Differential oxidation of iron sulfides to modify the Au:S ratio in the flotation concentrate product at Lihir

Sulfide associated refractory gold ores hold a majority of the gold within the pyrite, which has several forms. The high proportion of the gold atomically dispersed in the pyrite has been confirmed by various mineralogy techniques such as laser ablation analysis, optical microscopy, scanning electron microscopy and secondary ion mass spectrometry. Different types of pyrite exist within a refractory ore body and certain types possess a relative abundance of gold compared to other forms. The low gold pyrite influences the rate at which the concentrate can be processed by any particular route. If the different types of pyrite could be separated by flotation, then the gold grade of the final concentrate can be improved and the invisible gold could be recovered by downstream processing. This separation of low gold pyrite from the gold-rich pyrite would increase the gold:sulfur ratio (Au:S ratio) to the autoclave feed, thereby maximising the autoclave throughput and gold production per tonne. Different methods of extraction such as chemical oxidation, thermal oxidation and biological oxidation liberate gold from refractory ores. However, such oxidation methods have not been reported yet to be successful to allow separation of the low gold pyrite from the gold-rich pyrite and modify the Au:S ratio of a pyrite concentrate. This project is an attempt to develop a hydrometallurgical framework to modify the flotation response of gold-rich pyrite and low gold pyrite so that the Au:S ratio of the final flotation concentrate can be upgraded.