SIMS zircon U–Pb and molybdenite Re–Os geochronology, Hf isotope, and whole-rock geochemistry of the Wunugetushan porphyry Cu–Mo deposit and granitoids in NE China and their geological significance

Abstract

The geodynamic setting of magmatic rocks and geodynamic mechanism of Cu–Mo–Fe–Sn–Pb–Zn–Ag polymetallic mineralization in northeastern (NE) China are attracting increasing attention. This study explores these issues by providing SIMS zircon U–Pb dating, whole-rock geochemical, Hf isotopic data of magmatic rocks, and molybdenite Re–Os dating exposed in the Wunugetushan porphyry Cu–Mo deposit, NE China. This deposit is located in the western part of the Great Xing'an Range, on the southeastern margin of the Mongol–Okhotsk Orogenic Belt. Molybdenite Re–Os and SIMS zircon U–Pb dating of the host monzogranitic porphyry and the wall rock of biotite granite in the Wunugetushan porphyry Cu–Mo deposit indicate that the ore-formation, host porphyry, and wall rock-emplacement occurred at 180.5±2.0Ma, 180.4±1.4Ma, and 203.5±1.6Ma, respectively, and the mineralization of the Wunugetushan porphyry Cu–Mo deposit occurred during the same period as that of the host monzogranitic porphyry. Geochemically, the Wunugetushan granitoids are characterized by strong LREE/HREE fractionation, and pronounced negative Nb, Ta, and Ti anomalies, with slightly negative Eu anomalies (Eu/Eu*=0.71–0.97) of the host monzogranitic porphyry and pronounced negative Eu anomalies (Eu/Eu*=0.29–0.32) of the wall rock of biotite granite. In situ Hf isotopic analyses of zircons from the host monzogranitic porphyry and the wall rock of biotite granite yielded εHf(t) values ranging from 0.5 to 8.2, and from −6.9 to 5.9, respectively. The geochemical and isotopic data for the Wunugetushan granitoids imply that the primary magmas of the host monzogranitic porphyry could have originated by partial melting of a thickened lower crust, with input of mantle components, while the primary magmas of the wall rock of biotite granite could have been derived by partial melting of a thickened lower crust that mixed with ancient crustal materials. Based on the regional geological history, geochemistry of the Wunugetushan granitoids, and new isotopic age data, we suggest that the formation of the Wunugetushan porphyry Cu–Mo deposit was possibly induced in the Early Jurassic during the period of the southeastward subduction of the Mongol–Okhotsk oceanic plate beneath the Erguna Massif.