A new refractory gold process – concept to commissioning

Dale Harrison

Millennium Minerals Limited

Millennium Minerals owns and operates the Nullagine Gold Operation located in the Pilbara region of Western Australia. The Nullagine Gold Mine plant was designed to process free milling gold ores primarily from the adjacent Golden Eagle resource and other identified free milling satellite resources.

In addition to the free milling resources, there are significant refractory resources located across the operation which are not suited for processing in the existing plant in its current configuration.

Several studies have been undertaken to evaluate and identify a cost-effective processing route for the refractory ores. The ores have sulfide mineralogy varying from pyrite dominant to arsenopyrite dominant and as such, would require a suitably flexible and robust process to allow them to be effectively treated.   The identified process route was developed by Millennium with a tried and tested tails concentrating methodology followed by a unique mechanochemical oxidative leach stage to provide a cost effective and rapid oxidation and grinding of the sulfide minerals resulting in a physical and chemical liberation of the entrained gold for recovery through the CIL circuit.

The expanded plant functions as a “wicket keeper” and its ability to process varying ratios of free milling and refractory ore as well as changing pyrite and arsenopyrite ratios from the various ore sources, allow for a significantly expanded mine life.  This also assists in exploration success by having a processing route for refractory ores in the region, thereby allowing Millennium to efficiently exploit its landholding in the region.

This paper covers the development of the processing concept and the results of the commissioning of this fast-tracked and innovative process.

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