Geochronology and geochemistry of the Bangpu Mo–Cu porphyry ore deposit, Tibet

We have determined the ages of the ore-bearing Bangpu porphyries and the age of formation of an associated Mo–Cu ore deposit using the LA–ICPMS zircon U–Pb and the molybdenite Re–Os methods. Zircons from two adamellite porphyries give ages of 14.07 ± 0.08 Ma and 14.96 ± 0.16 Ma, and zircons from a diorite porphyry give an age of 15.30 ± 0.25 Ma. The ages of three molybdenite samples are 14.96 ± 0.23 Ma, 15.08 ± 0.23 Ma and 16.61 ± 0.23 Ma. Light Rare Earth Elements (LREE) are enriched in the ore-bearing adamellite, which is shoshonitic and peraluminous, while Heavy Rare Earth Elements (HREE) and Y are strongly depleted, indicating an adakitic affinity. In contrast to other deposits formed in the post-collisional Gangdese belt, the Rb/Sr ratio in Bangpu is high, demonstrating more crustal contamination. The geochemistry of the ore-bearing diorite porphyry differs significantly from that of the ore-bearing adamellite. The diorite porphyry displays a reverse slope in its REE (Rare Earth Element) pattern, and is shoshonitic and metaluminous. The geochronology and geochemistry of both ore-bearing rocks indicate that the Bangpu ore deposit is related to two different source regions in a post-collisional environment. The metallic minerals formed mainly during the older diorite porphyry stage, but they were recycled and reactivated during adamellite magmatism. The sources of the mineralising fluids, and the evolution of the northern GPCB (Gangdese Porphyry Copper Belt), where the Bangpu ore deposit is located, are more complex than in the southern GPCB.