U-Pb dating and Hf isotopic characteristics of zircons from granodiorite in the Dexing ore concentration area

Abstract：The Dexing ore concentration area located at the juncture between Qiantang body and Jiangnan body is one of the large ore concentration areas along the Qinhang metallogenic belt of eastern China. It includes Tongchang, Fujiawu and Zhushahong porphyry Cu-Mo-Au deposits, Yinshan Ag-Cu -Pb-Zn polymetallic deposit, Jinshan gold deposit and other large and superlarge ore deposits. Based on systematic field geological survey and sample acquisition, this paper presents in situ zircon U-Pb and Hf-isotopic data of Tongchang, Fujiawu, Zhushahong and Yinshan deposits: 171±1.2 Ma for Tongchang, 172 ±0.68 Ma Ma for Fujiawu, 173 ±1.3Ma for Zhushahong, and 176±1.5 Ma Ma for Yinshan. These data show that all the granodiorite-porphyry bodies were formed in the Early-Middle Jurassic period. Zircon in-situ analysis of four samples gives the average εHf(t) values of (4.34~5.54) with limited variation and Hf crustal model ages of 861Ma, 876 Ma, 904 Ma and 941Ma. The Zr/Hf ratios are close to the Zr/Hf ratio of the upper mantle . Zircon Hf isotopic composition suggests that the parental magmas of the rock bodies were mainly derived from a young mantle and partly mixed with old continental crust rock during the evolution. Mantle material in the Dexing ore concentration area played an important role in the formation of the granodiorite porphyry. The most important rock-forming and ore-forming period of the four deposits should be in 170 ~ 175 Ma. The continual magmatic hydrothermal activation might have been the important factor responsible for the formation of the Dexing ore district.