鄂尔多斯盆地北部底河道砂岩型铀矿地质特征

鄂尔多斯盆地北部直罗组中的铀矿,是典型的产于河道中的砂岩铀矿,该矿床发育较好的卷状矿体。通过对该铀矿地质特征的研究,认识到发育卷状矿体的底河道砂岩型铀矿必须具备两大条件:其一是成矿砂体条件,即砂体要有较好的成层性、连通性和渗透性;其二是地层结构条件,即砂体必须存在较好的上、下隔水岩层。就砂体而言,河流相辫状沉积砂体是形成卷状矿体的主要砂体,并且以具有从辫状河向曲流河完整演化的辫状沉积砂体较好。砂体的上、下隔水岩层则有多种表现形式:下隔水层可由不透水的基岩或湖相沉积泥岩等构成;上隔水层由不透水的湖相泥岩、曲流沉积地层或岩浆岩等构成。在层间氧化作用过程上,存在纵横两个方向的氧化,即存在与河道方向一致的纵向氧化和与河道垂直的横向氧化,两种氧化作用成矿常叠加形成复杂的矿体类型;在矿化赋存的部位上,铀砂体通常发育在基底之上或不同建造之间;在古气候演变上,成矿作用发生在干旱气候条件下,或由潮湿向干旱的气候转变阶段。

Geological Characteristics of Basal-channel Sandstone-type Uranium Deposits in the Northern of Ordos Basin

The uranium deposit occurs in Zhilu formation braided channel sandbody of north of Ordos basin,and it is a typical of basal-channel-type sandstone uranium deposit and there is better roll-type ore-body.On the base of the deposit researching,it is concluded that basal-channel sandstone-type uranium deposits with roll front must need two conditions: the first is the metallogenic sandbody has better stratified,connectivity and permeability;the second is the stratigraphic frame must be have better water-resisting overlying and underlying strata.The braided sandbody is matching the above conditions according to the characters of fluvial sandsbody.Usually,underlying of the braided sandbody is the water-resisting strata of water-proof bedrock or lacustrine mudstone and overlying of the braided sandbody is the water-proof of lacustrine mudstone,meander flood plain mudstone or basalt rocks.According to river evolution,it is better for form the basal-channel sandstone-type uranium deposits that the depositional strata are completely developed from braided to meander river deposit.To interlayer oxidization process,there are two directions of oxidization,that is,the lengthwise direction oxidization consistent with river channel and the side direction oxidization upright to river channel.The two types of redox front are often superimposed and form complex roll-type ore-body. On mineralization position,the uranium sandstone usually located above of basal rocks or between the formations.On paleo-climate evolution,the uranium metallization occur during arid climate condition or transition from humid to arid.