Petrogenesis of the Quanzigou porphyry Mo deposit at the northern margin of the North China Craton: Constrains from geochronology, geochemistry, and Sr–Nd–Hf isotopes characteristics

Abstract

The Quanzigou Mo deposit is located in the western portion of the northern margin of the North China Craton (NCC). The results of molybdenite Re–Os isotopes indicate that the mineralization occurred at 170.8 ± 2.0 Ma. It is coeval with the mineralization-related porphyritic biotite granite pluton and granite porphyry dykes of respectively 170.3 ± 1.1 Ma and 169.3 ± 1.0 Ma (zircon U–Pb ages). Thus, the Quanzigou deposit is confirmed to fill the gap of the regional early Yanshanian (i.e., Early–Middle Jurassic) porphyry Mo deposits in this study. Whole-rock εNd(t) (−12.09 to −9.72; mean = −10.80) and zircon εHf(t) values (−16.28 to −9.23; mean = −12.01) of the Quanzigou granites indicate that they originated from the lower continent crust involving some depleted mantle material. Zircon oxygen fugacity results (fO2) show that the mineralization-related granites are high magma fO2 with an average ΔFMQZr (departure from the fayalite–magnetite–quartz oxygen buffer) of +1.1 in the porphyritic biotite granite pluton and an average ΔFMQZr of +1.0 in the granite porphyry dykes, respectively. Because of the relative low-fO2 of the ancient lower continent crust, the high-fO2 source might be associated with continuously metasomatic fluids/melts from the high-fO2 lithospheric mantle, which was metasomatized by the fluids/melts of the preexisting high-fO2 sediments during the closure of the paleo-Asian Ocean. Therefore, the high-fO2 granites are formed during the tectonic setting of the post-collisional compression-to-extension transition caused by the continental collision between the Siberian plate and the NCC. Their high-fO2 characteristics were inherited from the early oceanic crust sediments during the closure of the paleo-Asian Ocean.