21st Sep 2026 12:01
(Alliance News) - Great Southern Copper PLC on Monday announced that tests at its Mostaza copper-silver deposit in Chile have confirmed high copper and silver recoveries at its Cerro Negro prospect, part of the company's Especularita project.
The Chile-focused copper, gold and silver explorer said metallurgical tests on two high-grade composite samples, completed by Chile-based metallurgical firm Aminpro, achieved copper recoveries above 90% and silver recoveries above 85%.
The resulting concentrate averaged 27% copper and 1,414 grams of silver per tonne. The composite samples had an average head grade of 5.1% copper and 279g/t silver.
Great Southern said the results indicate conventional flotation could effectively concentrate the Mostaza mineralisation.
Mineralogical testing confirmed that chalcocite was the dominant copper mineral, accounting for between 78% and 83% of copper in the samples, which the company said explained the high copper grades at Mostaza.
A separate acid leaching test achieved copper recovery of just under 50%, which Great Southern said was significantly below the recovery achieved through flotation.
The company said it plans further metallurgical testing using drill-core samples covering a broader range of copper and silver grades. The work will form part of the company's phase four drilling programme, which is expected to begin within the next month.
Great Southern holds the option to own 100% of the Cerro Negro prospect, including the Mostaza mine, which forms part of its Especularita project.
"This first metallurgical test programme on the high-grade mineralisation from Mostaza has indicated that a conventional flotation recovery process could be highly effective in concentrating the prospective ore into a copper-silver concentrate product," commented Chief Executive Officer Sam Garrett.
He added that the company was "particularly encouraged" by the scope to improve recoveries further by optimising grinding and regrinding processes.
Great Southern discovered high-grade copper-silver mineralisation beneath the historical Mostaza mine in 2025. It has since completed three phases of diamond and reverse-circulation drilling totalling 6,658 metres at the Cerro Negro prospect.
Shares in Great Southern Copper were down 3.7% to 1.85 pence on Monday morning in London.
By Niall Holden, Alliance News reporter
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