Petrogenesis and metallogenic implications of the Miocene granite porphyry in the Jiama Cu-polymetallic deposit, Gangdese belt, South Tibet

Abstract

Geochronology, geochemical and isotopic studies were carried out on granite porphyry from the Jiama Cu-polymetallic deposit, Gangdese porphyry copper deposit belt, to constrain the genesis and metallogenic potential. LA-ICP-MS zircon UPb dating indicates that the granite porphyry was emplaced at 14.9 ± 0.3 Ma to 16.0 ± 0.3 Ma, which is consistent with other felsic porphyries in the deposit. The granite porphyry shows high-K calc-alkaline and peraluminous signatures. In addition, the granite porphyry shows enrichment in large ion lithophile elements and depletion in high field strength elements. However, it has low Sr (76.13–401.90 ppm) contents, which is different from other felsic porphyries with high Sr contents in the deposit. The initial 87Sr/86Sr (0.7055 to 0.7070) and εNd(t) (−0.53 to -2.37) values of the granite porphyry are close to those of other felsic porphyries in this deposit. The granite porphyry and diorite porphyry have almost identical zircon δ18O (5.71–5.82‰) and εHf(t) (4.1–3.97) values. These results suggest that all the felsic porphyries in the Jiama deposit were derived from the same source. Geochemical characteristics show that the magma of the granite porphyry experienced fractional crystallization of hornblende and plagioclase, whereas other felsic porphyries experienced hornblende-dominated fractional crystallization. Zircon Ce4+/Ce3+ values indicate the high oxygen fugacity of granite porphyries, which is key for CuMo mineralization.