Lowry reserves extend Black Butte copper mine: economics and design notes for engineers
Reviewed by Joe Ashwell

First reported on MINING.com
30 Second Briefing
Lowry’s inclusion in Sandfire Resources America’s Black Butte copper project in Montana extends planned mine life from eight to 12 years, lifting probable reserves to 14.3 million tonnes at 2.6% copper (370,000 tonnes contained) across the Lowry and Johnny Lee deposits. The updated PFS, using mechanised long-hole stoping at Lowry to cut unit operating costs by US$2.28 to US$68.30 per tonne, projects average output of 31,000 tonnes copper per year, US$3.3 billion in revenue and US$476 million post-tax cash flow at US$4.70/lb. Copper. Despite this, after-tax NPV (8%) is only US$126 million with a 13.3% IRR on US$474 million initial capex.
Technical Brief
- Johnny Lee’s probable reserve is 9.5 Mt at 2.9% Cu, containing ~270,000 t copper.
- Johnny Lee mine, processing plant and associated infrastructure already hold state and federal permits.
- Study does not yet clarify whether incorporating Lowry will trigger permit amendments or new approvals.
- Mechanised long-hole stoping at Lowry is the key lever for reducing unit operating costs.
- Updated PFS increases post-tax cash flow by 34% relative to the 2025 economic study.
- Sandfire Resources America’s market capitalisation is about C$204.6 million at a share price of C$0.20.
Our Take
Within our 282 copper-tagged pieces, most US projects are either large porphyry developments or brownfield expansions, so a relatively high-grade underground project in Montana like Black Butte offers diversification for investors tracking US copper exposure beyond the usual Arizona–Nevada–Utah cluster.
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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