Mounting pressure, due to social and environmental concerns associated with cyanide extraction, as well as the decrease in available free milling gold deposits, continually complicates metallurgical processing of gold ores. The need for advancements in this field calls for research and the introduction of alternative extraction processes. Samples of several different types of gold deposits, from various localities in South Africa, have been collected to evaluate their refractory nature, response to cyanide, and mineralogical controls on amenability to alternative extraction methods. These deposits; the Ventersdorp Contact Reef (VCR) at Mponeng Mine in the Witwatersrand Basin, Fairview and Barbrook, at Barberton, Pilgrims Rest, and Consolidated Murchison, span a range of ore types and mineralogies. These include free milling, complex, and refractory ores. Complex mineralogies are defined by the presence of various reagent consuming and preg-robbing materials, while the presence of gold compound minerals, as well as sulphide-bound gold, results in refractory ore types. Understanding of the mineralogy of each deposit and its influence on gold extraction is paramount to effective extraction. Examples of deleterious mineralogies include base metal sulphides, specifically significant levels of pyrite, chalcocite, and chalcopyrite in Pilgrims Rest, and antimony minerals such as stibnite and berthierite in Consolidated Murchison. In addition, solid solution gold or discrete gold compound minerals, as found in Barberton deposits and Consolidated Murchison, reduce accessibility, and thus extraction. In evaluation of each deposit, cyanide leaching was undertaken and maintained at marked conditions. Cyanidation was then used as a standard, against which, other leaching methods were evaluated. Under certain mineralogical conditions, alternatives to cyanide, which are typically uneconomic, may outperform the cyanide leaching method.
CITATION:Youlton, K, Kinnaird, J A and Youlton, B, 2019. Mineralogical controls on gold extraction: a comparison of leaching techniques on South African ores, in Proceedings World Gold 2019, pp 312325 (The Australasian Institute of Mining and Metallurgy: Melbourne).