江西九瑞矿集区鸡笼山Cu-Au-Mo矿床含矿岩体的年代学及地球化学研究

ZIRCON U-Pb AGE AND GEOCHEMISTRY OF THE ORE-BEARING GRANITIC BODY FROM THE JILONGSHAN Cu-Au-Mo DEPOSIT,JIUJIANG-RUICHANG METALLOGENIC DISTRICT OF JIANGXI PROVINCE

鸡笼山是长江中下游成矿带九瑞矿集区西部的一处中小型斑岩-矽卡岩型Cu—Au—Mo矿床，与之成矿密切相关的岩体为花岗闪长斑岩。本文通过锆石LA-ICP—MSU—Pb定年，首次确定该岩体的形成于早白垩世早期（142．2Ma±1．1Ma）。元素地球化学分析结果显示，鸡笼山花岗闪长斑岩具有埃达克岩的地球化学特征，表现为Sr含量极高（〉562×10^-6）、Y含量极低（〈17．8×10^-6）、Sr／Y比值大（41．5～57．4）、轻重稀土分馏强烈（Yb〈1．60×10^-6；（La／Yb）n〉30）等特点。结合区域地质资料，认为鸡笼山岩体是在古太平洋板块俯冲作用导致板内伸展造山环境下成岩成矿作用的产物。

Jilongshan porphyry-skarn Cu-Au-Mo deposit is located in the northwest part of Jiu- jiang-Ruichang metallogenic district of the Middle-Lower Reaches of the Yangtze River. The ore- related granitic body is the Jilongshan porphyritic granodiorite. Zircon LA-ICP-MS dating sug- gests an emplacement age of 142.8 Ma±0.6 Ma. The Jilongshan porphyritic granodiorites have geochemical features of typicaladakites, such as highSr （〉618×10^-6）, lowY（〉17.1×10-6）, high Sr/Y ratios （39-61）, and low Yb （〈1.45 × 10-6） and La/Yb ratios （〉30）. Based on inte- gration of the geological characteristics of the studied area,it is suggest that the Jilongshan por- phyritic granodiorite probably formed in a transitional environment from the early orogeny stage of the paleo-Pacific plate subduction to the subsequent intraplate extensional environment.