Characterizing low-grade refractory gold ores using automated mineralogy coupled with LA ICP-MS

Researchers have made notable progress in quantifying refractory components causing gold losses in traditional extraction methods. The potential for improving gold recoveries lies in targeted re-treatment of the 'invisible' gold fraction hosted within various ore minerals, even at low concentrations. This study presents a methodology for analysing the refractory components that cause gold losses in traditional extraction methods. The approach utilizes automated mineralogical techniques in conjunction with in-situ laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) to characterize low-grade refractory ores and assess gold deportment. The methodology combines pre-concentration gravity separation, traditional chemical and mineral techniques, and LA ICP-MS to generate comprehensive datasets. To demonstrate the practical application of the methodology, a case study was conducted on historical tailings material from Witwatersrand's Evander Goldfield in South Africa. The case study aimed to determine the mineralogical distribution of gold that cannot be extracted through cyanidation. The results indicated that invisible gold is primarily hosted in pyrite (with an average concentration of 10.21 ppm representing 32 % of total gold), other sulphides (with an average concentration of 1.29 ppm representing 0.42 % of total gold), and oxides (with an average concentration of 0.50 ppm representing 1 % of total gold). The remaining gold is present in discrete fine cyanide amenable phases (with 28 % deportment) and silicate-hosted phases (with 39 % deportment). Environmental monitoring of the Witwatersrand tailings material revealed a net "acid-producing" nature, with high concentrations of heavy metals (such as As, Cu, Pb, Mn, Hg, and Ni) associated with sulphides (with over 78 % deportment). The deportment information obtained through this approach can optimize ore processing strategies and provide valuable insights for future remediation plans. By characterizing the refractory components causing gold losses and understanding the distribution of gold within the ore, this methodology offers the potential to enhance gold recovery and improve the efficiency of ore processing operations.