Permeability evolution mechanism and the optimum permeability determination of uranium leaching from low-permeability sandstone treated with low-frequency vibration

Low-frequency vibrations can effectively improve natural sandstone permeability,and higher vibration frequency is associated with larger permeability.However,the optimum permeability and permeability evolution mechanism for uranium leaching and the relationship between permeability and the change of chemical reactive rate affecting uranium leaching have not been determined.To solve the above problems,in this study,identical homogeneous sandstone samples were selected to simulate lowpermeability sandstone;a permeability evolution model considering the combined action of vibration stress,pore water pressure,water flow impact force,and chemical erosion was established;and vibration leaching experiments were performed to test the model accuracy.Both the permeability and chemical reactions were found to simultaneously restrict U6þleaching,and the vibration treatment increased the permeability,causing the U6þleaching reaction to no longer be diffusion-constrained but to be primarily controlled by the reaction rate.Changes of the model calculation parameters were further analyzed to determine the permeability evolution mechanism under the influence of vibration and chemical erosion,to prove the correctness of the mechanism according to the experimental results,and to develop a new method for determining the optimum permeability in uranium leaching.The uranium leaching was found to primarily follow a process consisting of(1)a permeability control stage,(2)achieving the optimum permeability,(3)a chemical reactive rate control stage,and(4)a channel flow stage.The resolution of these problems is of great significance for facilitating the application and promotion of lowfrequency vibration in the CO_(2)+O_(2) leaching process.

Origin and Superposition Metallogenic Model of the Sandstone-type Uranium Deposit in the Northeastern Ordos Basin,China

This paper deals with the metallogenic model of the sandstone type uranium deposit in the northeastern Ordos Basin from aspects of uranium source, migration and deposition. A superposition metallogenic model has been established due to complex uranium mineralization processes with superposition of oil-gas reduction and thermal reformation.

The First Discovery of a Large Sandstone-type Uranium Deposit in Aeolian Depositional Environment

The exploration depth of sandstone-type uranium deposits worldwide is mostly less than 700 m,and most of them occur in strata of fluvial facies(Adams et al.,1981;Jin et al.,2016;Hou et al.,2017).Only a few small uranium deposits have been reported in aeolian depositional environments(Isachsen et al.,1955;Li et al.,2001).In the Pcngyang Jingchuan region of the southwestern Ordos Basin,uranium ore bodies with large thickness and high grade in the aeolian sandstone of the Luohe Formation were newly found at depths from 700 to 1500 m,which have laid the foundation for increasing the uranium resources significantly in the Ordos Basin.

Genesis of green sandstone/mudstone from Middle Jurassic Zhiluo Formation in the Dongsheng Uranium Orefield, Ordos Basin and its enlightenment for uranium mineralization

The middle Jurassic Zhiluo Formation in the Dongsheng is comprised of a big set of green sandstone/mudstone with most of uranium orebodies occurring in close proximity to its footwall.By synthesizing field observations,region analysis,data collected from previous coal and uranium borehole,a regional north-south geological profile across the entire orefield is conducted.Experiments on sandstone/mudstone including rock mineral identification,clastic micromorphology and element geochemistry were carried out.Information from the geological profile indicates that green sandstone/mudstone is widely present in a stable horizon with clear boundaries to the country rock.Microscopic observations and geochemical data on sandstone/mudstone exhibit similar mineral composition with almost identical slightly flat,minor Eu enriched,Ce depleted chondrite-normalized REE patterns.Furthermore,the green clay membrane of the clasts has a complex composition containing chlorite/smectite,green smectite,chlorite,and green kaolinite,with elements including Fe,Mg,Si,and Al.These above results indicate that the green sandstone/mudstone underwent resemble sedimentary diagenetic processes as the country rock without transformation by large-scale regional fluid,while the existence of Fe2+-rich membrane is the main factor to the green sandstone/mudstone.Further concentration of the pre-enrichment uranium during diagenetic process led to the final formation for uranium deposits.The above studies are conducive to enrich the metallogenic mechanism of sandstone type uranium deposits and could provide certain reference for uranium exploration and deployment.

Zircon U-Pb ages and provenance characteristics of the Zhiluo Formation sandstones and the formation background of the uranium deposit in Huangling area,Ordos Basin,China

The newly discovered medium-scale Huangling uranium deposit is located in the Shuanlong area of the southeast Ordos Basin.This paper presents the systematic geochemical and zircon U-Pb studies on the Zhiluo Formation sandstones in the Huanling area.The data obtained play an important role in deducing the provenance and tectonic setting of the source rocks.The results show that the lower part of the Zhiluo Formation is mainly composed of felsic sedimentary rocks.The source rocks originated from a continental island arc environment in terms of tectonic setting.U-Pb ages of detrital zircons obtained can be roughly divided into three groups:170‒500 Ma,1600‒2050 Ma,and 2100‒2650 Ma.Based on the characteristics of trace elements and rare earth elements(REE)and the zircon U-Pb dating results,it is considered that the Cryptozoic Edo provenance of the Zhiluo Formation mainly includes magmatic rocks(such as granodioritic intrusions)and metamorphic rocks(such as gneiss and granulite)in the orogenic belts on the northern margin of the North China Plate and in the Alxa Block.Based on sedimentological and petrological results,it can be concluded that the provenance of clastic sediments in the Zhiluo Formation was in north-south direction.The preconcentration of uranium is relatively low in the Lower Zhiluo Formation in the Huangling area.Meanwhile,the paleocurrent system in the sedimentary period is inconsistent with the ore-bearing flow field in the mineralization period,which restricts the formation of large-scale and super-large-scale uranium deposits and ore zones in the southeast Ordos Basin.The understanding of provenance directions will provide crucial references for the Jurassic prototype recovery and paleo-geomorphology of the Ordos Basin and the prediction of potential uranium reservoirs of the basin.

The Relationship between Jurassic Coal Measures and Sandstone-type Uranium Deposits in the Northeastern Ordos Basin,China

Outcrop and drill hole data show that the Jurassic coal measures in the northeastern Ordos Basin are composed mainly of the Yan’an Formation and the lowstand system tract of the Zhiluo Formation, and there is a regional unconformity between them. The Dongsheng uranium deposit is associated with the Jurassic coal measures. Research data indicate that the Jurassic coal measures in the study area have a certain hydrocarbon-generating capacity, although the metamorphic grade is low （Ro=0.40%–0.58%）. In the Dongsheng region alone, the accumulative amount of generated coalbed methane （CBM） is about 2028.29 × 108 –2218.72 × 108 m3; the residual amount is about 50.92 × 108 m3, and the lost amount is about 1977 × 108 m3. Analysis of the burial history of the host rocks and the evolutionary history of the Dongsheng uranium deposit suggests that the Jurassic coal measures generated hydrocarbon mainly from Middle Jurassic to Early Crataceous, which is the main mineralization phase of the Dongsheng uranium deposit. By the Late Cretaceous, a mass of CBM dissipated due to the strong tectonic uplift, and the Dongsheng uranium deposit stepped into the preservation phase. Therefore, the low-mature hydrocarbon-containing fluid in the Jurassic coal measures not only served as a reducing agent for the formation of sandstone-type uranium deposits, but also rendered the second reduction of paleo-interlayer oxidation zone and become the primary reducing agent for ore conservation. Regional strata correlation reveals that the sandstone-type uranium reservoir at the bottom of the Zhiluo Formation is in contact with the underlying industrial coal seams in the Yan’an Formation through incision or in the form of an unconformity surface. In the Dongsheng region with poorly developed fault systems, the unconformity surface and scour surface served as the main migration pathways for low-mature hydrocarbon-containing fluid migrating to the uranium reservoir.

Elemental Geochemistry of the Interlayer Oxidation Zonein the Shihongtan Sandstone Type Uranium Deposit, Xinjiang

According to the oxidation intensity of ore-hosting sandstone, the interlayer oxidation zone of the Shihongtan sandstone-type uranium deposit in the Turpan-Hami basin can be divided into 4 geochemical subzones, namely, intenselyoxidized, weakly-oxidized, redox and unoxidized primary subzones. The elemental geochemical characteristics of the four subzones have been studied in detail, and the results show that U, together with other elements such as Re, Mo, Se, Sr, S, REE, Corganic etc., is enriched in the redox subzone. Re and U have similar geochemical properties in the reductionoxidation process. The geochemical properties of Mo and Se are similar to those of U in the reduction condition, but different from those of U in the oxidation condition. It is proposed that the ore-hosting layers can provide a curtain mount of uranium for uranium mineralization.

REE/trace element characteristics of sandstone-type uranium deposits in the Ordos Basin

The major elements, trace elements and REEs were analyzed on the samples collected from the sandstone-type uranium deposits in the Ordos Basin to constrain the mechanism of uranium enrichment. The total REE amount ranges from 36.7 to 701.8 μg/g and the REE distribution patterns of the sandstone-type uranium samples are characterized by LREE enrichment and high REE depletion. The results also indicated a high Y abundance and Eu anomalies between 0.77-1.81. High-precision ICP-MS results showed that U abundances are within the range of 0.73-150 μg/g, showing some strong correlation between U enrichment and related elements such as Ti, V, Zr, Mo, and Au. In addition, Th abundance is correlated with ΣREE.

In-situ Chemical Age of the Sandstone-hosted Uranium Deposit in Ningdong Area on the Western Margin of the Ordos Basin, North China

Objective The Ordos Basin located in the westem part of the North China Craton bears various energy resources such as oil, gas, coal and uranium. It is one of the richest uranium-bearing basins in China. Since the discovery of the large-scale Dongsheng, Hangjinqi and Daying uranium deposits in the north of the Ordos Basin, a new breakthrough of uranium exploration has been achieved in the Ningdong area （eastern Ningxia） on the western margin of the Ordos Basin （WMOB） in the past two years （Wang Feifei et al., 2017）.

Geochemical characteristics of Dongsheng sandstone-type uranium deposit, Ordos Basin

Generally, sandstone-type uranium deposits can be divided into three zones according to their redox conditions: oxidized zone, ore zone and reduced zone. The Dongsheng uranium deposit belongs to this type. In order to study its geochemical characteristics, 11 samples were taken from the three zones of the Dongsheng uranium deposit. Five samples of them were collected from the oxidized zone, four samples from the ore zone and two samples from the reduced zone. These samples were analyzed using organic and inorganic geochemical methods. The results of GC traces and ICP-MASS indicate that the three zones show different organic and inorganic geochemical characteristics.

Factors influencing in-situ leaching of uranium mining in a sandstone deposit in Shihongtan, Northwest China

The Shihongtan uranium deposit in northwest China is a sandstone-type deposit suitable for alkaline in-situ leaching exploitation of uranium. Alkaline leaching tends to result in CaCO3 precipitation there by affecting the porosity of the ore-bearing aquifer. CaCO3 deposits can also block pumping and injection holes if the formulation parameters of the leaching solution are not well controlled. However, controlling these parameters to operate the in-situ leaching process is challenging. Our study demonstrates that the dissolved uranium concentration in the leaching solution increases as HCO3-concentration increases. Therefore, the most suitable HCO3-concentration to use as leaching solution is defined by the boundary value of the HCO3-concentration that controls CaCO3 dissolution-precipitation. That is, the dissolution and precipitation of calcite is closely related to pH, Ca2+ and HCO3-concentration. The pH and Ca2+ concentration are the main factors limiting HCO3-concentration in the leaching solution. The higher the pH and Ca2+ concentration, the lower the boundary value of HCO3-concentration, and therefore the more unfavorable to in-situ leaching of uranium.

Geochemical Characteristics of the Sandstonetype Uranium Deposits in Northern Sichuan Province

Described in detail in this paper are the geochemical charederistics of thesandstone-type urboum deposits in northern Sichuan Province. Favoable and unfavor-able conditions for the enrichment of uranium are explored on the basis of the elementalabundances and ratios of U, Th and K determined by gamma-ray spectroscopy Gamma-ray spectroscopic (U, Th and K) and XRF analyses (As, Ba) are helpful to distinguishU-bearing light-colorea sandstones from U-barren light-colored ones and red sandstones(red claystone) from light-colored sandstones. Therefore, the favorable target area forprospecting the sandstone-type uranium deposits can be defined in northern SichuanProvince.

渗出砂岩型铀矿成矿预测与找矿标志

文章基于渗出砂岩型铀矿成矿机理和模式,认为渗出砂岩型铀成矿作用不同于渗入砂岩型铀矿成矿作用,其成矿预测和找矿标志也不同;提出了渗出砂岩型铀矿成矿作用两大基本关键条件识别标志:红杂色含矿建造原生成因和其中控矿灰色砂体的后生成因识别;在提出的红杂色沉积建造中渗出砂岩型铀矿“上红下黑、上下连通、红中找灰、灰中找矿”总体找矿新思路基础上,阐明渗出砂岩型铀成矿区域预测评价条件和标志:深部富铀富有机质沉积岩建造、区域构造、区域建造、放射性异常信息和综合预测标志等,提出并阐述“小凹陷成大矿”条件;系统建立渗出砂岩型铀矿床预测定位标志体系,特别是野外可识别的宏观标志,包括控矿构造、沉积建造、蚀变改造、铀矿化砂岩颜色、外来有机质特征等,并对比了渗入和渗出砂岩型铀成矿预测标志。提出的渗出砂岩型铀矿识别标志体系不仅对区分“渗入”和“渗出”两种矿化成因,而且对厘清控矿要素、指导成矿预测和找矿工程部署具有重要意义和价值。

鄂尔多斯盆地西北部特拉敖包矿产地铀矿石物质组成特征

鄂尔多斯盆地西北部下白垩统环河组是近期新发现的铀矿找矿“新层位”,文章对特拉敖包矿产地下白垩统环河组赋矿砂岩开展了详细的岩石学和矿物学研究,旨在为阐明该地区铀成矿机理及拓展区域找矿空间提供较全面、详实的基础地质信息。通过钻孔岩心观察赋矿岩石岩性、沉积结构和构造特征,利用扫描电镜及偏光显微镜对不同颜色赋矿岩石中的铀矿物、金属矿物、非金属矿物、黏土矿物及有机质等物质成分进行系统观察和鉴定,发现不同颜色赋矿砂岩中铀矿物主要为铀石,有机质主要为少量炭屑和流动态有机质,但金属矿物、非金属矿物和黏土矿物在各色矿石中种类多样且差异明显。认为特拉敖包矿产地及周边地区沉积环境为非典型、高含砂率的辫状河三角洲沉积环境;铀成矿过程具有多种成矿流体来源,成矿过程复杂,灰绿色砂岩至少经历过还原→氧化→再还原的过程。

松辽盆地西南部大林地区铀成矿特征分析

大林铀矿床是松辽盆地西南部新近探明的砂岩型铀矿床。文章对大林铀矿床的矿体产出特征、铀的赋存状态等成矿特征开展研究。研究表明,宏观上,含矿层姚家组下段氧化砂岩十分发育,铀矿体呈多层产出且受氧化带控制明显。微观上,铀主要呈吸附态,独立铀矿物与含铀矿物较少,沥青铀矿是主要的独立铀矿物,存在含钛铀矿物与闪锌矿的热液矿物组合。根据成矿特征初步判断,大林铀矿床与邻近的钱家店铀矿床和宝龙山铀矿床成因相似,是表生流体与深部流体叠加作用的结果。

鄂尔多斯盆地北部下白垩统赋矿砂岩中有机质特征及其与铀成矿的关系

近几年,鄂尔多斯盆地北部下白垩统铀矿找矿取得重大突破,在特拉敖包及其外围发现了多个产于环河组下段的厚大铀矿孔。有机质是砂岩型铀矿化的重要因素之一,环河组下段赋矿砂岩中缺乏肉眼可见的有机质,在铀矿化过程中起主导作用的有机质类型目前还缺乏研究,铀成矿作用过程还不清楚。本文以特拉敖包铀矿产地赋矿砂岩为研究对象,通过岩心观察与室内研究,厘定了赋矿砂岩中的有机质类型,探讨了有机质的来源及其与铀成矿的关系。研究结果表明:赋矿砂岩中几乎不含炭屑有机质,有机质主要为顺层沿砂岩孔隙充填、具有流动特征的浸染状有机质,它是一种具有与沥青相似的复杂结构、低演化程度的大分子物质,具有高等植物和低等水生生物混合来源的特点。铀矿化与固体炭屑有机质关系不大,主要与浸染状有机质密切相关,特拉敖包铀矿产地的成矿特征契合“渗出”砂岩型铀矿成矿模式的特点,深灰色、灰褐色铀矿石的形成可能主要与深部渗出的有机流体有关。成矿元素可能主要以有机质络合物的胶体形式迁移,物理化学条件的变化可能是导致成矿流体发生分解并沉淀成矿的主要因素。

四川盆地北部砂岩型铀矿岩石学特征及矿床成因研究

【研究目的】铀资源是中国重要的战略资源和能源矿产,为更好地勘探和开发四川盆地北部砂岩型铀矿,有必要深入了解其地质特征和成矿模式。【研究方法】本文通过野外调查、岩矿鉴定和地球化学分析研究了砂岩型铀矿的岩石学特征,分析了其成矿过程。【研究结果】含矿主岩主要为下白垩统苍溪组钙质胶结中—细粒砂岩和砾岩。铀以自生铀矿物的形式存在,铀矿物主要为铀石,呈他形、半自形和自形柱状。【结论】米仓山铁船山组变质酸性火山岩和花岗岩为盆地砂岩型铀矿的形成提供了初始铀源。铀在水溶液中以碳酸铀酰离子的形式迁移,富含有机质和黄铁矿的沼泽和停滞水还原环境破坏了碳酸铀酰离子,使铀元素以沉积成岩为主局部叠加后生富集作用成矿。

鄂尔多斯盆地西南部下白垩统铀矿化砂岩中有机质特征及其与铀成矿的关系

鄂尔多斯盆地西南部下白垩统铀矿找矿在近几年取得了重大突破,在镇原、彭阳等地区发现了新的铀矿产地,白垩系铀矿化主要赋存于洛河组与环河组,少部分赋存于泾川组和罗汉洞组,这些赋矿层位原生沉积均处在干旱环境条件下,其中缺乏肉眼可见的有机质。但在钻孔岩心中,铀矿化砂岩中往往富含浸染状的有机质,这类有机质的性质及其与铀成矿的关系目前还缺乏系统的研究。文章以鄂尔多斯盆地西南部镇原地区铀矿化砂岩为研究对象,通过岩心观察与室内研究,厘定了赋矿砂岩中的有机质类型,探讨了有机质的来源及其铀成矿的关系。研究结果表明:赋矿砂岩中的原生沉积炭屑有机质十分稀少,有机质主要为充填于砂岩微孔隙中、具有流动特征、低演化程度的大分子有机质,可能主要来源于“延7”段烃源岩。铀矿化与固体炭屑有机质关系不大,而主要与“可溶性”流动状有机质密切相关。研究区白垩系铀成矿特征具有“渗出”砂岩型铀矿成矿作用的特点。

砂岩型铀矿“源-汇”系统

把从“源”到“汇”的分析方法应用到我国北方盆地砂岩型铀矿成矿作用研究中来,确定不同时期含铀物质的汇流路径,有利于砂岩型铀矿的富集机理和成矿规律的研究和总结。砂岩型铀矿“源—汇”系统是富铀物质从蚀源区风化剥蚀或从盆地深部富铀烃源岩活化,经汇流体系运移,再到盆地有利赋矿砂体聚集成矿的物理、化学和生物作用的过程,主要包括铀源、汇流体系和富集体系三部分。铀源外源是指在产铀盆地边缘大面积出露的富铀基底和岩石;内源是指含矿目的层本身的含铀建造,是在沉积成岩过程中形成的铀预富集;盆地深部富铀烃源岩在高温-高压条件下排烃,通过活动断裂可为浅部砂岩铀矿提供铀源。富铀物质从铀源区风化或活化搬运迁移到赋矿砂体并在砂体中运移的统一过程称为铀成矿汇流体系,沉积盆地的含铀物质主要在沉积期和成矿期通过汇流体系进入赋矿层位中。铀富集体系是砂岩中还原性物质或微生物等将含铀流体还原沉淀富集成矿的相关整体。鄂尔多斯盆地西南部具有浅部渗入、深部渗出汇流体系特点,渗入与渗出汇流体系的相互叠加改造对铀成矿也起到了比较重要的作用。

隆起对砂岩型铀矿成矿的控制及找矿启示

沉积盆地古隆起对油气成藏起到明显控制作用,对砂岩型铀矿成矿的制约也不可忽视。砂岩型铀矿通常就位于盆地边缘构造斜坡带和盆地内部隆起附近。隆起对砂岩型铀矿成矿的控制具体体现在:控制地下水补-径-排体系、控制层间氧化作用、控制沉积相带发育、伴生断裂促进物质输运以及为成矿供给铀等。中国北方沉积盆地中新生代以来经历复杂的构造活动,盆地域内非均衡发展而多形成隆起,因此我国铀矿找矿尤其需要重视隆起对铀成矿的控制。其中,盆地内部找矿应重点关注被大幅抬升的隆起,而盆地边缘构造斜坡带上找矿需重视微隆起以及基底上覆地层的褶皱。将隆起作为关键控矿要素,优选适用的攻深找盲方法,精细刻画盆地基底隆升形成的背斜、褶皱及伴生断裂,可有效提高铀矿找矿效率并拓展铀矿找矿空间。