关键词: 仙人岩, 二长岩, 锆石U-Pb定年, Hf同位素, 地质意义, 金矿床

Abstract: The Xianrenyan pluton is located in the south of Shuikoushan ore field, Hunan Province. There develops Au, Cu, Mo and Zn mineralization in inner and outer contact zones of the pluton, which shows the colse relationship between the pluton and the metallic mineralization. Zircon LA-MC-ICP-MS U-Pb age of the monzonite suggests a weighted mean age of (156.09±0.46) Ma (MSWD=1.4) which implies that the pluton was emplaced in Early Yanshanian period. The in-situ Hf isotopic analysis reveals ¹⁷⁶Hf/¹⁷⁷Hf ratios in the zircon range from 0.282 243 to 0.282 904, and ε_Hf(t) from -15.55 to 7.87 (with peak value around -10), and the two stage Hf model ages(T_DM2) from 703 Ma to 2 188 Ma(with peak value around 1 800 Ma), which indicates that parental magma of the pluton  was derived from the mixed sources of the lower crust and mantle. Based on the geochemistry of the rocks, it can be concluded that the monzonite was mainly resulted from remelting of the Mesoproterozoic basement rocks and formed in Middle and Late Jurassic when the crust was in an extension-thinning geodynamic setting. In addition, the authors compare and analyze the lithogeochemical characteristics of the Xianrenyan pluton and the Shuikoushan stock. The fact that the Xianrenyan pluton has a weaker differentiation than the Shuikoushan pluton gives the reason for its unfavorable gold mineralization.

Key words: Xianrenyan, monzonite, zircon U-Pb geochronology, Hf isotope, geological significance, gold deposits