Multi-Stage Tungsten Mineralization: Insights from Scheelite Trace Elements and Geochronology of the Kalatawu–Kalasayi System (Western Tianshan, NW China)

The Kalasayi tungsten deposit is a medium-sized quartz-vein scheelite tungsten deposit in the Western Tianshan, Central Asia Orogenic Belt. The Kalatawu pluton yielded Late Carboniferous zircon U–Pb ages (313.99–310.32 Ma), and molybdenite Re–Os dating gives an isochron age of 302.3 ± 1.8 Ma for W mineralization, indicating an ~8–12 Myr magmatic-hydrothermal system. Whole-rock geochemistry classifies the pluton as aluminous A2-type granite formed in a post-collisional extensional setting. Zircon Hf isotopes (εHf(t) = +2.8 to +8.3) suggest a mixed juvenile lower crust source with mantle input. In situ LA-ICP-MS scheelite trace element analysis and REE geochemistry distinguish two populations: proximal Group I (high Mo, low Sr, low ΣREE, right-inclined REE patterns) is precipitated from oxidizing magmatic fluid, and distal Group II (low Mo, high Sr, high ΣREE, flat REE patterns, strong positive Eu anomalies) records reduced, mixed fluid with intense fluid–rock interaction. Fluid inclusion data show decreasing temperature and salinity proximally to distally, confirming that mixing of magmatic and meteoric water led to cooling and pH increase that caused W precipitation. A four-stage metallogenic model is proposed for a post-collisional extensional setting, providing robust evidence for A-type granite-related, multi-stage W mineralization and establishing exploration indicators for the southwestern Central Asia Orogenic Belt.