关键词: 大银山金矿, 矽卡岩, 岩石地球化学, 锆石U-Pb定年, 锆石Lu-Hf同位素

Abstract: The Dayinshan deposit, located in the conjunction zone between the lower Yangtze passive margin and the Jiangnan paleo-island arc, is a skarn gold deposit associated with the quartz diorites. In this study, U-Pb ages and Lu-Hf isotope compositions of zircon grains extracted from quartz diorites were measured combining with major and trace elemental geochemistry, with aims to elucidate the timing of the gold mineralization and the origin of the ore-related quartz diorites. LA-ICP-MS zircon U-Pb dating gives the weighted mean ages of 144 ±1 Ma for quartz diorites. The quartz diorites are high K calcium alkaline to calcium alkaline and aluminum to peraluminous. All the samples are enriched in large ion lithophile elements (Ba, Rb, Sr, K) and depleted in high field strength elements (Nb, Ta, Ti) and heavy rare earth elements, with weakly negative Eu anomalies. The results show that quartz diorites of Dayinshan have a similar characteristics of arc magmatic rocks associated with subduction zone. The quartz diorites also have lower Sr/Y value and higher Y and Yb content, indicating that its magma comes from the thinner continental crust. Zircon Hf isotope model ages vary from 1.51 to 1.82 Ga, with an zircon εHf(t) value of -5.0~-9.9. All of these features are consistent with the gold deposit from the Yangtze River metallogenic belt. Detailed elemental and isotopic data demonstrate that these rocks were derived from partial melting of the lower crust of the Yangtze plate induced by subduction of the paleo-Pacific in late Mesozoic.