ZHANG Xin-yue, HU Yu-zhao^*, LIU Xiao-zhen
(Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China)

Abstract: The Weiruo gold deposit is in the northwestern Nanpanjiang basin. It is a small-scale gold deposit in the periphery of the Lannigou gold orefield with good exploration potential. Based on the mineral association of pyrite and relationship of cross-cutting vein systems in ores, the pyrite of this deposit can be classified into the disseminated pyrite at stage S1 and veining pyrite in quartz-pyrite veinlets at stage S2. Based on the observation of characteristic textures and structures of metal sulfides in the deposit, the EPMA and Nano-SIMS are applied to analyze Au, As, S, Fe contents and sulfur isotopic compositions (δ34S values) of various sulfides, respectively, in order to investigate the occurrence of Au and source of sulfur in sulfides. The results show that dominated gold-bearing minerals of the Weiruo gold deposit include arsenian pyrite and arsenopyrite. The gold occurred in arsenian pyrite in the forms of major nanometer-sized particles of native Au (Au0) and minor gold solid solution (Au+). The δ34S values of studied sulfides vary from 10.6‰ to 14.0‰. The sulfides formed in two stages have similar sulfur isotope values, indicating a same sulfur source in ore-forming fluids of two hydrothermal periods. Our research suggests that the sulfur in sulfides of the Weiruo gold deposit could come from seawater sulfate and the reaction of thermo-chemical sulfate reduction (TSR) may be the mechanism of sulfate reduction for the Weiruo gold deposit.

Keywords: The Weiruo gold deposit; gold occurrence; the source of sulfur; EPMA; in-situ sulfur isotope

ACTA MINERALOGICA SINICA Vol. 39, No.1, 2019, page 98-107