江西大湖塘钨矿床似斑状白云母花岗岩锆石U-Pb年代学、地球化学及成因研究

Zircon U-Pb geochronology,geochemistry and petrogenesis of the porphyric-like muscovite granite in the Dahutang tungsten deposit,Jiangxi Province

江西省大湖塘钨(钼、铜、锡)矿集区位于江南造山带中段,九岭山脉中段北部之武宁、修水、靖安三县交界区域,是目前世界最大的钨矿之一。本文对该矿床中与成矿关系密切的似斑状白云母花岗岩进行了详细的锆石U-Pb年代学、云母矿物化学、主量元素、微量元素以及Sr-Nd同位素研究。结果表明,LA-ICP-MS锆石U-Pb定年测得大湖塘似斑状白云母花岗岩成岩年龄为144.2±1.3Ma。岩体中白云母显示原生白云母的特征;黑云母属于富铁黑云母,其物质来源是地壳物质,Fe3+/Fe2+组成表明岩浆氧逸度很低。岩石地球化学特征表明似斑状白云母花岗岩为强过铝质的S型花岗岩,表现为高的SiO2(72.88%～73.33%),轻重稀土分馏明显,Eu负异常明显,亏损Nb、Ta,Rb/Sr比值高。似斑状白云母花岗岩的εNd(t)值变化于-7.47～-7.78之间,两阶段模式年龄tDMC为1543～1568Ma,推测其源区很可能来源于双桥山群的富泥质岩石,双桥山群可能是大湖塘钨矿的初始矿源层。九岭燕山期的岩浆活动发生在侏罗纪和白垩纪之交的早白垩世早期,花岗岩形成于拉张的构造环境。

The Dahutang tungsten（molybdenum,copper,tin） ore fields are located in the middle part of the Jiangnan Orogen which is the junction of three counties of Wuning,Xiushui,Jing＇an area in the middle of the northern part of Jiuling Mountains.It is the world＇s largest tungsten mine.In this paper,we study the mineral chemistry,major elements,trace elements,and Sr-Nd isotopic compositions of the porphyric-like muscovite granite which is closely related to mineralization in the deposit.The results show that LA-ICP-MS zircon U-Pb age of the porphyric-like muscovite granite is 144.2±1.3Ma.The muscovite in the granite belongs to primary magmatic muscovite,and the biotite shows iron-rich characteristic,and its composition indicates a crust origin of the rock.The Fe^3＋/Fe^2＋ composition of biotite indicates a low oxygen fugacity for the magma evolution.The porphyric-like muscovite granite belongs to S-type granite which is characterized by high SiO2（72.88% to 73.33%）,strongly peraluminous,low Nb and Ta,high Rb/Sr,strong LREE/HREE fractionation,and pronounced negative Eu anomalies.The εNd（t） values of the rock varied from-7.47 to-7.78 with the two-stage model ages tDMC of 1543Ma to 1568Ma.It is suggested that the source region of the granite were from argillaceous sedimentary rocks,likely from the Neoproterozoic Shuangqiaoshan Group.We also suspected that the ore-forming metals such as tungsten in the deposit may have likely derived from the Shuangqiaoshan Group.Based on the geochronological framework of the granite,the Yanshanian magmatic activity took place during the transition of the Jurassic and Cretaceous period in an extensional tectonic environment in Jiuling area.