GEOLOGY AND GEOCHEMISTRY CONSTRAINTS ON THE GENESIS OF THE NO.2 PORPHYRY COPPER-GOLD DEPOSIT IN THE XIONGCUN DISTRICT, GANGDESE PORPHYRY COPPER BELT, TIBET, CHINA

The Xiongcun district is located in the western segment of the Gangdese porphyry copper belt (GPCB). The No.2 deposit in the Xiongcun district hosts a measured and indicated resource of 1.34 Mt copper, 76.34 t gold, and 193.78 t silver. The copper-gold mineralization of the No.2 deposit is mainly hosted in the Early Jurassic quartz diorite porphyry which intruded volcano-sedimentary rocks of the Early Jurassic Xiongcun Formation. S and Pb isotopic compositions of the ore sulfides and Re contents of molybdenite suggest a mantle source with minor contamination of subducted sediments for the ore-forming materials. Hydrogen and oxygen isotopic compositions of quartz from the quartz-sulfide veins suggest that the ore-forming fluid was a mixture of magmatic and meteoric water. Geochemical and Sr-Nd-Hf isotopic compositions of the Early Jurassic quartz diorite porphyry suggest that the mineralization of the No.2 deposit formed in an intra-oceanic island arc setting. The magmas of the Early Jurassic quartz diorite porphyry were likely sourced from partial melting of mantle with limited contamination by subducted sediments (ca. 5%). The formation of the porphyry and the No.2 deposit were related to the northward intra-oceanic subduction of the Neo-Tethys oceanic slab during the Early Jurassic.