U–Pb and Re–Os geochronological evidence for the Jurassic porphyry metallogenic event of the Xiongcun district in the Gangdese porphyry copper belt, southern Tibet, PRC

Abstract

Two large copper–gold porphyry deposits (No.I and No.II) were discovered in the last decade within the Xiongcun district, which is located along the south margin of the Gangdese porphyry copper belt. These two deposits are hosted by two porphyries that were emplaced into the Early Jurassic volcano-sedimentary rock sequences of the Xiongcun Formation. The porphyries are both quartz diorite bodies, with one of these distinguished by its large quartz eyes. Our new molybdenite Re–Os and zircon U–Pb dates for No.I and No.II deposits and host intrusions reveal the presence of two Middle Jurassic ore-forming episodes in the Xiongcun district. The No.II deposit is related to the 181–175Ma quartz diorite porphyry and formed ca. 172.6±2.1Ma. The No.I deposit is related to the 167–161Ma quartz diorite porphyry with large quartz eyes and formed ca. 161.5±2.7Ma. Geochronological and geochemical features of the Jurassic ore-bearing porphyries in the Xiongcun district indicate that the porphyry copper–gold mineralization formed in an island arc setting, which is related to the northward subduction of the Neo-Tethys oceanic plate. These observations, in combination with geochronological data reported at Gangdese porphyry copper belt, indicated four major metallogenic events existed in the Gangdese porphyry copper belt at 172–161Ma, 65–48Ma, 40–23Ma, and 20–12Ma. We have identified two mineralization episodes comprise Middle Jurassic metallogenic event (172–161Ma) in the Xiongcun district, which provides new constrains for the Middle Jurassic metallogenic event in the Gangdese porphyry copper belt.