2025 RGMP Implementation and Conformance Report

Responsible Gold Mining Principles Conformance Report

2025

OceanaGold recognizes the unique rights and interests of the Indigenous People and communities where we operate and the importance of maintaining their cultural values and heritage as described in the United Nations Declaration on the Rights of Indigenous Peoples. We conduct our business activities consistent with the principles of Free Prior and Informed Consent with effective and open engagement to enable informed decision making and due consideration of Indigenous People and community interests in our business activities.

OceanaGold Corporation's 2025 Responsible Gold Mining Principle (RGMP) Implementation and Conformance Report (this report) has been prepared for the Company and its subsidiaries (together referred to as "the Group"). Unless otherwise stated, references to "OceanaGold", "OGC", "the Company", "the Group", "we" and "our" in this report refer to OceanaGold Corporation and its subsidiaries.

This report summarizes how OceanaGold conformed with the requirements of the World Gold Council's (WGC) Responsible Gold Mining Principles ('RGMPs' or 'Principles') from January 1, 2025 to December 31, 2025.

For the purposes of this report, OceanaGold's organizational boundary includes the mining operations we own and control and our main corporate and administrative offices, during the reporting period.

OceanaGold's operating assets:

• Haile Gold Mine, our wholly owned open pit and underground operation located near Kershaw, South Carolina, United States ("Haile" or "Haile Gold Mine")

• Macraes Operation, our wholly owned open pit and underground operation located on the South Island, New Zealand ("Macraes" or the "Macraes Operation")

• Waihi Operation, our wholly owned underground operation which includes the Waihi North Project, located in the North Island, New Zealand ("Waihi" or the "Waihi Operation")

• Didipio Mine, our 80%-owned underground gold and copper mine and surface stockpile operation located in Luzon, Philippines ("Didipio" or "Didipio Mine")

  OceanaGold's corporate and administrative offices:

• Vancouver, British Columbia, Canada (head office)

• Brisbane, Queensland, Australia

• Melbourne, Victoria, Australia

• Manila, Philippines

• Dunedin, New Zealand

• Singapore

Unless otherwise stated, for the purpose of this report exploration properties through earn-in and partnership agreements with third parties have been excluded from the organizational boundary.

This report may contain statements that reflect the current beliefs and expectations of the Company about the future plans and results of the Company as of the respective dates indicated. These forward-looking statements are based

on a number of assumptions about the operations of the Company and factors beyond the control of the Company and are subject to significant risks and uncertainties, and, accordingly, actual results may differ materially from

these forward-looking statements contained in this report regarding past trends or activities should not be taken as a representation that such trends or activities will continue in the future. There is no obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise. You should not place undue reliance on forward-looking statements, which speak only as of the date of this report. The Company and its advisors have no obligation and do not undertake to revise

forward-looking statements contained in this report to reflect future events or circumstances.

This report does not contain all material information concerning the Company or its securities, particularly with respect to the risks and special considerations involved with an investment in any securities of the Company, and the information set forth in this report is subject to change

without notice. Certain data in this report was obtained from various external data sources, and the Company has not verified such data with independent sources. The Company is under no obligation to update or keep current the information contained herein.

The information contained in this report has been taken from sources deemed reliable by the Company. However, no representation or warranty (whether express or implied) is made as to the fairness, accuracy, completeness, or correctness of, and no reliance should be placed on, such information or opinions contained herein. None of the

Company, any of its advisors or any of its affiliates or any of its directors, officers, employees, advisers, or representatives shall have any liability whatsoever (for negligence or misrepresentation or in tort or under contract or otherwise) for any loss howsoever arising from any use of information presented in this report or otherwise arising in connection with this report.

We invite feedback on this report or any aspect of our sustainability performance via sustainability@oceanagold.com.

For enquiries, please visit the "Contact Us" section of our website at oceanagold.com

Front cover image: Team members from our Waihi Operation at a portal entrance to our Martha Underground Mine, New Zealand

OceanaGold 2025 Responsible Gold Mining Principles Conformance Report 2

OceanaGold Corporation is a global gold and copper producer head-quartered in Vancouver, Canada.

OceanaGold is a growing gold and copper producer with four producing mines. Our head office is in Vancouver (Canada), and we have support offices in Brisbane and Melbourne (Australia), Manila (Philippines), Singapore and Dunedin (New Zealand).

Didipio Mine

Luzon Island, Philippines

Waihi Operation

North Island, New Zealand

Macraes Operation

South Island, New Zealand

OceanaGold Head Office

Vancouver, Canada

Haile Gold Mine

South Carolina, U.S.A

OceanaGold 2025 Responsible Gold Mining Principles Conformance Report 3

We have a diversified portfolio of four operating mines: Haile Gold Mine in the U.S.A.; Macraes Operation and Waihi

Operation in New Zealand; and Didipio Mine in the Philippines. Our operations are supported by a global workforce of approximately 5,400 employees and contractors, with extensive experience in exploration, development and operations.

Our mines produce gold doré bars (containing both gold and silver). At our Didipio Mine in the Philippines, we also produce copper-gold in concentrate. Our gold doré is refined and cast into bars that meet the London Bullion Market Association Good Delivery Standard. Our gold is then sold to refineries

or financial institutions, including the Central bank of the Philippines.

OceanaGold is committed to implementing and conforming with the World Gold Council's Responsible Gold Mining Principles (RGMPs). These principles are embedded across our business operations. Each year, we commit to annually disclosing the status regarding of our RGMP conformance, including any instances of non-conformance and our efforts to address them. This transparency reflects our ongoing commitment to safe and responsible mining practices.

This RGMP Conformance Report outlines OceanaGold's performance in relation to the RGMPs for the year ending December 31, 2025. For this reporting period,

conformance with the RGMPs was independently assured by Pricewaterhouse Coopers (PwC). Further details can be found in Appendix A.

The Chief Sustainability Officer at OceanaGold is responsible for overseeing conformance with the RGMPs. This position reports directly to the Chief Executive Officer and provides regular updates on sustainability-related matters to the Board Sustainability Committee, ensuring robust oversight and governance of the Company's responsible mining initiatives.

Our Macraes Operation environment team for Korero Geckos during the Coronation North Lizard Relocation Project, New Zealand

We take a comprehensive, company-wide approach to embed safety and responsibility in our business. In 2025, we undertook the following measures to embed safe and responsible mining within our business activities; and reinforce our application of the RGMPs.

We refined, implemented, and maintained robust policies, systems, processes, and controls supported by our Responsible Mining Framework. These measures ensure consistent conformance with the RGMPs across our operations.

We disclosed information to help external stakeholders understand how we achieve conformance with the RGMPs. This included publishing our annual Sustainability Report, Modern Slavery Statement, performance data, and supporting information demonstrating responsible mining outcomes.

In accordance with the World Gold Council's Conflict-Free Gold Standard, OceanaGold prepared an annual Conflict-Free Gold Statement for the 2025 year of operation. This Statement substantiates our conformance with RGMP Principle 5: Human Rights and Conflict.

We obtained an independent assessment and limited assurance regarding our implementation and conformance with the RGMPs. This assessment also confirmed that our Conflict Free Gold Statement meets the requirements of RGMP Principle 5: Human Rights and Conflict (Appendix A).

Conformance Status Key: ● Conformant ● Partially conformant ● Non-conformant

To the best of our knowledge, and with reference to PwC's RGMP Independent Limited Assurance Assessment, in 2025, OceanaGold demonstrated overall conformance with the requirements of the World Gold Council's RGMPs, and their sub-principles.

In 2025, PwC conducted an evaluation of our ongoing implementation and adherence to the RGMPs. This assessment involved a comprehensive review of the integration of RGMPs within our Company-wide governance frameworks, including relevant policy documents, standards, and guidelines.

As part of the assurance process, PwC conducted a site verification at our Macraes Operation in New Zealand, to confirm that the RGMPs are effectively applied in practice at the operational level.

In addition to the Macraes site visit, supplementary conformance testing was undertaken for all remaining mining operations. This was completed in accordance with the World Gold Council's "Guidance on Implementing and Assuring the RGMPs", ensuring a consistent approach to the verifying of the implementation and conformance with the RGMPs across all sites.

PwC's Independent Assurance Report is presented in Appendix A.

To: Directors of OceanaGold Corporation

In accordance with the terms of engagement letter dated 5 September 2025 and its subsequent addendum dated 27 October 2025, we were engaged by OceanaGold Corporation ("OceanaGold") to perform an independent limited assurance engagement in respect of the identified Subject Matter Information (the "Subject Matter Information") for OceanaGold for the period ended 31 December 2025 (the "Period"). The criteria (the "Criteria") against which we assessed the Subject Matter Information is as follows:

The Responsible Party is responsible for the Subject Matter Information and for the preparation of the Subject Matter Information in accordance with the Criteria.

PricewaterhouseCoopers, ABN 52 780 433 757

2 Riverside Quay, SOUTHBANK VIC 3006,

GPO Box 1331 MELBOURNE VIC 3001

T: +61 3 8603 1000, F: +61 3 8603 1999, https://www.pwc.com.au

pwc.com.au

Liability limited by a scheme approved under Professional Standards Legislation.

We have complied with the ethical requirements of the International Ethics Standard Board for Accountants' (IESBA) International Code of Ethics for Professional Accountants (including International Independence Standards) (IESBA Code) issued by the International Ethics Standards Board for Accountants relevant to assurance engagements, which are founded on fundamental principles of integrity, objectivity, professional competence and due care, confidentiality and professional behaviour.

Our firm applies International Standard on Quality Management ISQM 1, Quality Management for Firms that Perform Audits or Reviews of Financial Statements, or Other Assurance or Related Services Engagements, which requires the firm to design, implement and operate a system of quality management including policies or procedures regarding compliance with ethical requirements, professional standards and applicable legal and regulatory requirements.

Our responsibility is to express a limited assurance conclusion based on the procedures we have performed and the evidence we have obtained.

Our engagement has been conducted in accordance with the International Standard on Assurance Engagements (ISAE) Revised Assurance Engagements Other Than Audits or Reviews of Historical Financial Information (ISAE 3000R). That standard requires that we plan and perform this engagement to obtain limited assurance about whether anything has come to our attention to indicate that the Subject Matter Information has not been prepared, in all material respects, in accordance with the Criteria, for the Period. The procedures we performed were based on our professional judgement and included:

• made inquiries of the persons responsible for the Subject Matter Information;

• obtained an understanding of the process for collecting and reporting the Subject Matter Information;

• obtained and evaluated a selection of information supporting OceanaGold's assertion regarding its conformance with the Responsible Gold Mining Principles;

• performed a site visit to the Macraes Mine; and

• considered the disclosure and presentation of the Subject Matter Information.

The procedures performed in a limited assurance engagement vary in nature and timing from, and are less in extent than for, a reasonable assurance engagement and consequently the level of assurance obtained in a limited assurance engagement is substantially lower than the assurance that would have

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been obtained had a reasonable assurance engagement been performed. Accordingly, we do not express a reasonable assurance opinion.

We believe that the evidence we have obtained is sufficient and appropriate to provide a basis for our conclusion.

This report was prepared for the Directors of OceanaGold for the purpose of providing limited assurance on the Subject Matter Information, using criteria designed for this purpose. We disclaim any assumption of responsibility for any reliance on this report to any persons or users other than the Directors of OceanaGold, or for any purpose other than that for which it was prepared.

Because of the inherent limitations of any unavoidable risk that work planned and executed during our engagement may not detect a fraud, error or non-compliance with laws and regulations, particularly where there has been concealment through collusion, forgery and other illegal acts, it is possible that fraud, error or non-compliance may occur and not be detected. A limited assurance engagement is not designed to detect all instances of non-compliance of the Subject Matter Information with the Criteria, as it is limited primarily to making enquiries, of the responsible party, and applying analytical procedures.

Additionally, non-financial data may be subject to more inherent limitations than financial data, given both its nature and the methods used for determining, calculating and estimating such data. The precision of different measurement techniques may also vary. The absence of a significant body of established practice on which to draw to evaluate and measure non-financial information allows for different, but acceptable, evaluation and measurement techniques that can affect comparability between entities and over time.

The limited assurance conclusion expressed in this report has been formed on the above basis.

Based on the procedures performed and evidence obtained, nothing has come to our attention that causes us to believe that the Subject Matter Information has not been prepared, in all material respects, in accordance with the Criteria for the period ended 31 December 2025.

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PricewaterhouseCoopers

Scott Thompson Melbourne

Partner 28 April 2026

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OceanaGold Corporation

Suite 1020 - 400 Burrard Street Vancouver, British Columbia V6C 3A6

Canada

+1 604 678 4123

For further information: sustainability@oceanagold.com

oceanagold.com

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