Geochemistry, Zircon U-Pb Dating and Geological Significance of Diorite Porphyrite in Xiarihamu Deposit, Eastern Kunlun Orogenic Belt, Qinghai

Diorite porphyrite mainly emerges in the north part of Xiarihamu Cu-Ni deposit in Qinghai province. The zircon LA-MC-ICP-MS U-Pb dating result of diorite porphyrite is 381.7±1.9 Ma (MSWD = 0.20), which falls into Middle Devonian. Considering field occurrence of diorite porphyrites intruding mineralization complex, it is demonstrated that the Xiarihamu Ni deposit formed before Middle Devonian. The petrology and chemical components of diorite porphyrite show that they are calc-alkaline and metaluminous rocks with the characteristics of high-Na (K₂O/Na₂O = 0.45-0.60), low ΣREE (128.28×10^-6-141.65×10^-6) and obvious fractionation of LREE and HREE ((La/Yb)_N = 6.86-7.96). It has relatively high ratio of La/Nb (3.32-3.76, and the average is 3.57), Th/Nb (0.95-1.02, and the average is 0.99) and Th/La (0.266-0.291, and the average is 0.278). It can be concluded that the diorite porphyrite is the product of lower crustal partly melting according to discrimination diagrams. Combining with the regional tectonic evolution background, the diorite porphyrite in Xiarihamu Cu-Ni deposit is formed in the extension to intraplate tectonic setting.