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VANCOUVER, BC, Sept. 11, 2025 /PRNewswire/ - OceanaGold Corporation (TSX: OGC) (OTCQX: OCANF) ("OceanaGold" or the "Company") is pleased to announce positive results from its exploration and resource conversion drilling programs at the Haile Gold Mine ("Haile") in the United States.

Gerard Bond, President and CEO of OceanaGold, said "With a record high exploration budget of $10 million at Haile this year, we are delighted by the excellent return on investment we continue to generate through exploration. These exciting results continue to demonstrate the continuity of high-grade mineralization at several deposits across the property, notably at Ledbetter Phase 4, Horseshoe Underground, and the promising new early-stage Pisces and Clydesdale targets. The exploration success continues to highlight the exceptional upside for low-risk organic growth we have within our existing portfolio of assets."

Drilling Highlights (core length):

Ledbetter Phase 4 (conversion drilling)

• 28.9 m @ 18.33 g/t Au (DDH1279)
• 8.7 m @ 22.30 g/t Au (DDH1281)

Horseshoe (conversion drilling)

• 16.1 m @ 16.33 g/t Au (UGD0082)
• 14.6 m @ 10.33 g/t Au (UGD0084)
• 24.0 m @ 7.99 g/t Au (UGD0085)
• 22.0 m @ 8.60 g/t Au (UGD0086)
• 10.2 m @ 11.12 g/t Au (UGD0084)

Pisces (Initial drilling, located 300 m south of Horseshoe)

• 7.6 m @ 10.39 g/t Au (DDH1271)
• 6.6 m @ 3.34 g/t Au (DDH1290)

Clydesdale(initial drilling, located 100 m northwest of Palomino)

• 26.2 m @ 4.11 g/t Au (DDH1282)

Results can be viewed in 3D using VRIFY at the following link:

https://vrify.com/meetings/recordings/c880f1e8-449e-41a1-916c-125c8df72661

VRIFY note: Drill results reflect only those set forth in OceanaGold's press release dated September 11, 2025, and do not include all historical drill results except those relevant to the current targets in this release.

Ledbetter Phase 4 – High-Grade Results Targeting Underground Resource Conversion

Mineralization in Ledbetter Phase 4 is located within the current final phase of the open pit Mineral Reserve (Figure 1). An ongoing resource conversion drill program is enhancing resource confidence and providing samples for metallurgical testing in support of the current trade-off study for the evaluation of a potential underground mine at Ledbetter, which has potential for improved overall site economics.

A zone of mineralization, down-dip of Ledbetter Phase 4 extension, has been tested with a total of four holes, or 1,975 metres ("m"). The program has returned results with strong mineralized intersections: 28.9 m @ 18.33 g/t Au from 489.1 mincluding1.3 m @ 189.22 g/t (DDH1279), and 8.7 m @ 22.30 g/t Au from 375.9 mincluding5.0 m @ 35.86 g/t (DDH1281).

Horseshoe Underground – Support for Additional Resource Growth

At Horseshoe Underground, drilling continues on both resource conversion and definition programs, totalling 7,467 m from 24 holes since the February 2025 news release. Conversion drilling totalling 4,261 m in 14 holes has targeted Inferred Mineral Resources in the lower levels of the deposit. Notable intercepts include: 16.1 m @ 16.33 g/t Au from 274.3 m (UGD0082) and 14.6 m @ 10.33 g/t from 235.6 m (UGD0084), 24.0 m @ 7.99 g/t from 258.6 m (UGD0085) and 22.0 m @ 8.60 g/t from 259.3 m (UGD0086); the latter three holes extending high-grade mineralization to the southwest.

Definition drilling totalling 10 holes for 3,206 m has targeted step-out opportunities, primarily south and west of the current resource. Assay results for nine holes have been received with the following significant intercepts: 7.6 m @ 3.63 g/t Au from 271.0 m and 9.1 m @ 3.40 g/t Au from 299.9 m (UGD0097) and 5.0 m @ 5.64 g/t Au from 267.9 m (UGD0100). The definition drill program is ongoing with 2,600 m remaining to be drilled in 2025. These results demonstrate the potential for continued resource growth, and drilling will remain focused on further defining step-out targets to support future underground development.

Pisces – Initial Drilling of High-Grade Target

The Pisces target is located along the prospective corridor between the Horseshoe and Palomino deposits at approximately 550 m below surface and close to existing and planned underground infrastructure.

A total of nine holes for 6,167 m has been drilled in 2025, with the testing of geological and grade continuity. Significant intercepts include: 7.6 m @ 10.39 g/t Au from 647.0 m (DDH1271), 6.8 m @ 2.60 g/t Au from 571.0 m (DDH1285) and 6.6 m @ 3.34 g/t Au (DDH1290), demonstrating continuity of mineralization in the eastern area of the target towards Horseshoe. See the VRIFY link for visual representation of the results.

In conjunction with previously reported results, 44.2 m @ 10.85 g/t Au from 591 m (DDH1267), 9.4 m @ 44.14 g/t Au from 686.1 m (DDH1269) and 42.7 m @ 6.07 g/t Au from 560.2 m (DDH1257), (released February 24, 2025), the highest-grade mineralization defines a 150 m strike length. This zone of higher-grade mineralization remains to be further tested, while the target remains open to the northeast towards Horseshoe and down-dip.

Clydesdale – Successful Early-Stage Result

The early-stage Clydesdale drill target is located 100 m northwest of Palomino and approximately 300 m stratigraphically lower at approximately 800 m below surface. The target is defined by anomalous gold grades in wall rock metasediments, anomalous pathfinder geochemistry, and alteration mineralogy (Table 2). A total of two holes totalling 1,600 m have been drilled in 2025 to test the target. Initial results have returned one significant intercept of 26.2 m @ 4.11 g/t Au from 780.7 m including 14.6 m @ 6.21 g/t Au (DDH1282). See the VRIFY link for visual representation of the results.

Follow-up drilling is ongoing with two additional holes to be completed by the end of the year for a total of 1,800 m.

Notes:

• Intervals are core length, not true width.
  "Initial Drilling" intercepts are associated with early-stage exploration drilling, "Definition" drilling intercepts are intercepts outside the current resource model shell directed at defining mineralization to an Inferred Resource category and "Conversion" drilling are intercepts converting Inferred Resources to Indicated Resources category. NSR = No Significant Result.

Table 2: Historical and OGC Haile drill intersections relevant to the Ledbetter 04, Pisces, and Clydesdale target areas.
Hole ID	From (m)	To (m)	Interval (m)	Au (g/t)	Target	Activity
DDH0436	NSR				Ledbetter 04	Initial Drilling
DDH0439	NSR				Ledbetter 04	Initial Drilling
DDH0450	NSR				Ledbetter 04	Initial Drilling
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