In this ore classification, the gold occurs both in the free state and disseminated in the sulfides. (Pyrite is found to some degree in most of the world's gold deposits. ) Sulfides tend to decompose in cyanide solutions. Pyrite is the most stable but when pyrrhotite is present trouble is usually experienced both in regard to cyanide consumption and gold extraction. Pyritic flotation concentrates are often reground for gold liberation before cyanidation as at Itogon-Suyoc Itogon, and Pamour. After fine grinding, long periods of agitation are often required to dissolve the gold. Gold-bearing pyrite concentrates are sometimes roasted and cyanided in separate circuits as at Kerr Addison. Also, high grade gold-pyrite flotation concentrates can be shipped to the smelter as is Knob Hill practice. Pyrite and pyrrhotite often occur together creating an overlap in treatment methods.
Gold with Pyrrhotite
Pyrrhotite readily reacts with cyanide to form cyanates and thiocyanates and it readily consumes oxygen. Aeration with lime ahead of cyanidation is usually used on ores in this classification. Aeration for preconditioning is used at Dome, Homestake, Kerr-Addison, and Pamour.
Gold with Arsenopyrite - Arsenic Minerals
Gold is occasionally associated with arsenic minerals as well as pyrite, stibnite, chalcopyrite, etc. Direct cyanidation in these cases is seldom possible. Additionally, when gold is associated with readily soluble arsenic compounds, there is the hazard, in precipitation, of forming arsine, AsH3. In plants where this extremely toxic gas is evolved, special ventilation techniques are required.
Giant Yellowknife produces a refractory flotation concentrate carrying gold in association with arsenopyrite, stibnite, and sulphantimonides of copper, lead and iron. Roasting liberates the sulfide-enclosed gold allowing the calcine to undergo conventional cyanidation. Campbell Red Lake roasts a flotation concentrate ahead of cyanidation.
Gold with Pyrrhotite
Pyrrhotite readily reacts with cyanide to form cyanates and thiocyanates and it readily consumes oxygen. Aeration with lime ahead of cyanidation is usually used on ores in this classification. Aeration for preconditioning is used at Dome, Homestake, Kerr-Addison, and Pamour.
Gold with Arsenopyrite - Arsenic Minerals
Gold is occasionally associated with arsenic minerals as well as pyrite, stibnite, chalcopyrite, etc. Direct cyanidation in these cases is seldom possible. Additionally, when gold is associated with readily soluble arsenic compounds, there is the hazard, in precipitation, of forming arsine, AsH3. In plants where this extremely toxic gas is evolved, special ventilation techniques are required.
Giant Yellowknife produces a refractory flotation concentrate carrying gold in association with arsenopyrite, stibnite, and sulphantimonides of copper, lead and iron. Roasting liberates the sulfide-enclosed gold allowing the calcine to undergo conventional cyanidation. Campbell Red Lake roasts a flotation concentrate ahead of cyanidation.
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