OceanaGold Corporation (TSX: OGC) (NYSE: OGC) is pleased to announce high-grade results from its ongoing exploration and resource conversion drilling program at the Haile Gold Mine in the United States.

Drilling Highlights (core length):

Horseshoe Underground (conversion and extension drilling):

• 15.5 m @ 30.64 g/t Au (UGD0121)
• 30.5 m @ 13.86 g/t Au (UGD0113)
• 22.5 m @ 13.42 g/t Au (UGD0122)
• 18.4 m @ 9.62 g/t Au (UGD0119)
• 21.9 m @ 6.48 g/t Au including 3.7 m @ 23.55 g/t Au (UGD0120)
• 26.3 m @ 3.41 g/t Au and 44.3 m @ 3.72 g/t Au (UGD0107)

Ledbetter Underground (conversion drilling):

• 27.9 m @ 8.60 g/t Au (DDH1313)
• 27.9 m @ 4.16 g/t Au (DDH1319)
• 18.4 m @ 3.68 g/t Au (DDH1317)
• 13.0 m @ 2.25 g/t Au and 17.1 m @ 8.20 g/t Au (DDH1283)
• 2.6 m @ 9.63 g/t Au and 3.3 m @ 40.45 g/t Au (DDH1315)

Clydesdale (initial drilling):

• 14.5 m @ 15.81 g/t Au including 4.5 m @ 41.6 g/t Au (DDH1305)

Gerard Bond, President and CEO of OceanaGold, said “Our ongoing exploration success at Haile continues to demonstrate our ability to add tremendous value through the drill bit. At Horseshoe, recent drilling points to reserve growth potential near existing infrastructure, with mineralization still open in multiple directions. Results from Ledbetter are strengthening confidence in down-plunge resource conversion, and a new significant high-grade intercept at Clydesdale confirms its potential as an emerging target area. As development of the Palomino decline progresses, we look forward to advancing these opportunities with further drilling from underground in the near term.”

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

https://vrify.com/meetings/recordings/3777660f-584a-43cb-82cc-c8fc9e773b08

VRIFY note: Drill results reflect only those set forth in OceanaGold’s press release dated May 12, 2026, and do not include all historical drill results except those relevant to the current targets in this release.

Horseshoe Underground

The Horseshoe Underground has defined Mineral Reserves (see news release dated February 18, 2026) as well as three discrete zones of mineralization to the southwest (Horseshoe extensions), known as the upper (surface to 900mRL), middle (900mRl to 730mRL) and lower (below 730mRL) zones. Notably, all three of these zones are near both existing and planned underground development infrastructure. Success from the 2025 exploration program added Inferred Mineral Resources to the upper zone for the first time, while also expanding the Inferred Mineral Resources in the middle and lower zones. On the main Horseshoe orebody, the 2025 resource estimate resulted in conversion of Inferred to Indicated Mineral Resources in the lower mineralized zones. The 2026 drill program focuses on both resource conversion and extension of the main Horseshoe orebody and the three zones at Horseshoe extensions.

At Horseshoe extensions (Figure 1), drilling totalling 14 holes for 4,372 m has targeted both conversion and extension opportunities. In the upper zone, the results of two holes – 15.5 m @ 30.64 g/t Au (UGD0121) and 18.4 m @ 9.62 g/t Au (UGD0119), confirm the continuity of the mineralization. Results from two extension holes in the upper zone – 21.9 m @ 6.48 g/t Au including 3.7 m @ 23.55 g/t Au (UGD0120) and 22.5 m @ 13.42 g/t Au (UGD0122), support expansion of the known mineralization in the area (Figure 2).

Significant results between the middle and lower zones include 25.8 m @ 3.63 g/t Au (UGD0126) and 16.4 m @ 4.11 g/t Au (UGD0104), extending known mineralization to the west (Figure 2). Extensional drilling at the bottom of the lower zone returned 26.3 m @ 3.41 g/t Au and 44.3 m @ 3.72 g/t (UGD0107), adding mineralization at depth outside of the known resource. The lower zone remains open in multiple directions with additional follow-up drilling planned in this area (Figure 2).

Since the last resource estimate, conversion drilling totalling 1,258 m in 4 holes has continued to target conversion of Inferred Mineral Resources in the lower levels of the main Horseshoe orebody (Figure 2). Notable intercepts include: 12.2 m @ 24.14 g/t Au (UGD0112); and 30.5 m @ 13.86 g/t Au (UGD0113). These results are in-line with the resource model and are expected to be included the next reserve update.

Ledbetter Underground

The Company announced in February 2026 a change in the mining method for the final pit phase of Ledbetter to an underground mining mine. This has expanded the exploration opportunity at Ledbetter, as mineralization outside the prior pit shell is now potentially economic.

In 2025, the Company began a drill program targeting known mineralization with the goal of converting Inferred Mineral Resources and increasing confidence down plunge of the existing reserve in an area referred to as Lobe 3. Eight holes have been drilled since the Company’s news release dated September 11, 2025, with new drilling totalling 4,306 m. The highlight of the Ledbetter drilling is 27.9 m @ 4.16 g/t Au (DDH1319) in Lobe 3, which has infilled a gap in known resources, demonstrating continuity of high-grade mineralization. To the northeast, holes DDH1315 and DDH1317 targeted the conversion of Inferred Mineral Resources and returned higher grades than the model predicted, including a result of 18.44 m @ 3.68 g/t Au (DDH1317) (Figure 3).

Advanced Drilling Targets – Clydesdale & Pisces

The Clydesdale target is located 100 m northwest of Palomino and approximately 300 m stratigraphically lower at approximately 800 m below surface. Drilling continues at Clydesdale with early-stage exploration results now reporting a second mineralized intercept showing good width and grade of 14.5 m @ 15.81 g/t Au (DDH1305) (refer to VRIFY). The Company has now defined two mineralized intercepts in this area (DDH1282, 6.2 m @ 4.11 g/t Au, previously reported), with additional drilling ongoing to further define the potential of this new mineralized zone.

The Pisces target is located along the corridor between the Horseshoe and Palomino deposits at approximately 550 m below surface and close to existing and planned underground infrastructure. Drilling at Pisces is ongoing, with ~6,500 m planned. The work is focused on further understanding the distribution of the high-grade mineralization in the area.

2026 Exploration Program

There are approximately 34,500 m of drilling planned at Haile for 2026 from both surface and underground. Drilling will continue to focus on resource conversion at Horseshoe Underground, including targeting expansions of the upper, middle and lower zones to the southwest. At Ledbetter Underground, drilling will continue to infill and test extensions to Lobe 3. Clydesdale and Pisces drilling will also continue from surface through the year, with the ability to accelerate the program once the Palomino decline is in place, providing access to new drill locations at shorter distances. Results from recent drilling and ongoing refinement of the geologic model have resulted in a better understanding on the structural controls on mineralization, allowing for the systematic generation of targets to be explored in the coming years.

Table 1: Haile drill intersections subsequent to the news release dated September 11, 2025, results update.

*Notes: Intervals are down hole core length, true widths have not been determined. “Initial Drilling” intercepts are associated with early-stage exploration drilling, “Extension” drilling intercepts are intercepts outside the current resource model shell directed at defining mineralization to an Inferred Mineral Resource category and “Conversion” drilling intercepts are intercepts converting Inferred Mineral Resources to Indicated Mineral Resources category. NSR = No Significant Result.

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.