The metallogenic age and geodynamic implications of the Pusangguo copper polymetallic deposit in central Tibet

Abstract

The Pusangguo is a substantial skarn Cu–Pb–Zn polymetallic deposit in the Gangdese metallogenic belt, characterized by its large scale, high-grade mineralization, and metal diversity. The minerals traditionally utilized in geochronological studies typically exhibit higher closure temperatures than those recorded during mineralization processes, while comprehensive genetic correlations between the diorite and granodiorite remain underexplored. To constrain the age of mineralization and elucidate the deposit’s petrogenesis, we conducted an integrated study involving ⁴⁰Ar/³⁹Ar dating of hydrothermal phlogopite, as well as chronology, geochemistry and mineralogy analyses of the mineralized intrusions. Our results indicate that the diorite, granodiorite and hydrothermal phlogopite formed at 15.75 ± 0.22 Ma, 14.90 ± 2.50 Ma and 14.98 ± 0.26 Ma, respectively. The diorite and granodiorite exhibit adakitic signatures, characterized by high Sr contents, low Y and Yb concentrations, and elevated Sr/Y and (La/Yb) _N ratios. Both rocks are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), but depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs). Notably, although they share similar Sr–Nd–Pb isotopic compositions, their ε_Hf(t) values differ significantly, ranging from + 0.4 to + 3.0 in the diorite but –9.7 to –2.3 in the granodiorite. The ⁴⁰Ar/³⁹Ar age of phlogopite indicates that the mineralization occurred at approximately 14.98 Ma, thereby constraining the timing for the late hydrothermal activity. Both the diorite and granodiorite exhibit typical adakitic geochemical characteristics, and their magmas were derived from juvenile lower crust. However, compared with the diorite, the granodiorite exhibits a greater contribution from ancient crustal components in its magma source. The combined temporal and geochemical evidence supports a genetic model involving partial melting of juvenile mafic lower crust, rather than direct input from Neo-Tethyan slab break-off or high-K magma underplating.