Arizona Sonoran Copper reported positive preliminary column leach metallurgical extraction rates for its Cactus mine project in Arizona, as part of a Phase 1 testing program with Nuton LLC, a Rio Tinto venture. Primary sulphide extraction ranged from 61% to 82% based on five columns, including two early cycle columns returning 83% and 61%, two mid-cycle columns above 70% and one with lower extraction based on biotite content. The company said Nuton is currently reassessing the additives for this low extraction column to address future biotite exposure, which accounts for approximately 1%–2% of the Cactus West deposit in the primary zone. A total of 13 ongoing columns were approximately 75–150 days through their 300-day leach cycle and include samples from the sulphide, both primary and enriched (secondary sulphide) zones from both Cactus and Parks/Salyer deposits, as well as from the tailing facility.

Nuton is a portfolio of proprietary copper leach-related technologies and capabilities, developed by Rio Tinto to deliver increased copper recovery and environmental performance. Samples were sent to the Nuton testing lab to begin column leach testing late in 2022. The columns were leached under a range of conditions and additive combinations with a view towards identifying the ideal Nuton offering for further test work and commercial deployment. 

The Nuton flowsheet is a conventional crushed and agglomerated feed, bio-heap leach flow sheet for heap leaching of copper sulphide minerals. However, it includes the addition of catalytic and other reagents, as well as a bacterial growth and inoculation facility. At a technical presentation given late last year at Rio Tinto’s Bundoora Technical Development Center in Melbourne, Australia, company personnel explained that the Nuton technology extracts up to >80% of copper from primary copper sulphides compared to 25%–35% in traditional heap leach processes. Nuton modelling capabilities reduce requirements for extensive test programs. 

In addition to the Cactus project, Nuton technology is also being evaluated at Lion Copper & Gold’s Yerington, Nevada project and at McEwen Copper’s Los Azules project in Argentina.