Monday 20 July 2026
A new deposit 400 metres south of the previously mined Brunswick vein at Costerfield in central Victoria is connecting deep gold mineralisation to historical surface workings, with bonanza-grade gold and significant antimony across the same structure. Alkane Resources (ASX: ALK) has drilled 91 diamond holes since October 2025, defining Brunswick South as a continuous high-grade gold-antimony system sitting 200 metres from existing underground access. Capital development commences Q3 2026.
The results reframe what Costerfield looks like as a producing asset: not a single-metal underground gold operation winding down, but a dual-commodity producer with a newly defined ore source and a strategic metal that the world is paying increasing attention to.
The result in context
Brunswick South delivers high-grade gold with co-product antimony across a narrow-vein structure characteristic of the Victorian goldfields: structurally controlled, steeply dipping, and vertically persistent. The headline intercepts span the upper portion of the structure and the deeper Kiwi zone below.
BD468: 50.1 g/t Au, 26.2% Sb over 2.17m (ETW 1.08m)
BD433: 109.9 g/t Au, 3.1% Sb over 0.65m (ETW 0.62m)
BD424: 50.2 g/t Au, 33.3% Sb over 0.86m (ETW 0.62m)
BD408: 39.8 g/t Au, 0.7% Sb over 1.3m (ETW 1.15m)
BD513 (Kiwi zone): 25 g/t Au, 0% Sb over 1.7m (ETW 1.64m)
BD496: 21.6 g/t Au, 6.7% Sb over 1.65m (ETW 0.92m)
The estimated true widths are narrow, as expected for Victorian orogenic gold-antimony veining. What matters here is the grade, the vertical extent, and the connection between the Kiwi zone at depth and the historical surface workings above. Ninety-one holes is a substantial infill and extension programme, and the grade continuity across that density of drilling supports confidence in the geological model.
The geology
Costerfield sits within the Bendigo Zone of the Lachlan Fold Belt, one of the most productive gold provinces in Australian mining history. The mineralisation style is mesothermal orogenic gold hosted in quartz-antimony veins within folded and faulted Ordovician sediments. The operation has been producing since 2006, working a series of narrow high-grade veins underground.
Brunswick South adds a new dimension to the system. The upper portions of the structure carry bonanza-grade gold with significant antimony, with BD468 returning 26.2% antimony alongside 50.1 g/t gold. The deeper Kiwi zone transitions to gold-dominant mineralisation with negligible antimony. That vertical metal zonation, gold-antimony upper and gold-only deeper, has direct implications for mine planning. It means different ore types feeding different processing and revenue streams from the same access infrastructure.
The geological interpretation indicates the Kiwi zone's mineralisation setting is similar to the Youle deposit currently being mined, suggesting the deposit's style and behaviour at depth are well understood from existing operational experience.
Project trajectory
Alkane has flagged capital development toward Brunswick South commencing in Q3 2026. The proximity to existing underground access, just 200 metres from planned development, means Brunswick South can be brought online without extensive new decline or shaft infrastructure. That is a material advantage for a mid-cap producer: the capital required to access a new ore source is a fraction of what a greenfields development would demand.
An updated mineral resource estimate with an initial ore reserve is expected later in 2026. Parallel veining intercepted approximately 200 metres west of the main Brunswick South structure is earmarked for follow-up drilling, suggesting the deposit's boundaries are not yet fully defined.
What this means for the sector
The antimony component of Brunswick South carries strategic weight that was less relevant five years ago. Antimony is now classified as a critical mineral across multiple jurisdictions, including Australia, the US, and the EU. China's export controls on antimony, tightened in 2025, have compressed global supply chains and elevated the value of domestic Western production. A producing Australian operation with defined gold-antimony ore reserves sits in a different commercial conversation than a pure gold play.
For Costerfield specifically, the dual-commodity endowment transforms the revenue model. Gold provides the price exposure the market understands. Antimony provides the strategic premium and potential offtake interest from defence and energy storage supply chains that pure gold operations cannot access.
This kind of geological and commercial complexity requires experienced underground geologists, core loggers, and structural geologists who understand narrow-vein mining environments. At Norwest Exploration and Mining Services, we deploy contract specialists into active underground programmes across Australia, matched to the geology and the operational requirements of each site.
Gold gets you started. Gold and antimony from the same underground structure, with depth continuity and development capital approved: that gets you into a conversation most single-commodity projects never reach.