Geochronology, Geochemistry, Lu-Hf isotope of Granites from the Tengjia Gold Mine in the Northwest Jiaodong and Its Geological Significance

The Jiaodong area is rich in gold resources, granite is often the ore-bearing rock of gold ore bodies, closely related to the formation of gold deposits in space. The Tengjia gold deposit in Zhaoyuan is a newly discovered super large gold deposit. The gold ore bodies mainly exists in altered and broken granite. To find out the formation age, petrogenesis, source characteristics and tectonic environment of the granite is the basis for understanding the genesis of the deposit. In this paper, the petrogeochemistry, zircon U-Pb chronology and Lu-Hf isotopic composition of two types of granites at different depths from boreholes in Tengjia mining area are studied. The granite is enriched in large ion lithophile elements( LILE) Rb, K, Th, U, and depleted high field strength elements( HFSE) Nb, P, Ti. The total amount of rare earth elements is high, the light rare earth is rich, and the heavy rare earth is deficient. They have the geochemical characteristics similar to adakitic rocks with high Sr( the average content of Sr is 436×10^-6), low Y( the average content of Y is 0.65×10^-6), and no obvious Eu negative anomaly( δEu=0.64~0.94). The LA-ICP-MS zircon U-Pb dating of the granite yields Late Jurassic age (the weighted average age is 158.9±2.0Ma and 158.7±1.7Ma).The ε_Hf(t) value in range of -29.44~-20.91, and the two-stage Hf ages (T_DM2) is 2528~3061Ma.The two types of granites in Tengjia deposit have the same geochemical characteristics, both belong to the Late Jurassic Linglong granites. The magma may originate from partial melting of the thickened lower crust, which is a response to the large-scale diagenesis and mineralization event caused by the subduction of the Yanshanian Pacific plate in eastern China.