皖南太子山含矿岩体辉钼矿Re-Os年龄与硫同位素特征

Re-Os Geochronology and S Isotope Geochemistry of Molybdenite from Taizishan Ore-Bearing Pluton,Jixi County,Anhui Province,China

皖南绩溪县太子山含矿岩体位于皖南绩溪县北东侧,为下扬子地块南缘与华夏地块的结合部位,属近年来该地区钨钼找矿新突破。太子山单元从属于伏岭复式岩体,辉钼矿化多呈细脉状及浸染状产出于似斑状花岗闪长岩中,为获得其成矿年龄,首次对7件辉钼矿样进行Re-Os同位素定年。数据显示,辉钼矿模式年龄介于（132.8±2.0）140.5±2.0Ma,加权平均年龄为（135.8±2.2）Ma,等时线年龄为134.6±3.5 Ma,与伏岭岩体花岗岩的锆石LA-ICP-MS U-Pb年龄（133.9±1.1 Ma）高度一致,表明太子山单元成矿作用发生于早白垩世,且成矿与岩体关系密切。辉钼矿Re质量分数介于0.706×10-612.190×10-6,平均值为4.648×10-6,表明成矿物质以壳源为主。4件辉钼矿δ34SV-CDT值介于7.20‰8.00‰,平均值为7.725‰,显示成矿物质硫源主要来自于岩浆热液。综合研究表明,研究区成矿时代处于中国东部中生代大爆发成矿的第2阶段,即构造体制大转折阶段。其与周边长江中下游及钦杭成矿带中典型钼矿床类似,同为中国东部燕山期大规模岩浆作用的产物,反映了当时该地区软流圈上涌、岩石圈伸展减薄、壳幔混合作用逐渐加强的动力学背景。

Taizishan ore-bearing pluton in Northeastern Jixi Country of Southern Anhui Province,China is located in the joint of the southern margin of lower Yangtze block and Cathaysian block,and is belonging to the breakthrough about prospecting for W/Mo in recent years. The molybdenum mineralization is predominately hosted in the porphyritic granodiorite of Fuling mass and molybdenite occurs as thin vein and dissemination. In order to obtain themetallogenic epochs,seven molybdenite samples have been carried out for Re-Os isotopic dating yielding a model age range of 132. 8±2. 0 140. 5±2. 0 Ma,with a weighted average age of 135. 8±2. 2 Ma and an isochron age of 134. 6±3. 5 Ma,in good agreement with zircon U-Pb age of Fuling granitic rocks,indicating that the mineralization of Taizishan ore-bearing pluton occurred in the Early Cretaceous. The mineralization was closely related to the Fuling mass. The Re content of molybdenite is 0. 706×10-6 12. 190×10-6 with an average of 4. 648×10-6,suggesting that the ore-forming materials are mostly derived from crust source with little involvement of mantle source. The δ34 S values of molybdenites show variations from 7. 20‰ to 8. 00‰,with the mean value being 7. 725‰,implying that oreforming material might come from the magmatic hydrothermal. According to these results,it is suggested that the mineralization of Taizishan ore-bearing pluton forms in the second stage of the Mesozoic metallogenic explosion in East China,corresponding to the timing of tectonic regime transformation. As same as the typical Mo deposits in the Middle-Lower Yangtze River Valley Metallogenic Belt and Qinhang Metallogenic Belt. The molybdenum mineralization of Taizishan ore-bearing pluton is the product of Yanshanian large-scale magmatism in Eastern China. The geodynamic background at that time is lithosphere extension-thinning and intensive crust-mantle mixing.