OGC.TO · 2025-09-11 12:00:00

OceanaGold Announces Ongoing Exploration Success at Haile (VANCOUVER, BC ) OceanaGold Corporation (TSX: OGC ) (OTCQX: OCANF) ("OceanaGold" or the "Company") is pleased to announce positive results from its exploration and resource conversion drilling

Exploration Programs

www.oceanagold.com

September 11, 2025 News Release

OceanaGold Announces Ongoing Exploration Success at Haile

(VANCOUVER, BC ) 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)

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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 test ing 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 m including 1.3 m @ 189.22 g/t (DDH1279), and 8.7 m @ 22.30 g/t Au from

375.9 m including 5.0 m @ 35.86 g/t (DDH1281).

Figure 1: Schematic cross section (looking northeast) showing Ledbetter mineralization with recent drill holes annotated.

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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 2 2.0 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.

Figure 2: Schematic long section (looking northwest) showing Horseshoe mineralization with recent significant intercepts

annotated.

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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 (DD H1257), (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.

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Figure 3: Plan map showing 2025 drillhole locations

Table 1: Haile drill intersections subsequent to the February 24, 2025, drill results update.

Hole ID From

(m)

Interval

(m)

(g/t) Target Activity

DDH1278 NSR Ledbetter 04 Conversion

DDH1279 489.1 519.2 28.9 18.33 Ledbetter 04 Conversion

Including 505.5 506.8 1.3 189.22 Ledbetter 04 Conversion

DDW1280 NSR Ledbetter 04 Conversion

DDH1281 375.9 384.5 8.7 22.30 Ledbetter 04 Conversion

Including 375.9 380.9 5.0 35.86 Ledbetter 04 Conversion

UGD0079 197.2 206.4 9.1 2.49 Horseshoe Conversion

And 275.5 276.9 1.4 12.14 Horseshoe Conversion

UGD0080 207.6 213.5 5.9 3.56 Horseshoe Conversion

UGD0081 NSR Horseshoe Conversion

UGD0082 274.3 290.3 16.1 16.33 Horseshoe Conversion

UGD0083 NSR Horseshoe Conversion

UGD0084 235.6 250.2 14.6 10.33 Horseshoe Conversion

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Including 244.8 247.8 3.1 37.14 Horseshoe Conversion

And 263.0 273.3 10.2 11.12 Horseshoe Conversion

UGD0085 258.6 282.6 24.0 7.99 Horseshoe Conversion

UGD0086 259.3 281.3 22.0 8.60 Horseshoe Conversion

UGD0088 238.6 247.8 9.2 1.97 Horseshoe Conversion

UGD0089 217.2 231.7 14.5 2.46 Horseshoe Conversion

And 236.0 243.8 7.8 9.24 Horseshoe Conversion

Including 242.7 243.4 0.7 42.60 Horseshoe Conversion

UGD0090 NSR Horseshoe Conversion

UGD0091 NSR Horseshoe Conversion

UGD0092 NSR Horseshoe Conversion

UGD0093 NSR Horseshoe Conversion

UGD0094 NSR Horseshoe Definition

UGD0095 NSR Horseshoe Definition

UGD0096 NSR Horseshoe Definition

UGD0097 271.0 278.6 7.6 3.63 Horseshoe Definition

And 299.9 309.1 9.1 3.40 Horseshoe Definition

UGD0098 NSR Horseshoe Definition

UGD0099 NSR Horseshoe Definition

UGD0100 267.9 272.9 5.0 5.64 Horseshoe Definition

UGD0101 NSR Horseshoe Definition

UGD0102 NSR Horseshoe Definition

UGD0103 NSR Horseshoe Definition

DDH1271 647.0 654.6 7.6 10.39 Pisces Initial Drilling

DDH1272 551.4 563.6 12.2 0.26 Pisces Initial Drilling

DDH1274 607.5 609.0 1.5 3.21 Pisces Initial Drilling

DDH1277 599.4 600.8 1.4 1.02 Pisces Initial Drilling

DDH1285 522.3 529.8 7.5 1.79 Pisces Initial Drilling

And 571.0 577.8 6.8 2.60 Pisces Initial Drilling

DDH1286 627.7 632.0 4.3 0.57 Pisces Initial Drilling

DDH1290 642.4 648.9 6.6 3.34 Pisces Initial Drilling

DDH1293 536.2 543.4 7.2 2.56 Pisces Initial Drilling

UGD0109 413.0 431.3 18.3 0.22 Pisces Initial Drilling

DDH1276 400.5 406.6 6.1 2.30 Clydesdale Initial Drilling

DDH1282 768.6 772.4 3.8 5.27 Clydesdale Initial Drilling

DDH1282 780.7 806.9 26.2 4.11 Clydesdale Initial Drilling

Including 792.2 806.9 14.6 6.21 Clydesdale Initial Drilling

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.

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Table 2: Historical and OGC Haile drill intersections relevant to the Ledbetter 04, Pisces, and Clydesdale target areas.

Hole ID From

(m)

Interval

(m)

(g/t) Target Activity

DDH0436 NSR Ledbetter 04 Initial Drilling

DDH0439 NSR Ledbetter 04 Initial Drilling

DDH0450 NSR Ledbetter 04 Initial Drilling

DDH0451 NSR Ledbetter 04 Initial Drilling

DDH0461 NSR Ledbetter 04 Initial Drilling

DDH0632^ NSR Ledbetter 04 Initial Drilling

DDH0638^ 469.2 478.9 9.8 2.42 Ledbetter 04 Initial Drilling

DDH0646^ NSR Ledbetter 04 Initial Drilling

DDH0653^* 465.8 478.1 12.3 1.82 Ledbetter 04 Initial Drilling

DDH0686^ NSR Ledbetter 04 Initial Drilling

DDH0841^ 401.4 407.5 6.1 3.81 Ledbetter 04 Initial Drilling

DDH1201^ NSR Ledbetter 04 Advanced Drilling

DDH1207^ NSR Ledbetter 04 Advanced Drilling

DDH1208^ NSR Ledbetter 04 Advanced Drilling

DDH1213^ 468.3 481.8 13.5 2.95 Ledbetter 04 Advanced Drilling

DDH1252^ NSR Ledbetter 04 Conversion

DDH1253^ NSR Ledbetter 04 Conversion

DDH1255^ 431.9 443.8 11.9 2.88 Ledbetter 04 Conversion

DDH1256^ 431.5 438.2 6.7 2.63 Ledbetter 04 Conversion

DDH1260^ NSR Ledbetter 04 Conversion

RC2002 NSR Ledbetter 04 Initial Drilling

RC2019 NSR Ledbetter 04 Initial Drilling

RC2058 441.9 461.8 19.8 5.27 Ledbetter 04 Initial Drilling

RC2064 NSR Ledbetter 04 Initial Drilling

RC2067 NSR Ledbetter 04 Initial Drilling

RC2108 NSR Ledbetter 04 Initial Drilling

RCT0050 NSR Ledbetter 04 Initial Drilling

RCT0067 NSR Ledbetter 04 Initial Drilling

RCT0068 NSR Ledbetter 04 Initial Drilling

RCT0088 NSR Ledbetter 04 Initial Drilling

RCT0134 432.8 445.0 12.2 2.16 Ledbetter 04 Initial Drilling

RCT0149 NSR Ledbetter 04 Initial Drilling

RCT0161 428.5 441.9 13.5 42.40 Ledbetter 04 Initial Drilling

Including 429.8 431.3 1.5 318.52 Ledbetter 04 Initial Drilling

RCT0167 410.7 441.9 31.2 4.85 Ledbetter 04 Initial Drilling

RCT0203 NSR Ledbetter 04 Initial Drilling

RCT0204 438.9 445.0 6.1 4.51 Ledbetter 04 Initial Drilling

DDH0599^ NSR Pisces Initial Drilling

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DDH0636^ 545.4 550.9 5.5 2.81 Pisces Initial Drilling

And 597.9 611.6 13.7 2.31 Pisces Initial Drilling

DDH1067^ NSR Pisces Initial Drilling

DDH1204^ NSR Pisces Initial Drilling

DDH1245^ NSR Pisces Initial Drilling

DDH1247^** NSR Pisces Initial Drilling

RCT0012 356.6 358.1 1.5 9.10 Pisces Initial Drilling

And 399.3 413.0 13.7 3.24 Pisces Initial Drilling

RCT0028 NSR Pisces Initial Drilling

RCT0077 NSR Pisces Initial Drilling

RCT0080 144.8 152.4 7.6 2.21 Pisces Initial Drilling

And 193.6 202.7 9.1 3.89 Pisces Initial Drilling

And 251.8 262.1 10.4 4.31 Pisces Initial Drilling

RCT0091 528.8 538.0 9.1 5.61 Pisces Initial Drilling

RCT0146 NSR Pisces Initial Drilling

DDH1177^ 527.7 535.2 7.5 3.65 Palomino Initial Drilling

RCT0051 510.5 521.4 10.9 1.65 Clydesdale Initial Drilling

And 634.0 649.8 15.9 1.90 Clydesdale Initial Drilling

And 713.2 725.4 12.2 3.16 Clydesdale Initial Drilling

RCT0110 269.8 281.9 12.2 1.89 Clydesdale Initial Drilling

And 507.2 511.9 4.7 3.33 Clydesdale Initial Drilling

And 526.8 538.0 11.2 3.41 Clydesdale Initial Drilling

And 774.2 780.3 6.1 3.39 Clydesdale Initial Drilling

And 823.0 827.5 4.6 5.36 Clydesdale Initial Drilling

RCT0117 502.9 509.0 6.1 2.22 Clydesdale Initial Drilling

And 600.5 614.2 13.7 3.35 Clydesdale Initial Drilling

And 641.6 649.2 7.6 1.66 Clydesdale Initial Drilling

And 688.9 693.4 4.6 4.70 Clydesdale Initial Drilling

RCT0118 519.6 527.3 7.7 2.37 Clydesdale Initial Drilling

Notes:

• Intervals are core length, not true width.

• “Initial Drilling” intercepts are associated with early-stage exploration drilling, while “ Conversion” drilling are

intercepts converting Inferred Resources to Indicated Resources category. NSR = No Significant Result. All data,

apart from holes marked “^”represent historical drilling conducted by Romarco Minerals prior to OceanaGold’s

ownership of Haile

• “^” represents OceanaGold holes.

• “*” represents drill hole results reported by OceanaGold in its press release dated November 8, 2017.

• “**” represents drill hole results reported by OceanaGold in its press release dated February 24, 2025.

• All historical drill data collected by Romarco Minerals are considered historical in nature and based on prior data

and reports prepared by Romarco Minerals. A qualified person from the Company has not undertaken independent

investigation of the sampling nor has it independently analyzed the results of the historical drilling to verify the

results. OceanaGold is not treating the historical data as current. There can be no assurance that any of the

historical drill data is representative.

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