Metallogenic Age and Fluid Evolution of Late Jurassic Tungsten Mineralization in the Shanxin Pluton, Xiangshan Uranium Ore Field: Insights from Mineral Textures, Geochemistry, and Wolframite U-Pb Chronology

The Xiangshan uranium ore field, located in the Gan-Hang uranium metallogenic belt of South China, hosts newly discovered greisen-related quartz-vein wolframite mineralization within the Shanxin pluton. However, its mineralization age and ore-forming fluid evolution remain poorly constrained. This study combines wolframite U-Pb geochronology, elemental and Sr isotope analyses, fluid inclusion microthermometry, and quartz hydrogen and oxygen isotope data to investigate tungsten mineralization. Wolframite yields a U-Pb age of 156.0 ± 4.8 Ma, consistent with the emplacement age of the Shanxin pluton. Two wolframite types with distinct Fe/Mn ratios and geochemical characteristics were identified, and scheelite micro-veinlets locally replace wolframite. Variations in Fe/Mn ratios, Nb + Ta contents, and Eu anomalies suggest increasing oxygen fugacity during mineralization. Scheelite rare earth element patterns and Sr isotopic compositions suggest that late-stage fluids had relatively high oxygen fugacity and acquired Ca and Sr from wall rocks. Fluid inclusion and stable isotope data indicate that the ore-forming fluids evolved from predominantly magmatic-hydrothermal fluids toward mixtures containing increasing proportions of meteoric water. Fluid mixing promoted cooling and oxidation, facilitating the sequential precipitation of wolframite and scheelite. These findings highlight the potential role of meteoric water in Late Jurassic tungsten–uranium polymetallic mineralization in the Xiangshan region.