Contrasting tungsten fertility in coeval granites controlled by late-stage melt segregation: Evidence from the Dongping ore field, eastern Qin–Hang belt

Granite-related tungsten systems are commonly associated with pre-enriched crustal sources and highly evolved granitic magmas, but the processes responsible for contrasting tungsten fertility among coeval granites remain insufficiently understood. The Dongping ore field in the eastern Qin–Hang belt contains the concealed ore-bearing Dongping plutonic system and the exposed ore-barren Shadian biotite granite, providing a natural comparison for evaluating the controls on tungsten endowment under broadly similar geological conditions. Zircon U-Pb dating shows that the Dongping and Shadian granites were emplaced during the same Early Cretaceous magmatic episode, and zircon Hf and apatite Nd isotopes indicate derivation from a similar Neoproterozoic crustal reservoir. Despite these similarities, the Dongping granite records more advanced magmatic differentiation than the Shadian granite, as indicated by stronger whole-rock Eu depletion, lower Nb/Ta ratios, and greater incompatible-element enrichment. Zircon and apatite geochemistry further indicate that this contrast was not mainly controlled by differences in magmatic temperature or redox state, but was more closely related to late-stage melt evolution. Apatite Eu systematics indicate more effective separation and continued evolution of residual melt in the Dongping system, whereas the Shadian granite records more limited melt segregation and greater retention of evolved melt within the crystallizing framework. Wolframite U-Pb dating, together with the spatial association between the concealed granite, greisenization, quartz–muscovite stringer zones, and quartz–wolframite veins, supports a close magmatic–hydrothermal relationship between granite emplacement and tungsten mineralization. These results indicate that source fertility provided the metallogenic potential for tungsten enrichment, but source characteristics and emplacement timing alone cannot explain the contrasting tungsten endowment of the Dongping and Shadian granites. Efficient late-stage melt segregation allowed evolved residual melt to separate from the crystal-rich framework and continue to differentiate, producing highly evolved geochemical signatures and promoting W enrichment before transfer into magmatic–hydrothermal fluids. This process-based interpretation highlights residual melt segregation as a key mechanism linking advanced magmatic differentiation with tungsten fertility and may help explain why concealed or small-volume highly evolved granitic bodies can generate large tungsten deposits.