Age, geochemistry, Nd-Hf isotopes and relationship between granite and gold mineralization of Zhongchuan granitoid pluton in West Qinling

The Zhongchuan granitoid pluton is located in the east of the Western Qinling. Zircon LA-ICPMS dating for the porphyritic monzogranite from the Zhongchuan pluton yielded an age of (221±1)Ma (MSWD=0.26), the age of fine-grained monzogranite is (217±1)Ma(MSWD=0.107), that of magmatic enclave include phenocryst is (220±1)Ma(MSWD=0.107), that of magmatic enclave is (216±1)Ma (MSWD=0.26) and that of fine-grained granite vein is 207±1Ma(MSDW=0.29). Magmatic enclave and rock mass have the same age, and the age of granite vein is the youngest, indicating that the ages gradually become younger from the edge to the center. The rock mass and magmatic enclave are respectively of meta-aluminous or weakly peraluminous, high-K calc-alkaline and high-K calc-alkaline or shoshonite series with the Litman index(σ) being 2.20-3.85, 2.24-9.22 and A/CNK being 0.99-1.15, 0.75-1.08. Their REE and trace elements are enriched in large ion lithophile elements (LREE, Rb, Ba, K) and depleted in high-field strength elements(HREE, Zr, Hf, Ta, Nb, P, Ti), with slightly negative to positive anomalies of Eu (δEu=0.29-0.91) and no anomalies of Ce. These characteristics suggest that the granitoids have I type granite features, and the fine-grained monzogranite is located in the center with some highly fractionated I type granite features. The main oxides of rock mass and MME have a good linear relationship in Harker diagram. Nd isotopic compositions of the rock mass and MME are mainly characterized by ε_Nd(t) values of -7.31--8.73 and-5.32--5.69, and T_DM2 of 1.59-1.71 Ga and 1.43-1.46 Ga. Zircon Hf isotopic compositions of the rock mass and MME are mainly characterized by ε_Hf(t) values of-7.02--0.31 and -3.0-0, T_DM2 of 1.27-1.70 Ga and 1.2-1.5 Ga. These characteristics suggest that the rock mass was derived from partial melting of ancient crustal material and magmatic enclave was derived from the lithospheric mantle, with some mixture. The formation of gold deposits was closely related to Zhongchuan granitoid pluton in time and space, and the age of the gold deposit are slightly later than that of Zhongchuan granitoid pluton and close to that of granite vein. Mineralization data indicate that ore-forming material and lithogenous material were similar to each other. These data indicate that magmatism not only provided a thermal source for the mineralization but also offered ore-forming material.