Solubility of Gold and Silver in Oxygen-Saturated Fluids and the Formation of High Fineness Gold Grains in the Lateritic Profile

This short note reports calculated solubilities of gold and silver in low-temperature, moderately saline, oxygen-saturated fluids. Based on the solubilities of goId and silver it is argued that the quantity of gold transported by the fluids depends on the concentration of silver in the primary ores. In ores, where silver/gold ratio is high (>1 to 10) the fluids become saturated in silver and cannot dissolve geologically significant concentrations of gold. In ores where the silverlgold ratio is low (< 1), the fluids remain undersaturated with respect to silver and can dissolve geologically realistic concentrations of gold and silver. The oxidised fluids will start depositing gold and silver as they move downwards and are reduced by the Fe⁺² bearing minerals of the primary ores. The formation of gold in the lateritic profiles can be explained by a prolonged process of interaction between the fluid and the primary ores.