Ziron U-Pb geochronology of Niubiziliang mafic-ultramafic intrusion on the northwest margin of Qaidam Basin, Qinghai

Abstract: The newly-discovered Niubiziliang Ni-Cu deposit is located in the intersection part of the Altum southern fault zone and the Qaidam northern fault zone, Northwest China. There are three mafic-ultramafic intrusions, of which No. Ⅱ and No. Ⅲ intrusions are Ni-Cu sulfide-bearing intrusions. The intrusions consisted of, from the south to the north, peridotite facies, pyroxenite facies and gabbro facies. The peridotite facies contains hornblende lherzolite, hornblende peridotite, lherzolite and plagioclase lherzolite, the pyroxenite facies contains olivine websterite and websterite, and the peridotite facies consists of Ni-Cu bearing rocks. High-precision LA-ICP-MS zircon U-Pb dating yielded the concordant ages of 388.0±2.8 Ma, 402.2±2.8 Ma and 402.8±2.6 Ma for diorites of No.Ⅰ intrusion, lherzolites of No.Ⅱ ore-bearing intrusion and plagioclase lherzolite of No. Ⅲ ore-bearing intrusion, respectively. Regional tectonic evolution background indicates that the Niubiziliang rocks were formed in a post-orogenic extension environment in early Devonian and that the magma originated from mantle material. The Niubiziliang mafic-ultramafic intrusions are new type rocks containing nickel mineralization, and they have good potential for Ni-Cu sulfide exploration.