Sandfire Resources (ASX:SFR) issued an updated pre-feasibility study (PFS) for its Black Butte Copper Project in Montana, outlining a substantially larger development with an extended mine life and enhanced project scale, according to an Australian bourse filing on Thursday after market hours.

The study reports a maiden ore reserve for the Lowry deposit of 4.7 million tonnes grading 2.1% copper, containing 100,000 tonnes of copper, alongside a 255% increase in the Lowry mineral resource to 31.5 million tonnes grading 1.3% copper, containing 400,000 tonnes of copper, per the filing.

Additionally, Black Butte's total ore reserves increased by 49% to 14.3 million tonnes grading 2.6% copper, containing 370,000 tonnes of copper, extending the planned mine life by about 50% to 12 years, the filing said.

The project is expected to produce 35,000 tonnes per annum of contained copper in its first four years, averaging 31,000 tonnes per annum over the initial mine life, with Johnny Lee fully permitted and Lowry advancing through approvals.

The PFS is based on a long-term copper price of $4.70 per pound, with initial capital expenditure estimated at around $474 million, life-of-mine sustaining capital of $180 million, an 88% metallurgical recovery rate, and a C1 cash cost of $2.68 per pound of payable copper, the filing added.