Magmatic controls on variable Cu mineralization at the cluster scale: Wubaduolai and Zhunuo porphyry Cu deposits, southern Tibet

The Gangdese metallogenic belt in southern Tibet hosts multiple Miocene porphyry Cu deposits formed in a post-collisional setting, yet their mineralization scales vary significantly despite similar ages and magma sources. This study focuses on the newly discovered Wubaduolai deposit and the adjacent, well-mineralized Zhunuo deposit within the same ore-concentration area to investigate the key factors controlling such variability. Zircon U-Pb dating, whole-rock geochemistry and Sr-Nd-Hf isotopes indicates that both deposits formed contemporaneously at ∼16–15 Ma and exhibit adakitic geochemical affinities, deriving from hybrid magmas involving juvenile lower crust and lithospheric mantle-derived melts. Amphibole thermobarometry and zircon-based oxybarometry reveal that the Wubaduolai magmas crystallized at higher pressures (∼136 MPa; ∼5.0 km), lower oxygen fugacity (ΔFMQ = 1.60 ± 0.24), and lower water contents (4.7 ± 0.8 wt%), whereas the Zhunuo magmas were emplaced at shallower levels (∼113 MPa; ∼4.2 km) with higher oxygen fugacity (ΔFMQ = 1.88 ± 0.29) and higher water contents (5.6 ± 1.0 wt%). Apatite compositions further show that the Wubaduolai is characterized by higher Cl contents (0.24–0.95 wt%) and higher X Cl values compared to Zhunuo, indicating less efficient Cl extraction during fluid exsolution and thus reduced volatile release. These differences indicate that the contrasting mineralization scales are closely related to variations in magmatic physicochemical conditions, particularly oxygen fugacity, volatile content, and emplacement depth, which together control the efficiency of fluid exsolution and metal transport. In addition, Sr–Nd isotope modeling suggests that ultrapotassic melt contributions are higher at Zhunuo (∼20%) than at Wubaduolai (∼5–10%), which may have influenced magma evolution and volatile characteristics. Overall, these results indicate that porphyry Cu mineralization at the cluster scale was governed by the combined effects of multiple magmatic factors, particularly oxygen fugacity, volatile content, and emplacement conditions, whereas differences in ultrapotassic melt involvement may also have contributed to variations in magma evolution between the two systems.