Anax Metals (ASX: ANX) has reported “excellent” results from heap leach test work undertaken on Mons Cupri low-grade middlings concentrates from bulk ore sorting at the Whim Creek copper project in Western Australia.
Middlings are the rejects from primary high-grade ore sorting that are sorted through a secondary process and directed to the heap for leaching.
According to the Perth-based explorer, more than 95% of copper and zinc was recovered in the bench-scale test work with rapid leach kinetics.
Anax managing director Geoff Laing said the “very positive” results indicated that the Mons Cupri ore sorter middlings were amenable to heap leaching using commercially available bacterial cultures.
“While the amenability tests were carried out under controlled laboratory conditions, and produced ‘best case’ outcomes, the rapid leaching of copper and zinc and the high levels of dissolution achieved increased Anax’s confidence that bioleaching has the potential to generate additional revenue streams for the Whim Creek project,” he said.
“The column test work currently in progress will provide key information for the ongoing feasibility study,” Mr Laing added.
Secondary ore sorting process
Anax’s conceptual ore sorting flowsheet separates primary, high-grade pre-concentrates for flotation, then secondary sorting directs the lower-grade middlings to the heap for leaching, with the final rejects regarded as barren aggregate for use on site or for sale.
As detailed in the recently completed scoping study for the Whim Creek project, the proposed bacterial heap leach will play an important role in optimising metal recovery. Up to 15% of the mined copper and zinc will be delivered to the heap through the secondary stage sorting process and fines gravity circuit.
Anax said this heap leaching of middlings, or secondary sorted products, through the refurbished site infrastructure is expected to generate additional revenue streams for the Whim Creek project and increase free cash.
The amenability tests were carried out at specialist laboratories BioHeap in Perth and Bureau Veritas in Adelaide with test work at a third (Perth) facility currently underway.
Anax said the next round of test work will make use of bacteria native to the Whim Creek project and these cultures are currently under development.
Column tests are also proceeding at Bureau Veritas, using coarser ore material to approximate to actual heap leaching conditions more closely, in order to assess recoveries and indicative operating costs.
Anax said future test work is likely to incorporate ore from the Whim Creek deposit and confirmed suitable ore sorter middlings are available for this work.