Geochronology and genesis of the magmatism in the Ri’a copper polymetallic deposit of the Nixiong orefield, Coqen, Tibet

Abstract: The Ri’a copper-polymetallic deposit, as a typical representative copper metallogenesis of the Nixiong orefield and an important part of Cuoqin-Shenzha iron-copper metallogenetic belt, is located in the middle north of Gangdise. The authors analyzed the mineral composition, major elements, trace elements, and U-Th-Pb composition of zircon from biotite granite associated with copper mineralization in the Ri’a copper polymetallic deposit by LA-ICP-MS. The results show that the biotite granite has typical characteristics of I-type granite, belongs to shoshonite series and must have originated from a crustal-mantle provenance. Zircon U-Th-Pb dating yielded 206Pb/238U age of （89.9±1.6）Ma, which is consistent with the age of mafic intrusive in the Ri’a copper-polymetallic deposit. Combined with the results of previous studies, the authors hold that the bimodal magmatism of Early Late Cretaceous was closely related to mineralization of the Ri’a copper-polymetallic deposit. In consideration of the tectonic environment, the authors propose that the magmatism was controlled by the subduction of both Bangong Co-Nujiang ocean crust and Brahmaputra ocean crust.