Search Results (45)

The discovery of a super-large sandstone-hosted uranium ore field in the eolian sandstones of the Pengyang area (Ordos Basin, North China) represents a major breakthrough, yet the relationship between chlorite alteration and uranium mineralization in this deposit type remains unclear. This study conducted detailed mineralogical and geochemical analyses of chlorite using SEM, TEM, and EPMA. Five distinct types of chlorite were identified from mineralized and non-mineralized sandstones from the Luohe Formation in the Pengyang area from the southwestern Ordos Basin. This study addresses the formation temperatures, material sources, and possible formation mechanisms of those chlorites. The chlorites closely associated with uranium minerals formed at temperatures ranging from 130 to 170 °C, which represent the true formation temperature of the uranium minerals in the Pengyang uranium deposit. Comparing chlorite from uranium deposits related to granitic and volcanic rocks hosted uranium deposits in South China and sandstone-hosted uranium deposits in northern Ordos, North China, it is revealed that the chlorites from the eolian sandstone depositional area of the Pengyang experienced multiple episodes of fluid alteration. In addition, the chlorites closely related to uranium mineralization were formed by relatively low-temperature and oxidizing fluids, which may indicate that the uranium-bearing oxidative fluids in this region were primarily derived from interlayer infiltration. Full article

The CO₂+O₂ in-situ leaching (ISL) mining process has been widely applied in the exploitation of sandstone-type uranium deposits; however, evaluating leaching efficiency remains a challenging issue. In this study, a sandstone-type ISL uranium deposit was selected, and based on comprehensive investigations of hydrogeological conditions and mineral geochemistry, a multi-physics coupled numerical model of uranium solute reactions during CO₂+O₂ leaching was established. The model fully accounts for variations in the groundwater flow field between injection and production wells and, on this basis, couples the chemical reaction field between the ore and the leaching solution. The model simulates the evolution of uranium concentration in the leaching solution and further calculates the leaching efficiency of the ore. The results indicate that groundwater flow velocity is highest between injection and production wells, where groundwater dynamics are strongest, and gradually decreases toward the interwell zones as hydrodynamic intensity weakens. Uranium concentration in the leaching solution is closely related to the groundwater flow field. In the early stage, high-uranium-concentration zones are mainly concentrated between injection and production wells. As time progresses, ore reactions in high-flow regions become more complete, leading to a decline in uranium concentration, while residual uranium ions within the formation diffuse outward under concentration gradients, causing high-concentration zones to expand outward. Sensitivity analysis shows that increasing CO₂ and O₂ concentrations significantly enhances uranium leaching concentrations, with increases of approximately 22.1% and 11.3%, respectively. Lower injection-production flow rates reduce dilution and promote more complete reactions, but may also introduce risks such as ore layer clogging. These results provide a theoretical basis and scientific guidance for flow-field regulation in situ leaching uranium mining. Full article

Sandstone-type uranium deposits represent one of the most significant uranium deposit types in China, predominantly hosted in Meso-Cenozoic sedimentary basins in the northern part of the country. Due to characteristics such as deep burial of orebodies, fine grain size of ores, and strong heterogeneity, traditional geological logging methods have limitations in rapidly and accurately identifying alteration minerals and mineralization indicator information. Core spectral technology (wavelength range approximately 400–2500 nm), particularly short-wave infrared spectroscopy (SWIR, 1300–2500 nm), enables rapid, non-destructive, and quantitative extraction of alteration mineral information from drill cores. This provides robust technical support for reconstructing metallogenic environments, delineating oxidation–reduction zones, and prospecting and prediction in sandstone-type uranium deposits. This review systematically examines the spectral absorption characteristics and geological significance of key alteration minerals (e.g., clay minerals, carbonate minerals, iron oxides, and hydrocarbon substances) in sandstone-type uranium deposits. It elaborates on the current application status of core spectral technology in sandstone-type uranium exploration within typical basins in northern China, such as the Ordos, Songliao, Erlian, and Qaidam Basins. These applications include alteration mineral mapping, oxidation–reduction zone delineation, and metallogenic fluid tracing. Due to the unique characteristics of host rock lithology, alteration mineral assemblages, and fluid properties in sandstone-type uranium deposits, the application of this technology also faces certain challenges, such as difficulties in spectral interpretation and insufficient accuracy in quantitative inversion. Integrating this technique with multiple methods, including petrography and X-ray diffraction (XRD), will facilitate more effective applications in both metallogenic research and prospecting practices for sandstone-type uranium deposits in northern China. Full article

The interlayer oxidation zone-type Mengqiguer uranium deposit in the southern Yili Basin is a typical sandstone-hosted uranium deposit in northwest China, and the lower member of the Jurassic Xishanyao Formation is its main ore-hosting stratum. However, mineralogical and geochemical responses to redox evolution in the deposit have not been systematically constrained. In this study, we carried out detailed petrographic observation, X-ray diffraction analysis, electron probe microanalysis, and whole-rock geochemical analyses on samples from the interlayer oxidation zone in the lower member of the Xishanyao Formation. Kaolinite and illite are the dominant clay minerals in the deposit, with higher contents in oxidation zones than in transition and unaltered zones, while the illite–smectite mixed-layer content shows the opposite trend. The main uranium minerals are uranium oxides and coffinite. U, S and organic carbon are enriched in the transition zone, while the Fe³⁺/Fe²⁺ ratio increases with the oxidation degree. Comprehensive analysis on clay minerals shows that the ore-forming fluids evolved from acidic oxidized meteoric fluids to weakly alkaline reduced fluids; the uranium was mainly derived from the leaching of uraniferous sandstone. The formation of the deposit is controlled by sedimentary facies, tectonic uplift, organic–inorganic fluid interaction and redox reaction. This study provides detailed mineralogical and geochemical evidence for the metallogenic mechanism of interlayer oxidation zone-type uranium deposits, and has important guiding significance for uranium prospecting in the Yili Basin. Full article

This paper presents a comparative determination of rare earth elements (REEs) in sandstone-type uranium ore samples from Kazakhstan using a proposed rapid ICP-MS method following microwave digestion in a MARS 6 system with a mixed acid solution of HNO₃, HCl, and HF. To validate the rapid REE determination method, comparative measurements were performed using a certified uranium ore reference material provided by Ore Research & Exploration, representing sandstone-hosted uranium mineralization from a Tanzanian deposit (OREAS 120). Fractionation patterns of chondrite-normalized REEs in uranium ores from Kazakhstan were evaluated. Comparative data on REE distribution in sandstone- and magmatic-type uranium deposits from Australia and Tanzania are presented. Uranium ores of magmatic- and sandstone-hosted types exhibit distinct REE distribution patterns, reflecting differences in the nature of ore-forming processes. This study provides chondrite-normalized REE distribution profiles for major uranium deposit types from three countries, which are subsequently used to assess uranium ore paragenesis through simple linear regression analysis. This study is intended as an applied comparative synthesis of REE fractionation patterns in genetically contrasting uranium deposits, with particular relevance to deposit classification. Full article

Tamusu, the only identified super-large sandstone-hosted uranium deposit in the Bayingobi Basin, provides an important natural laboratory for evaluating ore-controlling factors and genetic models of sandstone-type uranium mineralization. Based on core descriptions from more than 200 boreholes, log facies analysis and geochemical environmental proxies, this study constrains the sedimentary–mineralization architecture and key controlling factors of the deposit. Uranium orebodies are mainly hosted in the upper member of the Lower Cretaceous Bayingobi Formation (Sq2) within a gravity flow-dominated fan-delta–lacustrine system. Braided distributary channel sands on the fan-delta plain and subaqueous distributary channel sands on the delta front constitute the principal uranium reservoirs, controlling both the migration pathways and storage space for U-bearing fluids. Mineralization is jointly governed by fan-delta architecture, interlayer oxidation zonation and reducing agents. The interlayer oxidation zone displays a north-thick–south-thin geometry, and uranium orebodies are concentrated at redox transition positions, with grades of 0.01–0.33 wt%. The metallogenic evolution can be summarized in three stages: syndepositional uranium pre-enrichment, interlayer oxidation mineralization, and a late hydrothermal/diagenetic overprint that mainly modified reservoir properties, favored ore preservation, and did not contribute to the primary uranium budget. Accordingly, a genetic model of “fan-delta architecture + interlayer oxidation control + late overprint and preservation” is proposed to guide exploration in the Bayingobi Basin and analogous sandstone-type uranium systems. Full article

The Yaojia Formation in the northeastern Songliao Basin is a primary target horizon for sandstone-type uranium mineralization in the area. Understanding its provenance, composition, and depositional paleoclimate is of great significance for uranium exploration in the region. This study analyzed 58 sandstone and mudstone samples using petrographic thin-section observation, elemental geochemistry, and detrital zircon U-Pb geochronology. The results show that Yaojia Formation sandstones are feldspathic lithic quartzose sandstone (averaging 47% lithics, 32% quartz, and 21% feldspar, mainly K-feldspar), with moderate sorting and predominantly angular to subangular grains, indicating rapid denudation in the source area, medium- to short-distance transport, and rapid deposition. The chemical weathering index (CIA, 52–68) and the index of compositional variation (ICV, 0.83~1.26) are generally low, indicating moderate chemical weathering. Rb/Sr, Sr/Cu, Al₂O₃/MgO, CIA, MgO/CaO ratios indicate that the Yaojia Formation was deposited under predominantly arid–semiarid conditions, with later stages being wetter than earlier ones. Rare earth element (REE) characteristics indicate light REE enrichment, heavy REE depletion, and significant negative Eu anomalies. Combined with A-CN-K diagrams and discriminant plots such as La/Th-Hf and Co/Th-La/Sc, the provenance is primarily derived from felsic magmatic rocks in a post-orogenic extensional tectonic setting. Detrital zircon U-Pb ages are mainly concentrated at 119–153 Ma (64%), 160–183 Ma (14%), and 318.3–327.7 Ma (6%), showing the highest similarity to zircon age spectra from magmatic rocks in the Great Xing’an Range. The comprehensive results indicate that the clastic rocks of the Yaojia Formation in the study area were mainly sourced from Early Cretaceous felsic magmatic rocks in the Great Xing’an Range and have undergone short- to medium-distance transport and sedimentation under arid to semi-arid paleoclimatic conditions. Full article

The northern part of the Naomugeng Sag in the Erlian Basin shows favorable sandstone-type uranium mineralization in the lower member of the Saihan Formation. The sandstone thickness ranges from 39.67 to 140.36 m, with an average sand content ratio of 76.33%, indicating broad prospecting potential. This study focuses on samples from uranium ore holes and uranium-mineralized holes in the area, conducting grain-size analysis of uranium-bearing sandstones, heavy mineral assemblage analysis, and detrital zircon U-Pb dating to systematically investigate provenance characteristics. The results indicate that the uranium-bearing sandstones in the lower member of the Saihan Formation were primarily transported by rolling and suspension, characteristic of braided river channel deposits. The heavy mineral assemblage is dominated by zircon + limonite + garnet + ilmenite, suggesting that the sedimentary provenance is mainly composed of intermediate-acid magmatic rocks with minor metamorphic components. Detrital zircon U-Pb ages are mainly concentrated in the ranges of 294–217 Ma (Early Permian to Late Triassic), 146–112 Ma (Middle Jurassic to Early Cretaceous), 434–304 Ma (Late Carboniferous to Early Permian), and 495–445 Ma (Middle–Late Ordovician to Early Silurian). Combined with comparisons of the ages of surrounding rock masses, the provenance of the uranium-bearing sandstones is mainly derived from intermediate-acid granites of the Early Permian–Late Triassic and Middle Jurassic–Early Cretaceous periods in the southern part of the Sonid Uplift, with minor contributions from metamorphic and volcanic rock fragments. The average zircon uranium content is 520.53 ppm, with a Th/U ratio of 0.73, indicating that the provenance not only supplied detrital materials but also provided uranium-rich rock bodies that contributed essential metallogenic materials for uranium mineralization. This study offers critical insights for regional prospecting and exploration deployment. Full article

Sandstone-hosted uranium deposits represent one of the most critical global uranium resources suitable for in situ recovery, with their formation closely associated with organic matter (OM). We conducted a systematic literature review to synthesize over 100 published studies sourced from authoritative databases (Elsevier, Google Scholar, Web of Science, Scopus, CNKI, etc.). This study systematically summarizes the types and geological characteristics of OM in sandstone reservoirs and thoroughly analyzes the geochemical mechanisms by which OM regulates the transport and precipitation of aqueous uranium. By integrating case studies of representative sandstone uranium deposits globally, three major OM-related metallogenic models are proposed with distinct core characteristics: the humic-dominated model is driven by the complexation and direct reduction of uranium by humic substances/coal-derived OM; the roll-front model relies on reactions between oxidized uranium-bearing fluids and scattered OM, as well as microbially generated sulfides at the migration front; and the seepage-related model is fueled by upward-migrating deep hydrocarbon fluids (petroleum, methane) that act as both uranium carriers and reductants. Furthermore, this review explores the spatial coupling relationships between OM distribution and uranium mineralization in typical geological settings, evaluates the guiding significance of OM for uranium exploration, and outlines key unresolved scientific issues. The findings refine the genetic theoretical framework of sandstone-hosted uranium deposits and provide important technical support and theoretical guidance for future uranium exploration deployment and resource potential evaluation. Full article

A large-scale sandstone-type uranium deposit, recently discovered within the petroleum field of the Jingchuan area on the southwestern margin of the Ordos Basin, exemplifies a classic case of uranium exploration success achieved through the analysis of petroleum geological data including borehole logs. By synthesizing borehole radioactive logs and seismic surveys, we delineated target sandstone geometry, connectivity, and ore-controlling structures (e.g., paleochannels, redox interfaces). This study establishes a novel methodology for sandstone-type uranium exploration in petroliferous basins, unifying geophysical and geochemical datasets to define drill-validated targets. We integrated detailed core logging, petrography, and assay data to delineate the deposit’s geology. This included the host strata composition, ore-body morphology, mineralogy, and alteration assemblages. Our analysis identified the critical controls on mineralization: sandbody architecture, structural framework, and redox zonation. Based on these constraints, we constructed a genetic metallogenic model. Furthermore, we elucidated the mechanistic role of hydrocarbons in uranium mineralization and demonstrated the strategic potential of repurposing legacy oilfield data for synergistic uranium targeting. The Jingchuan uranium deposit provides both an exploration blueprint and theoretical foundations for uranium targeting in analogous sedimentary basins. Full article

The Erlian Basin, an important research area for sandstone-type uranium deposit exploration in China, is affected by overburden layers, resulting in indistinct characteristics of uranium anomalies in airborne gamma-ray spectrometry (AGS). To harness the potential of AGS, it is imperative to develop effective verification methods that can identify the spatial relationship between weak uranium anomalies and deep uranium-rich geological bodies. This study presents a comprehensive investigation of geophysical and geochemical measurements conducted in four distinct areas. There is a significant positive correlation between the ground gamma spectrometry equivalent uranium (eU_GGS) content, soil radon concentration (C_Rn), geoelectrochemical uranium (U_GEC), and metal activity state uranium (U_MAS) content directly above and at the edges of uranium-rich geological bodies. When the buried depth of the uranium-rich geological body exceeds 100 m, the eU_GGS content above these deep uranium bodies increases by (0.4–1.2) × 10⁻⁶ g/g compared to background areas, while the C_Rn levels at the edges of these bodies increase by more than 5000 Bq/m³, which is 3–5 times higher than the regional average. Meanwhile, the U_GEC and U_MAS contents show sawtooth-like uranium peak anomalies on their profiles, and their peak-to-background ratio is greater than 5. The verification methods and corresponding interpretation indicators, namely GGS, C_Rn, GEC and MAS measurements, can quickly reveal the spatial relationship and provide a reliable basis for concealed uranium deposit exploration. Full article

The characteristics of interlayer oxidation zones constrain sandstone-type uranium mineralization. This study conducted a quantitative characterization of the interlayer oxidation zones in the uranium-bearing reservoir of the Saihan Formation in the central Wulanchabu Subbasin of the Erlian Basin through sand dispersion system mapping, the analysis of sedimentary debris components, environmentally sensitive parameters, and elemental geochemical characteristics. The formation mechanisms and controlling factors of interlayer oxidation zones were investigated, along with uranium mineralization patterns. Research findings reveal that the sandbodies in the study area primarily consist of red sandstone, yellow sandstone, gray ore-bearing sandstone, and primary gray sandstone, representing strong oxidation zones, weak oxidation zones, transitional zones, and reduction zones, respectively. Although the mineral debris content shows minimal variation among different zones, feldspar dissolution is more prevalent in oxidized zones. During interlayer oxidation, environmentally sensitive parameters exhibit an ascending trend from strong oxidation zones through weak oxidation zones and reduction zones to mineralized transitional zones. Four transition metal elements (Co, Ni, Zn, and Mo) demonstrate enrichment in mineralized transitional zones. The development of interlayer oxidation zones is directly controlled by reservoir heterogeneity and sedimentary environments. Oxidation subzones primarily occur in sandbodies with moderate thickness (40–80 m), sand content ratios of 40%–80%, and 2–10 or 10–18 mudstone barriers (approximately 20 m thick), mainly in braided river channels and channel margin deposits. Reduction zones develop in thicker sandbodies (~100 m) with higher sand contents (~80%), fewer mudstone barriers (2–8 layers), greater thickness (40–80 m), and predominantly channel margin deposits. Transitional zones mainly occur in braided distributary channels and floodplain deposits. When oxygen-bearing uranium fluids infiltrate reservoirs, oxygen reacts with reductants like organic matter, whereFe²⁺ oxidizes to Fe³⁺, S²⁻ reacts with oxygen, and U⁴⁺ oxidizes to U⁶⁺, migrating as uranyl complexes. As oxygen depletes, Fe³⁺ reduces to Fe²⁺, combining with S²⁻ to form pyrite between mineral grains. Uranyl complexes reduce to precipitate as pitchblende, while some U⁴⁺ reacts with SiO₄⁴⁻, forming coffinite, occurring as colloids around quartz debris or pyrite. The concurrent enrichment of certain transition metal elements occurs during this process. Full article

The drilling core sampling and chemical analysis method for the quantitative determination of solid mineral deposits has several drawbacks, including a low core drilling efficiency, a high core sampling cost, and a long chemical analysis cycle. In current uranium quantification practices, advanced techniques have been developed to preliminarily determine the formation of uranium content based on the interpretation results of natural $\gamma$-ray total logging. However, such methods still require supplementary core chemical analysis to derive the uranium–radium–radon balance coefficient, which is then used for equilibrium correction to obtain the true uranium content within the uranium-bearing layer. Furthermore, conventional prompt neutron time spectrum logging is constrained by low count rates, resulting in slow logging speeds that fail to meet the demands of practical engineering applications. To address this, this study proposes a uranium quantification method that corrects the natural $\gamma$-ray total logging using prompt neutron time spectrum logging. Additionally, a calibration parameter determination method necessary for quantitative interpretation is constructed. Experimental results from standardized model wells indicate that, in sandstone-type uranium deposits, the absolute error of uranium content is within $\pm 0.002\%\mathrm{eU}$, and the relative error is within $\pm 2.5\%$. These findings validate the feasibility of deriving the uranium–radium–radon balance coefficient without relying on core chemical analysis. Compared with the prompt neutron time spectrum logging method, the proposed approach significantly improves the logging speed while producing results that are essentially consistent with those of natural $\gamma$-ray total logging. It provides an efficient and accurate solution for uranium quantitative interpretation. Full article

A combination of microstructural, fluid inclusion, and in situ sulfur isotopic analyses of pyrite, along with major and trace element studies of the mineralization-hosting sandstone, reveals the complexity of its genesis from the Jurassic Toutunhe Formation in the Liuhuanggou sandstone-hosted uranium deposit, Southern Junggar Basin. Based on field geological investigations and the geochemical characteristics, it is concluded that the source of the ore-bearing sandstones originates from felsic igneous rocks in the Northern Tianshan and Central Tianshan regions. Through optical microscopy and scanning electron microscopy (SEM), three generations of pyrite were identified: framboidal pyrite, concentric overgrown pyrite, and sub-idiomorphic to idiomorphic cement pyrite. The sulfur isotopes of the pyrite were analyzed using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The results indicate that each type of pyrite has distinct sulfur isotope compositions (the framboidal pyrite: −16.85‰ to +2.16‰, the concentric overgrown pyrite: −7.86‰ to +10.32‰, the sub-idiomorphic to idiomorphic cement pyrite: +9.16‰ to +16.77‰). The framboidal pyrite and the sub-idiomorphic to idiomorphic cement pyrite were formed through bacterial sulfate reduction (BSR), while the concentric overgrown pyrite was formed through thermochemical sulfate reduction (TSR) triggered by the upward migration of hydrocarbons. The discovery of hydrocarbon inclusions provides evidence for the involvement of deep-seated reducing fluids in uranium mineralization. Uranium mineralization occurred in two distinct stages: (1) The early stage involved the interaction of uranium-bearing fluids with reductants in the mineralization-hosting strata under the influence of groundwater dynamics, leading to initial uranium enrichment. (2) The later stage involved the upward migration of deep-seated hydrocarbons along faults, which enhanced the reducing capacity of the sandstone and resulted in further uranium enrichment and mineralization. Full article

This study focuses on the Hailijing sandstone-hosted uranium deposit in the Songliao Basin. Through a combination of petrographic analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and geochemical analysis, the epigenetic alteration of the deposit was systematically investigated, and the alteration zonation was delineated. On this basis, the metallogenic mechanisms were further explored. The results indicate that six major types of alteration can be identified in the ore-bearing strata of the Hailijing uranium deposit: hematitization, limonitization, carbonatization, pyritization, clay mineralization (including kaolinite, illite, and illite-smectite mixed-layer), and baritization. The mineral assemblages at different stages of alteration vary: during the sedimentary diagenetic stage, the assemblage consists of “hematite + clay minerals + II-type pyrite (framboidal pyrite) + III-type pyrite (euhedral granular pyrite)”; during the uranium mineralization stage, it transitions to “ankerite + barite + I-type pyrite (colloidal pyrite) + minor kaolinite”; and in the post-ore stage, alteration is characterized by calcite cementation in red sandstones. Based on petrological, mineralogical, and geochemical characteristics, as well as the spatial distribution of the host gray sandstones, it is inferred that during uranium mineralization stage, the ore-bearing strata underwent reduction by uranium-rich reducing fluids sourced from the Lower Cretaceous Jiufotang Formation. The primary red sandstones of the Lower Yaojia Formation, formed under arid to semi-arid conditions, experienced varying degrees of reduction, resulting in a color transition from light red, brownish red, and yellowish brown to grayish-yellow and gray. Accordingly, four alteration zones are distinguished in the Hailijing uranium deposit: the primary red zone, weakly reduced pink zone, moderately reduced grayish-yellow zone, and strongly reduced gray zone. Furthermore, as the uranium-rich reducing fluids migrated from a high-temperature, high-pressure deep system to the low-temperature, low-pressure ore-bearing sandstone strata near the surface, uranium was unloaded, precipitated, and enriched, ultimately forming multi-layered and tabular-shaped uranium orebodies within the gray sandstone. This study elucidates the epigenetic alteration processes and metallogenic mechanisms of the Hailijing uranium deposit, providing a critical theoretical basis for further uranium exploration in the southern Songliao Basin. Full article