The Datie bauxite deposit in Qiubei County, southeastern Yunnan Province, is a recently-discovered medium-size sedimentary diaspore deposit, and its ore -hosting strata are developed in the lower member of Upper Permian Longtan Formation. Through an analysis of mineralogy and petrography, the authors conducted a systematic research on the compositions and modes of occurrence of the ore minerals. The result indicates that diaspore is the main mineral, followed by kaolinite, illite, sericite, chlorite, anatase, goethite, hematite, rutile, chalcedonite, etc., presenting a diversity of crystalline morphologies and modes of occurrence. Five main dissernination characteristics of diaspore are observed: a) unevenly disseminated in gangue minerals with euhedral or subhedral granular textures ; b) in pisolitic, potato-shaped or oolitic forms; c) as aphanitic crystalline or microcrystalline aggregates or with irregular granular or microgranular texture; d) as veins, skeletal crystals; e) as aggregates of diaspore, alumina gel or gangue minerals assuming zonal patterns or concentric circles.%云南省丘北县大铁中型铝土矿是近年来在滇东南地区新发现并探明的一水硬铝石沉积型铝土矿床,矿体赋存于上二叠统龙潭组下段.通过矿相学分析,对大铁铝土矿矿石的矿物组成和主要矿物的赋存状态进行了系统研究.研究结果表明,矿石主要矿物组成为一水硬铝石,其次是高岭石、伊利石、绢云母、绿泥石、锐钛矿、赤铁矿、针铁矿、金红石、玉髓等.一水硬铝石呈现出多种结晶形态和复杂的赋存状态,其嵌布特征主要有以下5种:①呈自形、半自形粒状不均匀地嵌布在脉石矿物中；②呈豆状、土豆状、豆鲕状产出:③呈隐晶质、微晶集合体或极不规则的粒状、微粒状产出；④呈脉状、骸晶状产出；⑤一水硬铝石与铝凝胶或脉石矿物的集合体呈环带状或同心圆状产出.
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