东秦岭金堆城花岗斑岩体的锆石U-Pb年龄、物质来源及成矿机制

通过LA-ICP-MS方法测得金堆城和老牛山花岗岩体中锆石U-Pb年龄分别为143.7±3 Ma和144.5±4.4 Ma,与金堆城钼矿床中辉钼矿的Re-Os年龄139±3.0 Ma在误差范围内一致,界定了金堆城成岩成矿时代为侏罗纪末-白垩纪初,2个岩体为同期岩浆事件的产物,与燕山运动有关.金堆城岩体较老牛山岩体富SiO₂、K₂O,岩石地球化学数据显示2个岩体都具有一致的高硅、富碱、过铝质系列和钙碱性岩石系列特征;高的ε_Sr(t)、低的ε_Nd(t)及Pb同位素图解证明2个岩体主要来自下地壳物质部分熔融,可能有少量地幔物质加入.年代学与岩石地球化学数据证实老牛山岩体和金堆城岩体的岩浆源区与岩石成因相同,推测老牛山岩体在深部发生分异演化,为金堆城小岩体提供了大量的热液和矿物质,从而出现了金堆城小岩体成大矿现象. 

Metallogenic Mechanism,Magma Source and Zircon U-Pb Age of Jinduicheng Granitic Porphyry,East Qinling

Zircon U-Pb isotopic ages of Jinduicheng and Laoniushan granite are measured by LA-ICP-MS techniques, and we find that the mean ages are 143.7±3 Ma and 144.5±4.4 Ma respectively, which correspond to the molybdenite Re-Os age 139±3.0 Ma of Jinduicheng molybdenite polymetallic deposit. It indicates that the diagenetic and metallogenic ages of Jinduicheng deposit are between Jurassic and Cretaceous, related with Yanshan movement. Granites in Jinduicheng are richer in SiO₂, K₂O than those in Laoniushan. The geochemical data demonstrate that Jinduicheng and Laoniushan granites are both characterized with high Si, rich alkali, peraluminous rock series and the calcium alkaline rock series, which indicate that the rock-bodies belong to the continental crust granite; the high ε_Sr (t), low ε_Nd(t), and the Pb isotope values prove the main source of the rock-bodies is partial melting of lower continental-crust materials. The chronology and the litho-geochemical data confirm that Laoniushan and Jinduicheng granite are the same magma source area, and it is concluded that Laoniushan rock body has provided mass hydrothermal and mineral substance in depth for the small Jinduicheng rock body, which in turn led to the phenomenon of the Jinduicheng small rock body containing large ore deposit.