Origin and Geodynamic Implications of Concealed Granite in Shadong Tungsten Deposit, Xinjiang, China: Zircon U-Pb Chronology, Geochemistry, and Sr-Nd-Hf Isotope Constraint

Shadong deposit is the first large-scale tungsten deposit found in the East Tianshan orogenic belt, and the geologic characteristics of the deposit indicate that the deeply concealed granite body is genetically related with the mineralization. The LA-ICPMS U-Pb age of zircons from the Shadong concealed granite obtained in this research is 239 +/- 2.0 Ma, belonging to the Middle Triassic. The whole rock samples are metaluminous to slightly peraluminous (A/CNK=0.95-1.02) with low contents of SiO2 (64.0 wt.%-68.5 wt.%) and low K2O/Na2O ratios (0.73-0.96). The samples reveal enrichment of K, Rb, Th and depletion of Nb, Ta, P, Ti and have a negative slope from La to Lu (La-N/Yb-N=16.29-36.8) with weak negative Eu anomaly (Eu/Eu*= 0.71-0.82). Initial Sr-87/Sr-86 ratios of whole rock range of 0.706 59-0.707 75, epsilon (Nd)(t) values range from -1.77 to -2.53 and epsilon (Hf)(t) values of zircon are between 2.54 and 4.90. The lithogeochemistry and Sr-Nd-Hf isotopic characteristics revealed that the concealed granite in Shadong tungsten deposit is I-type granite, and occurs in an intraplate tectonic setting. The magma mixing during intraplating of mantle derived magma intruding into the crust in Indosinian Period is the major formation mechanism of the granite. Of which, the proportion of mantle derived magma ranges from 58% to 60%, and the crustal materials are mainly the metamorphic basement of Xingxingxia Group of Mesoproterozoic Changcheng System, which may provide the main source of ore forming metals of Shadong tungsten deposit.