Oxide Gold and Thiocyanate Gold Leaching

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oxide gold is the mineral oxide of gold with the chemical formula Au2O3. It is brown or black, and soluble in toluene, concentrated nitric acid, and sodium cyanide solution. It also has a pungent odor.

The origin of oxide gold is not completely understood but is thought to be related to the oxidation of metallic gold, which occurs in the Earth’s crust at temperatures of hundreds of millions of years ago. These deposits are often of very low grade (e.g., 3 to 10 parts per million) so that extensive mineral processing is not economically possible.

IOCG deposits are associated with iron-rich, felsic-intermediate type alteration rocks which may be metasomatised, brecciated or deposited as lithology-controlled replacements of preexisting ore bodies. The mineralogy of these deposits typically consists of copper-iron sulfide chalcopyrite and gangue minerals such as hematite, magnetite or pyrite.

Deposits in the IOCG style are typically hosted within ‘provinces’ where several deposits of similar genesis, mineralogy and structural controls develop in relatively uncomplicated settings. They are characterized by significant enrichment in iron oxide minerals, a lack of complex zonation in alteration mineral assemblies, and often contain host copper in addition to gold.

Thiocyanate leaching is the most common method for reducing and recovering gold from oxide ore. However, thiocyanate gold leaching is not straightforward as many factors affect gold recovery including pH and complexation of ions with the metal-bearing minerals.

Therefore, it is important to evaluate and understand the kinetics of gold oxidation and styles of thiocyanate gold leaching in order to determine optimum leaching conditions for gold recovery from oxide ore. Using the response surface methodology (RSM), pilot studies were conducted to determine optimal initial thiocyanate concentrations, pulp densities and ferric concentrations for maximum gold recovery from oxide ores. The results of this study, combining high gold recovery and optimal leaching conditions, are unique in the thiocyanate gold leaching literature and represent a major contribution to the understanding of gold oxidation from oxide ores.