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    西藏西南部达巴—休古嘎布绿岩带铬铁矿的找矿前景

    Chromite prospects in the Daba-Xiugugabu ophiolite zone southwestern Tibet

    • 摘要: 提要:雅鲁藏布江蛇绿岩带长1500 km以上,分为东段(曲水—墨脱)、中段(昂仁—仁布)和西段(萨嘎以西至中印边境)3部分。西段又进一步分为北亚带(达机翁—萨嘎蛇绿岩带)和南亚带(达巴—休古嘎布蛇绿岩带),以往的研究程度很低。达巴—休古嘎布蛇绿岩带的蛇绿岩体(块)由地幔橄榄岩组成,主要岩石类型是方辉橄榄岩和纯橄榄岩,极少量二辉橄榄岩,缺少典型蛇绿岩剖面中的洋壳单元。带内岩体规模大,岩相分带明显,出现较大面积的纯橄榄岩相。拉昂错、东坡、当穷岩体和休古嘎布岩体群发现有较多的铬铁矿化点,矿体呈透镜状(豆荚状)、短脉状、不规则状,矿石以致密块状为主,少部分为浸染状,Cr2O3含量一般达40%以上。矿化类型属于豆荚状铬铁矿。对比研究显示,该岩带的岩体在构造环境,蛇绿岩的类型,岩体规模,岩石组成,保存部位,部分熔融程度,岩石、矿物地球化学特征,铬铁矿化特征等许多方面与国内外大型豆荚状铬铁矿床的含矿岩体相似,成矿条件好,找矿前景较大。提出区内找矿前景最好的地段是拉昂错岩体西北部的纯橄榄岩相,其次是东坡岩体的纯橄榄岩相、纯橄榄岩-方辉橄榄岩相,以及当穷岩体的方辉橄榄岩-纯橄榄岩相。

       

      Abstract: Abstract:The Yarlung Zangbo ophiolite belt is >1500 km long and may be divided into three segments: the east (Qüxü-Mêdog), central (Ngamring-Rinbung) and west (from west Saga to the Sino-India national border) segments. The west segment is further divided into the Dajiweng-Saga ophiolite zone in the north and Daba-Xiugugabu ophiolite zone in the south. The previous research focused on the east and central segments and very limited work has been done in the west segment. Ophiolite masses (blocks) in the Daba-Xiugugabu ophiolite zone are composed of mantle peridotite. The main rock types are harzburgite and dunite with rare lherzolite, while oceanic crust is lacking in the typical ophiolite section. The ophiolite masses are large and have pronounced facies zoning with extensive dunite facies. Many chromite mineralization occurrences have been found in the La'nga Co, Dongpo, Dangqiong and Xiugugabu masses. Orebodies occur in lenticular (podiform), short-vein and irregular shapes. Ore is mostly massive in structure and in a few cases disseminated, generally with a Cr2O3 content of over 40%. The chromite deposits are of podiform type. Comparative study indicates that the rock masses in this ophiolite belt are similar to the mineralized rock bodies hosting large podiform chromite deposits in the world in respect to the tectonic setting, ophiolite type, size of rock masses, rock composition, location of preservation, degree of partial fusion, geochemical characteristics of rocks and minerals and chromite mineralization characteristics. The Daba-Xiugugabu ophiolite zone has good metallogenic conditions and better ore prospects. The authors suggest that: dunite facies in the northwest part of La'nga Co mass is the target with the best ore prospects, and next are dunite facies and dunite-harzburgite facies of the Dongpo mass and dunite-harzburgite facies of the Dangqiong mass.

       

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