Magma source, differentiation, and fluid-melt interaction as controls on tungsten fertility: Insights from the Hukeng tungsten deposit, South China

Tungsten (W) is a highly incompatible element progressively enriched in the continental crust and closely associated with granitic magmatism, yet the processes that concentrate it to ore grades remain debated. Reduced magmatic conditions have long been regarded as essential, but many reduced granites are barren, indicating that low oxygen fugacity (fO2) alone is insufficient. Here we investigate the large Hukeng W deposit in the Wugongshan Complex, South China, to identify the fundamental controls on W fertility. Integrated in situ U-Pb dating of wolframite, whole-rock geochemistry, and detailed zircon analyses (U-Pb geochronology, Lu-Hf isotopes, and trace elements) of both the Hukeng and barren Caledonian and Jurassic granites in the Wugongshan Complex demonstrate that mineralization at ca. 151 Ma is genetically linked to the small Hukeng granite. The Hukeng granite, derived from Paleoproterozoic metasedimentary crust, is highly evolved (differentiation index [DI] > 94) and records intense late-stage fluid exsolution. It exhibits strong depletion in Ba-Sr-Eu-Ti, elevated Rb/Sr and K/Ba, low K/Rb, La/Ta, (La/Yb)N, Zr/Hf and Nb/Ta, pronounced negative Eu anomalies ([Eu/Eu*]N < 0.12), and a clear lanthanide tetrad effect (TE1,3 = ~1.19). Zircon compositions further indicate advanced differentiation and strong melt-fluid interaction under reduced conditions, with estimated logfO2 = ~−13. In contrast, barren granites, although more reduced (logfO2 = ~−18), display weaker differentiation and minimal fluid signatures. We conclude that W fertility is governed by the combination of a fertile crustal source, extreme magmatic differentiation and efficient late-stage fluid exsolution, rather than redox state alone. Based on a global compilation of fertile and barren granites, we propose discriminant thresholds (DI > 88, TE1,3 > 0.96, K/Ba > 200, Rb/Sr > 7, [Eu/Eu*]N < 0.4, K/Rb < 105, La/Ta < 6, [La/Yb]N < 6, Zr/Hf < 38, Nb/Ta < 11) that serve as exploration criteria for granitic systems with significant W endowment.