OceanaGold Corporation (TSX: OGC) (NYSE: OGC) announces results from 16 new drill holes from the ongoing exploration and resource conversion program at Wharekirauponga, located approximately 10 kilometres north of the Company’s Waihi Operation in New Zealand.

The Company is also providing an update on the Waihi North Project, which continues to progress to plan, and on the evaluation of several value-enhancing technical studies which are expected to be included in the upcoming Waihi District technical report planned for release in January 2027. These include a potential processing plant expansion to 1.2 million tonnes per annum that would support the continuation of mining at the Martha Underground mine concurrent with mining the Wharekirauponga Underground mine once it is in production in 2032.

Figure 1: Wharekirauponga plan view of geology and drill traces highlighting the EG Vein zone, T-Stream Vein, and Western Veins, and drill platform locations.

Figure 2: Long section of the EG Vein with geology and new drill intercepts

Figure 3: Cross section 3 (looking NE) with drill results from the EG and EG FW Veins and EG Vein zone interpretation

Figure 4: Cross section 2 (looking NE) with drill results from the EG Vein and EG Vein interpretation

Figure 5: Cross section 1 (looking NE) with drill results from the EG and EG HW Veins and EG Vein zone interpretation

Wharekirauponga Drilling Highlights (estimated true width):

• 6.3 m @ 97.2 g/t Au from 481.5 m, East Graben Vein (WKP146C)
• 8.5 m @ 41.5 g/t Au from 399.0 m, EG Vein (WKP150)
• 9.6 m @ 18.5 g/t Au from 401.0 m, EG Hanging Wall Veins (WKP146A)
• 6.6 m @ 24.0 g/t Au from 403.4 m, incl. 1.2 m @ 107.7 g/t Au, EG HW Veins (WKP146C)
• 5.9 m @ 25.9 g/t Au from 485.6 m, EG Vein (WKP146B)
• 4.2 m @ 32.4 g/t Au from 602.9 m, EG Vein (WKP147A)

Gerard Bond, President and CEO of OceanaGold, said “Drill results from Wharekirauponga continue to demonstrate the exceptional grade and continuity of the EG Vein zone, and include some of the highest-grade intercepts reported to date. These results confirm further continuity and up-dip extension of the southern high-grade zone which currently lies outside of reported reserves, therefore representing outstanding conversion and growth potential. With five drill rigs now active and the Wharekirauponga orebody remaining open in multiple directions, we continue to accelerate drilling towards the southern end to further unlock value for shareholders at this phenomenal deposit.

“I am also excited about the upcoming Waihi District technical report. With the improved performance of the Martha Underground and good drilling results, we see the potential to extend the life of the Martha Underground and increase processing capacity from that assumed in our last technical report which would enable concurrent mining and processing of both Martha and Wharekirauponga ore, driving increased value for the Waihi District.”

Drill results can be viewed in 3D using VRIFY at the following link:
https://vrify.com/meetings/recordings/34562203-9dc1-4ccc-b36b-e8767be11a94

VRIFY note: Drill results reflect only those set forth in OceanaGold’s news release dated September 24, 2026, and do not include all historical results except those relevant to the current Wharekirauponga drill program.

Waihi North Project Development Update

Construction and underground tunnelling activities at the Waihi North Project continue to advance to plan. Decline development, which commenced in May 2026, has advanced approximately 350 metres to date. Construction of the first ventilation shaft has commenced, with a second jumbo expected to be added in the first half of 2027 to begin development of the twin tunnel toward the Wharekirauponga orebody. Bulk earthworks at the Willows Portal site continue, with water management related activities involving sedimentation ponds, haul roads, waste rock stack and magazine now completed, and the surface facilities area remaining on track for completion by year-end. The water treatment plant began staged commissioning in September 2026 and early works on the new tailings storage facility are expected to commence in the fourth quarter of this year.

Waihi District Technical Report

The Waihi District comprises the Company’s Waihi Operation, which includes the currently producing Martha Underground, and the Waihi North Project, which includes Wharekirauponga Underground.

An updated National Instrument 43-101 – Standards of Disclosure for Mineral Projects technical report on the Waihi District is planned for release in January 2027 and will include updated Mineral Reserves and Mineral Resources estimates.

The technical report is planned to include an updated mine plan for the Waihi District, incorporating the results of ongoing technical evaluations. These evaluations are assessing the potential to extend mining at MUG beyond 2033, in conjunction with the commencement of mining at WUG. To support this opportunity, the Company is also evaluating a potential processing plant expansion to increase throughput capacity up to 1.2 Mtpa from the 0.8 Mtpa contemplated in the previous technical report.

Wharekirauponga Drill Results

Drilling activity at Wharekirauponga has accelerated with the recent expansion of the fleet to five active rigs, and the construction of a new drill site (Drill Site 10), which is strategically positioned to better target the open southern high-grade zone.

Since the Company’s April 1, 2026 news release, a total of sixteen drill holes have been completed from five drill sites with results returned from the EG, HW and footwall Veins, collectively referred to as the “EG Vein zone” (Figure 1). Results both within the EG Vein and its HW structures continue to confirm continuity and quality of the southern high-grade zone. Importantly, this area remains unconstrained, with mineralization open along strike, up-dip and at depth, and significant scope remains to further grow the Mineral Resource through additional drilling.

East Graben Vein

Drilling on the EG Vein returned multiple wide, high-grade intercepts demonstrating the continuity of the system to the south (Figure 2). Results include 6.3 m @ 97.2 g/t Au (WKP146C) in the upper part of the vein, one of the highest-grade results returned to date. Nearby holes, including 5.9 m @ 25.9 g/t Au (WKP146B) and 4.2 m @ 32.4 g/t Au (WKP147A), also returned high-grade intercepts confirming the grade and continuity of the vein in this area. A further 110 m to the north, drill hole WKP150 returned 8.5 m @ 41.5 g/t Au, strengthening confidence in the continuity, thickness and grade of the EG Vein in this area.

Across the sixteen EG Vein intercepts reported, results continue to extend mineralization up-dip, demonstrating incremental growth of the southern high-grade zone (Figure 3, Figure 4).

This drilling supports the potential upgrade of a substantial portion of the southern high-grade zone from Inferred to Indicated Mineral Resources, underpinning an expected increase to Mineral Reserves in the Company’s 2026 year-end Mineral Resource and Mineral Reserve statement and in the upcoming NI 43-101 technical report.

Hanging Wall Veins

The HW Veins and associated sub-parallel structures that lie immediately west of the EG Vein also yielded strong results. Drilling of the HW Veins continues to demonstrate a broadening zone of mineralization, headlined by 9.6 m @ 18.5 g/t Au and 1.2 m @ 107.7 g/t Au (WKP146A and WKP146C, respectively) (Figure 5). Several holes, notably WKP146C, which returned three separate high-grade HW intercepts in addition to its EG Vein result, intersected multiple, closely stacked mineralized structures, pointing to a well-developed vein array in this part of the system. These results continue to highlight a zone of high-grade mineralization outside the current resource model, which remains a target for future growth.

Wharekirauponga 2026 Exploration Program

With five active drill rigs now operating at Wharekirauponga, drilling through the remainder of 2026 will focus on both resource conversion and growth-oriented step-out drilling along strike of the EG Vein, reflecting the substantial upside that remains in this open, unconstrained vein system.

Table 1: Wharekirauponga drill intersections subsequent to the news release dated April 1, 2026

For further information relating to drill hole data, please refer to the Company’s website at https://oceanagold.com/operations/additional-drillhole-data.

About OceanaGold

OceanaGold is a global intermediate gold and copper producer committed to safely and responsibly maximizing the generation of Free Cash Flow from our operations and delivering strong returns for our shareholders. We have a portfolio of four operating mines: the wholly-owned Haile Gold Mine in the United States of America; the wholly-owned Macraes and Waihi Operations in New Zealand; and the 80%-owned Didipio Mine in the Philippines.

Qualified Person Statement

The scientific and technical information in this news release relating to Mineral Reserves, mine planning, mine scheduling and mine development for the Waihi District, including the Martha Underground and Wharekirauponga Underground mines and the Waihi North Project, has been reviewed and approved by Mr. Euan Leslie, Chartered Professional Member of the Australasian Institute of Mining and Metallurgy, Group Mining Engineer for OceanaGold and an employee of the Company, a qualified person as defined by NI 43-101.

The scientific and technical information in this news release relating to exploration results, drilling, sampling, data verification, quality assurance and quality control, and Mineral Resources has been reviewed and approved by Mr. Leroy Crawford-Flett, Chartered Professional Member of the Australasian Institute of Mining and Metallurgy, Exploration & Geology Manager of the Waihi Operation and an employee of the Company, a qualified person as defined by NI 43-101. Mr. Crawford-Flett has verified the sampling, analytical and test data underlying the exploration information disclosed in this news release, including review of assay certificates and the performance of certified reference materials, blanks and duplicates against the Company’s QA/QC protocols, and the drillhole database. No limitations on that verification were identified other than the reduced core recovery in drill hole WKP146D described above.

Quality Assurance and Quality Control

All exploration samples are assayed for gold by 30g fire assay with Atomic Absorption Spectrometry finish. Since mid-2022, drill core sample intervals where visible electrum is logged are followed up by a subsequent screen fire assay after the routine 30g fire assay. Core samples were prepared and analyzed at the independent SGS Waihi NZ Ltd laboratory (Au by 30g fire assay and Ag by aqua regia digest and 0.3gm AAS finish. Samples post-April 2024 with Ag, As, Sb, Hg and S by ICP-MS after DIG12R Digest). Selected pulps are periodically sent to the independent ALS laboratory in Brisbane for a 4-acid digestion and 42 or 48 element Inductively Coupled Plasma geochemical analysis.

Quality of exploration assay results has been monitored in the following areas:

• Sample preparation at the independent SGS Waihi and Westport laboratories through sieving of jaw crush and pulp products; 
  
  
• Monitoring of assay precision through routine generation of duplicate samples from a second split of the jaw crush and calculation of the fundamental error; and
  
  
• Monitoring of accuracy of the primary SGS assay and ALS results through insertion of Certified Reference Materials and blanks into sample batches.

Blank, duplicate and CRM results are reviewed prior to uploading results in the acQuire database and again on a weekly basis. The QA/QC protocol at Waihi requires CRMs to be reported to within 2 standard deviations of the certified value, for preparation duplicates to have a relative difference (R-R1/mean RR1) of no greater than 10%, and for blanks to not exceed more than 5 times the lower detection value of the assay method. Failure in any of these thresholds triggers an investigation and, if appropriate, re-assay. Drill core is stored within secure facilities on site to which access is controlled. Site employees transport samples to the analytical laboratory which is also a secured facility. The SGS laboratory is an independent commercial geochemistry and energy assay laboratory with ISO 17025: 2017 accreditation, audited by an external consultant in 2020, and is inspected on a monthly basis by OceanaGold geologists. No sampling risks have been recorded during these visits.

Technical Report

For further information, please refer to the NI 43-101 technical report for the Waihi District available on the SEDAR+ website at www.sedarplus.ca under the Company’s profile or on the Company’s website at www.oceanagold.com titled “NI 43-101 Technical Report – Waihi District Study Pre-feasibility Study, New Zealand” dated December 11, 2024, with an effective date of June 30, 2024, prepared by D. Townsend, L Crawford-Flett, K. Hollis, E Leslie, and T. Maton (OceanaGold).