鄂尔多斯盆地塔然高勒地区直罗组上、下段的岩性-岩相特征及对铀成矿的差异性控制作用

为查明鄂尔多斯盆地塔然高勒地区直罗组上段、下段的岩性-岩相特征以及参与蚀变作用的流体强度差异,开展了系统的岩心观察、剖面对比,并结合黏土矿物、碳氧同位素和U、Th元素等手段进行分析。结果表明,研究区南部直罗组上段主要由灰绿色、红色泥岩夹透镜状红色、黄色、灰绿色砂岩组成,北部主要由红色泥岩与灰绿色砂岩构成,南北部下段均由灰白色、灰绿色砂岩或砂砾岩夹薄层泥岩组成。直罗组红色砂岩为原生沉积,灰绿色砂岩为后生改造类型;上段受含氧含铀水和深部还原性流体作用强度较下段变弱,且由北向南作用程度降低,北部还原蚀变岩石与原生岩石共存,南部基本保留原生岩石;下段则受流体改造更为充分,主体为后生蚀变岩石。直罗组不同类型砂体的展布兼受沉积相和后期流体双重作用,但强弱差异性明显,限制了铀矿化产出在直罗组下段砂体中的定位,因此,上、下段应作为不同的成矿体系讨论。

Lithologic-lithographic Characteristics of the Upper and Lower Members of the Zhiluo Formation and Their Differential Control of Uranium Mineralization in the Tarangaole Area, Ordos Basin

In order to find out the lithologic-lithographic characteristics and the differences in fluid strengths involved in the alteration of the Upper and Lower Members of the Zhiluo Formation in Tarangaole area, the authors used a series of methods and tests including core observation, section comparison, clay minerals, carbon and oxygen isotopes and U and Th elements analysis. The results show that the Upper Member of the Zhiluo Formation in the southern part of the study area is mainly composed of grayish green and red mudstones intercalated with lenticular red, yellow and grayish green sandstones, whereas that in the northern part is mainly composed of red mudstone and grayish green sandstone, and that both of the lower parts are composed of grayish white, grayish green sandstone or glutenite intercalated with thin layer of mudstone. The red sandstone is a primary sedimentary type and the grayish green sandstone is a type of post-regeneration. The interaction between oxygen-containing uranium water and reducing fluid is weaker in the Upper Member than in the Lower Member; besides, its degree of action is reduced from north to south, the northern restored altered rock coexists with primary rock, and the primary rock remains in the south. The Lower Member of the Zhiluo Formation is more fully modified by the fluid, and the main body is posterior altered rock. This distribution of different types of sand bodies in the Zhiluo Formation is affected by both sedimentary facies and diagenesis, but the difference between the degrees is obvious, which limits the positioning of uranium mineralization enriched in the Lower Member of the Zhiluo Formation. Therefore, the Upper and Lower Members should be regarded as different metallogenic systems.