Rio Tinto Nuton copper cathode at Gunnison: heap leach lessons for mine engineers
Reviewed by Tom Sullivan
First reported on MINING.com
30 Second Briefing
Rio Tinto’s Nuton venture has produced its first 99.99% copper cathode using proprietary sulphide bioleaching at Gunnison Copper’s Johnson Camp Mine in Arizona, just 18 months after starting work on site. The four-year demonstration aims to deliver about 30,000 tonnes of refined copper from the existing heap leach pad, with Nuton’s microorganisms in bioreactors achieving up to 85% recovery while eliminating milling, tailings, smelting and off-site refining. Gunnison’s 25-million-lb-per-year operation, with a 15–20-year mine life, is now focused on multi-year technical validation, third-party verification and Rio Tinto internal review.
Technical Brief
- Nuton’s natural microorganisms are cultured in proprietary bioreactors, then applied to sulphide ore heaps.
- Microbes accelerate sulphide oxidation, generating heat and enhancing copper dissolution into the heap leach solution.
- The process removes milling, tailings storage, smelting and off-site refining from the flowsheet at Johnson Camp.
- Water consumption is projected to fall by up to 80% versus conventional concentrator–smelter routes.
- Gunnison reports potential carbon emission reductions of up to 60% compared with traditional copper concentration.
Our Take
With a post-tax IRR of 30% and initial capex of $58.9 million for Johnson Camp Mine, Gunnison Copper sits in the more competitive cost tier of the copper projects in our database, which may make the 51/49 JV split with Nuton easier to finance without heavy equity dilution.
The ability of Nuton’s leach technology to reach 85% recovery on 0.31–0.32% copper grades at JCM is strategically significant, as many of the copper projects in our 152 Mining stories struggle to justify development at similar grades without higher metal prices or by-product credits.
The four-year demonstration period at Johnson Camp Mine, contrasted with the 18‑month concept-to-production claim for Nuton, signals that regulators and financiers in Arizona are likely to treat new in-situ or novel leach deployments conservatively, even when backed by a major like Rio Tinto.
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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