Mineralization Age and Ore forming–Source of Niukutou Pb–Zn Deposit, Qinghai: Evidence from Geochronology of Ore–forming Rock Bodies and Re–Os Geochemistry of Pyrite

The Qimantagh area of East Kunlun orogeninc belt is an important skarn–type polymetallic mineralization belt in Qinghai, and the Niukutou deposit is located in the central–western part of this area, which is one of the middle–large Pb–Zn skarn deposits in Qimantagh area. In view of the controversy about the diagenetic and metallogenic age and the source of the metal ore–forming materials of Niukutou ore district, the zircon and pyrite chronology has been studied by LA–ICP–MS and thermal surface ionization mass spectrometry Re–Os isotope testing technology in this paper. The results show that the ages of the ore-forming granite bodies at the bottom of the 10 line drill hole in the M1 ore block of Niukutou ore district are (362.2±2.7) Ma and (361.8±3.4) Ma respectively, and the Re–Os isochron age of the pyrite closely associated with the sphalerite in the main mineralization stage is (359.2±6.3) Ma. This shows that the diagenesis and mineralization age of the skarn Pb–Zn polymetallic deposit in Niukutou ore district are coupled at (362.2±2.7)～(359.2±6.3) Ma, which further indicates that the skarn Pb–Zn polymetallic deposit was formed in the late Devonian of Variscan. The initial ¹⁸⁷O_S/¹⁸⁸Os of pyrite is 0.13±0.24, which indicates that the metal ore–forming materials of Niukutou Pb–Zn deposit are of crust mantle mixed source, and formed under the extensional background of collision–post collision in the tectonic magmatic cycle from Early Paleozoic to early Late Paleozoic at Late Devonian.