Early Cretaceous adakitic granites and mineralization of the Yili porphyry Mo deposit in the Great Xing’an Range: implications for the geodynamic evolution of northeastern China

Abstract

The Yili porphyry-type molybdenum deposit is located in the Northeastern Inner Mongolia Autonomous Region in China. Mineralization occurs mainly as veins, lenses, and layers within the host porphyry. In order to better understand the link between mineralization and host igneous rocks, we studied samples from underground workings. We report new Sensitive High Resolution Ion Microprobe II (SHRIMP II) zircon U–Pb and Re–Os molybdenite ages and geochemical data from the Yili granitoids. Five molybdenite samples yield a Re–Os isochron weighted mean age of 131.1 ± 3.4 Ma, while two Early Cretaceous adakitic porphyry granite samples yielded crystallization ages of 128.1 ± 1.6 Ma and 129.0 ± 3.5 Ma. The U–Pb and Re–Os ages are analytically indistinguishable, suggesting that mineralization was genetically related to Early Cretaceous magmatism in northeastern China. δ34SV-CDT values of the sulphide vary from 0.3‰ to 3.8‰. We obtained two weighted mean U–Pb zircon ages of 287.7 ± 1.8 Ma for early Permian fine-grained granite and 349.8 ± 2.3 Ma for Early Carboniferous monzogranite in Yili area, respectively. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Yili deposit occurred at the same time as Early Cretaceous lithospheric thinning, which was caused by the delamination and subsequent upwelling of the asthenosphere under the intra-continental extension in northeastern China.