NI 43-101 Technical Report Macraes Gold Mine Otago, New Zealand

Effective Date: December 31, 2023

Report Date: March 28, 2024

Report Prepared for

OceanaGold Corporation

Suite 1020, 400 Burrard Street

Vancouver, British Columbia V6C 3A6 Canada

Report Prepared by:

OceanaGold (New Zealand) Limited

Golden Point Road

RD3

Macraes Flat 9483 East Otago

New Zealand

Signed by Qualified Persons:

Matthew Grant, PhD Applied Geology, MAIG, MAusIMM (OceanaGold Senior Geologist - Resource Development)

Jonathan Moore, BSc (Hons) Geology, MAusIMM CP (Geo), (OceanaGold Group Manager Resource Development)

Knowell Madambi, BSc Eng (Hons) Mining, MAusIMM CP (Min) (OceanaGold Manager - Technical Services & Projects)

Euan Leslie BEng Mining, BCom Economics, MAusIMM CP (Min) (OceanaGold Group Mining Engineer) David Carr, BEng (Hons) Metallurgical, MAusIMM CP (Met) Metallurgy (OceanaGold Group Manager Metallurgy)

Reviewed by:

Knowell Madambi, BSc Eng (Hons) Mining, MAusIMM CP (Min) (OceanaGold Manager - Technical Services & Projects)

TECHNICAL REPORT CERTIFICATION

The effective date of this Technical Report is December 31, 2023

Matthew Grant

Date:

March 28, 2024

Euan Leslie

Date:

March 28, 2024

Knowell Madambi

Date:

March 28, 2024

Jonathan Moore

Date:

March 28, 2024

David Carr

Date:

March 28, 2024

Forward-Looking Information

This report contains forward-looking statements. All statements, other than statements of historical fact regarding OceanaGold Corporation or Macraes Operations, are forward- looking statements. The words "believe", "expect", "anticipate", "contemplate", "target", "plan", "intend", "project", "continue", "budget", "estimate", "potential", "may", "will", "can", "could" and similar expressions identify forward-looking statements. In particular, this report contains forward-looking statements with respect to cash flow forecasts, projected capital, operating and exploration expenditure, targeted cost reductions, mine life and production rates, potential mineralisation and metal or mineral recoveries, and information pertaining to potential improvements to financial and operating performance and mine life at the Macraes Operations that may result from. All forward-looking statements in this report are necessarily based on opinions and estimates made as of the date such statements are made and are subject to important risk factors and uncertainties, many of which cannot be controlled or predicted. Material assumptions regarding forward-looking statements are discussed in this report, where applicable. In addition to such assumptions, the forward-looking statements are inherently subject to significant business, economic and competitive uncertainties, and contingencies. Known and unknown factors could cause actual results to differ materially from those projected in the forward-looking statements. Such factors include, but are not limited to: fluctuations in the spot and forward price of commodities (including gold, diesel fuel, natural gas and electricity); the speculative nature of mineral exploration and development; changes in mineral production performance, exploitation and exploration successes; risks associated with the fact that the Macraes Operations is still in the early stages of evaluation and additional engineering and other analysis is required to fully assess their impact; diminishing quantities or grades of reserves; increased costs, delays, suspensions, and technical challenges associated with the construction of capital projects; operating or technical difficulties in connection with mining or development activities, including disruptions in the maintenance or provision of required infrastructure and information technology systems; damage to OceanaGold Corporation's or Macraes Operations reputation due to the actual or perceived occurrence of any number of events, including negative publicity with respect to the handling of environmental matters or dealings with community groups, whether true or not; risk of loss due to acts of war, terrorism, sabotage and civil disturbances; uncertainty whether the Macraes Operation's will meet OceanaGold

Corporation's capital allocation objectives; the impact of global liquidity and credit availability on the timing of cash flows and the values of assets and liabilities based on projected future cash flows; the impact of inflation; fluctuations in the currency markets; changes in interest rates; changes in national and local government legislation, taxation, controls or regulations and/or changes in the administration of laws, policies and practices, expropriation or nationalisation of property and political or economic developments in Canada; failure to comply with environmental and health and safety laws and regulations; timing of receipt of, or failure to comply with, necessary permits and approvals; litigation; contests over title to properties or over access to water, power and other required infrastructure; increased costs and physical risks including extreme weather events and resource shortages, related to climate change; and availability and increased costs associated with mining inputs and labour. In addition, there are risks and hazards associated with the business of mineral exploration, development, and mining, including environmental hazards, industrial accidents, unusual or unexpected formations, pressures, cave-ins, flooding and gold bullion, copper cathode or gold or copper concentrate losses (and the risk of inadequate insurance, or inability to obtain insurance, to cover these risks).

Many of these uncertainties and contingencies can affect OceanaGold Corporation's actual results and could cause actual results to differ materially from those expressed or implied in any forward- looking statements made by, or on behalf of, OceanaGold Corporation. All of the forward-looking statements made in this report are qualified by these cautionary statements and OceanaGold Corporation and the Qualified Persons whoauthored this report undertake no obligation to update publicly or otherwise revise any forward‐looking statements whether as a result of new information or future events or otherwise, except as may be required by law.

Table of Contents

  • 1 Summary ................................................................................................................ 19

  • 1.1 Overview ............................................................................................................................................... 19

  • 1.2 Property Description and Ownership .................................................................................................... 19

  • 1.3 Geology and Mineralisation .................................................................................................................. 20

  • 1.4 Drilling and Sampling ............................................................................................................................ 21

  • 1.5 Exploration ............................................................................................................................................ 22

  • 1.6 Mineral Processing and Metallurgical Testing ...................................................................................... 22

  • 1.7 Mineral Resource Estimate ................................................................................................................... 22

  • 1.8 Mineral Reserve Estimate ..................................................................................................................... 24

  • 1.9 Mining Methods .................................................................................................................................... 24

  • 1.10 Infrastructure ......................................................................................................................................... 27

  • 1.11 Environmental Studies and Permitting ................................................................................................. 27

  • 1.12 Capital and Operating Costs ................................................................................................................. 27

  • 1.13 Conclusions .......................................................................................................................................... 30

  • 1.14 Recommendations ................................................................................................................................ 30

  • 2 Introduction ............................................................................................................ 32

  • 2.1 Terms of Reference and Purpose of the Report ................................................................................... 32

  • 2.1.1 Purpose of the Report ....................................................................................................................... 32

  • 2.1.2 Reporting Standards ......................................................................................................................... 32

  • 2.2 Authors of the Report ............................................................................................................................ 32

  • 2.3 Qualifications and Experience of Qualified Persons ............................................................................ 32

  • 2.4 Site Inspections .................................................................................................................................... 33

  • 2.5 Sources of Information .......................................................................................................................... 33

  • 2.6 Effective Date ....................................................................................................................................... 33

  • 2.7 Units of Measure ................................................................................................................................... 34

  • 3 Reliance on Other Experts .................................................................................... 35

  • 3.1 General ................................................................................................................................................. 35

  • 4 Property Description and Location ...................................................................... 36

  • 4.1 Property Location .................................................................................................................................. 36

  • 4.2 Ownership ............................................................................................................................................. 37

  • 4.3 Mineral Titles ........................................................................................................................................ 39

  • 4.4 Nature and Extent of Title ..................................................................................................................... 39

  • 4.5 Location of Mineral Resources ............................................................................................................. 40

  • 4.6 Royalties, Agreements and Encumbrances ......................................................................................... 41

  • 4.7 Environmental Permitting & Compliance .............................................................................................. 41

4.7.1

Overview ........................................................................................................................................... 41

4.7.2

Access Arrangements ....................................................................................................................... 44

4.7.3

Compliance ....................................................................................................................................... 44

5

Accessibility, Climate, Local Resources, Infrastructure and Physiography .... 45

5.1

Accessibility .......................................................................................................................................... 45

5.2

Physiography ........................................................................................................................................ 45

5.3

Climate .................................................................................................................................................. 45

5.4

Land Resources and Infrastructure ...................................................................................................... 45

5.4.1

Sufficiency of Surface Rights ............................................................................................................ 45

5.4.2

Power ................................................................................................................................................ 46

5.4.3

Water ................................................................................................................................................ 46

5.4.4

Communications ............................................................................................................................... 46

5.4.5

Mining Infrastructure ......................................................................................................................... 46

5.4.6

Labour ............................................................................................................................................... 46

6

History .................................................................................................................... 47

6.1

Historic Mining ...................................................................................................................................... 47

6.2

Prior Ownership .................................................................................................................................... 48

6.3

Previous Work pre-1990 ....................................................................................................................... 48

6.3.1

Geochemistry .................................................................................................................................... 48

6.3.2

Geophysics ....................................................................................................................................... 49

6.3.3

Drilling ............................................................................................................................................... 50

6.4

Historical Estimates .............................................................................................................................. 50

6.5

Previous Production .............................................................................................................................. 50

7

Geological Setting and Mineralisation ................................................................. 51

7.1

General ................................................................................................................................................. 51

7.2

Regional Geology ................................................................................................................................. 51

7.3

Local Geology ....................................................................................................................................... 52

7.4

Mineralisation ........................................................................................................................................ 53

7.4.1

Mineralised Zones ............................................................................................................................ 53

7.4.2

Mineralisation Types ......................................................................................................................... 56

7.5

Deposit Geology ................................................................................................................................... 57

8

Deposit Type .......................................................................................................... 58

8.1

General ................................................................................................................................................. 58

9

Exploration ............................................................................................................. 59

9.1

General ................................................................................................................................................. 59

9.2

Geology ................................................................................................................................................. 59

9.2.1

Geological Mapping .......................................................................................................................... 59

  • 9.3 Geophysics ........................................................................................................................................... 59

  • 9.4 Geochemistry ........................................................................................................................................ 61

  • 9.4.1 Stream Sediment Sampling .............................................................................................................. 61

  • 9.4.2 Soil Sampling .................................................................................................................................... 62

  • 9.5 Trenching .............................................................................................................................................. 64

  • 9.6 Remote Sensing ................................................................................................................................... 64

  • 9.7 Aerial Photography ............................................................................................................................... 64

  • 9.8 Exploration Statement .......................................................................................................................... 64

  • 10 Drilling .................................................................................................................... 65

  • 10.1 Summary ............................................................................................................................................... 65

  • 10.2 Historical Drilling ................................................................................................................................... 68

  • 10.3 OceanaGold Drilling .............................................................................................................................. 69

  • 10.4 Surveys ................................................................................................................................................. 71

  • 10.4.1 Magnetic to Macraes Grid Conversion ............................................................................................. 71

  • 10.5 Logging Procedures .............................................................................................................................. 72

  • 10.6 Drilling Orientation ................................................................................................................................ 73

  • 10.7 Sampling Methods and Approach ........................................................................................................ 74

  • 10.7.1 Introduction ....................................................................................................................................... 74

  • 10.7.2 RC Percussion Sampling .................................................................................................................. 74

  • 10.7.3 Diamond Core Sampling ................................................................................................................... 75

  • 10.7.4 Aircore Sampling .............................................................................................................................. 76

  • 10.7.5 Sonic Core Sampling ........................................................................................................................ 76

  • 10.8 Sample Quality ..................................................................................................................................... 76

  • 10.8.1 Summary ........................................................................................................................................... 76

  • 10.8.2 Sample Recovery ............................................................................................................................. 77

  • 10.8.3 RC Wet Sample Bias ........................................................................................................................ 77

  • 10.9 Definition of Sample Intervals ............................................................................................................... 77

  • 10.10 Summary of Mineralised Widths ....................................................................................................... 77

  • 11 Sample Preparation, Analysis and Security ........................................................ 78

  • 11.1 Sample Preparation Statement ............................................................................................................. 78

  • 11.2 Sample Preparation, Assay and Analytical Procedures ....................................................................... 78

  • 11.2.1 Graysons/AMDEL Limited ................................................................................................................ 78

  • 11.2.2 SGS New Zealand Limited ............................................................................................................... 78

  • 11.2.3 ALS Minerals Laboratory, Australia .................................................................................................. 79

  • 11.2.4 SGS NZ Limited 2013 Onwards ....................................................................................................... 79

11.2.5

Historical Analyses ........................................................................................................................... 80

  • 11.3 OceanaGold Tungsten Analyses .......................................................................................................... 81

  • 11.3.1 Introduction ....................................................................................................................................... 81

  • 11.3.2 QA/QC Studies for the Use of pXRF Analysers for Tungsten Analysis ............................................ 82

  • 11.3.3 Data Checking of Historical Assays .................................................................................................. 83

  • 11.4 Sample Security .................................................................................................................................... 83

  • 11.4.1 On-site sample preparation .............................................................................................................. 83

  • 11.4.2 Off-site sample preparation .............................................................................................................. 83

  • 11.5 Sample Analysis ................................................................................................................................... 84

  • 11.6 Quality Assurance/Quality Control Procedures .................................................................................... 84

  • 11.6.1 Standards .......................................................................................................................................... 84

  • 11.6.2 Blanks ............................................................................................................................................... 84

  • 11.6.3 Duplicates ......................................................................................................................................... 84

  • 11.6.4 Core and Sample Storage ................................................................................................................ 84

  • 11.6.5 Actions .............................................................................................................................................. 85

  • 11.7 Opinion on Adequacy of Sample Preparation, Analysis and Security .................................................. 85

  • 12 Data Verification .................................................................................................... 86

  • 12.1 Introduction ........................................................................................................................................... 86

  • 12.2 Drill Hole Database ............................................................................................................................... 86

  • 12.2.1 Historical Data .................................................................................................................................. 86

  • 12.2.2 Recent Data ...................................................................................................................................... 86

  • 12.3 Comparison of Wet RC Percussion Drilling .......................................................................................... 86

  • 12.4 Analysis of Assay Quality Control Data ................................................................................................ 87

  • 12.4.1 Blanks ............................................................................................................................................... 87

  • 12.4.2 Standards .......................................................................................................................................... 88

  • 12.4.3 Duplicates - SGS Macraes ............................................................................................................... 89

  • 12.5 Summary ............................................................................................................................................... 91

  • 13 Mineral Processing and Metallurgical Testing .................................................... 93

  • 13.1 Introduction ........................................................................................................................................... 93

  • 13.2 Throughput ............................................................................................................................................ 93

  • 13.3 Mass Pull .............................................................................................................................................. 93

  • 13.4 Flotation Tails Gold Grade .................................................................................................................... 93

  • 13.5 CIL Recoveries ..................................................................................................................................... 93

  • 13.6 Flotation Recovery ................................................................................................................................ 94

  • 13.7 Overall Recovery .................................................................................................................................. 95

  • 13.8 Future Ore Testing ................................................................................................................................ 95

10

  • 13.9 Golden Point Underground Testing ...................................................................................................... 96

  • 13.10 Innes Mills ......................................................................................................................................... 97

  • 13.11 Super Low Grade testwork ............................................................................................................... 98

  • 13.12 Issues ................................................................................................................................................ 99

  • 14 Mineral Resource Estimate ................................................................................. 101

  • 14.1 Introduction ......................................................................................................................................... 101

  • 14.2 Qualified Persons Responsible for Resource Estimates .................................................................... 101

  • 14.3 Open Pit Mineral Resource Estimate ................................................................................................. 101

  • 14.3.1 Drillhole Database .......................................................................................................................... 101

  • 14.3.2 Software Used ................................................................................................................................ 101

  • 14.3.3 Geologic Model Methodology ......................................................................................................... 101

  • 14.3.4 Assay Capping and Compositing ................................................................................................... 102

  • 14.3.5 Density ............................................................................................................................................ 102

  • 14.3.6 Variogram Analysis and Modelling ................................................................................................. 102

  • 14.3.7 Block Model .................................................................................................................................... 103

  • 14.3.8 Estimation Methodology ................................................................................................................. 103

  • 14.3.9 Model Validation ............................................................................................................................. 103

  • 14.3.10 Resource Classification .............................................................................................................. 104

  • 14.3.11 Resource Estimate Tonnes and Grade ...................................................................................... 104

  • 14.3.12 Nunns .......................................................................................................................................... 105

  • 14.3.13 Coronation North ........................................................................................................................ 105

  • 14.3.14 Coronation .................................................................................................................................. 107

  • 14.3.15 Deepdell ...................................................................................................................................... 109

  • 14.3.16 Round Hill/Golden Point Open Pit .............................................................................................. 110

  • 14.3.17 Innes Mills ................................................................................................................................... 110

  • 14.3.18 Frasers - Gay Tan ...................................................................................................................... 111

  • 14.3.19 Ounce ......................................................................................................................................... 113

  • 14.3.20 Relevant Factors ......................................................................................................................... 115

  • 14.3.21 Golden Bar .................................................................................................................................. 115

  • 14.3.22 Taylors ........................................................................................................................................ 118

  • 14.3.23 Stoneburn Group ........................................................................................................................ 119

  • 14.4 Underground Mineral Resource Estimate .......................................................................................... 122

  • 14.4.1 Drillhole Database .......................................................................................................................... 122

  • 14.4.2 Software Used ................................................................................................................................ 122

  • 14.4.3 Geologic Modelling ......................................................................................................................... 122

  • 14.4.4 Assay Capping and Compositing ................................................................................................... 122

  • 14.4.5 Density ............................................................................................................................................ 123

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OceanaGold Corporation published this content on 28 March 2024 and is solely responsible for the information contained therein. Distributed by Public, unedited and unaltered, on 28 March 2024 05:25:08 UTC.