Petrogenesis of the Yangchang Mo-bearing granite in the Xilamulun metallogenic belt, NE China: geochemistry, zircon U-Pb ages and Sr-Nd-Pb isotopes

The Yangchang granite-hosted Mo deposit is typical of the Xilamulun metallogenic belt, which is one of the important Mo-Pb-Zn-Ag producers in China. A combination of major and trace element, Sr, Nd and Pb isotope, and zircon U-Pb age data are reported for the Yangchang batholith to constrain its petrogenesis and Mo mineralization. Zircon LA-ICPMS U-Pb dating yields mean ages of 138±2 and 132±2Ma for monzogranite and granite porphyry, respectively. The monzogranites and granite porphyries are calc-alkaline with K₂O/Na₂O ratios of 0.75-0.92 and 1.75-4.42, respectively. 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. The monzogranites have relatively high Sr (380-499ppm) and Y (14-18ppm) concentrations, and the granite porphyries have lower Sr (31-71ppm) and Y (5-11ppm) concentrations than those of monzogranites. The monzogranites and granite porphyries have relatively low initial Sr isotope ratios of 0.704573-0.705627 and 0.704281, respectively, and similar ²⁰⁶Pb/²⁰⁴Pb ratios of 18.75-18.98 and 18.48-18.71, respectively. In contrast, the ε_Nd(t) value (-3.7) of granite porphyry is lower than those of monzogranites (-1.5 to -2.7) with Nd model ages of about 1.0Ga. These geochemical features suggest that the monzogranite and granite porphyries were derived from juvenile crustal rocks related to subduction of the Paleo-Pacific plate under east China.