Alkane Resources Grows Costerfield Reserve 13% to 170 koz Au, Extends to 2032
Key Takeaways
- Alkane Resources grew Costerfield's total gold Ore Reserves to 170 koz Au (+13.3%) and antimony to 15.0 kt Sb (+40.2%) as at 30 June 2026, net of 61 koz Au and 2.0 kt Sb mined during FY26.
- The mine life has extended from 5 to 6 years, with the life-of-mine plan now scheduled through to October 2032, directly supporting forward revenue visibility and capital planning.
- Reserve growth was driven by four near-mine lode systems — Brunswick South, Kendal, Cuffley, and Augusta — all accessible via existing underground infrastructure, keeping development costs low.
- Historical RC drilling data from 1994–1996 at the upper Kendal system has been formally validated and incorporated into the resource model for the first time, unlocking additional inventory without new drilling expenditure.
- Economic viability of the reserves has been confirmed at US$3,100/oz Au and US$22,000/t Sb — assumptions that are conservative relative to recent spot prices, particularly for antimony given ongoing geopolitical supply dynamics.
Alkane Resources grows Costerfield Ore Reserves to 170 koz Au and extends mine life to 2032
Alkane Resources has released its FY26 Mineral Resource and Ore Reserve update for the Costerfield Gold-Antimony Mine, effective 30 June 2026. Total Ore Reserves grew to 170 koz Au (up 13.3%) and 15.0 kt Sb (up 40.2%), both net of substantial production depletion of 61 koz Au and 2.0 kt Sb mined during FY26. The demonstrated mine life has increased from 5 to 6 years, with the life-of-mine plan now scheduled to October 2032. The Resource and Reserve estimates were independently verified by SRK Consulting.
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FY26 resource and reserve highlights
Key figures from the FY26 update as at 30 June 2026:
- Total Ore Reserves (Proved + Probable): 960 kt at 5.5 g/t Au and 1.6% Sb = 170 koz Au, 15.0 kt Sb
- Measured + Indicated Mineral Resources: 1,993 kt at 6.0 g/t Au and 2.1% Sb = 387 koz Au, 42.0 kt Sb
- Inferred Mineral Resources: 969 kt at 3.6 g/t Au and 1.3% Sb = 111 koz Au, 12.9 kt Sb
- Mine life: Demonstrated 6 years as at 30 June 2026, scheduled to October 2032
- Reserve growth drivers: Brunswick South, Kendal, Cuffley, and Augusta exploration and grade control in FY26, plus updated gold price assumptions
Year-on-year reserve comparison
The table below compares FY25 and FY26 Proved and Probable Ore Reserve totals, sourced from Table 4 of the technical report.
| Period | Tonnage (kt) | Gold grade (g/t) | Sb grade (%) | Contained Au (koz) | Contained Sb (kt) |
|---|---|---|---|---|---|
| FY25 Total (Proved + Probable) | 537.1 | 8.7 | 2.0 | 149.5 | 10.7 |
| FY26 Total (Proved + Probable) | 960 | 5.5 | 1.6 | 170 | 15.0 |
| Change | +422.9 kt | -3.2 g/t | -0.4% | +20.5 koz (+13.3%) | +4.3 kt (+40.2%) |
The lower grade profile in FY26 (5.5 g/t vs 8.7 g/t Au in FY25) reflects a volume-driven growth story. Significant new Probable material from Brunswick South and Kendal has been added at wider mining widths, substantially increasing total tonnes. The contained metal has grown despite depletion, which is the meaningful outcome for investors: this is not grade compression, it is a larger resource base.
What is a JORC Ore Reserve and why does this update matter?
An Ore Reserve is the subset of a Mineral Resource that has been demonstrated to be economically extractable under defined conditions. In plain terms, it is the material that can actually be scheduled for mining and included in production planning. Resources, by contrast, are estimates of mineralisation that may or may not be economically viable — they require further work before they can underpin a mine schedule.
The JORC Code (2012) requires that Ore Reserves be signed off by an independent Competent Person. In this case, SRK Consulting reviewed and took responsibility for both the Mineral Resource and Ore Reserve estimates, independent of Alkane.
What makes this update particularly meaningful is the net-of-depletion framing. Alkane mined 61 koz Au and 2.0 kt Sb during FY26 and still grew its gold reserve by 13.3%. That means near-mine exploration more than replaced every ounce extracted from the ground during the year, and then added more on top. That is not a common outcome for a producing mine.
The mine life extension from 5 to 6 years, with production now scheduled to October 2032, translates directly into forward revenue visibility. A longer mine schedule supports capital planning, workforce stability, and investor confidence in the continuity of the operation.
The antimony reserve growth is also worth noting. The 40.2% increase in Sb to 15.0 kt is relevant given the geopolitical backdrop: China’s introduction of antimony export restrictions in 2024 contributed to significant price volatility, with the Fastmarkets Rotterdam antimony price exceeding US$60,000/t during mid-2025, before declining to approximately US$20,000/t by mid-2026 as export restrictions partially eased.
What is driving reserve growth at Costerfield?
The primary differences between FY25 and FY26 reserves are additions in Brunswick South and Kendal, with notable contributions also from Cuffley and Augusta, partially offset by depletion in Youle and Shepherd.
New zones adding ounces
Four lode systems are the key contributors to FY26 reserve growth. Brunswick South and Kendal account for the bulk of the new Probable material, while Cuffley and Augusta have added incremental ounces through exploration and grade control work completed during FY26. The breakdown by lode from Table 6 of the technical report (excluding surface stockpiles) is as follows:
- Cuffley: 187 kt, 41 koz Au, 3.9 kt Sb
- Brunswick South: 171 kt, 35 koz Au, 1.8 kt Sb
- Kendal: 173 kt, 16 koz Au, 3.5 kt Sb
- Augusta: 74 kt, 12 koz Au, 2.2 kt Sb
These are near-mine discoveries, not step-out exploration. The lodes sit within the existing operational footprint at Costerfield, which means they can be accessed and mined using infrastructure already in place.
Upper Kendal: a newly validated resource
Historical reverse circulation (RC) drilling completed between 1994 and 1996 — targeting the upper Kendal system across the 522, 540, 541, and 542 veins — has been evaluated, validated, and incorporated into the Costerfield Mineral Resource Estimate for the first time in this update.
This is not new drilling. It is previously un-included historical data, now formally validated and included in the resource model. The upper Kendal system sits above the modern Youle and Shepherd mining area and represents additional inventory that systematic archival work has now unlocked.
Selected intercepts from the upper Kendal historical RC program (Appendix 2, Table 1) include:
- BD139: 0.71 m at 49.6 g/t Au and 0.15% Sb (540 vein)
- BD182: 0.41 m at 32.8 g/t Au and 6.38% Sb (540 vein)
- BD190: 1.55 m at 1.41 g/t Au and 5.72% Sb (540 vein, composite)
The validation involved compiling all available historical records, cross-checking downhole sample intervals and assay certificates against original paper logs, and testing interpretations with 2026 diamond drilling. Only RC samples meeting approved sample-weight and analytical-method criteria were included in the estimate.
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Alkane’s Costerfield operation: a snapshot for investors
Costerfield has been in continuous operation since 2006, with multiple lode systems feeding ore to the Brunswick Processing Plant, a conventional flotation concentrator with a current capacity of approximately 150,000 tpa.
Alkane is a multi-asset gold and antimony producer with three operating mines: Tomingley in New South Wales, Costerfield in Victoria, and Björkdal in Sweden.
Key context for investors evaluating this reserve update:
- All environmental approvals and permits are in place for the existing Costerfield operation and the full life-of-mine plan
- Economic viability of the Proved and Probable Ore Reserves has been confirmed at commodity prices of US$3,100/oz Au and US$22,000/t Sb, with the economic analysis indicating a robust net present value at a 5% discount rate
- Those price assumptions are conservative relative to prevailing spot and recent market conditions, particularly for antimony given the geopolitical supply backdrop discussed above
- The Ore Reserve is priced at US$3,100/oz Au and US$22,000/t Sb, while the Rotterdam antimony price has traded significantly higher in recent periods before partially retracing
The reserve update demonstrates that Costerfield’s exploration programme is generating real mine life extension, replacing mined ounces and growing the asset’s forward production profile from an already-producing base.
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