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 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.

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.

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.

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.

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）.

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.

New Evidence for Genesis of the Zoige Carbonate-Siliceous-Pelitic Rock Type Uranium Deposit in Southern Qinling:Discovery and Significance of the 64 Ma Intrusions

The carbonaceous-siliceous-argillitic rock type uranium deposit in the Zoige area is located in the northeastern margin of the Tibetan Plateau, and has gained much attention of many geologists and ore deposit experts due to its scale, high grade and abundant associated ores. Because of the insufficient reliable dating of intrusive rocks, the relationship between mineralization and the magmatic activities is still unknown. In order to study this key scientific issue and the ore-forming processes of the Zoige uranium ore field, the LA-ICP-MS zircon U-Pb dating of magmatic rocks was obtained：64.08±0.59 Ma for the granite-prophyry and ~200 Ma for the dolerite. U-Pb dating results of uraninite from the Zoige uranium ore field are mainly concentrated on ~90 Ma and ~60 Ma. According to LA-ICP-MS U-Pb zircon dating, the ages for the dolerite, porphyry granite and granodiorite are 200 Ma, 64.08 Ma approximately and 226.5-200.88 Ma, respectively. This indicates that the mineralization has close relationship with activities of the intermediate-acidic magma. The ages of the granite porphyry are consistent with those uraninite U-Pb dating results achieved by previous studies, which reflects the magmatic and ore-forming event during the later Yanshanian. Based on the data from previous researches, the ore bodies in the Zoige uranium ore field can be divided into two categories：the single uranium type and the uranium with polymetal mineralization type. The former formed at late Cretaceous（about 90 Ma）, while the latter, closely related to the granite porphyry, formed at early Paleogene（about 60 Ma）. And apart from ore forming elemental uranium, the latter is often associated with polymetallic elements, such as molybdenum, nickel, zinc, etc.

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.

Types of uranium deposits in central Zhuguang Mountains in Hunan Province,South China and their metallogenic regularity and prospecting directions

The central Zhuguang Mountains in Hunan Province is located at the junction of the three provinces,namely Hunan,Jiangxi,and Guangdong,where the famous Lujing uranium ore field lies.The uranium deposits occurring in this area are all granite-related and they can be divided into three types,namely endogranitic ones,perigranitic ones,and contact zone types.The endogranitic uranium deposits are mainly controlled by the structural alteration zones developing within granites,with fragmentation,hematitization,and alkali metasomatism as their main mineralization characteristics.The perigranitic uranium deposits are mainly produced in the carbonaceous,siliceous,and argillaceous composite layers of epimetamorphic rocks and are controlled by fractured zones formed due to interlayer compression.The contact zone type uranium deposits mainly occur in the contact parts between the granites and favorable horizons.They have developed in favorable sections where multiple sets of structures are combined and intersected.The main metallogenic regularities of uranium in the central Zhuguang Mountains are as follows.The basic conditions for the uranium mineralization in this area include the framework consisting of regional deep large faults and their associated multi-set multi-direction favorable metallogenic structures,multi-cycle and multi-stage uranium-rich rock masses,and uranium-rich folded basement.Meanwhile,the uranium deposits in this area are closely related to granites in terms of genesis and space and they are formed in different structural parts subject to the same metallization.Furthermore,based on the summary of the characteristics and regularities of uranium mineralization in this area,the controlling factors of different types of uranium deposits in the area were explored and six metallogenic target areas were predicted.All these will provide references for the exploration of uranium deposits in this area.

Mineralogy,Fluid Inclusion and H-O-C-S Stable Isotopes of Mengqiguer Uranium Deposit in the Southern Yili Basin,Xinjiang:Implication for Ore Formation

The Mengqiguer deposit in the southern Yili basin Ili Basin is a large interlayer-oxidation-zone type uranium deposit.In this paper,we applied multiple methods including microscopic observation,scanning electron microscope and electronic probe,to analyze the systematical alteration characteristics of the ore-bearing sandstone layer.Fluid inclusion and stable isotope studies on the ore-bearing sandstone have also been carried out to discuss the internal relations between fluid activities,epigenetic alteration and the uranium mineralization.Major epigenetic alteration include clay alteration,carbonatization and pyritization,of which biogenetic pyritization is most closely related to the uranium mineralization.This suggests the existence of microorganism during the uranium mineralization process.The mineralization fluids of low temperature,medium density but varied salinities are suggested to be derived from multi-source,including the meteoric water and organic acidic vapor components from coal-bearing strata.Uranium mineralization,grain-dispersed kaolinite,limonite,colloidal pyrite,and the carbonate cements associated with sulfate-reducing bacteria were formed by meteoric water and vermicular-shaped kaolinite,autologous pyrite,and the carbonate cementation associated with the dehydroxylation of organic matter was formed by organic acidic.Based on these results,we consider that the uranium mineralization and epigenetic alteration both resulted from the reciprocity of organic–inorganic fluid and fluid–rock during the formation of the interlayer oxidation zone.

REE geochemical characteristics of the No. 302 uranium deposit in northern Guangdong, South China

The No. 302 uranium deposit, located in Guangdong Province, is a typical granite-type uranium ore deposit. REE geochemical characteristics of the wall rocks, pitchblende, altered rocks, calcite and fluorite from this deposit have been systematically studied in this paper. The result showed that the alkali-metasomatic granites and other altered rocks have the same REE distribution patterns as Indosinian granites. It is indicated that the hydrothermal ore-forming solution had altered the Indosinian granites, and ore-forming materials may directly originate from the Indosinian granites. Calcite and fluorite of different stages are the products derived from the same source but different stages. The evolution and degassing of the mineralizing solution might induce LREE enrichment to varying degree. Mantle fluid and a large volume of mineralizer may be the crucial factors controlling uranium mineralization, and the hydrothermal solution with mineralizer played an important role in U transport and concentration. Meanwhile, the degassing of CO2 might promote U and REE precipitation.

Episodic sandstone-type uranium mineralization in Asia during the Late Mesozoic-Cenozoic

Sandstone-type uranium deposits(STUDs) are the most important global source of uranium. However, it is unclear why STUDs have a non-random distribution in time and space. It is generally thought that STUDs are formed by the circulation of groundwater in sandstone rocks. The groundwater is typically oxidized and sourced from local precipitation, which suggests the regional climate may have a role in the formation of STUDs. The groundwater circulation is mainly affected by basin evolution, which means that regional tectonism may also control the formation of STUDs. In this study, the author examined STUDs in Asia, and compiled previously reported ages for STUDs and compared these with the uplift history of the major orehosting regions and the late Mesozoic–Cenozoic climatic evolution of Asia. Apart from a few uranium deposits in the Transural region, most of the STUDs in Asia were formed during the Late Cretaceous to Quaternary, and can be classified into three stages:Late Cretaceous–early Paleogene(80–50 Ma;stage I), Oligocene–mid-Miocene(25–17 Ma;stage Ⅱ), and late Miocene–present(8–0 Ma;stage Ⅲ). The formation of STUDs in Asia was closely related to regional uplift caused by India–Eurasia collision,subduction of oceanic plates, and increased humidity during greenhouse climate periods and intensification of the Asian Monsoon.

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。

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。