Capstone approves Mantoverde pyrite plant

Canada’s Capstone Copper has approved a $45 million pyrite recovery project at its Mantoverde copper operation in Chile that will cut the mine’s sulphuric acid consumption by around 90,000 t/y, the company said in its second-quarter results on 30 July. The Board of Directors approved the Mantoverde Pyrite Augmentation (MVPA) project in July, with formal sanctioning expected in the third quarter of 2026 subject to approval from Mantoverde’s joint venture partner. The project is expected to be completed in early 2028.

MVPA will incorporate a pyrite recovery circuit into the existing Mantoverde concentrator plant. Pyrite (iron sulphide) will be recovered and concentrated from the tailings stream, then conditioned and transferred to the existing heap leach process. Based on 10 million t/y of oxide ore leaching at Mantoverde’s heap leach facility, the project is expected to reduce sulphuric acid requirements by approximately 20% — an average of 90,000 t/y of sulphuric acid — while also increasing cathode copper production by an average of about 3,500 t/y. At an assumed CFR Chile sulphuric acid price of $200 to $450 per tonne, Capstone estimates the acid cost savings at $18 million to $40 million per year. Capital cost of $45 million is expected to be incurred in 2027, with the incremental processing operating cost estimated at $0.22 per tonne of sulphide ore processed.

The after-tax NPV(8%) is estimated at approximately $200 million based on copper prices of $5.00/lb and sulphuric acid prices of $200/t. At spot prices — around $6.25/lb copper and about $475/t sulphuric acid — the NPV rises to approximately $350 million.

MVPA is also the first step in Capstone’s plan to unlock cobalt production in Chile’s Mantoverde–Santo Domingo (MV-SD) district. Cobalt solubilised from the pyrite could subsequently be recovered via an ion exchange plant. As currently envisioned, a smaller-capacity cobalt plant would initially treat by-product streams from Mantoverde only, producing up to 1,500 t/y of cobalt. Following sanctioning of Capstone’s Santo Domingo project, the facility would be expanded to handle by-product streams from Santo Domingo as well, with a combined MV-SD target of 4,500 to 6,000 t/y of cobalt. The cobalt recovery opportunity is currently at feasibility stage.

The pyrite decision came alongside a broader acid-management push at Mantoverde. Capstone said it had implemented a cash flow optimisation strategy at the mine in 2026 that reduces acid exposure by approximately 200,000 t/y and eliminates the need for spot market sulphuric acid purchases for the remainder of the year. Contracted volumes cover 100% of planned Mantoverde consumption of approximately 243,000 tonnes over the balance of 2026, with 80% locked in under fixed-price contracts at an average of $190/t CFR Chile and 20% on variable pricing. Supply is expected from domestic Chilean sources, Peru, Europe and Asian countries excluding China.

“Capstone’s Board approved the Mantoverde Pyrite Augmentation project, an EIA permit application was submitted for Mantos Blancos, and detailed engineering progressed at our transformational Santo Domingo project,” Capstone said in the results statement.