Genesis of the Huangshaping W–Mo–Cu–Pb–Zn deposit, South China: Role of magmatic water, metasomatized fluids, and basinal brines during intra-continental extension

The Huangshaping world-class W–Mo–Cu–Pb–Zn deposit formed during Jurassic intra-continental extension in the central Nanling region (South Hunan), South China. In order to assess the role of fluids in ore genesis and the origin of polymetallic mineralization, three types of mineralized porphyries (quartz porphyry, granophyre, and granite porphyry) were studied. The multi-method approach included whole-rock Sr–Nd isotopic geochemistry and determination of the trace element content and gaseous and aqueous composition of ore minerals from the three stages of intrusion and ore emplacement. Geochemical results show that the Sr–Nd isotopes in these altered porphyries were strongly affected by fluid metasomatism. The ⁸⁷Sr/⁸⁶Sr and ¹⁴⁷Sm/¹⁴⁴Nd ratios for the quartz porphyry and granophyre range from 0.72894 to 0.83093 and 0.1524 to 0.2080, respectively, whereas higher and considerably more variable ratios were determined for the granite porphyry (0.90396 to 1.51943 and 0.2391 to 0.2914). These observations imply that granite porphyry-associated W–Mo mineralization underwent more intensive fluid–rock interaction. The relatively low REE concentrations and high abundances of CH₄ and H₂ in the Cu ores associated with the quartz porphyry unambiguously suggest a deep-sourced magmatic fluid for the Cu mineralization. The high REE concentrations, pronounced negative Eu anomalies, M-type tetrad effects, and high CO₂, H₂O, and Ca²⁺ contents of the W–Mo ores associated with the granite porphyry imply that the W–Mo polymetallic mineralization was formed in a relatively oxidizing, high-temperature environment with strong metasomatism. In contrast, the slightly negative Eu anomalies, W-type tetrad effects, low CH₄, and high F⁻ and Cl⁻ concentrations of the Pb–Zn ores indicate involvement of a sediment-derived basinal brine and reducing mineralization conditions. Collectively, a three-stage genetic model is proposed for the Huangshaping polymetallic deposit. Corresponding to initiation, development, and cessation of Jurassic intra-continental extension, magmatic water, metasomatized fluids, and basinal brines played key sequential roles in Cu, W–Mo, and Pb–Zn mineralization.