内蒙古小东沟斑岩型钼矿床的成矿时代及成矿物质来源  

The Metallogenic Epoch and Source of Ore-forming Materials of the Xiaodonggou Porphyry Molybdenum Deposit,Inner Mongolia

作　　者：覃锋[1] 刘建明[1] 曾庆栋[1] 张瑞斌[1] 

机构地区：[1]中国科学院地质与地球物理研究所中国科学院矿产资源研究重点实验室

出　　处：《现代地质》2008年第2期173-180,共8页Geoscience

基　　金：国家科技部“973”项目(2006CB403507)

摘　　要：小东沟斑岩型钼矿床位于大兴安岭南段,距北部的西拉木伦河大断裂仅25 km。对小东沟岩体进行了Sr-Nd同位素和铅同位素分析,87Sr/86Sr(t)为0.705 0~0.705 5,εNd(t)为-2.4^-2.8;对主要钼矿体的6件辉钼矿样品进行了铼-锇同位素分析,所获同位素等时线年龄为(138.1±2.8)M a,表明小东沟钼矿床形成于早白垩世。铅同位素分析结果表明小东沟斑岩型钼矿床的成岩成矿物质具有不同来源,成岩物质来自俯冲洋壳衍生的新生地壳物质,而成矿物质来自地幔分异的产物(流体),属于壳源岩浆+幔源流体的组合。结合区域构造演化历史,对小东沟斑岩型钼矿的成因做出如下解释:在早白垩世,大兴安岭开始隆升,岩石圈拆沉,软流圈(层)物质上涌、基性岩浆的底侵以及地幔流体的加入,引起下地壳岩石的熔融,随后更多的地幔含矿流体进入到岩浆房。岩浆携带来自地幔的含矿流体,沿着区域性的EW、NE向深大断裂上侵定位,并在此过程中演化形成富硅、富钾质的花岗岩,最后沿近NS向的断裂侵位到二叠纪地层中,沉淀形成矿床。The Xiaodonggou porphyry Mo deposit is located in the southern part of Da Hinggan Mountains,with a distance of 25 km from the Xarmoron River huge fault northward.The Sr-Nd isotope and Pb isotope analyses of the Xiaodonggou intrusion show that the value of ^87Sr/^86Sr（t） ranges from 0.705,0 to 0.705,5,and εNd（t） ranges from-2.4 to-2.8.Re-Os isotopic age dating for six molybdenite sampled from the major orebody gives an isochron age of（138.1±2.8） Ma,indicating that this deposit formed in the early Cretaceous.Pb isotope analyses results show that the rock and ore-forming materials of the Xiaodonggou porphyry molybdenum deposit are from different sources.The rock-forming materials are from juvenile crust materials originating from subducted oceanic crust,while the ore-forming materials are from mantle fluid.Considering the tectonic history of this area,we explain the origin of the Xiaodonggou porphyry Mo deposit as following： as the Da Hinggan Mountains began to raise in the early Cretaceous,delamination of the lithosphere,upwelling of the materials from the asthernosphere,underplating of basic magmas and mantle fluid led the lower crust rocks melting,following with more mantle fluid entering the magma room.Carrying the mantle fluid,magma uplifted along the EW,NE huge fault and evolved into granite rich in silicate and potash,then invaded into the Permian strata and finally precipitated into Mo deposit.

关 键 词：SR-ND同位素 铅同位素 铼-锇同位素 幔源流体 小东沟斑岩型钼矿床 内蒙古 

分 类 号：P618.65[天文地球—矿床学]