Abstract:Lanjiagou molybdenum deposit is located in western Liaoning province and associated temporal–spatially with Lanjiagou granite which is composed of fine-grained and coarse-grained granite. The orebodies occurred at the inner of the fine-grained granite or the contact zone between the fine-grained granite and the coarse-grained granite. Main elements analysis of Lanjiagou granites shows that they are rich in Si (ω(SiO2)=73.65%~77.88%), alkalis (ω(K2O)+ω(Na2O)=5.92%~9.14%), metaluminous (A/CNK=0.99~1.07). The chondrite-normalized REE patterns are characterized by LREE enrichment with variable of middle negative Eu anomalous (δEu=0.52~0.66). The primitive mantle-normalized spidergrams show that they are depleted in Ba, Sr, P, Ti and Nb. In the SiO2-P2O5 diagram, the P2O5 contents show a decrease trend with increasing SiO2 contents. These geochemical characteristics suggest that Lanjiagou granite underwent less fractional crystallization processes and belong to differential I-type composite granite. The fine-grained granite and coarse-grained granite belong to the same evolutional series in source. They Zircon SHRIMP U-Pb dating for the fine-grained granite yields concordant ages from 184.7 to196.4 Ma, with a weighted mean age of (188.9±1.2) Ma. The U-Pb ages are almost identicalness with Re-Os age ((186.5±0.7) Ma), suggesting that the granite emplacement and Mo mineralization occurred in Early Jurassic and the mineralization is probably genetically associated with the granite. Base on regional geology data, we draw a conclusion that the emplacement of Lanjiagou granite and the mineralization timing of the molybdenum deposit occurred in Early Jurassic during the compression deformation period in Yan-liao area.