Geology, geochronology, and genesis of Au mineralization from the Huangshui'an Mo-Au-Pb deposit in Eastern Qinling, China

Huangshui'an deposit, situated in the Xiong'ershan area of Qinling orogenic belt (QOB) in China, is a globally rare carbonatite-type molybdenum polymetallic deposit that contains economic Mo, Au, Pb, and REE mineralization. The molybdenite Re-Os ages (Ca. 213.5–209.2 Ma) indicates that Huangshui'an Mo mineralization formed at Late Triassic. However, it is still unclear whether the Au mineralization is related to carbonatite dykes, and the formation age and genesis mechanism of Au mineralization remain poorly understood at Huangshui'an. This paper presents a comprehensive investigation of the Au mineralization events at the Huangshui'an deposit, including geology, mineralogy, and geochronology. The aim is to provide insights into its formation and mineralization processes and offer a broader understanding of regional Au metallogeny. Based on petrographic investigations, four stages are identified in the Au mineralization as follows: (I) quartz-K-feldspar stage; (II) quartz-pyrite-gold stage, including (IIA) pyrite-native gold sub-stage and (IIB) gold-tellurite-bismuthide sub-stage; (III) quartz-pyrite-polymetallic sulphide-oxide stage; and (IV) calcite-quartz-chlorite stage. The LA-ICP-MS titanite U-Pb dating yields a weighted mean age of 130.8 ± 0.63 Ma which determined that the Au mineralization at Huangshui’an was in the Early Cretaceous and was an independent mineralization event, which may be related to the lithosphere's destructive effect on the North China Craton (NCC). Combined with mineralography by automatic quantitative mineral analysis and testing system (TIMA), we consider that tellurium-bismuth minerals are closely associated with Au mineralization. The sulfur and tellurium fugacity of the ore-forming fluids in each stage were calculated using metal sulfide-oxides and tellurium-bismuth minerals. It was concluded that the precipitation of Au in the Huangshui'an deposit was mainly due to the combined effects of sulfidation, gold collection-redissolution by the low-melting point chalcophile elements (LMCE) melts, and the variation of sulfur fugacity and tellurium fugacity.