Fluid physicochemical conditions and critical element enrichment mechanisms of the Yinkeng Pb-Zn-Ag deposit in the eastern Jiangnan Orogen, South China

Abstract

The eastern segment of the Jiangnan Orogen, South China, hosts significant polymetallic Zn-Pb-Ag mineralization related to its complex multi-stage tectonic and magmatic history. The genesis of recently discovered Yinkeng vein-type Pb-Zn-Ag deposit remains poorly constrained, which has hindered a comprehensive understanding of the regional Zn-Pb-Ag metallogenic mechanisms. This study integrates detailed geological investigation, fluid inclusion Raman and microthermometry, and in-situ LA-ICP-MS trace element analysis of sulfides to characterize the ore-forming processes and critical metal endowment of the Yinkeng deposit. Our results reveal that Yinkeng sphalerite is enriched in Fe, Mn, and Cd (up to 17.6 wt%, 2.5 wt%, and 1.1 wt%, respectively) but depleted in Ga and Ge. These elements (Fe, Mn, Cd) are incorporated primarily via isomorphous substitution for Zn²⁺. Galena is significantly enriched in Ag and Sb, which enter the crystal lattice mainly through coupled substitution for Pb²⁺, with aggregates of discrete Ag-bearing minerals also present. Fluid inclusion data and sphalerite geochemistry indicate that mineralization occurred from a reduced, high-temperature (ca. 283.8–397.5 °C) hydrothermal fluid with low to moderate sulfur fugacity (log₁₀fS₂ in the range of − 8.38 to − 10.72). These conditions promoted the enrichment of Mn and Cd, while a decrease in sulfur fugacity during the middle stage facilitated Ag enrichment in the galena and the precipitation of discrete silver minerals such as freibergite and argentite. The trace element signatures (e.g., low Cd/Fe and Cd/Mn ratios of sphalerite, Co/Ni ratios of pyrrhotite) suggest that the Yinkeng vein-type mineralization likely represents the distal mineralization of a magmatic hydrothermal system. This study contributes to a refined regional exploration model for Zn-Pb-Ag ± critical mineralization systems within the eastern Jiangnan Orogen.