鄂尔多斯盆地东北部侏罗系含铀矿主岩的沉积环境分析
The Research on Depositional Environment of Uranium Host Rock in the Northeast Ordos Basin
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摘要: 鄂尔多斯盆地东北部富含砂岩型铀矿,对侏罗系含铀矿主岩进行砂体分布和沉积环境分析,对指导东胜地区未来找矿具有一定的实际意义。根据前人的研究成果,结合野外地质考察,指出铀矿主岩以中-粗砂岩为主,含大量植物碎屑化石,底部常有冲刷面,且发育大型槽状、板状交错层理。通过鄂尔多斯盆地东北部侏罗系南北向砂体沉积格架及钻孔柱状的分析,编制了含铀矿主岩的砂体厚度分布图和砂体沉积环境分布图。平面上,砂岩厚度变化8~75 m,砂体形态总体呈席状、带状展布;厚砂体带在瑶镇—新街镇一带最发育,达75 m厚,且岩性粗,底部冲刷剥蚀强烈,对延安组的冲刷最强烈。砂体分布与沉积环境的叠合显示,辫状河三角洲体系分流河道一侧,河道砂体的频繁分岔处是U成矿的有利环境。Abstract: The sandstone-type uranium deposit is abundant in Northeastern Ordos Basin. Analysis of Jurassic uranium host rocks sand body distribution and sedimentary environment has some practical significance to ore prospecting in Dongsheng Area in the future. Based on previous studies, combined with the field geological investigation, this paper indicates that the uranium host rock is mostly coarse sandstone, containing a large number of plant detritus fossil, with erosion surface often found at the bottom, and the development of large trough, tabular cross-bedding. Through the analysis of the despositional framework and borehole columnar section of sand body along south-north direction, sand thickness and sedimentary environment distribution map of sand body in uranium host rocks are drawn. Sandstone thickness varies from 8 to 75m, and the morphology shows sheeted, zonal distribution on the whole. The thickest sand bodies are in Yaozhen Town-Xinjiezhen Town, which is up to 75m thick. The sand body is coarse and has a strong basal scouring erosion, especially in the Yan'an Formation. The sand body distribution and sedimentary environment all show that the braided river delta system distribute to one side of river channel, and such frequent branching is favorable for uranium deposit enrichment.
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