庐枞盆地科学钻探地球物理测井及深部铀异常的发现

庐枞盆地砖桥科学钻探ZK01孔为深部探测技术与实验研究专项在庐枞盆地施工的钻探验证孔,全井段实施了连续取心和地球物理测井工作.测井工作分三次完成,测井总深度1994.02m.测井项目包括视电阻率、极化率、磁化率、纵波速度、超声成像、自然伽马、密度、井斜、井径、井温、泥浆电阻率、井中三分量磁测等10多种方法,获得了钻孔剖面原位物性参数、钻孔几何形态及井壁超声图像.通过对地球物理测井和钻孔岩心编录等资料的研究,完成了岩性的人工识别与支持向量机判别,建立了钻孔测井解释岩性剖面;通过对矿化地层的测井响应分析,将电阻率和磁化率作为粗安岩矿化的识别标识;根据超声成像测井资料推断本地区深部地层最大水平主应力方向为南北走向.在ZK01孔1500~1900m发现放射性异常,对铀当量大于万分之一的21处异常进行了定量解释,铀矿化段累积厚度93.02m,为庐枞地区深部找铀矿提供了重大线索.     

以中国铀成矿理论集成和创新为导向的 地质科技管理方式创新与实践

"十一五"以来,铀矿找矿难度不断加大与铀资源量需求持续上升的矛盾日益凸显,为抓住铀成矿理论研究这一天然铀产业链的源头,核工业北京地质研究院开展了以中国铀成矿理论集成和创新为导向的地质科技管理方式创新与实践,依托铀资源勘查技术与地质工艺创新科技平台,组建了以总指挥和总地质师——"两总"为主控,以资深老专家为核心,中青年骨干和辅助人员为外围的环形科研团队;通过创新地质科技管理方式,实施组织管控扁平化,赋予了科研团队更多的创新自主权;通过实施环境赋能、激励赋能和文化赋能,强化目标任务考核,建立"物质—薪酬,精神—知识传承"的双重激励机制,营造了百花齐放、鼓励创新、容许失败的学术氛围,激发了科研人员开展原始理论创新的积极性;通过开展成果宣传、出版专著,实现了成果沉淀和经典流传。经多年勘查实践,为我国铀矿大基地和重点勘查区铀资源扩大突破提供了理论和技术支撑,取得了显著的经济效益和社会效益。本文从实施背景、主要做法、实施效果三方面论述了该项管理创新成果,旨在为同行开展科技管理创新提供有益借鉴。     

沽源-红山子铀成矿带核桃坝铀矿床矿相学和成矿年代学研究

核桃坝矿床是著名的沽源-红山子铀成矿带上新近勘查突破的重要铀矿床之一。为恢复成矿过程、划分成矿阶段和探讨矿床成因,本文开展了系统的矿相学和成矿年代学研究,以期为区内铀矿勘查和找矿突破提供理论支持。矿相学研究表明,矿床矿石矿物以铀石为主,成矿作用可划分为早期钠长石化交代阶段、早期热液成矿阶段、晚期热液成矿阶段和成矿后阶段四个阶段。核桃坝矿床属于碱交代型(钠交代)热液铀矿床。沥青铀矿U-Pb同位素表观年龄、电子探针化学年龄以及等时线年龄综合研究显示,矿床形成时代应在99. 1Ma左右,是晚白垩世成矿作用的产物。核桃坝矿床可能是富铀岩体在碱交代作用后形成流体(富铀含硅酸成矿流体)在外部条件改变的情况下沉淀成矿。因此,矿体的定位与富铀岩体关系密切,富铀岩体附近的开放空间(断裂构造、层间破碎带等)是重要的找矿方向。     

贵州三穗龙湾铀矿床地质地球化学特征及成因

三穗龙湾矿床位于黔中-湘西北铀成矿带内,是近年勘查发现的贵州第一个大型碳硅泥岩型铀矿床。本文对龙湾铀矿床开展了矿物学、地质地球化学及矿床成因等方面研究。结果表明,该矿床矿石中的原生铀矿物主要为沥青铀矿,表生条件下形成的次生铀矿物较发育,主要有硅钙铀矿、硒铅矿、钛铀矿及铀酰磷酸盐矿物等,它们以纳米-微米级粒状(粒径多10μm)、细脉状或隐晶质形式赋存于有机质、粘土矿物等聚铀矿物中;成矿物质主要来源于赋矿层位,可能有少量来自基底岩浆岩,成矿流体为深部流体与大气降水的混合;铀及共伴生元素的富集与炭质泥岩中富含有机质、磷矿物、铁矿物、粘土矿物密切相关;铀矿形成受层位(老堡组)、岩性(炭质泥岩)、构造(三穗向斜及斜切向斜的断层、层间断层)、围岩沉积环境(陆缘裂谷、裂陷的海相还原沉积环境)等因素控制,经历了雪峰期海底喷流作用下形成含矿岩系过程中铀的初始富集→燕山-喜马拉雅期板内伸展构造背景下淋滤、热液叠加改造再富集的成矿过程,后生成矿特征明显,矿床属沉积-热液叠加改造型。本文研究成果对推进黔东地区铀矿成矿预测和找矿勘查,丰富碳硅泥岩型铀矿成矿理论具有重要意义。     

水文地质概化模型与铀成矿关系探讨——以伊犁盆地南缘铀矿田为例

伊犁盆地南缘铀矿田地下水是铀元素的主要载体及控制因素,前期认为构造均为单斜构造,研究区内新发现5条近NS向逆断层,将研究区分割为6个水文地质单元,因水动力差异,铀成矿作用相差较大。依据含矿含水层的补、隔、排条件及水动力变化情况,归纳总结了狭窄集中型、中间型、宽缓敞开型3类水文地质模型,结合铀矿床规模,得出狭窄型有利于成富大矿体,宽缓敞开型不利于形成工业铀矿体的结论。     

Detection of alteration at the Millennium uranium deposit in the Athabasca Basin: a comparison of data from two airborne electromagnetic systems with ground resistivity data

The Millennium uranium deposit is located within the Athabasca Basin of northern Saskatchewan. The basement rocks, comprised primarily of paleo‐Proterozoic gneisses, are electrically resistive. However, the deposit is associated with highly conductive graphitic metasediments that are intercalated with the gneisses. An unconformity separates the basement rocks from the overlying, horizontally stratified, Proterozoic sandstones of the Athabasca Group (which are also highly resistive). The strike extents of the graphitic metasedimenary packages are extensive and therefore electromagnetic (EM) survey techniques are successful at identifying these zones but do not identify the specific locations where they are enriched in uranium. Through drilling it has been noted that hydrothermal processes associated with mineralization has altered the rocks in the vicinity of the deposits, which should in theory result in a resistivity low. A significant resistivity low has been mapped coincident with the Millennium deposit using ground resistivity survey techniques. However, a comparison of the airborne EM and ground resistivity results reveals that the two data sets have imaged different features. The resistive‐limit (on‐time) windows of the MEGATEM data show conductive features corresponding to lakes located to the west and south of the deposit. The late‐time windows show a feature to the east of the deposit, interpreted as being associated with the east‐dipping graphitic basement conductors (similar to that observed in historical ground EM data collected in this area). The early‐time TEMPEST windows (delay times less than 0.2 ms) show a broad resistivity low located at approximately the same location as where the alteration has been identified through drilling. Modelling the data is not easy but a response that decays prior to 0.3 ms is consistent with 500 Ωm material in the sandstone, a resistivity value close to the lower limit with respect to the hydrothermally altered Athabasca group sediments in this area. The MEGATEM system does not see a conductive zone over the alteration as clearly but the high signal‐to‐noise ratio in the late‐time MEGATEM data means that the conductive material at a greater depth is more coherently imaged.     

滇东北会泽超大型铅锌矿床矿质来源与改造成矿作用

"改造成矿作用"理论是中国科学院涂光炽院士提出的完善矿床成因分类学"四分法"的新理论,是中国学者对世界地球科学的重要贡献。该文根据会泽铅-锌(银、锗)矿床地质地球化学特征,列举其沉积改造的充分证据,用改造成矿的四大要素审视其矿床成因,认同它是典型而独特的沉积—强烈改造矿床,并以重要的宏观地质为依据,注意到峨眉山玄武岩(260 Ma)本身及昆阳群褶皱基底均未赋存一定规模的铅锌矿床,认为玄武岩与基底供给会泽铅锌矿(245~246 Ma)成矿物质有限,成岩与成矿时差太大,且成矿断层切割玄武岩,说明玄武岩成岩在先,铅、锌成矿在后,二者无直接成因联系。对会泽铅锌矿床的物质来源,有主张来自地层、基底、玄武岩或多来源者,但以何者为主,多种金属是否同源尚缺深入讨论,文章特别对地层、基底、峨眉山玄武岩中各成矿元素的含量、富集系数及富集类型进行系统的求算与分析研究,以讨论各种成矿金属的可能来源几率及其对成矿的贡献估计。结果显示:银在各地质体中均高倍富集,可提供充沛矿质,铅次之;锌则相反,多为正常元素或亏损元素,锗、镓、铟亦然,故矿石中的锌、锗、镓、铟,更可能为深部提供。结合大量的微量元素、稀土元素、铅、硫、锶、碳、氢、氧同位素等地球化学资料分析研究,认为地层,特别是震旦—寒武系、泥盆系、下石炭统摆佐组(C1b)与深部是主要的矿质来源,不同金属可同源或异源。矿床受地层岩性与构造的双重控制,与岩浆活动无关,具备改造成矿要素,属典型的沉积—强烈改造铅锌矿床,且具超大、特富、多金属富集的独特性。海西期下石炭统摆佐组已沉积成岩成矿或形成矿源层,后经印支期构造运动强烈改造而超常富集成矿,多掩盖其沉积特征,它属于沉积改造矿床"会泽式"。     

Coupled uranium mineralisation and bacterial sulphate reduction for the genesis of the Baxingtu sandstone-hosted U deposit,SW Songliao Basin,NE China

The Baxingtu deposit is a typical redox front tabular-shaped uranium deposit hosted in sandstones of the Late Cretaceous Yaojia Formation deposited within a braided river environment during the post-rift stage of the Songliao Basin, in northeast China. This study proposes the first metallogenic model for the Baxingtu deposit and provides new data on genetic processes involved in the uranium mineralisation of sandstone-type deposits that were characterised through petrographic observations, whole-rock geochemistry, and geochemical and/or mineralogical study of iron disulphide, uranium minerals, Fe-Ti oxides (EPMA, LA-ICP-MS), and organic matter (REP). The δ³⁴S value has been measured in situ by SIMS on the different generations of iron disulphide.Within regional primary reduced sandstones, pre-ore uranium enrichment (U_mean = 7.6 ppm in whole rock) was identified on altered Fe-Ti oxides along with minor concentrations on organic matter (respectively 26.3% and 1.3% of the whole-rock U content), which together represent a significant source of uranium for the mineralisation. Additional pre-ore uranium concentrations may also be associated with clay minerals. Petrographic observations and REP data indicate that organic matter occurring in the host-sandstone is mainly inherited from land plants and corresponds to type III or type IV kerogens. Ore-stage iron disulphides largely occur as framboids and in replacement of organic matter or also as sub-idiomorphic to idiomorphic cement and crystal. Trace element signatures detected within framboids are likely indicative of formation mainly from a single event. Framboids and iron disulphide in replacement of organic matter have a light sulphur isotope signature characterised by δ³⁴S values from −72.0 to −6.2‰, suggesting that sulphur originated from bacterial sulphate reduction, which was mainly responsible for (1) the liberation of U from Fe-Ti oxides and organic matter, (2) the generation of ore-stage iron disulphides, (3) the bioreduction of uranium and (4) the production of a secondary H₂S-rich reducing barrier also involved in uranium reduction. Uranyl and sulphate ions were transported through the host sandstone by low-temperature oxygenated groundwater and U(IV) was precipitated at the redox interface as nano to microcrystals of pitchblende and coffinite, dominantly associated with bacterial substrate and as intergrowth with biogenic iron disulphide or directly associated with organic matter and residual Ti-Fe oxides. The uranium mineralisation does not replace ore-stage iron disulphides. Therefore, the combined mineralogical, geochemical, and isotopic characteristics of the Baxingtu tabular uranium deposit characterise dominantly biogenic processes for the genesis of the uranium mineralisation.     

伊犁盆地南缘有机-无机流体耦合铀成矿作用

伊犁盆地是中国西北部重要的产铀盆地,虽然前人对其成矿流体进行过较为系统的研究,但成矿流体的组分、来源等依然存在较大分歧,尤其是该区成矿流体与蚀变特征、铀成矿的内在联系研究较少。利用偏光显微镜、扫描电镜、电子探针等手段对含矿层砂岩蚀变特征进行系统分析,并通过分析流体包裹体特征、流体-围岩相互作用形成的蚀变矿物中稳定同位素的组成特征及该区构造演化特征,对有机-无机流体耦合铀成矿作用进行示踪。研究表明：该区流体包裹体主要含有气烃包裹体、液烃包裹体和盐水包裹体;与砂岩型铀矿有关的蚀变类型主要有黏土化、碳酸盐化、硅化及金属矿化,其中黏土化以高岭石化为主;高岭石δ¹⁸O_V-SMOW 为11.8‰～13.7‰,δD_V-SMOW 为-93‰～-48.3‰,与高岭石平衡流体的δ¹⁸O_{（水）V-SMOW}为-10.3‰ ～-5.1‰ ; 方解石胶结物δ¹³C^V-PDB 为-18.2‰ ～-7.2‰ , δ¹⁸O_V-PDB 为-14.5‰ ～-5.8‰ ,δ¹⁸O_V-SMOW 为15.9‰～24.9‰;黄铁矿δ³⁴S_V-CDT为-32.21‰～1.2‰。上述特征揭示,伊犁盆地南缘砂岩型铀矿成矿流体是由大气降水性质的地表水（无机）和煤系地层有机质热演化脱羧基作用产生的有机酸及伴生的CH₄ 等还原性气体（有机）两部分组成,铀矿体与蚀变矿物皆是有机-无机流体混合及其与周围砂岩相互作用的结果,且此过程伴有微生物的参与。     

中国多阶段活化构造与铀成矿作用

中国地质构造和铀成矿复杂,活化构造作用时间长,从早元古宙延续至今,以中新生代最为强烈。针对特定大区域内多种类型铀矿床并存,而主成矿期往往基本一致的特点,笔者从大地构造、深部地质结构、地球物理和地球化学等方面,就中国多阶段活化构造演化及其对铀成矿的控制作用进行了探讨。