Geochronology, geochemistry and Hf-Sr-Nd isotopes of the ore-bearing syenite from the Shapinggou porphyry Mo deposit, East Qinling-Dabie orogenic belt

The Shapinggou Mo deposit is located in the western Dabie mountains, the eastern part of the Qinling-Dabie molybdenum orogenic belt. Shapinggou Mo deposit is a concealed deposit with the ore body mainly hosted by explosive breccia of Gaijing and the granite porphyry as well as the syenite of Shapinggou. Geochemistry study show that the SiO2 contents of Shapinggou syenite range from 61.74 to 69.93%, and the A/CNK from 0.95 to 1.06, classified as metaluminous to weak peraluminous, belonging to alkalic to shoshonitic series. The Mo deposits in Qinling Mo belt formed in two main periods, i.e., the first period occurred in to the Early Cretaceous (145-130 Ma), the second period in the late Early Cretaceous (130-110 Ma). Most of the Mo deposits in Dabie region formed in the second period. The results of zircon U-Pb show that the age of the Shapinggou syenite is 111.3 ± 1.2 Ma, which belongs to the second period. Proterozoic-Archean inherited zircons suggest that it may include some more ancient crustal material like Kongling group. The ɛHf(t) values of Shapinggou syenite range from −15.6 to −8.0, TDM2(Hf) from 1.7 to 2.16 Ga, respectively. The ɛNd(t) values of the Shapinggou syenite range from −12.29 to −11.76, TDM2(Nd) from 1.85 to 1.89 Ga, the 87Sr/86Sr from 0.709 to 0.710, respectively. Results of zircon Hf isotope and whole rock Sr-Nd isotope of Shapinggou syenite indicate that the Mo ore-forming materials were mainly generated from old Yangtze craton, e.g., gneiss from Dabie orogeny, mixed with some juvenal mantle materials. The geodynamics of the Shapinggou Mo deposit corresponded to an extension period in Eastern China, which caused by large scale lithospheric thinning. The delamination caused asthenosphere upwelling and crust-mantle interaction, which provided the ore-forming material and heat.