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豆荚状铬铁矿按其矿物化学组分分为高铝型(Cr#值为20～60)和高铬型(Cr#值为60～80)两类(Thayer,1970),在全球已报道的豆荚状铬铁矿中普遍为在一岩体内只存一种类型的矿体,而在同一岩体内发现两种类型的铬铁矿体较少见。位于雅鲁藏布江缝合带西段普兰岩体中首次发现同时存在高铬型和高铝型铬铁矿,岩体由地幔橄榄岩、辉长辉绿岩、火山岩等组成。地幔橄榄岩主要为方辉橄榄岩、纯橄岩和少量二辉橄榄岩。在方辉橄榄岩中发现7处透镜状的铬铁矿矿体露头,矿石类型主要有致密块状、稠密浸染状和稀疏浸染状等。矿体长2～6m,厚0.5～2m,矿体的最大延伸方向为北西-南东向,与岩体的展布方向一致,矿石的Cr#=52～88,高铬型铬铁矿包括Cr-2～5矿体,Cr#值为63～89,高铝型铬铁矿有Cr-1和Cr-6矿体,Cr#=52～55。矿石中脉石矿物主要为橄榄石、角闪石、蛇纹石等。普兰地幔橄榄岩的矿物结构显示,岩体经历了强烈的部分熔融以及塑性变形作用,地幔橄榄岩的地球化学特征显示岩体形成于MOR,后受到SSZ环境的改造。并且依据铬尖晶石-橄榄石/单斜辉石的矿物化学成分,识别出普兰地幔橄榄岩至少经历了3次不同的部分熔融,包括早期部分熔融(～10%)、晚期部分熔融(20%～30%)和局部的减压部分熔融作用(～15%)。对比其他铬铁矿矿体和地幔橄榄岩的矿物组合,矿物化学和地球化学等,显示普兰豆荚状铬铁矿矿体与典型高铬型、高铝型铬铁矿具相似性,并存在较大的找矿空间。
According to their chemical composition, podded chromite is classified into two types (high chromium (Cr # 20-60) and high chromium type (Cr # 60-80)) (Thayer, 1970) Of the podiform chromite is generally only one type of ore body in a rock mass, and in the same rock mass found two types of chromite ore body less common. It is the first time that the high-chromium type and high-type chromite are found in the Pulan rock mass in the west section of the Yarlung Zangbo suture zone. The rock mass is composed of mantle peridotite, gabbro, volcanic rock and so on. The mantle peridotites are mainly harzburgite, dunite and a small amount of lherzolites. In the hibernation, seven lenticular ore bodies are found outcrops. The types of ore are mainly dense, densely disseminated and sparsely disseminated. The ore body is 2 ~ 6m long and 0.5 ~ 2m thick. The maximum extension direction of the ore body is northwest-south east, consistent with the distribution direction of the rock mass. Cr # of ore is 52 ~ 88, Cr-2 ~ 5 ore body with Cr # value of 63 ~ 89, Cr-1 and Cr-6 ore bodies of high-aluminum type chromite and Cr # = 52-55. Ore in the gangue minerals mainly olivine, hornblend, serpentine and so on. The mineral structure of the Permian peridotite shows that the rock mass undergoes a strong partial melting and plastic deformation. The geochemical characteristics of the mantle peridotite show that the rock mass is formed in the MOR and then transformed by the SSZ environment. Based on the mineral chemistry of chromium spinel-olivine / clinopyroxene, the Permian peridotite has been identified to have undergone at least three different partial melts, including early partial melting (~ 10%), late partial melting (20 % ~ 30%) and local decompression partial melting (~ 15%). Comparing the mineral assemblages, mineral chemistry and geochemistry of other chromite ore bodies and mantle peridotites, it shows that Pulandian pod chromite ore bodies have similarities with typical high-chromium and high-aluminum chromite ore, Large looking for space.