尼日尔特吉达地区砂岩中铀的热流体成矿作用

Hydrothermal Mineralization of Uranium in Sandstone,Teguida,Niger

通过野外详细地质调查、钻孔观察、岩芯编录、地质现象素描等方法,结合室内工作及前人的研究成果,对非洲尼日尔共和国特吉达地区的铀矿化的研究成果显示,特吉达地区砂岩中铀主要为热流体成矿,与前人的氧化带成矿作用认识完全不同。区内主要含矿目的层(白垩世早期阿萨乌阿组)为中粒—中粗粒石英砂岩、长石石英砂岩,多数含砾。根据阿萨乌阿组砂岩的磨圆、分选好和发育向上变粗序列以及冲洗交错层理等特征确定,阿萨乌阿组形成于湖滨浅湖砂坝沉积。电子探针成分和背散射电子图像分析表明:铀矿物主要为沥青铀矿、铀石、吸附铀等,沥青铀矿和铀石常紧密共生,呈粒状、微脉状或浸染状,伴有较强的铜矿化。热流体蚀变形成的方解石、棕色方沸石、绢云母等大量出现,它们与铀成矿关系密切。成岩期的菱铁矿在后来的氧化中形成赤铁矿/针铁矿(褐铁矿)化。根据与方解石共生的白云石的摩尔数计算的方解石的形成温度表明,最高温度为385℃,最低为178℃,平均为251～300℃。

Based on geological survey,core observation and documentation,the authors have found that the ura-nium mineralization related to hydrothermal fluids in the Teguida ore deposit of Niger is genetically quite different from previous researchers’ assumption.The target layer sandstones for mineralization were deposited from the lacustrine beach or shallow lake.Sandstones assume conglomeratic characteristics and are well sorted and rounded,with upward coarsening sequence and wash cross-bedding.Electron microprobe analyses show that uranium min-erals mainly occur as pitchblende,coffinite and absorption and are granular,tiny veinlike and disseminated in form,associated with copper mineralization.Calcitization,analcitization and sericitization in the mineralized sandstone are closely related to uranium.The diagenetic siderite was altered into hematite and goethite during later oxidation.According to the dolomite molecular numbers in cogenetic calcite,the carbonate mineral temperature should range from 178 ℃ to 385 ℃,averaging 251～300 ℃.