| 内蒙古克鲁伦凹陷伊敏组下段砂岩铀成矿条件、特征及成因 |
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| 引用本文： | 黄少华,秦明宽,周文博,刘章月,刘彤,赵志伟,东艳.内蒙古克鲁伦凹陷伊敏组下段砂岩铀成矿条件、特征及成因[J].地球科学与环境学报,2020(2):199-214. |
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| 作者姓名： | 黄少华 秦明宽 周文博 刘章月 刘彤 赵志伟 东艳 |
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| 作者单位： | 核工业北京地质研究院;中核集团铀资源勘查与评价技术重点实验室;核工业二四三大队 |
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| 基金项目： | 核工业地质局地勘科研项目(地D1804);核工业地质局地勘生产项目(201911);中核集团启明星项目(QNYC2018-1);国家自然科学基金项目(41902084)。 |
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| 摘 要： | 为查明内蒙古克鲁伦凹陷伊敏组下段砂岩铀成矿规律和成因,系统总结了内外部铀源、构造环境、岩性-岩相特征、后生氧化作用等关键控矿条件以及铀成矿特征,较精准厘定了目的层时代及其铀成矿年龄,进而构建了砂岩铀成矿模式。结果表明:克鲁伦凹陷的主攻找矿目的层为伊敏组下段,侏罗纪中酸性火山岩、海西期花岗岩、下白垩统伊敏组和地下水的U含量高,指示了内外部铀源十分丰富;目的层形成于断-坳转换期,发育扇三角洲相—滨浅湖相沉积体系,(水下)分流河道微相灰色砂体发育,岩性以含砾粗砂岩、砂砾岩为主,结构疏松,透水性好;原生砂体中富含碳屑及植物茎干,自身还原容量较高,是一套良好的含矿建造;该砂体普遍发育强烈的褐黄色面状古潜水(局部古潜水-层间)后生氧化作用,进而控制了矿体的形成和形态;矿体埋深一般小于150 m,每平方米U质量为0.46~1.00 kg,主要呈透镜状和似层状;铀矿化砂岩全岩U-Pb定年获得了(67.1±5.9)Ma和(63.7±5.2)Ma的等时线成矿年龄;结合凹陷构造演化史,建立了伊敏组下段4个阶段的古潜水-层间氧化铀成矿模式,即早白垩世早期成矿前富铀建造准备阶段、早白垩世中晚期含矿目的层形成阶段、古近纪主成矿阶段和新近纪成矿停滞保存阶段,并指出区内深部(500 m以浅)仍具有较好的古潜水-层间氧化带型铀矿成矿潜力。
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| 关 键 词： | 砂岩型铀矿 伊敏组 控矿条件 矿化特征 成矿年龄 古潜水氧化 成矿模式 内蒙古 |
Metallogenic Conditions,Characteristics and Genesis of Sandstone-type Uranium Deposit of the Lower Member of Yimin Formation in Kelulun Sag of Inner Mongolia,China |
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| HUANG Shao-hua,QIN Ming-kuan,ZHOU Wen-bo,LIU Zhang-yue,LIU Tong,ZHAO Zhi-wei,DONG Yan.Metallogenic Conditions,Characteristics and Genesis of Sandstone-type Uranium Deposit of the Lower Member of Yimin Formation in Kelulun Sag of Inner Mongolia,China[J].Journal of Earth Sciences and Environment,2020(2):199-214. |
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| Authors: | HUANG Shao-hua QIN Ming-kuan ZHOU Wen-bo LIU Zhang-yue LIU Tong ZHAO Zhi-wei DONG Yan |
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| Institution: | (Beijing Research Institute of Uranium Geology,Beijing 100029,China;CNNC Key Laboratory of Uranium Resources Exploration and Evaluation Technology,Beijing 100029,China;No.243 Geological Party,CNNC,Chifeng 024000,Inner Mongolia,China) |
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| Abstract: | In order to investigate the metallogenic genesis and potential of sandstone-type uranium deposit of the lower member of Yimin Formation in Kelulun sag of Inner Mongolia,the key ore-controlling conditions,such as inner and external uranium sources,tectonic setting,characteristics of lithology-lithofacies,epigenetic oxidation,and characteristics of uranium mineralization,were summarized.Moreover,the ages of uranium mineralization and target strata were determined,which can be used to build a reasonable sandstone-type uranium metallogenic model.The results show that the main exploration target in Kelulun sag is the lower member of Yimin Formation;meanwhile,the uranium contents of Jurassic intermediate-acid volcanic rocks,Hercynian granitoids,Lower Cretaceous Yimin Formation and groundwater are relatively high,indicating that inner and external uranium sources are abundant in the area;the target strata mainly develop fan delta-shore shallow lake sedimentary system during the fault-depression transition period,and are characterized by(underwater)distributary channel grey sand bodies;the lithology is mainly composed of gravel-bearing coarse sandstone and glutenite with loose structure and well permeability;the primary sandstone has a high reduction capacity owing to abundant charcoal and plant stems,which is a good ore-bearing construction;the sand bodies generally develop strong brownish yellow planar paleophreatic epigenetic oxidation with paleophreatic-interlayer oxidation locally,which significantly control the formation and shape of the orebodies;correspondingly,the discovered orebodies with a burial depth of less than 150 m and a uranium content of 0.46-1.00 kg·m-2,mainly have lenticular and stratoid shapes;furthermore,the isochron metallogenic ages of(67.1+5.9)Ma and(63.7+5.2)Ma are obtained by whole-rock U-Pb isotope dating with different grades of uranium-mineralized sandstones;finally,a four-stage paleophreatic-interlayer oxidation uranium metallogenic model is established based on tectonic evolution history,including preparatory stage of uranium-rich formation in early Early Cretaceous,development stage of ore-bearing target strata in middle-late Early Cretaceous,main metallogenic stage in Paleogene,and metallogenic cessation and preservation stage in Neogene.In general,there is a favorable potential for the formation of paleophreatic-interlayer oxidation zone type of sandstone uranium deposit in the deep part(<500 m)of the study area. |
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| Keywords: | sandstone-type uranium deposit Yimin Formation ore-controlling condition mineralization characteristic metallogenic age paleophreatic oxidation metallogenic model Inner Mongolia |
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