Underreported Antimony Could Boost Bulla Park Project Economics

Reassessing Antimony Grades at Bulla Park

West Cobar Metals Limited (ASX – WC1) has announced a significant update to the understanding of antimony grades at its Bulla Park copper-antimony-silver deposit in New South Wales. A recent re-analysis of selected drill core samples using a peroxide-fusion digest method revealed that previous assay results, which employed a four-acid digest technique, had under-reported antimony concentrations by an average of 14%, with some samples showing increases as high as 62%.

The four-acid digest method, while effective for copper analysis, is known to potentially volatilise certain elements like antimony during digestion, leading to underestimation. The peroxide fusion digest method, by contrast, provides a more complete assay of antimony content, prompting West Cobar to pilot this re-analysis on 19 mineralised samples from 2023 and 2024 drill holes.

Implications for Resource and Project Economics

This upward revision in antimony grades is particularly timely given the metal's rising global demand and price, which is approaching USD 60,000 per tonne. Managing Director Matt Szwedzicki highlighted that the findings suggest the Bulla Park deposit may contain more antimony than previously estimated, potentially improving the project's economic outlook.

Currently, Bulla Park holds an inferred mineral resource of 20 million tonnes grading 0.30% copper, 0.10% antimony, and 4.7 grams per tonne silver. The company also estimates an exploration target ranging from 30 to 50 million tonnes with similar grades. The re-assay results could lead to an upward revision of these figures once the full dataset is analysed.

Next Steps – Comprehensive Re-analysis and Drilling

West Cobar is moving swiftly to re-analyse all available mineralised intersections at Bulla Park using the peroxide fusion method to confirm the extent of under-reporting. Additionally, the company plans to undertake approximately 5,000 metres of diamond drilling starting early 2026 to test and potentially expand the resource base.

Metallurgical testwork to date has demonstrated strong recoveries of copper (94.6%), antimony (82.6%), and silver (84.1%), supporting the deposit's commercial viability. Further testwork is expected to enhance these recoveries, bolstering the project's attractiveness.

Strategic Positioning and Market Context

Located 110 kilometres west of the Cobar mining hub, Bulla Park benefits from established infrastructure, which could facilitate future development. The deposit's stratabound and fault-controlled mineralisation style has attracted interest from major players in the past, including BHP and Sandfire, underscoring its potential.

West Cobar's proactive approach to refining assay techniques and expanding exploration efforts reflects a broader industry trend of leveraging improved technologies to unlock hidden value in known deposits. Investors will be watching closely as the company updates its resource estimates and advances towards development decisions.