摘要：
丁青蛇绿岩体位于班公湖-怒江缝合带东段,该缝合带与雅鲁藏布江缝合带并列,是寻找我国铬铁矿床的重要地区.该蛇绿岩体呈近南东向展布,总面积近600 km2,主要由地幔橄榄岩、辉石岩、辉长岩、辉绿岩、玄武岩、斜长花岗岩、硅质岩和泥质岩组成.根据空间分布,丁青蛇绿岩分为东、西两个岩体.在前人工作基础上,通过地质填图、实测剖面、探槽和钻孔编录,共发现豆荚状铬铁矿矿点83处,其中东岩体27处,西岩体56处.根据铬铁矿产出和围岩特征,丁青铬铁矿可分为4种产出类型.类型I:矿体呈脉状产出,围岩为条带状或透镜状纯橄榄岩和块状方辉橄榄岩;类型II:矿体呈透镜状、豆荚状或不规则团块状产出,围岩为薄壳状纯橄榄岩和斑杂状或块状方辉橄榄岩;类型III:矿体呈浸染状弥散分布于纯橄榄岩中,围岩为条带状纯橄榄岩和块状或斑杂状方辉橄榄岩;类型IV:矿体呈条带状产出,围岩为条带状或透镜状纯橄榄岩和具定向结构的方辉橄榄岩.根据矿石构造特征,主要分为块状、脉状、浸染状、浸染条带状4种类型.块状和脉状铬铁矿为矿石的主要类型,少量为浸染状和浸染条带状,局部纯橄榄岩中发育极少量瘤状或豆状构造.本研究选择了13处代表性铬铁矿点开展了详细的岩石学、矿相学、矿物学和矿物化学等工作.根据矿石中铬尖晶石的矿物化学特征,可将丁青铬铁矿矿体分为高铬(Cr#=78～86)、中高铬(Cr#=60～74)、中铬(Cr#2=30～51)和低铬(Cr#=9～14)4种类型(Cr#=100×Cr/(Cr+Al)).丁青东岩体赋存有中高铬型和中铬型铬铁矿,缺少高铬型铬铁矿;西岩体赋存有高铬型和中铬型铬铁矿,缺少中高铬型铬铁矿.同时在丁青东、西岩体内均发现存在一种Cr#极低的铬铁矿,暂定为"低铬型铬铁矿".这些不同类型的铬铁矿体与野外产出有一定的对应关系,也可能后者制约了它们的成因.与罗布莎岩体中的典型高铬型铬铁矿对比,丁青豆荚状铬铁矿在矿物组合和矿物化学成分等方面具有许多相似性,认为存在较大的找矿空间.%The Dingqing ophiolite is located in the eastern segment of the Bangong Co-Nujiang suture zone which is juxtaposed with the Yarlung Zangbo suture zone, and is an important area for finding chromite deposits in China. The ophiolite body is distributed in the southeast direction, with a total area of nearly 600 km2. It is mainly composed of mantle peridotite, pyroxenite, gabbro, diabase, basalt, plagiogranite, siliceous rock and argillaceous rock. According to the spatial distribution, the Dingqing ophiolite is divided into east and west ophiolite bodies. On the basis of previous work, 83 chromite ore spots were discovered through geological mapping, measured sections, trench recording and drilling, including 27 in the east ophiolite body and 56 in the west ophiolite body. According to the production characteristics of the chromite spots and types of wall rock, Dingqing chromite can be divided into four types: Type I: chromite orebodies are vein-like, the wall rock is stripe-like or lenticular dunite and massive harzburgite; Type II: chromite orebodies are lenticular, podiform or irregularly agglomerated, the wall rock is thin-shelled dunite and porphyry or massive harzburgite; Type III: chromite is diffusely distributed in dunite, and the wall rock is stripe-shaped dunite and massive or porphyry harzburgite; Type IV: chromite orebodies are produced in stripes, and the wall rock is stripe-like or lenticular dunite and directional harzburgite. According to the structural characteristics of chromitites, they are mainly divided into four types: massive, vein, disseminated and disseminated stripe. Massive and veined chromitites are the main types of chromitites, a small amount is disseminated and disseminated stripe, with a small amount of nodular or bean-like structure developed in local dunite. In this study, 13 representative chromite ore spots were selected for detailed studies of petrology, mineralogy, and mineral chemistry. According to the mineral chemistry characteristics of chrome spinel in the chromitites, the chromite bodies can be divided into four types, i.e., high chromium (Cr#78-85), medium-high chromium (Cr#60-74), medium chromium (Cr#30-51) and low chromium (Cr#9-14) (Cr#=100×Cr (/Cr+Al)). The east ophiolite body contains medium-high chromium and medium chromium type chromitite, with the lack of high chromium type chromitite; the west ophiolite body contains high chromium and medium chromium type chromitite, and lacks medium-high chromium type chromitite. At the same time, there is a very low Cr# chromitite in the east rock mass and the west rock mass, which is tentatively assigned to"low chromium type chromitite". These different types of chromitites have a certain correspondence with the field output, and may also restrict their geneses. This content will be expanded in subsequent articles. A comparison with Luobusa podiform chromitite and peridotite in mineral assemblages and mineral chemistry shows that they have many similar characteristics, even with the probable existence of a good prospecting space.
