| Some Au deposits in the Jiangnan transition zone at southern Anhui Province have recently been found to be closely associated with late Mesozoic intrusions.Examples include the Huashan Au(Sb)deposit and Au deposits at Zhaojialing,Wuxi,and Liaojia.In order to understand the mechanisms that led the formation of these Au deposits,we present new LA-ICP-MS zircon U-Pb dating,along with elemental and Hf isotopic data from our case-study the Huashan Au(Sb)deposit.Our data suggest that the ore-related intrusions were emplaced during the late Jurassic and early Cretaceous periods(144-148 Ma).They are characterized by arc-magma features and high oxygen fugacity and are rich in inherited zircons,and underwent fractional crystallization and crustal assimilation processes during their evolution.Relatively low contents of Sr and Eu,as well as positive correlation between(Gd/Yb)N and(La/Yb)N suggest that the magmas have evolved from a moderate deep environment,which is correspond to a relatively thick continental crust.Zircon U-Pb ages and Lu-Hf isotopes from intrusions suggested that Proterozoic juvenile lithosphere was the main source of these intrusions.The regional geological history implied that lithosphere beneath southern Anhui was produced during a Proterozoic subduction and was fertilized with Au(Cu)in the process.Integrated with the results of previous studies,we inferred that late Mesozoic intrusions formed by the remelting of the lithosphere could provide the metal endowment for the Au-rich deposits in southern Anhui.Results from electron probe micro-analysis showed that pyrite and arsenopyrite are the main Au-carrying ore minerals present in Huashan,where Au is unsaturated and occurred as a nanoparticle(Au0).Some antimony minerals have detectable Au contents.According to the spatial relationship among minerals,we suggest that the Au-bearing antimony could overlie on previous stage Au-bearing pyrite-arsenopyrite veins,and contain Au nanoparticles. |
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