A comprehensive mineralogical and physico-chemical examination of two refractory gold ores and concentrates from the Ghanaian gold province was conducted to gain a better understanding of the differences in performance of gold cyanidation. Both ore were mainly silicates, carbonates, oxide, phosphate and sulphides. Flotation of the ground ores produced concentrates with noticeable differences. Whilst both mainly contained sulphides and silicates, apatite was present in one flotation concentrate and dolomite in the other. Biooxidation of the apatite-bearing concentrate produced jarosite-bearing bio-oxidised product. Bio-oxidation of the dolomite-bearing concentrate yielded a jarosite-free bio-oxidised product with lower bassanite content but higher gypsum, graphitic carbon, and pregrobbing effect compared with the jarosite-bearing bio-oxidised product. The jarosite minerals appeared to aid gangue mineral agglomeration and also encapsulated auriferous minerals which attenuated the bio-oxidation process and reduced gold extraction.
Gold mineralisation and deportment in two refractory flotation concentrates and their corresponding bio-oxidised products were investigated using several analytical techniques. One concentrate and its product show higher gold grades (28 and 38 g/t, respectively) than the other (17 and 23 g/t, respectively). The results showed that both visible, polydispersed and invisible gold particles were present in all four samples. The invisible gold was disseminated in arsenian pyrite and arsenopyrite mineral phases. Unliberated, visible gold particles were in complex gold associations with sulphides, silicates, and oxides. In addition, visible gold-sulphate mineral associations were also noticeable in the bio-oxidised products. Marked differences in gold mineralisation and association such as occurrence of gold in muscovite and jarosite-cemented gangue mineral agglomerates were notable between the two bio-oxidised products. Furthermore, combined jarosite and gypsum mineral encapsulation accounted for ≈ 43 wt.% Gold refractoriness in the lower gold-bearing biooxidised product.
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