Geochronology and zircon Hf isotope geochemistry of granites in the giant Chalukou Mo deposit, NE China: Implications for tectonic setting

Abstract

In this contribution, the largest porphyry Mo deposit in NE China, Chalukou, is selected to provide insights into the tectonic evolution of NE China. The deposit was considered to be rift-related (or Climax-type) porphyry Mo deposit developed in an extensional setting, while other researchers attributed its formation to the subduction of the Paleo-Pacific Ocean. In view of different granite petrogenesis between rift-type and subduction-type porphyry Mo deposits, geochronological and zircon Lu–Hf isotope studies have been carried out on granitic rocks associated with the Chalukou deposit. Zircon grains from the ore-host monzogranite and ore-causative granite porphyry yield weighted mean 206Pb/238U ages of 166±2Ma and 152±2Ma, with molybdenite samples yielding a Re–Os isochron age of 150±2Ma, indicating a Jurassic age for both granitic intrusion and Mo mineralization. Zircon εHf(t) values of monzogranite and granite porphyry range from 0.9 to 3.0 and from −1.4 to 0.5, respectively. When integrated with published zircon Lu–Hf isotopic data, our data suggest that the barren granites (both pre- and post-ore) were mainly derived from mantle-derived juvenile rocks, whereas the syn-ore granite requires additional involvement of old continental crust. Thus, a contribution of continental crust to Mo mineralization is suggested. The petrogenesis and geochemical data reveal that the Chalukou deposit is a subduction-related porphyry Mo deposits and not rift-related. Integrated evidence links its formation to the southeastward subduction of the Mongol–Okhotsk Ocean, instead of the westward subduction of the Paleo–Pacific Ocean.