鄂尔多斯盆地西南缘镇原地区砂岩型铀矿元素地球化学特征及地质意义  

Geochemical Features and Geological Significance of Sandstone-type Uranium Deposit in Zhenyuan Area,Southwestern Ordos Basin

作　　者：胡妍 胡永兴[1] 张翔[1] 杨涛[1] 欧扬剑 HU Yan;HU Yongxing;ZHANG Xiang;YANG Tao;OU Yangjian(Geological Survey of Gansu Province,Lanzhou,Gansu 730030,China)

机构地区：[1]甘肃省地质调查院,甘肃兰州730030

出　　处：《现代地质》2020年第6期1153-1165,共13页Geoscience

基　　金：中国地质调查局项目“甘肃省鄂尔多斯盆地南缘泾川一带铀矿地质调查”(DD20160128-06);甘肃省科技重大专项“核铀矿分布规律研究及核储存取样装置研发”(18ZD2GF019)。

摘　　要：通过分析鄂尔多斯盆地西南缘镇原地区下白垩统洛河组含铀砂岩的主、微量元素特征,初步探讨了该区砂岩型铀成矿条件及成矿规律。研究结果表明,研究区下白垩统洛河组铀矿石主要为沥青铀矿(UO2),含铀砂岩可能来自古老沉积地体或克拉通/再旋回造山带的石英岩沉积物源区。含铀砂岩富集轻稀土(LREE),亏损重稀土(HREE),且具明显的Eu负异常,一致的稀土元素特征表明该区成矿围岩具有统一的物源、沉积环境和构造背景。含铀砂岩的V/Cr、Ni/Co、U/Th、V/(V+Ni)比值特征说明,该区铀矿化主要发育于弱氧化—弱还原的过渡环境;其δEu和δCe值均随U含量的增加而增大,反映U元素的富集成矿经历了由氧化向还原环境转化的过程,砂体颜色由浅红色褪色蚀变为灰白色。含铀砂岩中Th、Sc、Co、Mo含量与U含量呈正相关关系,认为Th、Sc、Co、Mo可作为研究区洛河组砂岩型铀矿富集的指示元素。研究区砂岩型铀矿的形成与深部向上逸散的还原性油气流体作用关系密切,油气流体的侵入增加了砂体的还原容量,有利于含铀含氧水中铀离子在氧化—还原过渡带发生沉积富集,形成洛河组大面积的铀异常。This study presents major and trace element data of the uranium-bearing Lower Cretaceous Luohe Formation(Fm.)sandstones in Zhenyuan area(southwestern margin of the Ordos Basin),and the metallogenic conditions and regularity.The results show that the uranium ores in the Luohe Formation is mainly uraninite(UO2),and the uranium-bearing sandstone may have sourced from the quartzite in ancient sedimentary terranes or craton/recycled orogenic belts.These sandstones have the same REE patterns with LREE-enrichments,HREE depletions and negative Eu anomalies,suggesting that the wallrocks have a uniform detrital source,sedimentary environment and tectonic setting.The V/Cr,Ni/Co,U/Th and V/(V+Ni)features of the uranium-bearing sandstone indicate that the local uranium mineralization was mainly developed in a weakly-oxidizing to weakly-reducing transitional environment.TheδEu andδCe values increase with the U content,reflecting that the U enrichment and mineralization have experienced the transformation from oxidizing to reducing environment,and the sand body colors have changed from light red to grayish white.The contents of Th,Sc,Co,Mo in the uranium-bearing sandstones are positively correlated with that of U,and thus the former four elements can be used as fertility indicators for sandstone-type uranium deposits in the Luohe Formation.Formation of sandstone-type uranium deposits in the study area is closely related to the reduction caused by the upward seeping of oil and gas from depth.The incursion of oil and gas fluids likely increases the reducing capacity of the sand body,which promotes the uranium deposition and concentration from the oxidizing uranium-bearing fluid in the redox transition zone.This eventually formed the widespread uranium anomalies in the Luohe Formation.

关 键 词：砂岩型铀矿 氧化—还原作用 元素地球化学特征 镇原地区 鄂尔多斯盆地西南缘 

分 类 号：P619.14[天文地球—矿床学]