鄂尔多斯盆地风成含铀岩系的识别——以XX井为例  

Identification of Eolian Sandstone in Cretaceous Uraniferous Sandstone in Ordos Basin,China

作　　者：乔大伟 旷红伟[1] 柳永清[1] 彭楠[1] 刘燕学[1] 许欢 崔立伟 李佐强[4] QIAO Dawei;KUANG Hongwei;LIU Yongqing;PENG Nan;LIU Yanxue;XU Huan;CUI Liwei;LI Zuoqiang(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;College of Earth Science,East China University of Technology,Nanchang 330013,Jiangxi,China;China University of Geosciences,Beijing 100081,China;College of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,Sichuan,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]东华理工大学地球科学学院,江西南昌330013 [3]中国地质大学(北京),北京100081 [4]成都理工大学沉积地质研究院,四川成都610059

出　　处：《大地构造与成矿学》2020年第4期648-666,共19页Geotectonica et Metallogenia

基　　金：国家重点研发计划项目(2018YFC0604201);国家自然科学基金面上项目(41672111);国际地球科学计划(IGCP675)联合资助。

摘　　要：本文以XX井为例,通过详细的岩心观察和描述,结合岩石薄片鉴定、扫描电镜观察及粒度分析等方法,对鄂尔多斯盆地西南部工业含铀岩系下白垩统洛河组开展了系统的沉积学研究。在洛河组中共识别出风成沙漠(下段)和洪泛河流(上段)2种沉积相,风成沙漠沉积相又分为沙丘、沙丘间、沙席、旱谷4种亚相,洪泛河流沉积相又分为河床和堤岸2种亚相。洛河组下段砂岩段主要由红色、黄色、灰绿色粗‒细砂岩组成,矿物成分以石英为主,佐以少量岩屑(沉积岩屑)和长石(微斜长石、条纹长石),砂粒干净、明亮,含较少胶结物与杂基,成分成熟度较高;以中‒细砂为主,粒径范围在2.2~3ϕ之间,次棱角‒次圆状;粒度概率累积曲线显示以跳跃搬运组分为主体,伴随有少量悬浮搬运组分,粒度分选性好,结构成熟度高。沉积构造广泛发育大型高角度交错层理、平行层理和波状层理等;层内可见呈舌形向上或向下尖灭的垮塌层,具有逆粒序的风成沙波层以及形似暗色条纹的条纹层等特殊风成沉积构造。砂岩颗粒表面具有一系列碟型和新月型撞击坑、麻坑、化学溶蚀与沉淀以及沙漠漆等现象。将洛河组下段砂岩与典型河流相砂岩、风成砂岩进行对比,表明鄂尔多斯盆地西南部洛河组下段含铀砂岩符合典型风成砂岩的特征。该风成含铀岩系的发现为国际上砂岩型铀矿增添了新的类型,为中国北方铀矿勘探拓展了找矿空间和找矿潜力,为砂岩型铀矿的进一步勘探提供了新思路。Uraniferous rocks in the lower part of Cretaceous Luohe Formation of Well XX located at the southwestern Ordos Basin have been investigated through core logging,microscopic observation,scanning electron microscope and granularity analyses.The desert(lower part)and ephemeralalluvial(upper part)sedimentary facies,composed of dune,interdune,sandsheet,wadi,and channel,bank subfacies are identified.The lower part of the Luohe Formation consists of red,yellow,and grayish green coarse-to fine-grained sandstone.The sandstone lacks cement and matrix,and quartz grains as the main mineral component are commonly clean and bright,with a small amount of debris(sedimentary debris)and feldspar(microcline and striped feldspar),indicating a high composition maturity.These particles are mostly medium-fine,sub-angular to sub-rounded,and the grain size distribution is mainly concentrated between 2.2ϕand 3ϕ.The grain size curve shows that the sandstone is mainly composed of jumping transport components,with a small amount of suspended transport components,which means that the sandstone is well sorted and structurally high mature.Large scale and high angle cross bedding,parallel bedding,and wavy bedding are common,and tongue shaped grain flow with upward or downward pinching,wind ripple strata with reverse grain sequence,pin stripe lamination with dark color can be identified in the layer.Under scanning electron microscope,a series of dished and crescent impact craters,pockmarks,chemical dissolution and precipitation,desert paint,and other phenomena are identified on the surface of sandstone particles.Comparing with the characteristics of typical fluvial sandstone and eolian sandstone,the uraniferous sandstone in the lower part of the Luohe Formation in the southwestern Ordos Basin is of typical eolian sandstone.The eolian uraniferous sandstone is a new type of uranium-bearing sandstone reservoirs in the world,and this discovery expands the exploration space and potential for uranium deposits in North China,and provides new direction

关 键 词：鄂尔多斯盆地 含铀岩系 白垩系 洛河组 风成砂岩 

分 类 号：P536[天文地球—古生物学与地层学] P588.21[天文地球—地质学]