INVESTIGATION OF THE AMENABILITY OF A COPPER-RICH REFRACTORY GOLD ORE TO CYANIDE LEACHING

Abstract

The production of gold from refractory gold ores has been increasing due to the exhaustion of free milling gold ores. The presence of cyanicides (e.g., copper minerals) and encapsulation of gold in minerals such as pyrite and arsenopyrite are common reasons for refractoriness of gold ores. In this study, the amenability of a copper-rich gold ore (108 g/t Au, 1.60% Cu) to cyanide leaching was investigated. Direct cyanide leaching of the ore showed that the gold extraction was very low by 18.4% over 24 h., indicating that the ore is highly refractory. Sulphuric acid pretreatment for the removal of acid-soluble copper was found to be not effective to achieve high gold extractions at the subsequent cyanide leaching. Leaching at high NaCN concentrations (1-8 g/L) yielded limited Au extractions of ≤47.2%. Ultra-fine grinding (UFG) (d80: 8-73 µm) as a pretreatment route followed by cyanide leaching also could provide Au recoveries of just below 54.1%. The findings showed that the ore is double-refractory and needs the employment of more effective pretreatment process(es) to achieve acceptable gold extractions (>90%) in subsequent cyanidation stage.