Project Studies

De Grey is advancing project studies based on a development scenario involving a centralised mining and processing operation at the Hemi discovery and satellite feed from deposits in the wider Mallina Project region, including Greater Hemi.

These project studies include metallurgy and long lead time areas such as environment, water and infrastructure requirements. These components will form the basis of a future Scoping Study.
The Company is 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. 

Positive results have been returned from ongoing testwork on oxide ore and hydrometallurgical pathways including pressure oxidation, Albion® and biological oxidation for fresh ore from Hemi.

To date, this testwork has demonstrated gold recoveries of +93% can be achieved using CIL leach of oxide ore and the sulphide flotation, oxidation and CIL leach of fresh ore as shown in the simplified flowsheet below.

The other main regional deposits of Toweranna and Wingina are free milling and will be able to be treated through a conventional CIL circuit.

Simplified process flowsheet incorporating pressure oxidation (POX)

These strong results give the Company confidence that high gold recoveries can be achieved from Hemi.

A high level, initial trade-off study considering the three potential oxidation processes has been conducted by GR Engineering Services. The study considered the capital and operating costs, commissioning, operational simplicity and metallurgical recoveries of the three oxidation process options.

POX and biological oxidation are well known technologies used at gold projects throughout the world. The Albion® process has also been identified as having potential application at Hemi with benefits including:

  • Capital and operating costs
  • Flexibility to cope with changes in ore type and sulphide content
  • Circuit and operational simplicity
  • Straightforward start-up and shutdown
  • Atmospheric leaching
  • Low pressure oxygen plant

The Albion® process is currently in use at large base metals refineries in Spain and Germany and at a sulphide gold mine and plant in Armenia.

However, metallurgical testwork and studies remain at an early stage and POX, Albion® and biological oxidation processes all remain under active consideration for use at Hemi.

As noted, further oxidation testwork will be conducted on each of the zones at Hemi before one or more preferred oxidation process routes are selected to be carried forward into optimisation metallurgical testwork and engineering studies.

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