OceanaGold Waihi expansion: design, throughput and tailings notes for engineers
Reviewed by Joe Ashwell

First reported on MINING.com
30 Second Briefing
OceanaGold is weighing a 50% expansion of its Waihi plant to 1.2 Mt/y after Wharekirauponga drilling returned standout intercepts including 6.3 m at 97.2 g/t Au from 481.5 m in the East Graben vein and 8.5 m at 41.5 g/t from 399 m. The move would enable concurrent feed from Martha Underground and Wharekirauponga post‑2032, building on a 2024 plan outlining 1.6 Moz over 15 years and an initial 4.1 Mt reserve at 9.2 g/t. Underground development is advancing, with the Waihi North decline now 350 m, first vent shaft under construction, staged commissioning of a new water treatment plant, and early works on a new tailings storage facility due in Q4.
Technical Brief
- Standout WKP146C hit: 6.3 m @ 97.2 g/t Au from 481.5 m in East Graben vein.
- Additional WKP146C interval: 6.6 m @ 24 g/t from 403.4 m, including 1.2 m @ 107.7 g/t.
- WKP150 returned 8.5 m @ 41.5 g/t from 399 m; WKP146A cut 9.6 m @ 18.5 g/t from 401 m.
- Five drill rigs now operating at Wharekirauponga, up from three in April, accelerating resource conversion drilling.
- December 2025 resource: 2.63 Mt M&I @ 17.3 g/t (1.46 Moz) plus 2.9 Mt inferred @ 8.5 g/t (0.8 Moz).
- Waihi North decline, started May, has advanced ~350 m; first ventilation shaft construction underway.
- About 6.5 km of underground development is planned to connect Waihi North decline to Wharekirauponga, ~10 km north.
- Water treatment plant is in staged commissioning; early works for a new tailings storage facility scheduled Q4, with Willows portal surface facilities due by year-end.
Our Take
With Waihi plant throughput planned at 1.2 Mt/y and Didipio in the Philippines already moving from 1.7 Mt/y to 2.5 Mt/y underground, our coverage suggests OceanaGold is systematically scaling processing and underground capacity across its portfolio rather than relying on a single flagship mine.
Earlier work on mine fleet electrification at Waihi North in OceanaGold’s 2025 Sustainability Report means the 6.5 km of underground development to Wharekirauponga is likely to be an early test bed for lower-emission haulage and ventilation strategies compared with legacy operations such as Martha Underground.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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