The cyanidation of copper-gold ores is a difficult issue owing to the ready formation of copper cyanide complexes during gold leaching. Moreover, the speciation of other metal cyanides in leach slurries and the interaction between them have not been researched extensively, and are of fundamental importance to gold mills. In this paper the role of the cyanide complexes of copper, silver, nickel, iron and zinc in gold leaching was investigated by examining the leaching of a copper concentrate. It was found that copper-cyanide and other metal cyanide species, including Ag, Fe, Ni and Zn, all play an important role in gold cyanidation hinder conditions of zero free cyanide. These species dissociate, and the cyanide made available by the dissociation leaches gold. These metals species then precipitate, usually as a hydroxide under typical leaching conditions. Silver is an exception, which may precipitate as a metal or AgCN species. When cyanide is present, the mechanism of copper-cyanide assisted gold leaching is the dissociation of the weakly bound fourth ligand of Cu(CN)(4)(3-). The cyanide made available can then be used to leach gold and other metals.