Genesis of the Chehugou Mo-bearing granitic complex on the northern margin of the north China Craton: geochemistry, zircon U-Pb age and Sr-Nd-Pb isotopes

The Chehugou granite-hosted molybdenum deposit is typical of the Xilamulun metallogenic belt, which is an important Mo-Ag-Pb-Zn producer in China. A combination of major and trace element, Sr and Nd isotope, and zircon U-Pb isotopic data are reported for the Chehugou batholith to constrain its petrogenesis and Mo mineralization. The zircon SIMS U-Pb dating yields mean ages of 384.7 ± 4.0 Ma and 373.1 ± 5.9 Ma for monzogranite and syenogranite and 265.6 ± 3.5 Ma and 245.1 ± 4.4 Ma for syenogranite porphyry and granite porphyry, respectively. The Devonian granites are calc-alkaline with K ₂O/Na ₂O ratios of 0.44-0.52, the Permian granites are alkali-calcic with K ₂O/Na ₂O ratios of 1.13-1.25, and the Triassic granites are calc-alkaline and alkali-calcic rocks with K ₂O/Na ₂O ratios of 0.78-1.63. They are all enriched in large-ion lithophile elements (LILEs) and depleted in high-field-strength elements (HFSEs) with negative Nb and Ta anomalies in primitive mantle-normalized trace element diagrams. They have relatively high Sr (189-1256 ppm) and low Y (3.87-5.43 ppm) concentrations. The Devonian granites have relatively high initial Sr isotope ratios of 0.7100-0.7126, negative ε _Nd(t) values of -12.3 to -12.4 and ²⁰⁶Pb/ ²⁰⁴Pb ratios of 16.46-17.50. In contrast, the Permian and Triassic granitoids have relatively low initial ⁸⁷Sr/ ⁸⁶Sr ratios (0.7048-0.7074), negative ε _Nd(t) values of -10.1 to -13.1 and ²⁰⁶Pb/ ²⁰⁴Pb ratios of 17.23-17.51. These geochemical features suggest that the Devonian, Permian and Triassic Chehugou granitoids were derived from ancient, garnet-bearing crustal rocks related to subduction of the Palaeo-Asian Ocean and subsequent continent-continent collision between the North China and Siberian plates.