The identification of refractoriness in gold ores by the selective destruction of minerals

Abstract

With the increasingly lower grades of ore mined, the introduction of backfill mining, and the reduction of profit margins, it has become imperative to increase the efficiency of gold dissolution. Diagnostic leaching (selective decomposition of refractory minerals associated with gold) tests conducted on a large number of composite residue samples, indicated that a large portion of the gold in the residue was leachable (up to 60%). About half of this leachable gold was dissolved by a quick cyanide wash, indicating that it was precipitated gold. A significant portion of the non-leachable gold in the residue was coated with various films, of which iron oxide was the major one. These films varied in nature from oxides, sulphates, carbonates and cyanide complexes. The complexes can be destroyed, depending on the nature of the film by interstage dilute acid and/or cyanide washes in an agitated vessel. The major cyanide consumers in the residue streams were found to be copper, nickel and soluble sulphides. The reality of an ultimate residue (thus only gold enclosed in fine quartz remains), is within the reach of most of the major gold producing mines, as at least 50% of the gold in the residue could be recovered at little additional cost. It is suggested that residue values at many gold plants are unsatisfactorily high due to the complex nature of the ore and because plant personnel do not utilize all available knowledge on gold dissolution.