西藏申扎县侧波积异地区超基性岩成因特征及找矿意义  

Cause Features and Prospecting Significance of Ultrabasic Rocks in Cebojiyi Area,Xainza County,Tibet

作　　者：李小赛[1] 赵元艺[2] 黄道袤[2] 曲晓明[2] 许虹[1] 

机构地区：[1]中国地质大学(北京),北京100083 [2]中国地质科学院矿产资源研究所,北京100037

出　　处：《地质学报》2014年第10期1843-1860,共18页Acta Geologica Sinica

基　　金：国家973项目<青藏高原南部大陆聚合与成矿作用>之课题三<青藏高原南部增生造山成矿系统发育机制>(编号:2011CB403103);国家科技支撑课题<西藏班公湖岛弧带铜;金;富铁矿评价与综合找矿技术方法示范研究>(编号:2006BAB01A05)之专题<区域成矿模型与典型矿床成因模型研究>;中国地质调查局青藏专项<西藏班公湖怒江成矿带找矿远景区评价>(1212010818097)共同资助

摘　　要：侧波积异地区位于西藏申扎县城东北约40km处,区域构造上位于班公湖-怒江成矿带中段南侧。该区除在超基性岩及灰岩中均发现有镍的硫化物矿物外,在超基性岩中还产生铬、钴的矿化。因此,研究区内超基性岩的地球化学特征及成因等,对侧波积异,乃至整个班公湖-怒江成矿带的资源潜力评价和找矿勘查具有十分重要的理论指导意义。侧波积异赋镍岩石主要为方辉橄榄岩,普遍发生较强烈的蛇纹石化。镍矿物主要为镍铬铁合金、铁镍合金等合金矿物,针镍矿、铁针镍矿、六方硫镍矿等硫化物矿物,以及含镍橄榄石、含镍蛇纹石等硅酸盐矿物。方辉橄榄岩的Mg^#为87.03~88.25,平均为87.82,接近蛇绿岩中变质橄榄岩的Mg#（89~91）。m/f为6.71~7.51,平均为7.22,为镁质超基性岩。侧波积异方辉橄榄岩为碱性系列。总体上明显富集U、Th、Pb等大离子亲石元素和Ta、P等高场强元素,明显亏损Ba、K、Sr等大离子亲石元素和Nb、Ti等高场强元素,大体符合岛弧岩浆的特征。稀土元素总量很低,∑REE=0.39×10^-6~1.37×10^-6,平均值为0.94×10-6。LREE/HREE为5.07~6.04,（La/Yb）N为2.98~6.08,轻重稀土元素分异较明显。δEu=1.15~1.54,平均值为1.42,有较弱的Eu正异常。δCe=0.93~1.15,平均值为1.04,无明显Ce异常。206 Pb/204 Pb为18.428~18.554,平均值为18.476;207 Pb/204Pb为15.498~15.614,平均值为15.575;208 Pb/204 Pb为37.712~38.730,平均值为38.386。87 Rb/86 Sr比值为0.8686~3.8985,平均为2.1145,87 Sr/86 Sr比值为0.709148~0.711524,平均为0.710257,147 Sm/144 Nd比值为0.1090~0.1237,平均为0.1178,143 Nd/144 Nd比值为0.512028~0.512112,平均为0.512075。结果表明,侧波积异方辉橄榄岩产出的构造环境为岛弧环境,岩浆来源于下地壳与上地幔混合的俯冲带,岩浆源区为尖晶石角闪二辉橄榄岩富集型地幔源区。侧波积异方辉橄榄岩中的Ni含量平均为2017.3×10-6,蛇纹石化方辉橄榄岩中的NCebojiyi area,belonging to southern middle Bangong Co-Nujiang River metallogenic belt,is located at the northeast of Xainza county about 40 km.There are produced with nickel sulfide minerals in the ultrabasic rocks of this deposit,also with chromium and cobalt mineralization been found.It plays an important role in resource potential evaluation and mineral exploration for Cebojiyi,even the whole Bangong Co-Nujiang River metallogenic belt that researching the geochemical characteristics and origin of the ultrabasic rocks in this area.The rocks containing nickel are mainly ultrabasic rocks such as harzburgite,most of which were strongly serpentinized.Nickel minerals are mainly alloy minerals such as inconel alloy,iron-nickel alloy,sulfide minerals such as millerite,iron millerite and heazlewoodite,silicate minerals such as nickel-containing olivine,nickel-containing serpentine and so on.The Mg#values of Cebojiyi harzburgite are in the range of 87.03~88.25,with an average of 87.82,close to the Mg#（89~91）of metaperidotite in ophiolite.The m/f values are in the range of 6.71~7.51,with an average of7.22,suggesting the harzburgite are magnesia.And the Cebojiyi harzburgite are alkaline series.In the rocks,large ion lithophile elements such as U,Th,Pb and high field strength elements such as Ta,P are enriched,while the elements such as Ba,K,Sr and Nb,Ti are poor,which roughly comply with the characteristics of island arc magmas.The total REE of the rocks are very low,and the∑REE values are in the range of 0.39×10^-6~1.37×10^-6,with an average of 0.94×10^-6.It is obvious of light and heavy REE fractionation,with LREE/HREE ranging from 5.07 to 6.04and（La/Yb）Nfrom 2.98 to 6.08.The rocks have a weak positive Eu anomaly（δEu=1.15~1.54,with an average of 1.42）and no obvious Ce anomaly（δCe=0.93~1.15,with an average of 1.04）.The 206Pb/204 Pb values are 18.428~18.554（average is 18.476）,207Pb/204 Pb are 15.498~15.614（average is 15.575）,and 208Pb/204 Pb are 37.712~38.730（average is 38.386）.While the

关 键 词：方辉橄榄岩 地球化学特征 Pb、Sr、Nd同位素 侧波积异 西藏 

分 类 号：P588.125[天文地球—岩石学]