De Grey Mining Limited (ASX: DEG) announced that gold recoveries of 94% were reported from the pressure oxidation testwork on refractory mineralisaton from the Aquila prospect at Hemi in Western Australia.
The company said that the head grade of the composite was 1.67g/t Au and the overall tail grade achieved was 0.10g/t Au.
DEG said that the flowsheet for the primary mineralisation bulk composite comprised sulphide flotation followed by oxidation of the flotation concentrate through pressure oxidation and then cyanide leaching of the pressure oxidation residue. Flotation tailings were treated by cyanide leaching.
De Grey reported that individual composites of transition and primary mineralisation at Aquila achieved overall recoveries of between 89.8% and 97.2% via the same process used for the primary mineralisation bulk composite.
The company said that a composite of oxide mineralisation at Aquila achieved a recovery of 94.9% after 24 hours through cyanide leaching. The head grade of the oxide composite was 1.08g/t Au and the tail grade was 0.06g/t Au.
DEG said that separate gravity testwork was conducted on the oxide mineralisation composite from Aquila and achieved a gravity recovery of 18.5%.
Metallurgical testwork program at Hemi
The company is currently undertaking a comprehensive metallurgical testwork program across each of the mineralised zones at Hemi (Aquila, Brolga, Crow, Diucon, Eagle, and Falcon) as well as the regional deposits of Mallina and Withnell. The company noted that other main regional deposits of Toweranna and Wingina are free milling and will be able to be treated through a conventional CIL circuit.
Results for the testwork conducted on oxide, transition, and primary mineralisation from the Brolga zone were previously announced. The company said that a full suite of metallurgical testwork has commenced on composite samples from Crow and Falcon. DEG said that the same program will be conducted for the Diucon and Eagle zones when core for testwork becomes available from diamond drilling at those zones.
The Company said that it is utilising multi-element analysis to determine mineralogical variability and the requirements to conduct metallurgical testwork based on this mineralogical variability.
Cyanide leach testwork
DEG said that cyanide leach testwork is being conducted on samples taken every five metres downhole for every hole drilled at Hemi.
The company said that cyanide leach testwork, along with multi-element analysis will assist in the modelling of oxide, transition and primary mineral domains for the maiden mineral resource estimate (MRE) for Hemi proposed to be announced mid-2021.
Metallurgical testwork at Aquila
DEG had recently commenced metallurgical testwork at its Aquila zone at Hemi, located approximately 60km south of Port Hedland in Western Australia.
Testwork at Aquila was conducted on 12 individual composites representing oxide, transition, and primary mineralisation and one bulk composite comprising primary mineralisation. The company said that the samples were sourced from the top 200vm of the Aquila zone early in the drilling program.
The company said that additional samples of oxide, transition and primary mineralisation will be collected from the Aquila zone for further testwork as necessary and as studies progress.
DEG reported that the multi-element analysis indicates that the primary mineralisation tested at Aquila to date is similar to primary mineralisation at depth.
High-grade overall recovery at Aquila
The company reported that at the Aquila zone, the flowsheet for the primary mineralisation bulk composite comprised sulphide flotation followed by oxidation of the flotation concentrate through pressure oxidation and then cyanide leaching of the pressure oxidation residue. Flotation tailings were treated by cyanide leaching.
Primary mineralisation bulk composite
The company said that a bulk composite of primary mineralisation at Aquila was obtained by combining individual composites, 2, 5 thru 9, and 11. The overall gold recovery achieved was 94.0%.
Overall recovery of primary mineralisation bulk composite is as shown below.
DEG said that eleven individual composites of transition and primary mineralisation were tested using the same flowsheet as used for the primary mineralisation bulk composite.
DEG reported that the overall recovery from the individual composites varied between 89.8% and 97.2%. The head grades of the composites varied from 0.6g/t Au to 3.6g/t Au.
Results are as shown below.
The company said that a composite (composite 1) of oxide mineralisation from Aquila was tested through cyanide leaching. DEG reported that the sample head grade was 1.08g/t Au and achieved an overall recovery of 94.9% after 24 hours. The company said that the testwork showed rapid leach kinetics with 90% recovery achieved after 2 hours.
Updates and next steps
The company said that follow up aircore drilling will be undertaken to test for strike extensions to mineralisation. DEG said that programs of follow up RC and diamond drilling aimed at extending resources at depth and laterally are underway. The company said that further metallurgical testwork is in progress on each of the identified Hemi zones.
De Grey Managing Director, Glenn Jardine, said: “The new metallurgical testwork results on oxide, transition and primary mineralisation from the Aquila zone at Hemi are encouraging. These results from Aquila are consistent with the positive results previously achieved from the Brolga zone at Hemi. Our ongoing metallurgical testwork program continues to provide confidence in the multiple pathways available to achieve high gold recoveries from Hemi and the regional deposits across the Mallina gold project.
Each of the three potential oxidation processes has delivered high gold recoveries for the Brolga and Aquila zones. Each of the oxidation processes will be carried forward into future testwork. Further testwork and trade off studies underway will enable the Company to optimise the various aspects of our metallurgical testwork program in terms of capital, operating costs, recoveries and operability.”
Image Source: De Grey Mining Limited