Mineralogy and Processing Characteristics of Archean Gold Ores from Western Australia

The Archean ores of Western Australia are in total the largest producers of gold in Australia. In addition to numerous small and medium sized deposits, the province also contains the giant Kalgoorlie Golden Mile deposits. A variety of different gold ore mineralogical associations has lead to the development of a number of different processing routes for both refractory and non-refractory ore types. Intense weathering and lateritization of Archean greenstones in the semi-arid Yilgarn region have resulted in the development of a deeply oxidized profile (60-100m) above most sulphide orebodies. Residual and re-deposited supergene gold within iron oxide/silica gangue of this zone responds well to CIP, CIL, heap and vat leaching techniques. Although gold is easily liberated in principal from oxidized gangue, in practice recoveries are sometimes affected by iron oxide coatings on gold grains, and by clay minerals which can interfere with plant performance. Refractory ore types in the Eastern Goldfields fall into three main categories - pyritic, arsenopyritic and telluride-bearing. Pyritic ores may be either free milling or require roasting. The difference appears to depend largely on whether gold occurs along grain boundaries or fractures, which can be liberated by grinding, or whether gold occurs as inclusions within pyrite grains and therefore cannot be satisfactorily liberated by grinding. Arsenopyrite bearing ores are not well understood and are complicated by what appears to be a variable degree of gold solid solution, in addition to included gold. Gold occurring in complex gold-silver telluride assemblages has traditionally been recovered by roasting in the Eastern Goldfields.