New Geochemical Insights into the Genesis of the Kalasayi Tungsten Deposit, Western Tianshan Mountains: Multistage Mineralization within a Progressive Orogenic Evolution Model

This study builds upon our prior publication concerning the Kalasayi tungsten deposit (DOI: https://doi.org/10.1007/s12517-022-10272-6[1]). The Kalasayi tungsten deposit (ca. 30 kt WO ₃ , avg. 1.05% WO ₃ ), situated within the Western Tianshan Mountains of NW China, constitutes a significant vein-type tungsten system genetically linked to the Late Carboniferous Kalatawu pluton. New zircon U-Pb ages (313.9 ± 0.7 to 310.3 ± 1.0 Ma) and molybdenite Re-Os ages (302.6 ± 1.4 to 302.3 ± 1.8 Ma) constrain the timing of magmatism and mineralization to the latest Carboniferous. The Kalatawu pluton comprises high-K calc-alkaline, metaluminous to slightly peraluminous A-type granites (subtype A ₂ ), exhibiting a geochemical continuum indicative of fractionation from I-type to highly fractionated A-type compositions. Zircon Hf isotope signatures (εHf(t) = + 2.8 to + 8.3; T _DM (Hf) = 605–1714 Ma) reveal a hybrid magma source involving juvenile lower crust with significant assimilation of ancient Kazakhstan-Yili continent crust. Integrated fluid inclusion microthermometry documents a pronounced thermal gradient from proximal zone (avg. homogenization temperature Th = 285°C) to distal zones (avg. Th = 135°C), accompanied by a corresponding decrease in fluid salinity from 10–13 wt.% to 5–7 wt.% NaCl eq. Scheelite geochemistry delineates two distinct genetic groups: Group I (proximal) is characterized by high Mo content (avg. 4000 ppm), low Sr content (avg. 58 ppm), and Eu variables (δEu), consistent with precipitation from oxidizing magmatic fluids. Group II (distal) exhibits low Mo content (avg. 43 ppm), high Sr content (avg. 253 ppm), and consistently positive δEu (avg. 2.15), reflecting precipitation under reducing conditions influenced by fluid-rock interaction and influx of meteoric water. The spatial and temporal evolution of the hydrothermal system records a transition from syn-collisional to post-collisional tectonic regimes during the terminal collision between the Junggar Ocean Plate and the Kazakhstan-Yili Plate. Tungsten precipitation was primarily driven by substantial cooling (150°C) and pH increase during fluid ascent, while oxygen fugacity (fO₂) exerted a key control on the partitioning of accessory metals (Mo, Eu). This integrated study establishes a holistic multistage mineralization model intimately associated with the progressive orogenic evolution of the Western Tianshan Mountains.