鄂尔多斯盆地西南部下白垩统洛河组灰色砂岩的两种成因及其含铀性  

Two Geneses of Gray Sandstone and Their Uranium⁃Bearing Analysis of Lower Cretaceous Luohe Formation in Southwestern Ordos Basin

作　　者：朱强 司庆红 李建国 苗培森[1,2,3] 文思博 李光耀 张博 Zhu Qiang;Si Qinghong;Li Jianguo;Miao Peisen;Wen Sibo;Li Guangyao;Zhang Bo(Tianjin Center,China Geological Survey,Tianjin 300170,China;Key Laboratory of Uranium Geology,China Geological Survey,Tianjin 300170,China;North China Geological Science and Technology Innovation Center,Tianjin 300170,China;Cores and Samples Center of Natural Resources,China Geological Survey,Yanjiao 065201,China)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170 [2]中国地质调查局铀矿地质重点实验室,天津300170 [3]华北地质科技创新中心,天津300170 [4]中国地质调查局自然资源实物地质资料中心,河北燕郊065201

出　　处：《地球科学》2023年第11期3995-4016,共22页Earth Science

基　　金：国家重点研发计划项目(No.2018YFC0604200);中国地质调查局地质调查项目(Nos.DD20190119,DD20221678⁃1);国际地球科学计划项目(No.IGCP675);国家自然科学基金项目(No.92162212);国家重点基础研究发展计划项目(No.2015CB453000).

摘　　要：为了查明鄂尔多斯盆地西南部下白垩统洛河组灰色砂岩的成因,深化铀矿富集规律,定位砂岩型铀矿体产出部位,利用岩矿鉴定、XRD和元素地球化学分析等方法,对洛河组砂岩进行精细研究.结果显示研究区灰色砂岩有两种不同的成因:(1)洛河组下部砂岩具有典型的风成沉积特征,碎屑颗粒分选性和磨圆度较好,石英含量较高,粘土矿物总量较低,孔隙度大,具备较好的流体运移通道,经受后期还原流体的改造程度较高,为主要的富铀砂体;(2)洛河组上部砂岩为辫状河河道、河道边缘和泛滥盆地沉积,碎屑颗粒分选性和磨圆度中等‒较差,石英含量较低,粘土矿物总量较高,孔隙度低,经受还原改造程度较弱或基本未被改造.两种成因灰色砂岩元素地球化学特征总体一致,部分元素有所差异,在U含量富集部位,主量元素中CaO、P_(2)O(5)和MnO含量升高,Fe_(2)O_(3)/FeO降低,风成灰色砂岩中δEu既有正异常又有负异常,δCe以负异常为主,河流沉积灰色砂岩中δEu和δCe均为负异常.研究得出,洛河组河流沉积砂岩以还原环境为主,为原生沉积砂岩,风成沉积砂岩则可能经受了由氧化向还原环境的转变,为蚀变改造砂岩.铀矿多产出于风成沉积的灰色砂岩中,U含量的增高伴随有P、Ca和ΣREE的相对富集,风成沉积灰色砂岩的生成以及铀矿的富集与烃类流体的蚀变作用紧密相关.In order to find out the genesis of the gray sandstones of the Lower Cretaceous Luohe Formation in the southwestern Ordos basin,deepen the understanding of the law for uranium mineral enrichment,and locate the occurrence area of sandstone type uranium ore body,the gray sandstone of Luohe Formation is studied by means of rock and mineral identification,XRD analysis and element geochemical analysis.The results show that there are two different genetic types of gray sandstone in the study area.(1)The sandstone in the lower part of Luohe Formation has typical aeolian sedimentary characteristics,with good separation and roundness of clastic particles,high quartz content,low total clay minerals content,the inter-particle porosity is large,indicating that it has a better fluid migration channel,and it has undergone a higher degree of transformation by the later reducing fluid.Meanwhile,this type of sandstone is also the most important uranium rich sand body.(2)The sedimentary types of the upper part of Luohe Formation are mainly braided river channel,channel edge and flooding basin.with medium-poor separation and roundness of clastic particles,low quartz content,high total clay mineral content,the inter-particle porosity is slightly low,and the reduction transformation degree of sandstone is weak or even basically not transformed.The geochemical characteristics of the two genetic gray sandstones are generally consistent,and some elements are different.When the content of U is higher,the contents of Cao,P_(2)O(5)and MnO in the major elements increase obviously,while the ratio of Fe_(2)O_(3)/FeO decreases obviously.TheδEu has both positive and negative anomalies andδCe shows mainly negative anomaly in the gray sandstone of aeolian deposition,while bothδEu andδCe show negative anomalies in the gray sandstone of fluvial sedimentation.It is concluded that the fluvial sedimentary sandstone of the Luohe Formation is dominated by a reduction environment,which is primary sedimentary sandstone,while aeolian sedimentary sandst

关 键 词：灰色砂岩 成因类型 含铀性 洛河组 彭阳铀矿床 鄂尔多斯盆地 矿床地质 

分 类 号：P611[天文地球—矿床学] P619[天文地球—地质学]