Metallogenic Controls of the Jurassic Arc, Xizang: Insights from Geochemistry, Zircon Chronology, Hf Isotopes, and In Situ Trace Elements

Magma oxidation state and water content are pivotal factors governing porphyry copper mineralization. The Xiongcun deposit, the only super-large porphyry copper deposit (PCD) formed in an oceanic subduction environment in the Gangdese belt, has been the primary focus of prior research, with limited systematic comparisons conducted among Xiongcun, weakly mineralized, and barren igneous rocks across the Jurassic Arc. Furthermore, the interaction between ore-controlling factors and deep-seated magmatic processes remains poorly understood. This study examines Xiongcun volcanic rocks, as well as weakly mineralized and barren volcanic rocks from the Jurassic Arc, with Dazi and Jiamagou samples from the eastern segment of Jurassia Arc (ESJA) and Xiongcun, Chucun, and Qinze samples from the western segment of Jurassia Arc (WSJA). All samples (168.0–184.8 Ma) are predominantly calc-alkaline, which is typical of arc magmas. Zircon Hf isotopic data reveal pronounced E-W variations but minimal N-S differences, dividing the arc into the WSJA and ESJA subzones. The WSJA volcanic rocks exhibit uniform Hf isotopic signatures (εHf(t) = 11.2–16.3) and young crustal model ages (186–500 Ma), whereas the ESJA mantle source region is heterogeneous, reflecting greater retention of ancient crustal material. Compared to the ESJA, new data from WSJA samples display higher zircon Ce4+/Ce3+ ratios (454 vs. 145), lower T(Zr-Ti) values (716 °C vs. 779 °C), and elevated whole-rock Ba/La ratios. These differences suggest that mineralization contrasts between the two segments arise from varying fluid metasomatism in their source regions, leading to divergent magma oxygen fugacity and water content—critical controls on porphyry Cu formation. The WSJA magmas exhibit higher values in both parameters, while the ESJA lacks significant mineralization potential.