Implications of Ore Textures for Gold Recovery at Esaase Deposit, Asanko Gold Mine

Abstract

The Esaase Deposit of the Asanko Gold Mine Ltd (AGM) contains a system of epigenetic gold-related quartz veins hosted by tightly folded and foliated metasedimentary rocks. The gold mineralisation is associated with disseminated sulphide minerals in the quartz-carbonate veins and within the alteration zones of the host metasedimentary rocks. AGM employs a combination of Gravity Concentration and Carbon-In-Leach (CIL) methods to recover its gold and this has resulted in a recovery rate that ranges from 81.3% to 94.1%. The high recovery rate (>90%) suggests that the gold is free and therefore not locked up in the sulphides that are associated with the mineralisation. However, the recovery rate drops from 94.1 to 81.3% even when the samples contain high amount of sulphides. Since the presence of sulphides in altered rock is one major indicator of gold mineralisation, this research was conducted to determine the ore textural relationship between gold and sulphides and the implication of the ore textures on the current gold recovery methods employed on the deposit. Polished block sections were prepared from samples from the ore zones: Transition and Cobra. Petrographic studies were conducted on the samples using the Leica DM2700P petrographic microscope. These studies revealed that the low gold recoveries may be attributed to the gold occurrence as inclusions in the sulphides, which is typical for refractory ores, thus, making it difficult to be extracted by the current method employed at Asanko. Therefore, AGM may have to consider the economics of employing a combination of other methods to liberate the refractory gold and possibly, result in optimum recovery.

Keywords: Ore Textures, Gold Recovery, Refractory Ore, Ghana, Asanko