Gold in the 'Mundic': The Saga of Dargue's Reef, Majors Creek, NSW

Gold is found in bedrock reefs and lodes, generally in its elemental form, as well as in secondary deposits formed by weathering and erosion of these primary occurrences (for example, alluvial gold). After quartz, the mineral most commonly associated with gold is pyrite (iron sulphide) also known colloquially as 'fools gold' or 'mundic'. This association has guided prospectors to new lode gold deposits, but also plagued attempts to extract the gold where the two minerals are rather too intimately associated. In these refractory ores the gold is commonly locked in the pyrite as small, in some cases sub-microscopic, inclusions or even dissolved in the pyrite host. Up until the end of the nineteenth century refractory gold ores, including those at such famous deposits as the Golden Mile, Kalgoorlie, and some of the ores on the Witwatersrand in South Africa, posed a major challenge to metallurgists. In many cases, some gold could be released by fine grinding, but a significant proportion was lost with the pyrite in the tailings. Various methods of roasting and chemical treatment, particularly using chlorination and cyanidation, were ultimately developed to recover this 'lost' gold.