Geochronology and geochemistry of granite of the Luming molybdenum deposit in Heilongjiang and their geological significance

Abstract：The recently-discovered Lumin molybdenum deposit is located in the southern section of the Yichun-Yanshou polymetallic ore-forming belt. The ore-forming rocks mainly include adamellite -granite porphyry, and the LA -ICP - MS micro- situ isotopic analysis shows that their ages are195.4±1.4 Ma and 197.6±1.3 Ma, suggesting products of the late Indosinian - Early Yanshanian period. Geochemical studies indicate that SiO2 (wt%) values vary in the range of 3.36%~5.78%，whereas K2O and Na2O vary in the range of 3.36%~5.78% and 2.60%~3.78% respectively. Rittmann indexes vary between 0.9 and 3.1. Analysis shows that the intrusions belong to high-K calc-alkaline-shoshonitic series. The ΣREE values are low with a strong fractionation between light and heavy rare earth elements（LaN/YbN=7.76~26.47） and obvious Eu negative anomaly（Eu/Eu?鄢=0.34~0.62）. Trace elements display enrichment of Rb, Th , U , K and depletion of Nb , Ta, Ti, Y, Yb , suggesting that the source might have been a relatively water-rich magma, or the magma might have suffered from metasomatism by subduction zone fluid. Combined with results of previous studies, it is concluded that the formation of the deposit was probably controlled by the subduction of Pacific plate in early Mesozoic.