西准噶尔萨吾尔地区黑山头金矿点二长岩锆石U-Pb年代学和地球化学特征:对成矿前景的指示

摘要

黑山头金矿点是西准噶尔萨吾尔地区最新发现的金矿化点,通过对该金矿点赋矿岩石的LA-ICP-MS锆石U-Pb年龄以及地球化学特征的研究,探讨其构造背景及成因信息.黑山头金矿点赋矿岩石主要为二长岩,矿化区内发育钾长石化、硅化、青磐岩化、碳酸盐化等蚀变.二长岩LA-ICP-MS锆石U-Pb年龄为351.1±3.2 Ma,表明其形成于早石炭世早期.主量元素特征显示其属于钙碱性准铝质岩石,相对洋中脊玄武岩富集Sr、Ba、Th等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素.二长岩为典型的I型花岗岩,区域地质及地球化学特征指示其形成于岛弧环境.矿区内二长岩具有高Sr、Na2O和A12O3,低Y和HREE等特征,与埃达克岩地球化学特征一致.样品具有较高的εNd(t)和较低的(87Sr/86Sr)t,结合它们形成于晚古生代岛弧环境,暗示这些埃达克岩可能由俯冲洋壳熔融形成;而萨吾尔地区早石炭世晚期(＜340 Ma)中酸性侵入岩可能为玄武质下地壳熔融的产物.本次新发现的埃达克岩为该区进一步寻找斑岩矿床提供了有用线索,并且矿床围岩蚀变特征、矿化特征与斑岩矿床相似,暗示黑山头矿点具有良好的成矿条件和找矿潜力.%The Heishantou gold deposit was discovered recently in the Sawuer region,West Junggar.The tectonic setting and the genetic mechanism of the ore-related Heishantou intrusion in the Sawuer region are discussed based on the LA-ICP-MS U-Pb ages of zircons and their geochemical characteristics.The Heishantou gold deposit is hosted mainly in the monzonite.The gold mineralization of the deposit is closely associated with hydrothermal alteration including potassium feldspathization,silicification,propylitization,and carbonatization.LA-ICP-MS analyses of the zircon crystals from the monzonite yielded a concordant U-Pb age of 351.1±3.2 Ma.Geochemical analyses show that the monzonite belongs to metaluminous calk-alkaline I-type granite,enriched in large iron lithophile elements (such as Sr,Ba,Th) and deleted in high field strength elements (such as Nb,Ta,Ti).The geochemical characteristics of the monzonite and the regional geological background indicate that the deposit was formed in an island arc setting.The monzonites in the deposit have high Sr,Na2O and A12O3 contenst and low Y,HREE contents,which is similar to those of the adakites.These rocks have high εNd(t) and low (87Sr/86Sr)t ratios,indicating that the magma was generated by melting of the subducted oceanic crust in the subduction-related setting.Whereas the late Early Carboniferous (＜340 Ma)intermediate-felsic intrusive rocks were formed by melting of basaltic lower crust.The discovery of the adakitic rocks and the porphyry mineralization in Heishantou are helpful guidance for future exploration in the Sawuer area.