Geochronology and pyrite geochemistry of the early Neoproterozoic Shuiyuesi orogenic gold deposit, northern Yangtze Craton: Implications for ore-forming fluid source and enrichment processes

Abstract

Gold deposit formation related to the Neoproterozoic orogeny were unusual throughout Earth’s history. As the most productive gold deposit in the metamorphic basement of the Huangling gold field, the Early Neoproterozoic Shuiyuesi deposit is characterized by high Au grade and abundant Au–Te minerals, providing a natural lab to investigate ore-forming fluid source and gold enrichment processes in response to Neoproterozoic orogeny. Based on in-situ U–Pb dating of hydrothermal monazite and apatite in paragenesis with pyrite, this study precisely constrains the mineralization age to ca. 806 Ma. Trace element compositions of pyrite from pre-, main-, late-, and post-ore stages indicate that they have low Au contents, reflecting Au mineralization is predominantly expressed as visible gold. Combined with the widespread occurrence of Te minerals and contemporaneous mafic dikes derived from metasomatized lithospheric mantle, in-situ S isotopic (δ³⁴S values of −0.84 to 5.24 ‰), and Pb isotopic (²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of 15.53–16.08, 15.16–15.28, and 37.05–37.83, respectively) compositions of pyrites from different stages reflect a deep fluid source related to metasomatized lithospheric mantle. Petrographic observations and trace element mapping of pyrite reveal that the precipitation of early-formed Te–Au minerals and electrum metallic droplets as inclusions in pyrites are related to efficient gold extraction by Te-rich LMCE (low-melting point chalcophile elements) melt from hydrothermal fluid; late-formed fracture gold (native gold and electrum) precipitates from the residual fluid. This study promotes a deeper understanding of ore genesis of the Au mineralization related to the Neoproterozoic orogeny.