尼日尔阿泽里克地区砂岩型铀矿控矿因素研究

【作者】 许强；

【导师】 秦明宽； 范洪海；

【作者基本信息】 核工业北京地质研究院 ， 矿产普查与勘探， 2013， 博士

【摘要】 通过研究阿泽里克地区野外露头剖面、钻孔岩芯、测井曲线等，结合室内镜下薄片鉴定，认为阿萨乌阿组沉积相为辫状河三角洲，亚相为辫状河三角洲前缘。分流河道砂岩以中-粗粒砂岩为主，富含酸性火山碎屑，泥质含量少，成分成熟度低、结构成熟度低。分流河道砂体孔隙度、渗透率高，在纵向、横向上连通性好，利于成矿流体在砂体中流通，并为铀成矿提供了良好的容矿空间和铀源。在野外蚀变现象研究的基础上，通过光学显微镜、电子探针、扫描电镜技术手段分析了阿萨乌阿组砂岩中蚀变类型。与铀成矿关系密切的蚀变类型主要有还原蚀变、泥微晶碳酸盐化、方沸石化、火山玻璃脱玻化。酸性火山物质方沸石化与火山玻璃脱玻化可为铀成矿提供铀源。运用电子探针、光学显微镜及扫描电镜手段，研究了铀赋存形态及其伴生矿物。铀主要以独立铀矿物的形式存在，多以胶结物形式充填于碎屑粒间孔隙、碎屑裂隙及溶蚀孔洞中；沥青铀矿、铀石等伴生矿物主要有黄铁矿、黄铜矿、辉铜矿、自然铜等。通过流体包裹体分析、方解石碳氧同位素分析、沥青铀矿氧同位素分析，追踪了成矿流体来源。成矿流体来自大气水和深部还原性流体。方解石氧同位素显示成矿流体δ18O值为-0.01，沥青铀矿氧同位素显示成矿流体δ18O值为-1.05，说明大气水对铀成矿有重要作用。方解石碳同位素显示成矿流体δ¹³C值为-6.63，接近地幔碳(δ¹³C=-7³‰)的边界值，说明深部还原性流体可能有地幔碳的加入。流体包裹体中检测出H2，显示来自深部的H2为还原剂之一。大气水流体提供铀，深部流体提供还原剂。在对阿泽里克铀矿床进行分析的基础上，总结归纳出铀成矿的控矿因素。构造、沉积、成矿流体三者共同控制了阿泽里克铀矿床的铀矿化。河道砂体为铀成矿提供了良好的容矿空间；北西向断层控制了还原蚀变砂体的分布；三元流体的叠合作用控制了铀矿化沿砂体顶部，并形成分散的板状、透镜状矿体。通过综合运用沥青铀矿物稀释法和LA-ICP-MS微区U-Pb同位素测年，测出沥青铀矿物形成年了为101.3⁶4.5Ma。以砂岩型铀矿床成矿理论为指导，在分析大地构造背景、盆地演化的基础上，综合构造活动、沉积建造、矿化特征、地球化学特征、成矿流体活动特征、控矿因素、铀成矿年龄等提出了“三元流体叠合成矿“理论，建立了矿床成因模式。更多还原

【Abstract】 After studies on outcrops and drill cores and logs associating with thin sectionanalysis under microscope,the conclusion is that the sedimentary facies of Assaouasfromation is braided river delta and subfacies is delta front; distributary channelssandstone characters medium-coarse grains and rich acid volcanic debris and poorlyargillaceous material whose compositional maturity and textural maturity arelow;channel sandstone bodies are high porosity and permeability and goodcommunication horizontally and vertically which favor circulation of mineralizingfluids and provide favorable host room and uranium resource for uraniummineralization.Alterations are analyzed by methods such as optical microscope and electronmicroprobe and scanning electron microscope,based on studies on alterations in thefield.There mainly are reduction and micrite carbonatization and analcitization anddevitrification of acidic volcanic glasses which are relational with uraniummineralization. Analcitization of acidic volcanic and devitrification of acidic volcanicglasses provide uranium for uranium mineralization.The paper studies existent forms of uranium by utilization of electronmicroprobe and optical microscope and scanning scanning electronmicroscope.Uranium mainly existence as forms of uranium minerals which cementand infill intergranular pore and fissures and cavities corroded of clastics. Pitchblendeand coffinite associate with pyrite and chalcopyrite and chalcocite and native copperet al.Origins of mineralizing fluids are traced by analysis of fluid inclusion and C-Oisotope of calcite and O isotope of pitchblende. Mineralizing fluids comes fromatmospheric water and reducing fluid from the deep. δ18O of mineralizing fluidsfrom O isotope of calcite and pitchblende are-0.01and-1.05which revealatmospheric water signifies uranium mineralizing. δ¹³C of mineralizing fluids fromcalcite is-6.63which is close to the boundary value of mantle carbon(δ¹³C=-7³‰)and indicates reducing fluid from the deep probability blends with mantle carbon. H2is detected form fluid inclusion which reveals one type of reductants is H2from the deep. Atmospheric water fluid provides uranium as well as fluid from thedeep does reductants.Ore controling fectors of uranium mineralization are concluded based on analysisof the Azelik uranium deposit. Structure and sedimentarion and mineralizing fluidstogether control uranium mineralization. Channel sandstone badies providefavourable host room; NW faults control the rang of reduced sandstone badies; Thesuperposition of three types of fluids contros forms of mineral ore which is at the topof sandstone and tablet and discrete.Pitchblende minerogenic age is dated by utilization of pitchblende mineraldilution method and LA-ICP-MS pitchblende microzone U-Pb isotope dating which is101.3⁷6.6Ma.With theories of sandstone type uranium deposit,the theory of the superpositionof three typies of fluids and metallogenetic model is established,based on analysis ofgeotectonic and basin’s structure setting, after multidisciplinary analysis of structurescharacteristics and sedimentation and mineralization features and geochemicalbehavior and mineralizing fluids characteristics and ore controling fectors ofmineralization and minerogenic age.更多还原