Permian Crustal Reworking and Rare-Metal Mineralization in the Halajun Area, the Southwest Tianshan, NW China

Permian A-type granites and associated rare-metal mineralization are widespread in the Halajun area, southwestern Tianshan; however, petrogenetic controls on rare-metal enrichment and mineralization remain under-constrained. Here, we integrate zircon and monazite geochronology, whole-rock geochemistry, and zircon Hf-O isotopes from Halajun I and II plutons to constrain the origin of these granites and their metallogenic significance. Zircon U–Pb and monazite ages indicate emplacement at 274–273 Ma, coeval with regional magmatism associated with the Tarim large igneous province. Geochemical signatures—high SiO2, alkali, and rare-earth element (REE) contents, enrichment of HFSE (e.g., Nb, Zr, and Hf), coupled with LILE (e.g., Ba and Sr) depletion—classify these granites as highly differentiated alkaline A-type rocks. Positive εHf(t) values and intermediate δ18O compositions of zircons suggest derivation from partial melting of Neoproterozoic lower crust with input from mantle-derived melts, reflecting significant crust–mantle mixing. Magmatic differentiation, in concert with regional crustal reworking driven by mantle plume activity, produced granites enriched in Nb, Ta, Zr, and REEs, which host the rare-metal mineralization in the region. These results indicate that Permian crustal reworking in the southwestern Tianshan was a driver of high-differentiation magmatism and rare-metal enrichment, highlighting the potential of similar A-type granitic systems in Central Asia for rare-metal exploration.