_PAL_137	92.2	97	68.2	94.7
MET_PAL_138	89.3	89.7	66.9	87.3
MET_PAL_139	87.8	92.6	69.3	89.8
MET_PAL_158	90.9	90.5	76.1	89.2
MET_PAL_159	89.5	35.6	70.4	39.3
MET_PAL_160	90.5	84.5	71.8	83.3
MET_PAL_161	93.1	92.3	69.3	90.7
MET_PAL_162	89.5	94.9	75.7	92.9
MET_PAL_163	92.9	92.1	66.7	90.3
MET_PAL_164	91.0	95.9	76.6	94.1
MET_PAL_165	95.9	61.9	63.6	62.0
MET_PAL_166	93.7	94.5	73.1	93.1
MET_PAL_167	93.7	87.9	50.3	85.5
MET_PAL_168	91.2	92.3	69.9	90.4
MET_PAL_169	94.8	87.4	64.8	86.2
MET_PAL_170	86.6	98.1	74.0	94.9
MET_PAL_171	94.7	93.0	66.1	91.6
MET_PAL_172	94.8	75.2	45.0	73.7
MET_PAL_173	95.9	92.1	66.9	91.1

Source: OceanaGold, 2025


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Three samples demonstrated low recoveries in comparison with the Haile recovery database as can be seen graphically in Figure 13-3 with the points identified by ore source. Two of these low recovery samples were from the siltstone geomet domain (MET_PAL_129 (RF8), MET_PAL_132 (RF11) and one was from the rhyodacite geomet domain (MET_PAL_122 (RF3)). The low recoveries are primarily due to poor leach performance of the flotation concentrate, and tails residues from each of these bottle roll tests were submitted for diagnostic leach test work. This test work indicated up to 60% of losses were accounted for through sulfide locked in pyrite suggesting a finer inclusion size of some of the gold in these samples.

Further review of MET_PAL_129 to identify the nearest composites and their performance was undertaken with this sample taken on the edge of the mineralized contact of the orebody. The three NN composites with a 25 to 30 m lateral distance tested in the Prefeasibility or Feasibility phase returned recoveries in the expected 80% to 86% range suggesting the effect observed to be quite localized.

Source: OceanaGold, 2025

Figure 13-3: Haile Global Recovery Database Results by Source

13.3Ledbetter Underground Deposit

In 2024, a Prefeasibility Study evaluated changing the mining method for the proposed fourth phase of the Ledbetter open pit to an underground mining method targeting the higher-grade mineralization and extending below the designed pit shell. As part of this study the resource model was used to generate sample number requirements and distribution allow testing of this deeper


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material. As with the open pit Resources the Siltstone / Metasediment domain was the prevalent domain and in addition a new gold-bearing domain was identified labelled Intrusive Breccia.

The same parameters were used for sample selection as with the Palomino deposit given the similar mining method with three grade bins and for the Feasibility program the Measured, Indicated and Inferred material was used. A total of 18 composite samples were selected with 16 located in the primary Lobe 1 structure and two in the smaller Lobe 3 structure. The distribution of samples in Lobe 1 is shown in Table 13-24.

Table 13-24: Ledbetter Underground Lobe 1 Sample Distribution


Ore Class	Tonnes (kt) for each Lithology and Domain				Representative Samples (no.) for each Lithology and Domain
	LG Au (1.3-1.7)	MG Au (1.7-3)	HG Au (>3)	Total	LG Au (1.3-1.7)	MG Au (1.7-3)	HG Au (>3)	Total
Metasediment	366,203	850,866	517,860	1,734,929	1	3	2	6
Basalt	3,349	9,914	441	13,704	0	0	0	0
Intrusive Breccia	669,833	1,488,656	977,069	3,135,558	2	5	3	10
Basement	43,112	103,093	20,079	166,284	0	0	0	0
Total (Panels 1 and 2)	1,082,497	2,452,529	1,515,449	5,050,475	3	8	5	16

Source: OceanaGold, 2025

A competency test program was conducted on 10 of the Ledbetter Underground samples as outlined for Palomino with SMC competency testing and Bond ball mill work index testing for these samples. It was expected that the material being the bottom of the previously proposed open pit would be competent based on previous open pit competency testing with the results summarized in Table 13-25 below.

The second phase on all 18 composites involved:

•Stage crushing and homogenization to -10 mesh followed by head assay analysis

•Batch flotation testing to produce a bulk concentrate on standard flotation conditions provided by OceanaGold based on prior programs to assess flotation response for sulfur and gold recovery

•Fine grinding of the flotation concentrates to a P80 of 13 µm

•Cyanide leach tests on both flotation tailings and reground flotation concentrate streams to assess gold recovery in the leach circuit

•Mass balance of results to estimate overall gold and silver recovery for each composite


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Table 13-25: Ledbetter Underground Prefeasibility Program Sample Source Summary


Sample ID	Program	SMC Parameters				Milling Parameters
		A x b	ta	DWi	SCSE	BRWi	BBWi
MET_LUG_140	Breccia	30.5	0.29	9.01	11.39	13.7	12.5
MET_LUG_143	Breccia	29.0	0.28	9.13	11.47	13.7	11.2
MET_LUG_145	Breccia	33.1	0.32	8.23	10.82	13.3	11.4
MET_LUG_147	Breccia	34.0	0.33	7.95	10.66	14.5	13.5
MET_LUG_149	Breccia	37.0	0.35	7.35	10.25	13.7	13.3
MET_LUG_150	Siltstone	29.8	0.27	9.39	11.72	13.8	11.2
MET_LUG_152	Siltstone	44.2	0.40	6.49	9.8	12.8	10.2
MET_LUG_154	Siltstone	34.3	0.32	7.92	10.71	16.5	14.5
MET_LUG_156	Breccia	42.4	0.40	6.42	9.67	11.5	9.3
MET_LUG_157	Lobe 3	48.9	0.45	5.73	9.17	11.3	8.7

Source: OceanaGold, 2025

All samples were subjected to a suite of chemical analysis as shown in Table 13-26. Tellurium assays were obtained toward the end of the first phase of the metallurgical program and are reported below.

The gold grades of the composites ranged from 1.45 to 7.44 g/t, with an average gold grade of
3.18 g/t. Silver grades varied from 2.65 to 74.0 g/t, with an average of 14 g/t with gold to silver ratios significantly lower in the siltstone domain compared to other areas of the Haile deposit.

The total sulfur grade ranged from 0.9% to 4.4%, with an average of 2.2%; sulfur was present mainly as sulfide (S2-) with a low sulfate (SO4) content. This indicates low sample oxidation which gives confidence that laboratory test results will mirror plant performance.

All other analytes were at low levels and not considered to be a risk for processing. During the infill drilling program in 2024 for the Ledbetter Underground deposit visible tellurides were observed in fresh drill core that had not been logged in the historical records. Tellurium assays were obtained towards the end of the first phase of the metallurgical program and are reported below.


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Table 13-26: Geochemical Analysis of Ledbetter Underground Composites


Composite	Au (g/t)	Ag (g/t)	Cu (%)	Fe (%)	As (%)	Hg (g/t)	S (%)	S2 (%)	TIC (%)	TOC (%)	Te (g/t)
MET_LUG_140	1.56	4.1	< 0.01	2.4	0.0	< 0.3	2.6	2.3	0.1	< 0.05	17.8
MET_LUG_141	1.69	5.0	0.0	1.8	0.0	< 0.3	1.9	1.6	0.4	< 0.05	18.1
MET_LUG_142	2.25	9.0	< 0.01	1.2	0.0	< 0.3	1.3	1.1	0.1	< 0.05	21.2
MET_LUG_143	5.90	8.6	< 0.01	1.5	0.0	< 0.3	1.4	1.4	0.2	< 0.05	24.3
MET_LUG_144	1.96	6.6	0.0	1.4	0.0	< 0.3	1.4	1.2	0.1	< 0.05	15.6
MET_LUG_145	1.97	2.7	< 0.01	1.4	0.0	< 0.3	1.4	1.4	0.2	< 0.05	20.3
MET_LUG_146	2.30	3.8	< 0.01	1.9	0.0	< 0.3	2.0	1.6	0.2	< 0.05	24.5
MET_LUG_147	2.75	3.5	< 0.01	2.2	0.0	< 0.3	2.4	1.7	0.1	< 0.05	21.9
MET_LUG_148	3.59	4.3	0.0	1.0	0.0	< 0.3	1.0	0.9	0.1	< 0.05	21.2
MET_LUG_149	6.32	15.3	< 0.01	2.1	0.0	0.4	2.2	2.0	0.1	< 0.05	29.3
MET_LUG_150	1.45	7.0	< 0.01	4.0	0.0	< 0.3	4.4	3.5	0.3	< 0.05	18.6
MET_LUG_151	2.15	11.3	< 0.01	2.2	0.0	< 0.3	2.9	2.7	0.2	< 0.05	16.8
MET_LUG_152	2.12	8.3	< 0.01	4.0	0.0	< 0.3	4.2	3.2	0.2	< 0.05	23.0
MET_LUG_153	1.75	10.9	< 0.01	2.1	0.0	< 0.3	2.2	2.0	0.3	< 0.05	12.2
MET_LUG_154	6.79	64.0	< 0.01	2.0	0.0	0.5	1.7	1.4	0.3	< 0.05	84.7
MET_LUG_155	7.44	74.0	< 0.01	2.2	0.0	0.3	2.3	1.8	0.6	< 0.05	58.5
MET_LUG_156	2.80	6.2	< 0.01	1.4	0.0	< 0.3	1.5	1.4	0.2	< 0.05	19.6
MET_LUG_157	2.57	8.2	< 0.01	3.0	0.0	< 0.3	3.0	2.5	0.1	< 0.05	21.3

Source: OceanaGold, 2025

All the composites responded well to flotation under the standard conditions for the bulk rougher test with 74% to 88% of the gold present and 91% to 97% of the sulfur present reporting to the flotation concentrate. Mass pull was in line with the expectations from the given sulfur grade, and with the expected strategy of Ledbetter Underground representing 25% of mill feed it is not expected to be an issue for the regrind circuit capacity.

The overall gold extractions from the flotation products (concentrates and tailings) corresponding to gold extractions by cyanidation from the head samples varied from 39.3% to 94.9%, with an average value of 84.9% in the Siltstone samples but a significantly lower 61.4% in the Intrusive Breccia samples. It was observed that the 24-hour kinetic leach curves were significantly retarded with significant amount of leachable gold extracted from 8 to 24 hours whereas in other areas of the Haile deposit the majority of leachable gold is extracted in the first 8 hours. The summary of the overall recovery results is shown below in Table 13-27 below.


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Table 13-27: Ledbetter Underground First Round Recovery Results


Sample ID	Domain	Flotation Recovery Au %	Leach Recovery		Overall Recovery Au %
			Concentrate Au %	Flotation Tailings Au %
MET_LUG_140	Intrusive Breccia	88.0	85.0	43.0	80.0
MET_LUG_141	Intrusive Breccia	81.6	91.4	79.2	89.2
MET_LUG_142	Intrusive Breccia	78.6	76.5	69.5	75.0
MET_LUG_143	Intrusive Breccia	87.1	48.8	48.9	48.8
MET_LUG_144	Intrusive Breccia	73.7	70.5	55.3	66.5
MET_LUG_145	Intrusive Breccia	80.6	45.0	33.2	42.7
MET_LUG_146	Intrusive Breccia	75.5	55.5	48.2	53.7
MET_LUG_147	Intrusive Breccia	80.7	39.6	38.3	39.3
MET_LUG_148	Intrusive Breccia	80.9	53.7	46.8	52.3
MET_LUG_149	Intrusive Breccia	84.7	61.1	48.7	59.2
MET_LUG_150	Siltstone	81.5	76.7	66.1	74.8
MET_LUG_151	Siltstone	85.8	84.6	82.9	84.4
MET_LUG_152	Siltstone	85.1	79.5	61.3	76.8
MET_LUG_153	Siltstone	82.6	89.9	81.2	88.4
MET_LUG_154	Siltstone	86.6	92.4	75.8	90.2
MET_LUG_155	Siltstone	87.8	95.8	88.7	94.9
MET_LUG_156	Pipe Breccia Lobe 3	78.1	68.0	53.1	64.7
MET_LUG_157	Pipe Breccia Lobe 3	80.1	68.4	51.5	65.0

Source: OceanaGold, 2025

From the remaining sample material of the Intrusive Breccia samples repeated flotation tests were used to produce additional concentrate to conduct extended kinetic leaches to 72 hours at both the standard 13 micron and a finer 8 micron grind size to investigate if inclusion size of gold had reduced or slower leaching phases were present. The results of these tests indicated minimal improvement from finer grinding with slow leaching of gold continuing to occur out to 72 hours with the rate fairly constant from 24 to 72 hours.

A second round of samples was collected from the 2024 infill program focussing on the lower area of the Intrusive Breccia domain where recovery was noticeably affected by lower concentrate leach recovery in the first round of testing. Smaller composites were targeted with material of a singular lithology (several sub-variants identified within the Intrusive Breccia domain) and geological structure to look to see if either of these models would correlate to the difference in recovery compared to the first three composites that demonstrated “normal” kinetic recovery response.

A total of 19 additional samples were submitted to SGS Burnaby in this program from crushed reject samples with head grades ranging from 1.88 to 88 g/t Au and 0.4% to 3.4% S. With the second round program the concentrate kinetic leach time was extended out to 96 hours, and the summary of the overall recovery results is shown below in Table 13-28. Overall recovery with concentrate leach time extended to 96 hours showed a significant improvement relative to 24 hours with overall recovery varying from 36.4% to 92.8% averaging 65.3% a significant improvement from an average of 46% at 24 hours.


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Whilst no correlation was noted between the recovery and either the structural or lithological models volumetrically it allowed better definition of where the poorer performing material was located.

Table 13-28: Ledbetter Underground Second Round Recovery Results


Sample ID	Flotation Recovery Au %	Leach Recovery Tailings Au %	24 Hrs		72 Hrs		96 Hrs
			Leach Recovery Con Au %	Overall Recovery Au %	Leach Recovery Con Au %	Overall Recovery Au %	Leach Recovery Con Au %	Overall Recovery Au %
MET_LUG_231	85.2	46.4	30.2	32.6	48.4	48.1	55.6	54.3
MET_LUG_232	78.0	46.2	31.0	34.4	60.7	57.5	65.2	61.0
MET_LUG_233	76.2	31.7	42.1	39.6	66.4	58.2	72.6	62.9
MET_LUG_234	82.7	23.8	28.8	27.9	33.6	31.9	39.0	36.4
MET_LUG_235	82.4	33.5	39.5	38.5	63.7	58.4	69.7	63.3
MET_LUG_236	78.5	34.3	37.1	36.5	66.0	59.2	75.4	66.5
MET_LUG_237	69.6	55.7	48.9	51.0	72.0	67.1	79.9	72.5
MET_LUG_238	88.0	53.7	43.5	44.7	66.3	64.8	70.6	68.5
MET_LUG_239	90.5	48.8	46.6	46.8	60.6	59.5	65.2	63.6
MET_LUG_240	90.7	32.1	31.1	31.1	55.2	53.0	64.6	61.5
MET_LUG_241	87.6	70.2	65.4	66.0	80.0	78.8	83.5	81.9
MET_LUG_242	82.7	54.2	64.3	62.6	76.1	72.4	81.4	76.7
MET_LUG_243	76.8	50.6	64.3	61.1	76.1	70.2	81.4	74.2
MET_LUG_244	82.0	81.0	85.4	84.6	94.3	91.9	95.4	92.8
MET_LUG_245	83.8	77.3	92.7	90.2	95.5	92.5	95.4	92.4
MET_LUG_246	82.2	33.8	42.6	41.0	58.8	54.3	67.0	61.1
MET_LUG_247	73.9	34.2	35.4	35.1	57.6	51.5	65.8	57.6
MET_LUG_248	66.6	24.1	19.7	21.1	39.3	34.2	48.8	40.5
MET_LUG_249	74.2	30.5	29.6	29.8	54.9	48.6	61.7	53.6

Source: OceanaGold, 2025

A follow up third round of testing was undertaken in 2025 focusing on the upper half of the moderate-recovery material looking to better understand where the boundaries were and to better tie this with gold deportment. A total of 10 composites sourced from coarse crushed rejects were submitted to SGS Burnaby to repeat the extended concentrate kinetic leach test to 96 hours with head grades ranging from 1.67 to 16.7 g/t Au and 0.76% to 2.22% S. Recovery at 96 hours ranged from 62.3% to 96.44% and averaging 85.1% compared to an average of 72% at 24 hours with details provided in Table 13-29 below.


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Table 13-29: Ledbetter Underground Third Round Recovery Results


Sample ID	Flotation Recovery Au %	Leach Recovery Tailings Au %	24 Hrs		72 Hrs		96 Hrs
			Leach Recovery Con Au %	Overall Recovery Au %	Leach Recovery Con Au %	Overall Recovery Au %	Leach Recovery Con Au %	Overall Recovery Au %
MET_LUG_250	74.2	63.7	71.5	69.5	89.0	82.4	86.8	80.8
MET_LUG_251	91.2	71.8	90.1	88.5	92.6	90.8	92.9	91.0
MET_LUG_252	75.3	57.2	77.3	72.3	90.0	81.9	88.9	81.1
MET_LUG_253	80.6	52.5	62.3	60.4	87.2	80.5	82.8	76.9
MET_LUG_254	80.0	40.5	61.5	57.3	86.6	77.3	84.0	75.3
MET_LUG_255	83.8	34.4	45.2	43.5	78.2	71.1	67.7	62.3
MET_LUG_256	94.5	86.0	97.8	97.1	97.7	97.1	97.7	97.1
MET_LUG_257	88.4	45.5	51.1	50.5	82.1	77.9	76.0	72.4
MET_LUG_258	84.2	85.5	92.5	91.4	95.5	93.9	93.8	92.5
MET_LUG_259	84.5	89.6	98.5	97.1	98.5	97.1	97.6	96.4

Source: OceanaGold, 2025

As part of the second and third phase test programs, samples of flotation concentrate were submitted for gold deportment analysis by Tescan Automated Mineral Analysis (TIMA) to check for the inclusion size of gold inclusions within pyrite. The results of this work indicated in the Intrusive Breccia domain the deportment of gold was significantly different to the Metasediment domain and samples from the Palomino deposit. Typically, at Haile in the Metasediment zones, gold in the concentrate is present as native gold inclusions within pyrite accounting for 80% to 95% of the total content. In the Intrusive Breccia domain less than 15% of the gold was present as native gold with the remainder present in a variety of telluride minerals dominated by muthmannite, calaverite, and petzite. Analysis of the data showed a strong positive correlation between the percentage of gold present as petzite at 6, 24 and 96 hours and a strong negative relationship with the percentage of gold present as muthmannite and calaverite. This is graphically presented below in Figure 13-4 and has provided an understanding of the key driver in variable gold recovery within this domain.


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Source: OceanaGold, 2025

Figure 13-4: Relationship Between Gold Deportment and Concentrate Leach Recovery at 24 Hours

Further regression analysis of the second and third round results allowed recovery estimation to be made both for concentrate leach recovery and overall recovery when knowing the deportment of gold in the key telluride minerals and leach rate at 24 and 48 hours. This is graphically presented below in Figure 13-5 showing what gold recovery is expected to be with a 24 hour or 96 hour concentrate leach residence time.


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Source: OceanaGold, 2025

Figure 13-5: Overall Gold Recovery Estimation from Gold Telluride Deportment at Varying Concentrate Leach Residence Times

From the testwork programs recovery estimates were used to develop a Leapfrog recovery model using a NN method for the Intrusive Breccia domain and this was then added to the Resource block model. This allows for the Deswik mine schedule to estimate mill recovery and expected gold produced for each stope to be used in the overall production schedule. For the Metasediment domain the current gold recovery model for the site is used.

As part of the Ledbetter Underground Study the testwork results were used to develop a design criteria to modify the current plant flowsheet to keep concentrate leaching separate from the flotation tails stream and to extend it to 96 hours to maximize gold recovery opportunity for the Intrusive Breccia domain hosted ore. An Engineering Feasibility study was conducted by Ausenco to divert the concentrate leach stream after the current pre-aeration and CIL #1 leach tank to a new train of four agitated leach tanks providing 96 hours of total leach residence time followed by a Kemix Carousel modular adsorption circuit running in parallel to the flotation tails stream utilizing the remaining seven CIL tanks. The capital cost estimate for the modification was used to compare to mine schedules assuming 24 hours and 96 hours to evaluate the improved economics that led to the decision of proceeding with the modification to the plant.

13.4Recovery Estimate Assumptions

The recovery estimate model developed in the Romarco Feasibility study based on the interpretation of test work results from a range of samples and test work campaigns and shown in Figure 13-2 as a function of gold grade. This was based on the original flowsheet incorporating sulfide flotation and open circuit regrind of concentrate in the SMD circuit to a target P80 of 13 µm.

The completion of the replacement of the regrind circuit in 2019 with a two stage Towermill / Isamill circuit operating in closed circuit has achieved the targeted regrinding product size. In addition, a


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number of plant modifications have been implemented to address mechanical issues in the CIL circuit and to convert the pre-aeration tank to a leach tank duty. The overall effect has been to achieve gold recoveries in excess of that predicted by the original Feasibility study model when feeding the plant predominantly fresh sulfide ore. The performance of the plant from 2020 to 2022 resulted in a 2.5% increase on the Feasibility model used during LoM planning process.

The operating strategy for ROM management is based on segregating significant quantities of oxidized ore and campaign milling when possible to minimize the impact on the flotation circuit performance on fresh ore. This is used to create maintenance windows for the regrind circuit without mill downtime.

Given the mill feed schedule over the LoM tracks the major sources the following criteria have been applied to estimate overall gold recovery for production forecasting:

•Fresh sulfide ore delivered to the ROM above 1.7 g/t Au from open pit, Horseshoe, Palomino, and Ledbetter Metasediment domain UG utilize the feasibility recovery plus 2.5%

•Fresh sulfide ore delivered to the ROM below 1.7 g/t Au from open pit, Horseshoe, Palomino, and Ledbetter Metasediment domain UG utilize the feasibility recovery

•Oxide ore assumes a flatline 68% gold recovery based on direct leach flowsheet

•Sulfide ore that is stockpiled and then rehandled to the ROM will attract a 5% recovery penalty compared to the freshly mined recovery assumption

•Fresh sulfide ore from the Ledbetter UG Intrusive Breccia domain utilizes the Leapfrog model developed from metallurgical testing based on a 96 hour concentrate leach residence time

A flatline assumption of 70% silver recovery continues to be used in metal production forecasting. Silver revenue accounts for less than 1.5% of overall total sales and as such the impact of changes to the silver recovery have a marginal impact on overall economic outcomes. The doré product from Haile is gold containing moderate amounts of silver. The doré bars are 95% pure with minimal or no deleterious elements.


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14 Mineral Resource Estimates

This section describes the Mineral Resource estimation methodology and summarizes the key assumptions adopted by OceanaGold. In the opinion of OceanaGold, the Mineral Resource estimates reported herein are a reasonable representation of the Mineral Resources at Haile. The Mineral Resources and their classification have been prepared in accordance with the CIM Standards on Mineral Resources and Reserves: Definitions and Guidelines, May 10, 2014 (CIM, 2014). Mineral Resources, which are inclusive of Mineral Reserves, are reported in accordance with NI 43-101. There is no certainty that Mineral Resources that are not Mineral Reserves will be converted into Mineral Reserves.

The Haile open pit and Horseshoe underground Mineral Resource estimates were prepared under the supervision of Mr. Jonathan Moore, BSc (Hons) Geology, GradDip Physics, member and Chartered Professional of the Australasian Institute of Mining and Metallurgy. Mr. Moore is OceanaGold’s Head of Resource Development, a QP as this term is defined pursuant to NI 43-101 for Mineral Resources. The effective date of the Mineral Resource statement is December 31, 2025.

The Palomino and Ledbetter underground Mineral Resource estimates were prepared under the supervision of Mr. Douglas Corley, BSc (Hons) Geology, Registered Professional Geoscientist with the Australian Institute of Geoscientists. Mr. Corley is OceanaGold’s Principal Geologist, a QP as this term is defined pursuant to NI 43-101 for Mineral Resources. The effective date of the resource statement is December 31, 2025.

Due to different mining selectivity and CoG assumptions, separate block models were generated for the open pit and underground areas. The open pit Resource model is “HA0725OLM_v6”. The lithological model for all deposits was provided by the OceanaGold Haile Exploration department. Implicit gold grade shell generation, grade estimation and block model construction were completed within VulcanTM software. Resource reporting pit shells were generated using VulcanTM software.

The Horseshoe, Palomino and Ledbetter underground models are “HA0925ULM_v2”, “PA_1023_URR” and “LB1125URR” respectively. The implicit gold grade shells were generated in Leapfrog software whilst grade estimation and block model construction were completed in VulcanTM software (except “LB1125URR”, which was completed in Leapfrog Edge).

The following sections are grouped:

•Sections 14.1 to 14.7 (drillhole database, geological model, lithology, domaining, compositing, top capping and bulk density) apply for all open pit and underground estimates.

•Sections 14.8 to 14.11 (estimation methodology and parameters) are specific to each individual estimate.

•Sections 14.12 to 14.14 (resource classification, validation, reconciliation and resource reporting) apply for all open pit and underground estimates.

14.1Drillhole Database

During 2016, the Romarco Minerals drilling database was migrated to OceanaGold’s standard acQuire database platform. Where available, original source assay and survey data were used for


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the acQuire translation and database validation. There was an additional internal database review in late 2018 / early 2019. No material errors were identified.

The assay coverage for gold includes all core and RC drilling. However, the collection of carbon (Open Pit Mineral Resource Model), sulfur and silver assay data has largely been retrospective and is significantly sparser than gold. Sulfur and carbon data are primarily used for the prediction of overburden classification types. Sulfur grades are also used for mill feed sulfur estimates. Silver grades are provided for metallurgical considerations (carbon stripping and electro-winning) as well as revenue estimation, albeit silver being a minor contribution relative to total revenue.

Historical drilling (i.e., prior to 2007) accounts for approximately 16% of the data, although much of the Resource associated with this data has been mined. The sample procedures applied to the historical drilling (i.e., drilling prior to Romarco) at Haile were not well documented. Pre-Romarco RC holes drilled by Piedmont were downgraded by 5%. (RC0039 – RC1303).

An analysis of rotary split sub-sample mass for Romarco RC holes (RC1502 to RC2216) was undertaken. Rotary splitter ratio settings ranged from 8% to 17%. Based on back calculating the range of likely total sample weights, RC recoveries appear to have been largely acceptable. As a precautionary measure, sample intervals with low estimated sample recoveries and >200 m sample depths, have had the gold grades factored in relation to sample recovery. The global impact on the Resource estimate is less than 1%. These factors will remain until verified and/or replaced by new drilling. Sensitivity analysis shows. Given this mitigation, the residual risk is low.

14.1.1Data Cut-Off Date – Mineral Resource Models

The data cut-off dates used Mineral Resource Models at Haile are listed in Table 14-1.

Table 14-1: Data Cut-Off Dates for Resource Models


Area	Model Name	Data Cut-Off Dates
Haile Open Pit	“HA0725OLM_v6”	July 21, 2025
Horseshoe Underground	“HA0925ULM_v2”	September 29, 2025
Palomino Underground	“PA_1023_URR”	October 11, 2023
Ledbetter Underground	“LB1125URR”	October 29, 2025

Source: OceanaGold, 2025

For Palomino, no drilling has occurred since October 2023

14.2Geologic Model Concepts

A detailed 3D geological model, including weathering, has been constructed. This model, which has evolved over time, has been used to assign variable bulk densities to the various block models. Faults have also been modeled. However, other than post-mineralization dikes and post mineralization erosion / deposition interfaces, there are few geological features that represent hard mineralization boundaries.

Gold mineralization at the Haile Gold Mine is hosted within deformed greenschist facies MS and MV which define a large scale antiform that plunges at a low angle to the northeast. Mineralization occurs as discrete bodies, variously located on the limbs and hinge zone of this antiform. Diabase


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and Lamprophyre dykes, which exploited pre-existing sub-vertical, NW-SE striking fractures, cut across mineralization. The structures that host the dikes are post-date folding, do not demonstrate fault offset, yet seem in some cases to influence gold grade distribution.

The interplay between the contacts, bedding (S0), regional foliation (S2), and the fractures is important to understanding the current distribution of gold mineralization at Haile. The overarching relationship between these elements changes across the antiform; bedding and the MS-MV contact dip steeply to the SE on the southern limb (Horseshoe and Palomino) whereas dip moderately to the NW on the northern limb (Mill Zone, Haile, Red Hill, Ledbetter and Snake). Red Hill SE and Snake are located in hinge zones. Importantly, the S2 foliation dips consistently to the NW, intersecting bedding and contacts at a high angle on the southern limb. By contrast, the S2 foliation is typically sub-parallel to bedding and contacts on the northern limb (Figure 14-1).

Source: OceanaGold, 2025

Figure 14-1: Schematic Cross-Section Looking NE – Showing Relationship of UG Deposits to MS / MV Contact (Blue line) and Regional Foliation (Orange Line)

14.3Lithology

Lithologic codes used at Haile capture many geologic attributes including the primary rock type, presence of brecciation, silicification, lamination, and numerous variations on the general rock unit.

Most of the mineralization is hosted within the Metasediments and the lithological units are as follows:

•S - sand

•Sap - saprolite

•MV - metavolcanics

•DB - intrusive dikes

•Fill - back-fill from historical mining


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•Ml - laminated metasediments (MS)

•Ms - silicified metasediments (MS)

•Basalt

•Intrusive Breccia

•Undifferentiated Basement Material

14.3.1Silicification

The intensity of “silicification” increases from 0 (absent) to 3 (pervasive) and is logged visually by site geologists. The minor silicification (1) population has an average grade of about 0.5 g/t. The average grade of moderately silicified (2) rocks is 1.0 g/t and the very silicified (3) average grade increases to approximately 2.0 g/t. Whilst there is a broad gold to silicification relationship, it is not strong enough to guide gold estimation.

14.3.2Pyrite

Multiple morphologies of pyrite have been identified at Haile, ranging from fine to coarse cubic pyrite. Based on logging, it has been established that fine-grained pyrite is commonly associated with gold mineralization, however pyrite is not used to guide gold estimation.

14.4Domaining

Estimation domaining methodology used for the open pit and three underground Resource models, was similar. Grade-based implicit wireframes were generated using Leapfrog numerical modeling or Vulcan implicit grade function. The grade threshold used for each model depended on the deposit, element being estimated, nature of the grade boundaries, cut-off grade and geostatistics.

The implicit wireframes were implemented as hard boundaries for grade estimation.

14.4.1Gold

A summary of Au value used for the hard boundary gold domains is summarized in Table 14-2.

Table 14-2: Hard Boundaries Au Domain Thresholds


Area	Model Name	Au (g/t) Threshold	Probability above Threshold (%)
Haile Open Pit	“HA0725OLM_v6”	0.065	50
Horseshoe Underground	“HA0925ULM_v2”	1.0	25
Palomino Underground	“PA_1023_URR”	0.8	25
Ledbetter Underground	“LB1125URR”	0.7	25

Source: OceanaGold, 2025

There was some sub-domaining used in the Au estimation for the Open Pit and Palomino Mineral Resource models.

•Open Pit: sub-divided into two domains based upon gold distribution and orientation, albeit the differences were not large between the two domains. The mineralized zones within


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domain 1 approximate a dip direction of 40 to 330. In domain 2, mineralized zones approximate a dip direction of 30 to 335.

•Palomino: low grade (=<0.25 g/t Au) and high grade (>0.25 g/t Au) sub domains were identified within the 0.8 g/t Au domain and estimated using Indicator Kriging.

14.4.2Silver

Silver grade estimates are provided for metallurgical considerations (carbon stripping and electro-winning) as well as for revenue estimation; despite contributing only ~1.5% of total revenue. Silver content is not used as a gold-equivalent input for cut-off calculation nor to guide mine design decisions.

The selection of samples for silver assaying was undertaken retrospectively, based upon previously assayed gold grades, resulting in less than 10% coverage of that for gold. Sample selection for silver assaying tended to favor more strongly gold-mineralized intervals, leaving less intensely mineralized intervals, on the flanks of the mineralization under represented. To mitigate the impacts of the selection bias, bivariate simulation was implemented (“simulate missing data” program in GS3 proprietary software). This non-spatial stepwise simulation assigned silver grades to locations with gold assays, but no silver assays, based upon relationships between silver and gold in the assay database.

An example of the comparison of actual Ag data compared to the simulated Ag is shown at the Ledbetter UG deposit in Figure 14-2. It presents a log scale scatter plot of Ag vs. Au grades, both the original dataset and with the simulated data added. The two population distributions (actual Ag assays vs Ag values simulated from established Ag / Au relationship) compare well.


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Source: OceanaGold, 2025

Note: left: Original Ag Data / right: Simulated and Original Ag Data

Figure 14-2: Ledbetter UG deposit log-scale scatter plot of Ag (Original / Simulated) vs Au

The same domaining and search orientations used for gold were used for silver, in all models except for Ledbetter UG (“LB1125URR”).

The tenor of Ag mineralization is much higher in the Ledbetter UG area than elsewhere at Haile. An additional Ag domain was required to better estimate the Ag distribution. Nested within the lower grade domain, a higher-grade domain was generated from the intersection of the Intrusive Breccia and the low-grade domain.

There is a strong correlation between tellurium (Te) and Ag, so the Ag domain was used for the Te estimate also.

14.5Compositing

The Haile Open Cut Mineral Resource DH database was composited to 2.5 m downhole lengths with breaks at domain contacts. The merge function was used, where intervals are less than or equal to 1.25 m minimal and coverage 50% of residual are merged with the adjacent sample, resulting in lengths ranging from 1.25 to 3.75 m with a mean of 2.5 m. No compositing was used for total carbon and total sulfur due to discontinuous sampling.

For all UG Mineral Resources, the DH databases were composited to 3 m downhole lengths with breaks at domain contacts. The 3 m length was chosen to reflect mining selectivity and the parent block dimensions used. The merge function was used, where intervals less than or equal to 1.5 m minimal and coverage 50% of residual are merged with the adjacent sample, resulting in lengths ranging from 1.5 to 4.5 m with a mean of 3 m.


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14.6Top-Capping

Top-capping is reviewed on a deposit-by-deposit basis, with the purpose of managing the influence of outliers in highly skewed grade distributions. Actual top cap values are discussed in the respective sections.

14.7Bulk Density

Mineral Resource block model in situ dry bulk densities (BD) are based on lithology averages, as shown in Table 14-3. The BD was assigned for each lithology type (and oxidation state used for Open Pit Mineral Resource Model, all UG lithologies are fresh).

In situ density determinations have been carried out at regular intervals on drill core samples (approx. 10 to 20 cm billets), and over 46,000 measurements have been collected to date. The “Archimedes method” involved weighing the sample both in air and in water. The measurements were then averaged for each lithology. The BD is reported as tonnes per cubic metre (t/m3).

Table 14-3: Assigned Lithological Bulk Density Values


BD Assignment Criteria (tonnes/m3)
Sand	Saprolite	PAG Fill	Tails	Heap	Dike	Meta Volcanics		Meta Sediments		Basalt	Intrusive Breccia	Basement
2.06	2.18	1.89	2.14	1.7	2.88	Oxidized	Fresh	Oxidized	Fresh	2.81	2.68	2.74
						2.52	2.7	2.57	2.78

Source: OceanaGold, 2025

•That Sand, Saprolite, PAG fill, Tails, Heap and oxidized Meta-Volcanics / Meta-Sediments are only used in Haile Open Pit Mineral Resource models. UG Resource Models contain fresh material only.

14.8Mineral Resource – Open Pit

The Haile open pit Resource comprises Champion, Small, Haile, Red Hill, Ledbetter, and Snake deposits through various stages of mining. The location of the various deposits is shown in Figure 14-3 (red shapes are Open Pit deposits, blue shapes are UG deposits). These deposits are on the shallow-dipping limb to the northwest and extend from the surface to a depth of approximately 275 m.


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Source: OceanaGold, 2025

•Haile Open Pit deposits are shown in Red (UG deposits colored blue). Approximate Axial fold hinge trace of the Metasediment / Metavolcanic contact is shown in pink; deposits to the NW of the fold hinge are at shallow angle to the Mineralization Foliation and deposits to the SE of the fold hinge are at a steep angle to the Mineralization Foliation.

Figure 14-3: Haile Open Pit

For the Open Pit Mineral Resource model, the 2.5 m composited gold grades were top capped to
50 g/t Au to temper mean grades above the top-class indicator threshold. Only nine and 15 composites required capping from domain 1 and 2 respectively.

Gold grade indicator thresholds were determined for each domain based on their histograms and cumulative distribution functions (CDF). Thresholds were set at 10th, 20th, 30th, 40th, 50th, 60th, 70th, 75th, 80th, 85th, 90th, 95th, 97.5th and 99th percentiles. Statistics for capped Au indicator class thresholds are summarized in Table 14-4.

Total sulfur was top capped to 33% for extreme values (one composite only). No top-cap was applied for total carbon.


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Table 14-4: Haile Open Pit Indicator Gold Class Thresholds and Means


Summary of Grade Thresholds and Mean Values for MIK
Statistics Length Weighted Domain 1					Statistics Length Weighted Domain 2
Bin #	Class	Mean	Median	Count	Bin #	Class	Mean	Median	Count
1	>=0.00, <0.05	0.03	0.03	2,830	1	>=0.00, <0.03	0.01	0.01	2,444
2	>=0.05, <0.07	0.06	0.06	2,275	2	>=0.03, <0.06	0.04	0.04	2,422
3	>=0.07, <0.10	0.09	0.09	3,400	3	>=0.06, <0.09	0.07	0.07	2,646
4	>=0.10, <0.13	0.12	0.12	3,384	4	>=0.09, <0.13	0.11	0.11	3,115
5	>=0.13, <0.18	0.15	0.15	3,927	5	>=0.13, <0.19	0.16	0.16	3,317
6	>=0.18, <0.25	0.21	0.21	3,853	6	>=0.19, <0.28	0.23	0.23	3,479
7	>=0.25, <0.37	0.30	0.30	4,186	7	>=0.28, <0.43	0.35	0.34	3,693
8	>=0.37, <0.46	0.41	0.41	1,933	8	>=0.43, <0.55	0.49	0.48	1,968
9	>=0.46, <0.59	0.52	0.52	1,994	9	>=0.55, <0.71	0.62	0.62	1,774
10	>=0.59, <0.79	0.68	0.68	1,945	10	>=0.71, <0.97	0.83	0.82	1,925
11	>=0.79, <1.17	0.96	0.96	1,943	11	>=0.97, <1.48	1.19	1.18	2,049
12	>=1.17, <2.07	1.55	1.51	2,006	12	>=1.48, <2.71	1.99	1.95	2,125
13	>=2.07, <3.05	2.49	2.46	781	13	>=2.71, <4.16	3.33	3.27	929
14	>=3.05, <6.00	4.13	3.98	759	14	>=4.16, <9.20	5.92	5.62	1,034
15	>=6.00, <50	11.34	8.85	403	15	>=9.20, <50	16.60	13.71	534

Source: OceanaGold, 2025

Gold estimation was completed using MIK, while carbon and sulfur were estimated using OK. Carbon and sulfur values are used for classification of overburden material.

For gold estimation, two domains were used:

•Domain 1 (Mill Zone, Haile/Red Hill, Champion)

•Domain 2 (Snake, Ledbetter)

Indicator variograms were produced for all grade thresholds in both domains. Variograms were generated in GS3 software and exported in VulcanTM format.

Each domain area was estimated in three passes, with a larger subsequent search ellipse than the previous domain. Each of the main two open pit domain areas has unique search parameters based upon indicator variogram models for 14 different gold indicator thresholds.

Grade estimation was completed with VulcanTM software, using MIK based on 2.5 m composites to produce grade estimates into a 10 m E x 10 m N x 5 m RL model blocks. Model block grade estimates for post-mineralization dikes were reset to zero gold grades after estimation.

14.8.1Block Model

The HA0725OLM_V6 Mineral Resource block model was constructed in VulcanTM and the parameters are listed below in Table 14-5. The block model is based on a parent block size of 10 m x 10 m x 5 m in x, y, z respectively, without sub-blocking or rotation.


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Table 14-5: HA0725OLM_V6 Block Model Dimensions


Variable	X	Y	Z
Minimum	539,810	3,825,575	200
Maximum	544,510	3,827,725	1,200
Block Size (Parent)	10	10	5
No. of Blocks (Parent)	470	215	200

Source: OceanaGold, 2025

14.8.2Estimation Methodology

Top caps of 50 g/t Au were applied to temper mean grades above the top class indicator threshold. Acceptable long term model to mill-adjusted mine reconciliation suggests this as a reasonable approach.

OK was used for silver, sulfur and carbon estimates.

The general workflow for model generation was as follows:

•Drillhole data extraction from acQuire database

•Data validation

•Exclusion of drillholes from early drilling campaigns with poor documentation

•Drillhole composite to 2.5 m for Au

•No composite (straight) for total carbon and total sulfur due discontinuous sampling

•Duplicates removal

•Grade shell generation in VulcanTM using Implicit modeling tool using 0.065 g/t Au threshold

•Composite flagging including domain area and Au grade shell

•Block model creation in VulcanTM including lithology, domain area and grade shell

•Run multi-pass MIK estimation for Au

•Set block grades to zero for blocks coded as post-mineralization dike

•Run OK estimation for Ag (using stepwise simulated Ag values for intervals with gold assays but no silver assay), total carbon and total sulfur

•Deplete resource with historical open pit and underground workings

•Assign model bulk densities based on lithology

•Model classification

For Mineral Resource classification, see section 14.12.

14.8.3Open Pit Geometallurgical Model

An open pit geo-metallurgical model was first developed in 2023 based on historic rock hardness data (see Section 13.1). Model dimensions were the same as the open pit Mineral Resource model. BBWi and DWi were assigned to resource model blocks.

Between 2024 and 2025, additional samples were collected and analyzed for BBWi and DWi (See section 13.1.1), primarily from future Ledbetter pit phases. The Geometallurgical model was updated in 2025 with revised estimation parameters and provided the basis for the current mill throughput schedules. The model will continue to be developed as new input data is evaluated


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(such as Equotip1 drill core readings and production drilling penetration rates) and the impacts of blast fragmentation and plant utilization on reconciliation / calibration are accommodated.

14.9Mineral Resource - Horseshoe Underground

The Horseshoe deposit is the highest grade and eastern-most known gold deposit in the Haile district (Figure 14-4). Mineralization extends over a vertical distance of 350 m, length of 200 m and width of 120 m, albeit with a complex geometry. The top of the deposit is about 120 m below.

Source: OceanaGold, 2025

Figure 14-4: Plan View showing Horseshoe (Red) Relative to Open Pit Areas

The composite statistics for Au g/t and Ag g/t are shown in Table 14-6. A 90g/t Au top cap and 12.5g/t Ag top cap were applied. Sixteen gold and thirty silver composites are affected by top capping. Furthermore, domain 3 (dilution domain) composites for Au and Ag were severely capped to account the high-grade outliers.

1 Equotip enables portable hardness testing. The hardness measurements are made by using the dynamic rebound testing method according to Leeb, the static Portable Rockwell hardness test and the Ultrasonic Contact Impedance (UCI) method


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Table 14-6: Horseshoe UG 3 m Composite Statistics Comparison by Domain


DOMAIN	FUNCTIONS	Raw		3 m Composite		Top Capping
		Au	Ag	Au	Ag	Au	Ag
1	No. of Samples	12,328	603	4,817	2,607	4,817	2,607
	Minimum	0.003	0.005	0.003	0	0.003	0
	Maximum	1,080	83.0	275	71.0	90	12.5
	Range	1,079	83.0	275	71	89.997	12.5
	Mean	5.47	2.26	4.69	1.97	4.54	1.82
	Standard Deviation	17.4	3.69	11.1	3.34	9.24	2.19
	Variance	596	13.6	124	11.1	85.3	4.79
	Coef. of Variance	4.46	1.63	2.38	1.70	2.03	1.07
	Skewness	23.5	7.89	9.32	8.13	5.51	2.35
	Median	1.42	1.50	1.67	1.11	1.67	1.11
3	No. of Samples	10,496	192	4,911	1,837	4,911	1,837
	Minimum	0.003	0.005	0.002	0	0.002	0
	Maximum	66.4	4.1	34.0	31.3	0.6	1.5
	Range	66.3	4.11	33.7	31.3	0.598	1.5
	Mean	0.20	0.43	0.19	0.40	0.13	0.31
	Standard Deviation	0.897	0.48	0.64	1.48	0.19	0.33
	Variance	0.80	0.23	0.414	2.18	0.04	0.11
	Coef. of Variance	4.39	1.12	3.44	3.73	1.44	1.07
	Skewness	42.4	3.27	32.3	18.6	1.59	2.35
	Median	0.03	0.25	0.04	0.15	0.13	0.15

Source: OceanaGold, 2025

14.9.1Block Model

The block model is rotated in VulcanTM with a 60° bearing with 0° plunge and dip. The dimension, origin, and cell size are provided in Table 14-7.

Table 14-7: Block Model Dimensions and Origin


Variable	X	Y	Z
Origin	542,900	3,826,100	600
Minimum	0	0	0
Maximum	1,250	700	580
Block Size (Parent)	10	10	10
Sub-block size	2.5	2.5	2.5

Source: OceanaGold, 2025


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14.9.2Estimation Methodology

The general workflow for model generation was as follows:

•Drillhole data extraction from acQuire database

•Data validation

•Construct 1 g/t gold grade shell and 15 m offset dilution shell

•Export updated grade shell and database from Leapfrog

•Drillholes flagged using Au and S grade shell

•Composite drillholes to 3 m within the grade shell for Au, Ag, and S

•Top capping analysis for Au, Ag, and S

•Generate Vulcan block model within lithological wireframes, topography, and grade shells

•Run estimation for Au g/t, Ag g/t, and S % using OK

•Estimation validations

•Assign model densities

•Use interpretated dike solids to zero Au and Ag values

•Classification and reporting.

For Resource classification, see section 14.12.

14.10Mineral Resource - Palomino Underground

The Palomino deposit is located approximately 650 m southwest of Horseshoe, and 300 m below surface (Figure 14-5). The Palomino Resource estimate is based on the current drillhole database, interpreted lithologies, geologic controls, and current topographic data.

Source: OceanaGold, 2025

Figure 14-5: Long-Section Looking NNW, showing Palomino Mineralization, Horseshoe, HEX and, Entire Haile Drilling Intercept Dataset Shown (colored by Au g/t)


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Statistical analysis of the composite data for Au and Ag resulted in a capping value of 28 g/t Au and 15 g/t Ag for the 0.8 g/t Au threshold shell. Capping analysis for the dilution domain resulted in values of 4.5 g/t and 2.5 g/t for Au and Ag respectively. Table 14-8 summarizes the length-weighted statistics of 3 m composites within the 0.8 g/t Au threshold shell (pug 0p8=1) and dilution domain (expanded 10m around the mineralized domain).

Table 14-8: Palomino UG Basic Statistics for 3 m Composites by Domain


Variable	Domain	Count	Minimum	Maximum	Mean	Variance	CV
AU_PPM	pug_0p8=1	2,475	0.003	39.8	2.5	12.4	1.4
	dilution	1,943	0.003	37.2	0.2	1	4.2
AU_CAP	pug_0p8=1	2,475	0.003	28	2.5	11.7	1.4
	dilution	1,943	0.003	4.5	0.2	0.2	1.9
AG_PPM	pug_0p8=1	599	0.029	22.2	2.5	8.8	1.2
	dilution	174	0.007	10.7	0.6	1.3	2
AG_CAP	pug_0p8=1	599	0.029	15	2.4	7.7	1.1
	dilution	174	0.007	2.5	0.5	0.3	1.2

Source: OceanaGold, 2023

A probability kriging methodology was used to separate the higher grade (HG) and lower grade (LG) portions (grade and probability) for estimation into the parent block. The two estimates were then weight-averaged for whole block grade estimates. This was based on the probability (proportion) of the high- and low-grade domains within the block, where:

Block grade = ((Proportion HG x Grade HG) + (Proportion LG x Grade LG))

Statistics of the data within the sub-set HG and LG domains, are based on the 0.25 g/t Au indicator.

14.10.1Block Model

The block model is rotated to align with the primary 060° mineralization direction with the long axis. The block model parameters are listed in Table 14-9.

Table 14-9: Palomino Block Model Dimensions and Origin


Variable	X	Y	Z
Rotation	060o
Origin	542,500	3,825,800	250
Length	920	520	750
Block Size (Parent)	10	10	10
Sub-block size	2.5	2.5	2.5
No. of Blocks (Parent)	92	52	75

Source: OceanaGold, 2023


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14.10.2Estimation Methodology

Gold

Post-mineralization dikes were assigned a zero grade.

The following methodology was used:

•Build a variogram for the 0.25 g/t Au indicator for data within the 0.8 g/t Au threshold shell

•Search orientation essentially parallel to the plane of gold continuity

•Estimate LG indicator probability (LG ind prob)

•Calculate HG indicator probability (HG ind prob) where:

•HG ind prob = 1 – LG ind prob

•Build a variogram for the Au grade in the LG and HG domains

•Estimate Au grade for HG and LG Domain

•Limit data to four samples per DH

•No octant restriction applied

•Post estimation – calculate final block grade where:

Block grade = ((Proportion HG x Grade HG) + (Proportion LG x Grade LG))

Silver

Silver (Ag) grades for the 0.8 g/t Au threshold shell (Domain 1) were estimated into parent blocks built within Isatis-Neo modeling software using Ordinary Co-Kriging (COK) on 3 m composites to address the paucity of silver analyses. Only 773 silver composites were available compared to 4,418 composites for gold. The COK estimates leverage the spatial correlation between Au vs. Ag using a cross-variogram to estimate at locations where gold assays were present, but no Ag assays were available.


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14.11Mineral Resource – Ledbetter Underground

In contrast to elsewhere at Haile, Ledbetter is underlain by a series of diabase dikes and a basaltic unit (Figure 14-6). The highest-grade gold-silver-telluride mineralization is located predominantly within a unit mapped as the Intrusive Breccia, which hosts the majority of Lobe 1.

Source: OceanaGold, 2025

•Key Lithologies (labelled), Mineralization Foliation Trends (blue) and Mineralized Lobes (red) are shown

Figure 14-6: Ledbetter UG Lithology Slice View, Along Strike of Mineralization (striking NW), Looking NE


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The Ledbetter underground deposit dimensions are approximately 450 m long x 200 m thick x 250 m wide, sitting below the Ledbetter Phase 3 open pit (see Figure 14-7), comprising three separate mineralized lobes, dipping approximately 40° to the northwest.

Source: OceanaGold, 2025

Figure 14-7: Looking South – Ledbetter UG Deposit, Relative to the Final Ledbetter Open Pit

Statistical analysis of the drillhole sample data has resulted in a capping value of 60 g/t Au, 8 g/t Au,10 g/t Au, and 1.5 g/t Au for the composites used in Lobe 1 to 3 and the dilution domain (expanded 10 m around lobes 1 to 3) respectively.

Table 14-10 summarizes the length weighted statistics of 3 m composites within the 0.7 g/t Au indicator shell (Lobe=1 to 3) and dilution domain.

Table 14-11 and Table 14-12 summarize the statistics of 3 m composites (of the two datasets, actual Ag data and the combined simulated Ag data) within the 1 g/t Ag indicator shell (agdom=1) and higher-grade domain (agdom=2). Statistical analysis of the combined sample data has resulted in a capping value of 55 g/t Ag and 115 g/t Ag for the composites used in agdom 1 and 2 respectively.


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Table 14-10: Ledbetter UG Basic Statistics for 3 m Au Composites by Domain


Variable	Domain	Count	Mean	Std Dev	CV	Variance	Minimum	Maximum
Au g/t	Lobe 1	1,798	4.15	21.5	5.19	463	0.01	547
	Lobe 2	66	3.63	15.8	4.34	249	0.09	127
	Lobe 3	211	3.63	13.3	3.66	176	0.01	173
	dilution	2,865	0.20	0.40	2.05	0.16	0.003	12.1
Au CAP	Lobe 1	1,798	3.11	7.19	2.31	51.6	0.01	60
	Lobe 2	66	1.76	1.50	0.85	2.25	0.09	8
	Lobe 3	211	2.09	2.36	1.13	5.59	0.01	10
	dilution	2,865	0.17	0.18	1.06	0.03	0.003	0.70

Source: OceanaGold, 2025

Table 14-11: Ledbetter UG Basic Statistics for 3 m Ag Composites (Based Only on Actual Ag Data) by Ag Domains


Variable	Domain	Count	Mean	Std Dev	CV	Variance	Minimum	Maximum
Ag g/t	agdom 1	312	5.90	10.4	1.76	108	0.182	102
	agdom 2	393	20.1	98.6	4.90	9,727	0.250	1,386
Ag CAP	agdom 1	312	5.59	8.15	1.46	66.5	0.18	55
	agdom 2	393	10.5	22.4	2.15	502	0.25	115

Source: OceanaGold, 2025

Table 14-12: Ledbetter UG Basic Statistics for 3 m Ag Composites (Based on Actual and Simulated Ag Data) by Ag Domains.


Variable	Domain	Count	Mean	Std Dev	CV	Variance	Minimum	Maximum
Ag g/t	agdom 1	3,654	4.2	9.2	2.19	84.6	0.02	102
	agdom 2	2,120	16.3	80.2	4.91	6,432	0.07	1386
Ag CAP	agdom 1	3,654	3.96	7.3	1.84	53.3	0.02	55
	agdom 2	2,120	9.79	20.6	2.1	424	0.07	115

Source: OceanaGold, 2025

14.11.1Block Model

The Mineral Resource block model was constructed in Leapfrog EDGE® software. Parent blocks dimensions are 10 m E x 10 m N x 10 m RL; the model was sub-blocked to 2.5 m E x 2.5 m N x 2.5 m RL for better volumetric determination. No rotation was applied to the Mineral Resource model. The block model parameters are summarized in Table 14-13.


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Table 14-13: Block Model Dimensions and Origin Setup


Variable	X	Y	Z
Rotation	0o
Origin	541,700	3,826,500	1,100
Length	1100	800	500
Block Size (Parent)	10	10	10
Sub-block size	2.5	2.5	2.5
No. of Blocks (Parent)	110	80	50

Source: OceanaGold, 2025

14.11.2Estimation Methodology

Gold, silver, sulfur, and tellurium grades were estimated using OK on top capped 3 m composites.

The summary of methodology was used for the mineralized domains for Au, Ag, Te, and S as follows:

For Au

•Build a variogram for the top capped Au grade in the mineralized and dilution shell

•Variable orientation (VO) function used, based on mineralized foliation surfaces, for lobe=1 to 3. Search orientation matches variogram orientation for audom=3 (15 m dilution)

•Estimate Au grade within mineralized / dilution shell (hard boundary) via OK

•Limit data to three samples per DH

•Quadrant restriction applied

For Ag, S and Te

•Build a variogram for the top capped grade in the mineralized shells

•Search orientation matches variogram orientation, no VO

•Estimate top-capped grade within mineralized shells (hard boundary) via OK

•Limit data to three samples per DH

•Quadrant restriction applied

For resource classification, see section 14.12.

14.11.3Ledbetter Underground Geometallurgical Model

The Ledbetter underground deposit has both high telluride and high silver content, distinguishing it from the other deposits (Horseshoe Underground, Palomino Underground, and Haile open pit). During 2024 and 2025, 47 samples were collected for metallurgical testing and revealed some locally depressed gold recoveries, which although not directly correlated with tellurium content, appear correlated specifically with muthmannite and calaverite telluride mineral species (see Section 13.3).

The test work looked at gold recoveries for 24 hour, 72 hour, and 96 hour leach residence times. Each incremental increase in leach residence time saw significant improvements in gold recovery. Using these test results, gold recoveries have been estimated using NN attribution into the


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Ledbetter Underground block model. Three recovery estimates have been included for each model block; gold recovery at 24 hour, 72 hour, and 96 hour leach residence times allowing cost benefit analysis for each leach residence scenario.

14.12Open Pit and Underground Resource Classification

Mineral Resources are classified as Indicated and Inferred in accordance with CIM guidelines. Classification of the Mineral Resources reflects the relative confidence of the grade estimates and the mineralization continuity. This classification is based primarily on the drillhole spacing, geological complexity, and in some cases, Kriging Neighborhood Analysis (KNA). No single factor controls the Mineral Resource classification. Rather, each factor influences the result. Summary of classification criteria used is shown in Table 14-14.

Table 14-14: Haile Open Pit and Underground Resource Classification Criteria


Type	Classification	Criteria
OP	Measured	Blocks estimated within first pass.
		A minimum of 4 drillholes.
		Typically, 18 m x 18 m drill spacing but variable.
	Indicated	Blocks estimated within first pass and second pass.
		A minimum of 2 drillholes.
		Typically, 40 m x 40 m drill spacing but variable.
	Inferred	Blocks estimated within second and third pass.
		A minimum of 2 drillholes.
		Typically, 60 m x 60 m drill spacing but variable.
UG	Measured	The area is defined within 15 m x 15 m drill spacing.
	Indicated	The area is guided by approx. 35 m x 35 m drill spacing, tested by kriging properties such as kriging variance, slope of regression, etc.
		Measured blocks within Metavolcanics demoted to Indicated.
	Inferred	Indicated blocks within Metavolcanics demoted to Inferred.
		Estimated blocks inside the implicit wireframes not meeting the Measured or Indicated criteria. Estimated blocks within the dilution wireframes were treated as unclassified (used to represent mining dilution).

Source: OceanaGold, 2025

14.13Open Pit and Underground Model Validation

All open pit and underground models have undergone comprehensive validation including:

•Sample data validation

•Cross-sectional checks on composite file and block model coding from lithological wireframes, domain area, and grade shell

•Visual checks of estimated block grades (gold, sulphur, carbon and silver) on sections, plan and in 3D to ensure good correlation with underlying composite data

•Visual validation of resource classification


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•Swath plots X, Y, and Z comparing gold, sulphur, carbon and silver estimates with underlying composite grades

•Detailed comparisons to previous model at global and local scales (i.e., grade tonnage and curve, contained gold by benches)

•Review methodology and validation of the scripts used

Examples of gold swath comparison plots for the Open Pit, Horseshoe Underground, Ledbetter Underground and Palomino Underground Resource estimates are shown in Figure 14-8 to Figure 14-11 respectively.

Source: OceanaGold, 2025

•Green line – Block model / Red line – DH Composite

Figure 14-8 Swath Plot Open Pit (Domain 1) Block Model Grade (vol weighted) vs. 2.5 m Top Capped Composite (Declustered Weighting)


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Source: OceanaGold, 2025

•Dark Blue line – Block model / Light Blue line – DH Composites

Figure 14-9 Swath Plot Horseshoe UG (Domain 1) Block Model Grade (vol weighted) vs. 3 m Top Capped Composite (length Weighted)


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Source: OceanaGold, 2025

•Red line – Block model / Green line – DH Composites

Figure 14-10 Swath Plot Ledbetter UG (Lobe 1) Block Model Grade (vol weighted) vs. 3 m Top Capped Composite


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Source: OceanaGold, 2023

•Green line – OK Check Estimate Block Model / Black line – OK Final Indicator Kriged Block Model

Figure 14-11 Swath Plots Palomino UG (Easting only) Domain 1 Block Model Grade (vol. weighted) vs. 3 m Top Capped Composite (Length and Declustered Weighting)

No material flaws were identified. All Resource estimates completed after the reviews capture key recommendations where practical.

14.13.1Open Pit and Underground Model Reconciliation

Table 14-15 summarizes the Haile open pit Resource model reconciliations from 2018 to 2025.

OceanaGold’s corporate Resource model to mill reconciliation metrics are based upon Model-to-Mine Factors established by the late Harry Parker of AMEC. The associated “90/15” performance guidance for Indicated Resources was developed by Harry Parker and Christina Dohm in the 1990s. On this basis, annually, Indicated Resources are expected to be +/- 15% accuracy at a 90% confidence, that is, nine years out of ten the annual production profile must be within 15% variance of that predicted by the model.

A summary of the Haile combined open pit Resource models performance for Measured and Indicated Resources versus mill-reconciled production from 2018 to 2025 is presented in Table 14-15. Annual performance is variable but typically positive, averaging +11% tonnes, -3% grade for +8% contained gold. Although Inferred Resources are considered too low confidence to have performance metrics applied to them, their exclusion from reconciliation does introduce a positive reconciliation bias.


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Table 14-15: Open Pit Resource Model Reconciliation


Year	Open Pit Resource Model			Mine (Mill-Reconciled)			Mine / Model Factor (%)
	Mt	Au g/t	Moz	Mt	Au g/t	Moz	Mt	Au g/t	Moz
2025	1.43	2.02	0.09	1.63	1.92	0.10	114	95	108
2024	2.31	2.23	0.17	2.48	2.27	0.18	107	102	109
2023	2.73	1.91	0.17	2.96	1.64	0.16	109	86	94
2022	3.39	1.59	0.17	4.13	1.75	0.23	122	110	134
2021	3.11	2.19	0.22	3.29	2.32	0.25	106	106	112
2020	2.57	2.08	0.17	3.33	1.59	0.17	130	76	99
2019	2.87	1.96	0.18	3.18	1.78	0.18	111	91	101
2018	2.85	1.67	0.15	2.57	1.93	0.16	90	116	104
Total	21.3	1.94	1.32	23.6	1.88	1.43	111	97	108

Source: OceanaGold, 2025

•Reduced mining selectivity during 2020 led to increased mining dilution.

•3D void model built using historical cross sections, led to under-estimating gold in 2022, adjacent to historical workings.

The project to-date cumulative milled tonnage from Horseshoe is 0.98 Mt with the model to mine reconciliation at approximately -5%, +8% and +3% for tonnes, grade and ounces respectively

(see Table 14-16).

Table 14-16: Underground Resource Model Reconciliation


Year	Underground Resource Model			Mine (Mill-Reconciled)			Mine / Model Factor (%)
	Mt	Au g/t	Moz	Mt	Au g/t	Moz	Mt	Au g/t	Moz
2025	0.63	3.50	0.07	0.62	3.55	0.07	98	101	99
2024	0.41	5.05	0.07	0.36	5.97	0.07	90	118	106
Total	1.04	4.11	0.14	0.98	4.45	0.14	95	108	103

Source: OceanaGold, 2025

Whilst annual reconciliation fluctuations are expected to continue, both the open pit and underground Resource estimates are believed to provide an acceptable basis for medium- to long-term mine planning purposes.

14.13.2Open Pit and Underground Model Reviews

All open pit and underground Resource models are independently reviewed by OceanaGold’s Resource Development Group, based in Brisbane.

OceanaGold ensure that in addition, independent external reviews are completed for milestone Resource model updates. The most recent independent external reviews were:

•Haile Open Pit Resource Model; July 2021 by Ginto Consulting Inc.

•Horseshoe Underground Resource Model; November 2021 by SD2 Pty Ltd.

•Palomino Underground Resource Model; November 2023 by ERM International Group Ltd.


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•Ledbetter Underground Resource Model; September 2024 by ERM International Group Ltd.

•Ledbetter Underground Geometallurgical Model; September 2025 by ERM International Group Ltd.


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14.13.3Open Pit and Underground Combined Mineral Resource Statement

Table 14-17 presents the combined open pit, stockpiles, and underground Resource statement for the Haile Property.

Table 14-17: Haile Open Pit and Underground Resource Statement as of December 31, 2025


Gold	Measured			Indicated			Measured & Indicated			Inferred
	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Au (g/t)	Contained Oz (Moz)	Tonnes (Mt)	Au (g/t)	Contained Oz (Moz)	Tonnes (Mt)	Au (g/t)	Contained Ozs (Moz)
Haile
Horseshoe Underground	1.98	5.11	0.33	2.76	5.11	0.45	4.74	5.11	0.78	0.5	2.7	0.0
Palomino Underground	.	.	.	4.19	3.38	0.45	4.19	3.38	0.45	0.8	2.5	0.1
Ledbetter Underground	.	.	.	4.07	4.12	0.54	4.07	4.12	0.54	1.2	2.9	0.1
Open Pits	2.58	1.21	0.10	16.1	1.64	0.85	18.7	1.58	0.95	0.6	0.9	0.0
Haile Total	4.56	2.91	0.43	27.1	2.63	2.30	31.7	2.67	2.72	3.1	2.4	0.2
Silver	Measured			Indicated			Measured & Indicated			Inferred
	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)	Tonnes (Mt)	Ag (g/t)	Contained Ozs (Moz)
Haile
Horseshoe Underground	1.98	1.9	0.1	2.8	2.1	0.2	4.7	2.0	0.3	0.5	1.0	0.0
Palomino Underground	.	.	.	4.2	2.8	0.4	4.2	2.8	0.4	0.8	2.1	0.1
Ledbetter Underground	.	.	.	4.1	12	1.6	4.1	12	1.6	1.2	7.5	0.3
Open Pits	2.58	2.2	0.2	16 .1	2.5	1.3	18.7	2.5	1.5	0.6	2.4	0.0
Haile Total	4.56	2.0	0.3	27.1	4.0	3.5	31.7	3.7	3.8	3.1	4.0	0.4