Magma Source, Differentiation, and Fluid-Melt Interaction as Controls on W Fertility: Insights from the Hukeng W Deposit, South China

Tungsten (W) is a highly incompatible element enriched in the crust through time and closely associated with granitic magmatism. While reduced-conditions have long been emphasized as the critical control, many reduced granites are barren, indicating redox alone is insufficient. Here we examine the giant Hukeng W deposit in the Wugongshan Complex in South China to identify the fundamental factors controlling W-fertility. Integrated zircon geochronology, Lu–Hf isotopes and trace element data, wolframite geochronology, and whole-rock geochemistry of the W-related Hukeng and barren Caledonian–Jurassic granites demonstrate that Hukeng formed at ~150 Ma. The Hukeng granite, derived from Paleo-Proterozoic metasedimentary crust, had underwent extreme differentiation (DI ≈ 95) and fluid–melt interaction. It exhibits strong Ba–Sr–Eu–Ti depletion, high Rb/Sr (~18) and K/Ba (~740), low K/Rb (~79), La/Ta (<2.1), (La/Yb)_N (<3.6), Zr/Hf (~18) and Nb/Ta (~7.6), significantly negative Eu anomalies ((Eu/Eu*)_N <0.12), and pronounced lanthanide tetrad effects (TE_1,3 ≈ 1.19). Zircons display decreasing negative Eu and increasing positive Ce anomalies through advanced magma fractionation and fluid–melt interaction under reduced conditions. In contrast, barren granites, though more reduced, display weaker differentiation and minimal fluid signatures. We conclude that the combination of fertile-crust source, extreme differentiation, and vigorous fluid exsolution—rather than oxygen fugacity—was decisive in concentrating and precipitating W. A discriminant model based on DI >88, TE_1,3 > 0.96, (Eu/Eu*)_N <0.4, K/Rb <105, Rb/Sr >7, La/Ta < 6, (La/Yb)_N <6, Zr/Hf < 38, and Nb/Ta <10 provides refined exploration criteria for W-related granites in South China and globally.