Tests on mineralisation at Brolga prospect achieved excellent gold recoveries with 93% in oxide based on CIL leach and 96.3% in fresh based on sulphide flotation, oxidation and CIL leach.
Comprehensive test-work is in progress on composites obtained from two diamond drill holes at Brolga, with three of the composite samples containing fresh mineralisation and another composite of transitional mineralisation.
“De-risks potential development”
De Grey managing director Glenn Jardine said that the gold recoveries achieved in the initial metallurgical test-work of oxide, transition and fresh mineralisation at Brolga were very encouraging.
He said: “The test-work significantly de-risks the potential development of Hemi as a Tier 1 gold project in a Tier 1 jurisdiction."
Twelve samples of oxide mineralisation were taken from two RC holes drilled at Brolga.
Additional samples from Brolga and Aquila covering oxide, transitional and fresh mineralisation will be tested to assess variability and to optimise the flowsheet.
Jardine said: “The test-work flowsheet used for Hemi can also be applied to De Grey’s other regional resources in the Mallina Basin.
“We will continue to increase our understanding of the scale and metallurgical properties of each of these domains across the deposit with ongoing test-work.
“Hemi’s excellent location along major transport, gas and power corridors all within 60 kilometres of Port Hedland, is a major advantage for a Tier 1 gold resource and development project.”
Section showing the location of metallurgy composites.
The test-work flowsheet comprised a conventional carbon in leach (CIL) circuit to treat oxide mineralisation.
An industry-accepted circuit comprising sulphide flotation to generate a concentrate prior to oxidation was used to treat fresh mineralisation, which was followed by pressure oxidation of the concentrate and subjected to conventional CIL to recover gold.
The company is confident that, based on previous test-work conducted on other regional resources (2.2 million ounces) outside Hemi, the Hemi test-work flowsheet would be suitable to treat those deposits.
An additional six dedicated larger diameter (PQ and HQ) diamond core holes have been completed to provide larger volume samples within the oxide, transition and fresh domains throughout the deposit.
These holes, which have been drilled and are being sampled and transported to ALS Metallurgy in Perth, will provide a detailed assessment of metallurgical variability across the deposit.
Further test-work will include optimising the grind size, flotation grade, mass pull, flotation recovery and flotation tail recovery.
Detailed results of this comprehensive program are expected later this current September quarter.