Pyrite from Zarshuran Carlin-type gold deposit: Characterization, alkaline oxidation pretreatment, and cyanidation

Different types of pyrite exist within a refractory ore body and certain types possess a relative abundance of gold compared to other forms. Accordingly, identification and characterization of the different types of pyrite may represent a beneficial effect on the gold recovery by downstream processes. The main purpose of this study was to establish a connection between the mineralogy, leaching behavior and gold recovery of such gold bearing pyrites during alkaline pretreatment and cyanidation processes. The pyrite concentrate used in this study was obtained from the refractory Carlin-type gold deposit of Zarshuran, Iran. Characterization studies were done using SEM/EDX and EPMA analyses which revealed that pyrite was generally in the two form of euhedral pyrite including pyritodrone and cubic pyrite and subhedral to anhedral pyrite including large particles or fine-grained aggregates. The later type of pyrite was identified as the best host with gold occurring more likely in rims rather than the center of pyrite particles. A positive correlation of Au and As, Ni, and Pb was also found in gold-bearing rims. Alkaline oxidation experiments were conducted to liberate gold from pyrite context. The results showed that leaching rate increases with pH, temperature, oxygen overpressure and surface area where orders of reaction equal to 0.24 and 0.22 were calculated with respect to [OH+] and PO2 respectively. Kinetic analysis showed that pyrite leaching fitted well to the shrinking core model with surface chemical reaction control with the activation energy of 38.41 kJ/mol. Gold cyanidation experiments after alkaline oxidation pretreatments correlated well with the results of characterization and leaching studies in which heterogeneous distribution of Au was identified in pyrite context. It was found that oxidative pretreatment is required for the gold-bearing pyrite to improve gold recovery. However, because much of the gold is in the rims, high gold recovery is possible by the application of only partial oxidation.