投稿时间：2017-08-05
修订日期：2018-03-08
网络发布日期：2018-09-10
中文摘要:鄂尔多斯盆地东北部的铀成矿作用过程比较复杂，是多种流体叠加作用的结果。文章在梳理、分析前人资料和研究成果的基础上，通过对铀的存在形式、砂岩的地球化学特征及C、S同位素组成特征、矿物蚀变特征及成矿年龄的研究，总结了铀的富集特征，划分了铀的成矿期次，补充、完善了铀的成矿模式。研究表明，该区直罗组砂岩中的铀主要以独立矿物及吸附态2种形式存在，与黄铁矿、有机质、方解石、黏土矿物等关系密切，独立矿物以铀石为主。含矿砂岩的还原性物质含量（有机质、黄铁矿等）高于其他类型砂岩。碳酸盐胶结物中δ13CV-PDB值为-24.6‰~-6.8‰，反映了碳酸盐胶结物中的碳与生物成因有关。各类砂岩中黄铁矿的δ34SV-CDT值均为负值，分布在-8‰~-40‰，显示出明显的富32S、贫34S的特点，生物成因的分馏特征明显。镜下鉴定结果表明，研究区的古氧化砂岩中多处可见铁的氧化产物以及黑云母的强绿泥石化。结合对铀成矿年龄的研究和总结，提出了研究区铀的富集具有"充足的还原性条件、强改造过程、微生物参与和多期次叠加"的特征，既与潜水氧化作用有关，又受古层间氧化作用的控制，成矿后期还有深部还原性气体的二次还原改造，地层的强还原环境是导致铀富集的主要原因；在古层间氧化作用过程中，地层中的微生物在铀的活化和沉淀过程中发挥了重要的作用；成矿年龄反映出该区铀成矿具有多阶段性，大致可分为中侏罗世直罗早期、中侏罗世直罗期-晚侏罗世、早白垩世-始新世以及渐新世之后等4个阶段。
Abstract:Uranium mineralization process in northeastern Ordos basin was complicated and it was a result of several kinds of fluids superimposing. Through the researches on uranium occurrence forms, geochemical characteristics and C-S isotopic composition of sandstone, features of altered minerals and mineralization ages, this paper summarized the uranium enrichment characteristics, divided the stage of uranium mineralization and improved a uranium metallogenic model based on an analysis of the previous data and achievements. It is shown that uranium in Zhiluo Formation in this region occurs as either independent minerals or adsorbent form. Uranium mineralization has a close relationship with pyrite, organic matters, calcite, clay minerals and some other minerals. Independent mineral of uranium is mainly coffinite. The content of reducing matter (organic matter, pyrite, etc.) of ore-bearing sandstone is higher than that of other types of sandstone. The δ13CV-PDB values range from -24.6‰ to -6.8‰ in carbonate cement, and these data indicate that the carbon in carbonate cements is related to biological causes. The δ34SV-CDT values range from -8‰ to -40‰, and these data show the characteristics of rich 32S and poor 34S, with obvious fractionation characteristics of biogenic factors. The results of microscopic examination show that the oxidation products of iron and the strong chloritization of biotite can be seen in the paleo-oxidation sandstone of this area. Based on the research on mineralization ages, the authors believe that the enrichment of uranium was characterized by adequate reduction conditions, strong transformation process, participation of microorganisms and multistage superimposition, and this was not only related to phreatic-oxidation but also controlled by paleointerlayer-oxidation and by secondary reducing transformation of gases at later stage of metallogenesis. Strong reducibility of the strata was the main reason leading to the enrichment of uranium and microorganism in the strata, which played an important role in uranium mobilization and precipitation during the paleo-interlayer oxidation. The mineralization ages show that uranium mineralization was characterized by multi-stages, and could be generally divided into the stage of syngenetic sedimentary enrichment in early Zhiluo period in middle Jurassic, the stage of phreatic-oxidation from Zhiluo period of middle Jurassic to late Jurassic, the stage of paleo-interlayer-oxidation from Early Cretaceous to Eocene and the stage of secondary reducing transformation of gases from Oligocene to the present.
keywords:geology uranium occurrence forms uranium mineralization age isotope uranium enrichment characteristic metallogenic model northeastern Ordos Basin
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基金项目:本文受中核集团集中研发项目（龙腾二期）“鄂尔多斯盆地北部砂岩型铀矿关键因素识别与靶区优选”（编号：地LTD1601-2）和国家重点基础研究发展计划（“973”计划）（编号：2015CB453004）项目联合资助
引用文本：
易超,王贵,李西得,张康,王永君.2018.鄂尔多斯盆地东北部直罗组铀富集特征及铀成矿模式探讨[J].矿床地质,37(4):835~852YI Chao,WANG Gui,LI XiDe,ZHANG Kang,WANG YongJun.2018.A tentative discussion on uranium enrichment characteristics and metallogenic model in Zhiluo Formation, northeastern Ordos Basin[J].Mineral Deposits37(4):835~852
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