Metallurgical test work on samples taken from De Grey’s Brolga zone to assess potential oxidation processes have returned excellent gold recoveries.

Gold recoveries of 97 per cent, 98 per cent and 94 per cent were achieved for the pressure oxidation (POX), Albion and biological oxidation (BOIX) respectively.

Additionally, gravity test work on samples from Brolga achieved gold recoveries of up to 27.3 per cent while overall recoveries of 95 per cent were achieved using a flowsheet combining gravity, flotation/oxidation and carbon-in-leach (CIL).

More importantly though, flotation recoveries into gold-rich concentrates were achieved at mass pulls of approximately 7.5 per cent, which means that the oxidation circuit will be about 15 times smaller than the front-end comminution and flotation circuits.

In non-technical speak, that translates into “lower capital costs”.

De Grey Mining (ASX:DEG) plans to continue both gravity and oxidation test work on samples from the Aquila, Crow and Falcon zones from its highly-prospective Hemi discovery within the Mallina project in Western Australia’s Pilbara region.

“The results from our ongoing metallurgical testwork program continue to give us confidence in the multiple pathways we have to achieve high gold recoveries from Hemi and the regional deposits at Mallina,” managing director Glenn Jardine.

He added that each of the potential oxidation processes delivered high recoveries and that further test work and trade-off studies are now under way to optimise the various aspects of the company’s metallurgical program in terms of capital, operating costs, recoveries and operability.

Test work will test the Aquila, Crow and Falcon projects while the study will assess the three potential oxidation processes.

Brolga test work and other activity

Gravity test work was carried out using a Knelson concentrator on three composite samples of Brolga mineralisation, returning recoveries of 12.1 per cent, 12.4 per cent and 27.3 per cent.

The company said that achieving more than 10 per cent recoveries without the need for CIL or flotation/oxidation is a positive though it may not be representative of other mineralised zones at Hemi.

De Grey’s oxidation test work was conducted on five deposits from Brolgas and one composite from Withnell and Mallina.

Analysis of results from the POX, Albion and BIOX show minor differences in the recoveries with the company saying that further work will be required to assess them.

POX and BIOX are well known technologies used at gold projects throughout the world while Albion is currently in use at large base metals refineries in Spain and Germany along with a sulphide gold mine in Armenia.

Separately, a high-level initial trade-off study considering options for the comminution circuit has identified the SABC circuit as having potential benefits such as the ability to cope with changes in ore type, circuit simplicity, ramp-up period and capital cost.

The comminution circuit selection will be subject to ongoing review with further comminution test work on other zones at Hemi and as plant throughput rates become clearer.


This article was developed in collaboration with De Grey Mining, a Stockhead advertiser at the time of publishing.


This article does not constitute financial product advice. You should consider obtaining independent advice before making any financial decisions.