Abstract: The Luming Molybdenum deposit is one of newly discovered large porphyry deposits in Xiao Hinggan Mountains metallogenic belt. The deposit occurs in the monzonitic granite. In the monzonitic granite, SiO₂ contents are 71.98％ and 77.17％, K₂O+Na₂O  8.06％ and 9.07％, K/Na ratios 1.14 and 7.25 and A/CNK ratios are 0.95 and 1.05, with high silica and alkalirich. It’s abundant amount of HFSE. The average of FeO^T is 2.0%，Ga×104/Al is 2.75，Zr content are 76.2×10^-6 and 134×10^-6，which showed the characteristics of A-type granite. The granite from Luming area has content of δEu(0.36~0.56), and ratios of element couples (K/Rb, K/Cs, Rb/Cs, Rb/Li, Li×10³/Mg, Rb/Sr) are similar to those of syntexis-type granitoids in South China, showing the characteristics of crustalmantle magma mixing. In the trace element spider diagram, there are a negative anomaly of Ba, Y and positive anomaly of Rb, Th, Ce, Sm. To determine the age of Luming monzonitic granite, the LA-ICP-MS zircon U-Pb dating is applied and gives a diagenesis age of (187.1±1.2) Ma. The Re-Os contents of molybdenite from Luming Mo deposit are determined by ICP-MS. The results show the Re-Os isochron age of (177.4±3.5) Ma and weighted mean age of (178.08±0.79) Ma, which indicate that the mineralization is later than the diagenesis. Trace element and isotopic tracing show that both diagenesis and mineralization of the Luming Mo deposit were related to changes of tectonic environment from compression to extension. Ore-forming materials were derived from upper mantle and lower crust.

Key words: zircon LA-ICP-MS U-Pb dating, alkali-rich monzonitic granite, Re-Os dating, molybdenum deposits, Xiao Hinggan Mountains