Economics of treating gold ores

"This paper gives an insight into the various processes available to treat gold ores. A brief overview is given of the various types of refractory gold ores. Particular emphasis is given /0 comparing the costs of oxide vs refractory gold ore processes, inclusive of grinding through to dore bar.HistoryThro ugh time gold has been recovered from the earth's crust by various mean s. Five major historical steps can be identified for metallurgical processing as shown in Table I .Gravity concent ration started with, for example, river bed panning and developed to more sophisticated processes such as the Johnson concentrator, belt concentrator and jigs. The South African gold fields were a major developer of gravity concentration processes during the first half of the twentieth century.As coarse free gold became depleted, stamp milling, in conjunction with amalgamat ion , was developed. Basically, rock was crushed under large mechanical hammers an d the gold collected in mercury . The mercury was then evaporated in a retort to leave sponge gold for further fire refining.As deposits became deeper and gold finer, the gold became more difficult to recover ; fine grinding was required to liberate the gold. In the 18905, MacArthur and the Forrest Brothers of Glasgow, Scotland, introduced the cyanide pro cess for dissolution of gold and its subsequent precipitaiton by means of zinc. This process, in vogue until the early 1970s, was commonly referred to as the Merrill-Crowe process for recovering fine gold .Activated charcoal was used as a means of recovering gold from solution in the 1880s, especially in chlorination plants in Australia( l). Two factors probably retarded the development of carbon instead of zinc-based processes during those year s. First , there was no satisfactory procedure for the elution of carbon to allow its recycling and, second, the development of the Merrill-Crewe process for gold recovery by zinc cementation probably discouraged any further work on the use of carbon"