Fluid Inclusions and Geochronology of Wulunbulake Copper Deposit in Xinjiang

Wulunbulake copper deposit is located at the north-western segment of the Yemaquan-Qiongheba Cu-polymetallic metallogenic belt, East Junggar, Xinjiang. However, its genetic type and mineralizing age has been debated. This study presents new results on fluid inclusions and zircon U-Pb dating to precisely constrain the type and time of mineralization. The dominant fluid inclusions in Wulunbulake copper deposit are liquid-rich type, with low homogenization temperature (136.9-224.5℃), low salinity (1.7%~5.6% NaCl eqv.) and low density (0.97-1.01 g/cm³), the mineralizing pressure is 2.76×10⁷-4.49×10⁷ Pa and the corresponding depth is 1.04-1.95 km. The laser Raman spectroscopy results indicate that the ore-forming fluids consist of H₂O, CH₄, N₂, H₂. Zircon U-Pb dating results show that the formation age of ore-bearing quartz diorite and quartz porphyry is 440.5±3.3 Ma, and 419.7±3.3 Ma, respectively, indicating that there had experienced two-stage magmatic activities from Early Silurian. From the interior to the outer part of the deposit, there exist typical alteration zonation characteristics of porphyry deposits (silica alternation-potassic alternation-phyllic alternation-propylitization), and the geochemical characteristics of ore-bearing indicate that they were most possibly formed in arc setting. Its genetic type should be typical porphyry copper deposit and related to the southward subduction of the Paleo-Asian oceanic crust in the Early Silurian period. The East Junggar even northern Xinjiang was in the island arc environment in the Silurian, and the magmatic zone is a potential area for formation and prospecting of porphyritic Cu deposit.