OceanaGold Studies 50% Waihi Plant Expansion After High-Grade Gold Results

OceanaGold is studying a 50% expansion of its Waihi processing plant in New Zealand after drilling at the Wharekirauponga project delivered some of the highest-grade results recorded to date, including an intersection grading 97.2 grams of gold per tonne.

The proposed expansion would increase processing capacity from 800,000 tonnes per year to 1.2 million tonnes, potentially allowing the existing Martha underground mine and Wharekirauponga to operate at the same time once the new mine begins production.

The expansion will be assessed as part of an updated Waihi District technical report expected in January.

OceanaGold President and CEO Gerard Bond said the latest drilling confirmed the continuity and up-dip extension of the southern high-grade zone, which currently sits outside the reported reserves.

The standout result came from hole WKP146C, which intersected 6.3 metres grading 97.2 grams of gold per tonne at the East Graben vein. Other results included 8.5 metres at 41.5 grams per tonne from WKP150 and 9.6 metres at 18.5 grams per tonne from WKP146A.

A further intersection from WKP146C returned 6.6 metres at 24 grams per tonne, including 1.2 metres grading 107.7 grams per tonne.

OceanaGold said the latest 16 holes continue to extend the southern high-grade zone up-dip, with mineralisation remaining open along strike and at depth. The company expects the drilling to support the conversion of a substantial portion of the zone from inferred to indicated resources and contribute to reserve growth in its year-end estimate.

Five drilling rigs are currently operating at Wharekirauponga, compared with three during the company’s previous drilling update in April.

The December 2025 resource estimate contained 2.63 million measured and indicated tonnes grading 17.3 grams of gold per tonne, representing 1.46 million ounces of contained gold. A further 2.9 million inferred tonnes graded 8.5 grams per tonne for 800,000 ounces.

Expanding Waihi

The proposed plant expansion would change the production sequence outlined in OceanaGold’s 2024 prefeasibility study, which assumed the 800,000-tonne-per-year plant would process ore primarily from Martha until 2033 before Wharekirauponga became the main source.

The earlier study outlined 1.6 million ounces of payable gold over a 15-year Waihi District mine life through 2038, with peak production of 253,000 ounces in 2035. Wharekirauponga was assigned an initial reserve of 4.1 million tonnes grading 9.2 grams per tonne for 1.2 million ounces of gold.

Running Martha for longer while Wharekirauponga ramps up could allow OceanaGold to use the expanded processing capacity more efficiently and potentially increase long-term production from the district.

Development work at Waihi North is already progressing. The underground decline, which began in May, has advanced about 350 metres, while construction of the first ventilation shaft is underway.

The company plans to add a second jumbo in the first half of next year to begin development of the twin tunnel towards Wharekirauponga. A water treatment plant entered staged commissioning this month, while preliminary work on a new tailings storage facility is scheduled for the fourth quarter.

Wharekirauponga is located about 10 km north of Waihi on New Zealand’s North Island. The 2024 development plan includes approximately 6.5 km of underground development to access the deposit.

OceanaGold is also pursuing the acquisition of Australian gold developer Ausgold, whose Katanning project would provide another potential growth asset. The transaction is targeted for completion in December.

Image:An expansion plan for the Waihi district is due in January. Credit: OceanaGold