鄂尔多斯盆地东北部纳岭沟铀矿床元素地球化学特征及其地质意义

纳岭沟铀矿床位于鄂尔多斯盆地北部,是我国目前已发现的可地浸砂岩型铀矿床之一。其受古层间氧化带控制,呈板状产于中侏罗统直罗组下段辫状河砂体中。笔者从元素地球化学分析入手,通过对不同蚀变砂岩的地球化学特征进行对比,认为蚀变砂岩主要化学成分的变化受成岩作用、水-岩作用,以及油气二次还原作用等影响,并且有机碳含量在矿化砂岩中较高,说明铀矿化与有机质关系密切。矿化砂岩中的微量元素相对富集或亏损明显,可能与成岩后期(热液)的改造作用有关。蚀变砂岩均表现出壳型花岗岩的微量和稀土元素特征,LREE相对富集,说明盆地北部的阴山、大青山古陆壳富铀花岗岩体是直罗组的主要物源。此外,δEu和δCe特征也表明纳岭沟铀矿床是在弱氧化-弱还原过渡性环境下形成。这些特征可作为找矿勘探的重要指示或标志。

Element Geochemical Characteristics and Geological Significance of Nalinggou Uranium Deposit,Northeastern Ordos Basin

Nalinggou uranium deposit is one of the newly discovered in situ leachable sandstone-type uranium deposits in China.The orebody is of platy shape which is localized in sandbody of braided river in Zhiluo formation of middle Jurassic and controlled by paleo-interlayer oxidation zone.Study on the geochemical features of rock with different alteration shews that the change of the main elements in the alteration sandstone is mainly affected by sedimentary after diagenesis,water-rock interaction and the second reduction of oil and gas.Organic is higher in the mineralized sandstone,closely associated with organic matter content in the sandstone type uranium mineralization.Trace element enrichment or loss is relatively obvious in the mineralization of sandstone that could be affected by the late diagenetic reformation (hydrothermal).The alteration sandstone show the trace elements and rare earth elements features of crustal source type granite and LREE enrichment,which indicated that uranium rich granite from Yinshan and Daqingshan anciant land were an significant material source for Lower Zhiluo formation deposition in this area.δEu andδCe characteristics show that Nalinggou uranium deposits formed in weak oxidation-reduction transitional environment.These characteristics will provide a good indicator for the future prospecting exploration as well as the important exploration marks.