In recent years, economically significant sandstone-hosted uranium mineralization has been identified in the Louzhuangzi area along the southern margin of the Junggar Basin. However, the controls on uranium enrichment and their links to depositional architecture and post-depositional fluid processes remain insufficiently constrained. This study integrates field geological investigations, drill-core lithofacies logging, and systematic sampling with petrographic and micro-analytical techniques, including optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). The objective is to elucidate the depositional characteristics, alteration processes, and uranium occurrence mechanisms of the ore-bearing sandstones within the Toutunhe Formation (J2t). Results show that the upper member (J2t2) represents meandering-river deposits, whereas economically significant uranium mineralization is hosted in the lower member (J2t1), characterized by braided-river sandstone units with high permeability. The sandstones of the Toutunhe Formation (J2t) exhibit intense oxidation by surficial fluids, overprinted by post-mineralization hydrothermal alteration and sulfide-forming alteration associated with reducing fluids. Uranium is closely associated with pyrite, organic matter, and clay minerals. Uranium minerals are dominated by coffinite and pitchblende (~68%), with UO₂ contents of 52.89-86.07%. Minor Ti-bearing uranium phases (~16%), interpreted as possible brannerite, contain 38.01-41.46% UO₂ and 31.67-36.09% TiO₂, while nanoscale uranium minerals (~16%) show UO₂ contents of 9.15-60.28%. These results indicate that uranium mineralization was controlled by the coupling of braided-channel architecture and multi-stage fluid processes. Uranium was initially precipitated from oxidized fluids and subsequently modified and preserved by later thermal and reducing fluids, highlighting the importance of multi-fluid interactions in sandstone-hosted uranium systems.

In practical dual-energy X-ray (DE-XRT) copper ore sorting industrial settings, process parameters such as belt speed, X-ray source intensity, and ore particle size are typically maintained relatively stable, while the thickness of ore particles naturally fluctuates significantly due to the randomness of crushing, making it a key factor affecting sorting stability. To address the sorting instability stemming from thickness variations, this paper proposes a robust classification method centered on thickness-consistency regularization. The method is based on the X-ray attenuation mechanism, constructing logarithmic-domain thickness perturbations to simulate the input distribution shift caused by thickness variations. Experiments are conducted using a two-channel ResNet18 as the base model on 7,245 DE-XRT images, comparing three methods—Baseline, Brightness, and Consistency—and employing the Swin Transformer backbone to validate the architectural generalizability of the proposed method. Results show that Consistency achieves 92.18% accuracy on the clean test set, which is comparable to the 92.16% of the strong Brightness baseline. Under a large positive thickness shift (δ = +0.25), Consistency yields higher Macro-F1 and Worst-group accuracy, improving over Brightness by 7.76 and 11.09 percentage points, respectively. Consistency also demonstrates superior robustness over Brightness under substantial negative thickness shifts. These findings demonstrate that the proposed method effectively enhances model robustness under extreme thickness variations and is applicable to multiple deep learning architectures.

Mineral prospectivity mapping for sandstone-hosted uranium deposits commonly relies on isotropic distance decay, despite the fact that ore-forming fluids are typically guided by faults and paleochannel systems with strong directional organization. As a result, structurally controlled geological signals may be diffused into quasicircular anomalies, weakening the geological realism of prospectivity predictions. To overcome this limitation, we propose a Direction-Aware Geographically Weighted Neural Network (DA-GWNN), which embeds expertdefined structural orientation priors into neighborhood weighting to preferentially capture spatial influence along plausible ore-forming directions. In addition, a criteria-based consensus soft-labeling scheme is developed at the grid-cell scale to represent different levels of mineralization evidence under sparse supervision. The method was tested in the Kailu Basin against six benchmark models under nested spatial blocked crossvalidation. DA-GWNN achieved the best predictive performance, with a mean AUC of 0.912 +/- 0.019 and a mean AUPRC of 0.794 +/- 0.026. SHAP analysis indicates that the oxidation-reduction transition zone is the principal control on prospectivity, whereas the role of fault proximity is conditional and varies with the local redox buffering capacity reflected by the gray-sand ratio. Area-constrained analysis shows that the 36.6% P-A envelope captures 78.2% of all positive-labeled cells and represents a basin-scale mineralization-system footprint. Under the stricter economic-positive definition (y = 1.0), DA-GWNN captures 45.0%, 67.5%, and 80.0% of economic positive cells within the Top 5%, Top 10%, and Top 15% cumulative area budgets. These results indicate that DA-GWNN supports a hierarchical exploration workflow from regional system recognition to focused target verification.

While compressional tectonics has long been recognized as a significant factor in uranium mineralization, the role of extensional tectonics remains comparatively understudied. This investigation analyzes representative sandstone-hosted uranium provinces, including the Colorado Plateau (North America), the Agadez region (West Africa), the North China–Transbaikal region (Northeast Asia), and the Massif Central (Western Europe). Our systematic analysis reveals that extensional tectonics, building upon pre-existing rifting structures, amplify tectono-magmatic activity, which in turn exerts spatiotemporally control on uranium deposition and gives rise to diverse mineralization ages. Key structural elements within tectonic transition zones, such as uplifts, fault systems, and volcanism, play critical roles: uplifts and shallow-level faults govern the recharge and migration of supergene fluid, whereas deep-seated faults facilitate the transport of reductants (e.g., hydrocarbons) and magma. These deep pathways provide the essential thermal energy and additional components for uranium precipitation. Collectively, these processes collectively form high-relief transition zones that act as prime sites for uranium enrichment. In addition, multi-phase extensional events generate permeable conduits and thermal anomalies that are crucial for mobilizing and concentrating uranium from source rocks. This study provides an enhanced understanding of the genesis of sandstone-hosted uranium deposits and offers a theoretical framework for future exploration targeting.

The Guyuan-Hongshanzi uranium metallogenic belt (GHUMB) in North China, particularly the Hongshanzi area within the southern Great Xing'an Range (GXR), hosts uranium mineralization significantly impacted by post-mineralization uplift and exhumation. Field investigations, drill core analysis, electron probe microanalysis (EPMA) and apatite fission track (AFT) dating reveal that uranium orebodies occur within basement uplift zones hosted by the Upper Jurassic Manketou'ebo and Xinmin formations, Lower Permian Dashizhai Formation and Hercynian granodiorite. These orebodies are predominantly shallow and are structurally controlled, associated with hydrothermal alteration including carbonatization, silicification, hematitization, chloritization, fluoritization and sulfidization. Critically, deep-seated potash feldspathization and albitization features are now exposed at shallow depths or the surface. AFT analysis and thermal history modelling indicate rapid cooling during 70-50 Ma, signifying rapid uplift through the partial annealing zone to near-surface levels. This evidence, combined with the surface exposure of deep alteration, demonstrates that primary uranium mineralization initially formed at depths of similar to 2-4 km during the Cretaceous. Subsequent rapid uplift triggered intense erosion, preserving some orebodies shallowly while eroding others and transporting uranium into adjacent basins, potentially contributing to secondary sandstone-type mineralization.

Calcrete-type uranium prospectivity prediction is challenged by the strong heterogeneity of multi-source geoscientific raster datasets, weak anomaly responses, and the lack of explicit heterogeneous information organization in conventional deep learning models. In this study, the Yilgarn Craton of Western Australia was selected as the study area, and a geology-guided fixed-group fusion ResUNet model (GGF-ResUNet) was developed based on 12-channel multi-source geoscientific raster datasets. At the input stage, the evidence layers were divided into four fixed geoscientific proxy groups according to their data modality and geological interpretation, namely gravity, aeromagnetic, radiometric, and geochemical groups, and intra-group channel weighting together with inter-group gating was introduced to enhance the hierarchical representation and adaptive fusion of heterogeneous information. Ablation results showed that GGF-ResUNet achieved better performance than the baseline ResUNet, with AUC increasing from 0.9340 to 0.9740 and F1-score improving from 0.7264 to 0.8356. Further comparative experiments with Attention U-Net, U-Net, SegNet, and FCN showed that GGF-ResUNet achieved comparatively better quantitative performance and more spatially coherent prediction results under the current experimental setting. Without substantially increasing model complexity, the proposed method improves the representation and integration of heterogeneous geoscientific information and provides a feasible technical pathway for calcrete-type uranium prospectivity prediction under weak-anomaly conditions.

Uranium mineral prospectivity mapping is of great significance for uranium exploration and the identification of prospective mineralized areas. Hard labels constructed from buffer zones around known uranium occurrences tend to discretize continuously varying mineralization responses, making it difficult to adequately characterize the continuous variation in mineral prospectivity and the uncertainty associated with mineralization boundaries. To address this issue, this study focuses on sandstone-hosted uranium deposits in the Beverley–Four Mile area, South Australia, and introduces a self-distillation strategy into the ResNet50 model. Soft labels generated by the model are employed to supplement the differences in mineral prospectivity and spatial transitional information that are difficult to represent using hard labels, thereby enhancing the model’s ability to learn mineralization-related features. Experimental results show that, after incorporating the self-distillation strategy, ACC, AUC, F1, and PR-AUC are improved by 3.13

The formation of sandstone-type uranium deposits is closely related to the local tectonic evolution of basins. However, while existing studies mainly focus on qualitative analyses at the regional scale, quantitative research on tectonic ore-controlling mechanisms at the local scale remains relatively limited. Focusing on the Daqing Placanticline and adjacent areas in the northern Songliao Basin, this study applied back-stripping inversion, based on interpretations of seismic and borehole profiles, to quantitatively characterize spatiotemporal variations in local tectonic subsidence since the Late Cretaceous and reveal their controls on sedimentary filling and uranium mineralization. The results show that tectonic subsidence in the study area exhibited distinct staged evolution and regional differentiation. Strong tectonic inversions at the end of the Nenjiang and Mingshui periods caused the greatest uplift and denudation in the southern Daqing Placanticline, forming a large structural window and activating faults that served as channels for the upwelling of deep reducing fluids. Differential tectonic subsidence and sediment supply jointly controlled sedimentary filling patterns. Under the combined influence of low tectonic subsidence rates and sufficient sediment supply, the southern study area exhibited an overcompensated filling pattern and developed meandering river facies with high sandstone percentages, thereby providing favorable channels for fluid migration. In contrast, under the influence of relatively high tectonic subsidence rates or insufficient sediment supply, the central and northern parts of the study area exhibited undercompensated or weakly overcompensated to quasi-balanced filling patterns and were dominated by meandering river, shallow lake, or meandering river–shallow lake facies, with sandbodies generally less developed than those in the south. The spatiotemporal coupling between sedimentary filling during the Sifangtai period and tectonic inversion at the end of the Mingshui period established a uranium metallogenic framework characterized by more favorable conditions in the south than in the central and northern areas. The southern area contains a favorable configuration of three core metallogenic elements—structural window recharge, conductive migration, and fault-related reduction—and therefore represents the most favorable area for sandstone-type uranium mineralization. This study advances quantitative research on local tectonic ore-controlling mechanisms and provides new insights for uranium exploration in the Songliao Basin and similar continental basins.

Data scarcity remains a major challenge for the deployment of dual-energy X-ray transmission (DE-XRT) in intelligent copper ore sorting. Although generative adversarial networks (GANs) have been widely used for data augmentation, most existing methods treat X-ray images as generic visual data and overlook the underlying attenuation mechanism, which may result in physically inconsistent synthetic samples. To address this issue, we propose PhysDualR-GAN, a physics-informed data augmentation framework guided by the Beer-Lambert law. Instead of directly synthesizing low-energy X-ray images, the proposed model predicts attenuation-ratio maps from high-energy images and reconstructs the corresponding low-energy images through a differentiable physics layer, thereby introducing explicit physical constraints into adversarial training. Experimental results on industrial copper ore datasets show that the proposed method generates physically consistent R-value maps that better preserve X-ray attenuation characteristics. The generated samples achieve a radial-spectrum correlation coefficient of 0.9999, an average MSE of 2.73 × 10-2, and an FID of 83.58. More importantly, when used for downstream sorting, the augmented data improve mean Average Precision (mAP) from 90.77% to 98.95%. The proposed framework also maintains competitive sorting performance under reduced training-data conditions. These results demonstrate that PhysDualR-GAN provides an effective physics-informed solution for data-efficient training in X-ray-based mineral sorting.

Mineralization in the sandstone-type uranium deposits of the Songliao Basin is characterized by hypogene fluid alteration, as recorded at the regional tectonic, deposit, and mineral scales. However, the mechanism of uranium enrichment under the influence of hypogene fluids remains poorly understood. Based on their spatial distribution and cross‑cutting relationships, the carbonate minerals are divided into four stages, and this study focuses on the hydrothermal ore‑forming stage. Petrographic observations show complex textures and compositional zoning in carbonate minerals, indicating multiple precipitation–dissolution stages and synchronous precipitation of U‑minerals and pyrite, which provide a basis for evaluating the influence of hypogene fluids on uranium enrichment. In situ U-Pb dating using laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS) provides well-defined ages of 40.1 ± 1.3 Ma for U-rich ankerite (Ank-2), 36.3 ± 0.2 Ma for U-poor high-Mg siderite cement (Sd-3), and 35.6 ± 3.4 Ma for U-poor calcite vein (Cal-5). These ages are approximately synchronous with widely distributed diabase dikes (zircon ages of 39.1 ∼ 42.0 Ma) in the southern Songliao basin. Compared with siderite and dolomite, U-rich ankerite shows higher enrichment in middle and heavy rare earth elements. Hydrothermally altered sandstone, especially the red altered uranium ore, shows higher contents of U, Co, Ni, V, Mo, Zr, Y, W, Pb, and HREE, and U exhibits positive correlations with W, As, Zr, and P. Most uranium minerals (including pitchblende, titanium-bearing uranium minerals, and coffinite) contain high concentrations of elements such as P, Ca, Zr, La, and Ce. Sr isotope ratios decrease progressively from early calcite (Cal-1) through ∼60 Ma microbial dolomite (Dol-1) to hydrothermal carbonates, with U enrichment confined to 87Sr/86Sr of 0.706–0.709. The above evidence indicates that thermal fluids activate and alter the uranium already present in the ore-bearing target layer, leading to further uranium enrichment and the formation of high-grade uranium ores. Because carbonate is a common mineral in U deposits worldwide, and other minerals in such deposits suitable for isotope dating are generally absent, in situ U-Pb dating of carbonates opens a new window for better defining the ore genesis of this globally important U deposit and for tracking hydrothermal fluid flow in sedimentary basins.

In recent years, the Telaaobao Mineral Area in the Northwestern Ordos Basin has been newly discovered as a uranium mineralization area with its ore-bearing target layer located within the Lower Cretaceous Huanhe Formation, belonging to a new area and a new layer, and has great uranium deposit formation potential. In order to deeply study the issues of the ore-bearing target in this area, such as the petrology, mineralogy, and uranium mineralization of the ore-bearing sandstone, based on the data from field geological investigation and drill core logging, the petrological characteristics of the ore-bearing sandstone of the target layer are preliminarily interpreted using a polarizing microscope and a scanning electron microscope, and the uranium mineral composition, uranium occurrence state, and uranium deposit mineralization are investigated through the electron probe microanalysis technique in this paper. The results show that the target layer sandstone in the study area has the characteristics of proximal deposit and has undergone significant epigenetic alteration and transformation, producing favorable conditions for uranium- and oxygen-containing water transportation and uranium mineralization. The uranium minerals are dominated by the independent coffinite with the UO2 content ranging from 40.93 to 60.45%, followed by the titanium-uranium oxides. The uranium minerals occur in various forms, mainly in the edge or fissure of the debris particles, in the edge of the framboidal pyrite, around the biotite or within its cleavage fissures, and on the surface of the chlorite. In addition, a preliminary uranium mineralization model was also established in the Telaaobao Mineral Area. The uranium mineralization in the Telaaobao Mineral Area results from the combined action of the infiltrating and ascending fluids. The uranium- and oxygen-containing fluids from the source area infiltrate downward into the target sandstone layer and meet the ascending reducing fluids from the depth, producing a redox barrier in Huanhe Formation, within which U6+ is reduced to U4+ for precipitation, leading to the formation of uranium mineralization.

The middle segment of the northern margin of the North China Block is heavily covered by thick Quaternary strata, and as a result, only limited physical research data have provided restrict understanding of the tectonic evolution of this area and the neighboring eastern section of the Central Asian Orogenic Belt. This article presents detailed petrographic observations and rock geochemistry, zircon U-Pb dating, zircon trace elements, and in-situ Hf isotopic analysis of the Baimashigou pluton by drilling-core samples in the coverage area. The study shows that the Baimashigou pluton formed in the Late Permian (254 +/- 0.7Ma). The analyzed rock samples are characterized by high silicon contents (SiO2=69.13%similar to 72.27%), alkali and potassium-rich (K2O+Na2O=8.20%similar to 9.51%, K2O/Na2O=0.98 similar to 2.52) and (weak) peraluminous (A/CNK=0.98 similar to 1.10), indicating they belong to high-K peraluminous unfractionated S-type granite. Furthermore, the geochemical characteristics of these samples also reveal that they are formed by the partial melting of metasandstone with low clay content (CaO/Na2O=0.27 similar to 0.38) and rich in primary crustal debris (epsilon(Hf)(t)=-3.93 similar to 6.36) on top of the descending slab under a relatively low temperature (612.9 similar to 799.8 degrees C), high pressure ((Gd/Yb)(N)=0.88 similar to 2.41, delta Eu=0.72 similar to 0.83, Sr=405.1x10(-6)similar to 545.6x10(-6), Y=11.13x10(-6)similar to 14.55x10(-6), Sr/Y=27.83 similar to 41.16), and high oxygen fugacity (QFM similar to QFM+10) environment. Combined with previous research results, it is believed that the middle segment of the northern margin of the North China Block had entered the collision orogeny stage before the end of the Permian Period. The Baimashigou pluton provides direct petrological evidence of the plate collision and amalgamation. The study holds significant importance for further analyzing the geological structure and tectonic evolution of the eastern segment of the Central Asian Orogenic Belt, particularly within the coverage area.

Brannerite (UTi2O6) is typically considered indicative of hydrothermal conditions in uranium mineral systems. In this study, we conducted a comprehensive mineralogical investigation of uranium-bearing sandstones from the Louzhuangzi area along the southern margin of the Junggar Basin. Scanning electron microscopy (SEM) and electron microprobe analysis (EMPA) were used to characterize the alteration features of titanium oxides. However, we recognize that SEM-EDS data alone are not sufficient for the conclusive identification of brannerite, as similar spectra may be produced by other titanium-uranium-bearing phases. To overcome this limitation, focused-ion-beam (FIB) sample preparation combined with transmission electron microscopy (TEM) was employed to examine the crystal structure and nanoscale chemistry of selected titaniumuranium mineral particles. Selected-area electron diffraction (SAED) patterns and high-resolution TEM imaging, together with EDS elemental mapping, confirm the presence of discrete nanocrystalline brannerite aggregates. The identification of brannerite in the Louzhuangzi deposit suggests that hydrothermal activity played a role during ore formation or post-ore modification in this sandstone-type setting. A comprehensive investigation indicates that uranium mineralization in the Louzhuangzi area is controlled by the coupled effects of oxidation, superimposed hydrothermal processes, and hydrocarbon-mediated fluid interactions.

The sandstone uranium deposits in the Kelulun Depression are the first commercially viable uranium deposits discovered in the Hailar Basin and the ore-bearing strata corresponding to the Lower Cretaceous Yimin Formation. To elucidate the origins and formative mechanisms of pyrites and investigate their relation to uranium mineralization, both the characteristics of pyrites and uranium minerals and the S isotope and the trace element composition of pyrites were investigated. Results indicated that coffinites (as cements and star-like clusters) are the most common uranium mineral type, followed by pitchblendes and U-Ti oxides. Pyrites are mainly framboidal, cement, or euhedral. S isotope fractionation in the pyrites varies due to different S sources (biogenic or abiotic), with framboidal, cement, and euhedral pyrites showing δ34S values of -63.70 to -3.38‰, -30.26 to 9.52‰, and 3.32 to 8.27‰, respectively. As and Tl enrichment indicates formation in a low-temperature environment. High Ca and P levels in the uranium minerals are indicative of microbial participation. The carbonaceous clasts, pyrites, and microbes of the Yimin Formation in the Kelulun Depression played synergistic roles in uranium mineralization, which resulted in highly diverse uranium ore occurrences.

The Ordos Basin is a key district for sandstone-hosted uranium, yet host-rock controls and uranium sources remain debated. We integrate measured sections, whole-rock geochemistry, and detrital zircon U-Pb-Lu-Hf data from the Cretaceous Huanhe Formation (Yihewusu, northern Ordos) to resolve provenance, transport, and enrichment pathways. Uranium enrichment is concentrated in feldspathic-lithic sandstones deposited in proximal fluvial-lacustrine settings. Detrital zircon ages define three clusters—Phanerozoic (500–200 Ma), Paleoproterozoic (2000–1700 Ma), and Neoarchean (2600–2300 Ma)—with Proterozoic grains >60%, indicating derivation from Archean–Paleoproterozoic TTG gneisses, granulites, and khondalites of the Yinshan Block and the northern Central Orogenic Belt. Zircon εHf(t) values (−10.84 to +7.76) and crustal model ages (3.2–2.1 Ga) record substantial Meso- to Neoarchean crustal growth in the source terranes. Critically, Permian-Cretaceous intermediate-felsic igneous rocks along the northern margin of the Western North China Block—marked by elevated U, Th/U > 5 (indicative of U loss), pervasive feldspar micro-fractures, and proximity to basin-margin uranium belts—are identified as the principal uranium reservoirs. We propose a dual uranium supply: soluble uranium mobilized from leached igneous rocks during weathering and fluid-rock interaction, and U-enriched detritus delivered to the basin. Uranium concentrated in redox-sensitive, feldspathic-lithic sandstones of the Huanhe Formation, which effectively trapped advected uranium at proximal facies transitions. These findings establish a direct genetic link between basin-margin uranium sources and in-basin mineralization, providing a predictive framework for regional uranium exploration in North China.

The sandstone-type uranium deposit of the Kelulun Depression is the first industrially valuable uranium deposit discovered in the Hailar Basin. This study performed a systematic examination of 17 sandstone samples from the Yimin Formation in the Kelulun Depression based on various analytical techniques. The findings of the current study were synthesized with previous research to investigate the impact of the redox conditions and the tectonic background of the source area, as well as the paleoclimatic evolution of the Yimin Formation on uranium mineralization. The elemental Mo, U/Th, V/Cr, Ni/Co, and V/(V + Ni) ratios indicate that the paleowater was in an oxygen-rich environment during the deposition of the Yimin Formation. Additionally, the C-value, Sr/Cu, Al2O3/MgO, and Rb/Sr ratios indicate that the Yimin Formation was formed in a paleoclimate characterized by arid-to-semi-arid conditions. The geochemical characteristics of the observed elements indicated that the sediment source of the Yimin Formation was mainly felsic rocks from the upper continental crust, the weathering of the rock was weak, and the tectonic background was a passive continental margin. Coffinite is distributed in the form of cementation and stellates within or around pyrite crystals, and uranium-titanium oxide is mostly distributed in an irregular granular distribution in the biotite cleavage fractures of the study area. In summary, the findings of this study reveal that the tectonic settings, provenance, uranium source, paleoclimate, and oxygen-rich paleowater of the Yimin Formation have important geological significance for the large-scale uranium mineralization of the Kelulun Depression.

The Ordos Basin is an important sandstone-type uranium enrichment region in China, and the Lower Cretaceous Huanhe Formation has attracted significant attention as a newly discovered ore-bearing stratum. To elucidate the provenance, tectonic background, and sedimentary environment constraints on uranium enrichment in the Huanhe Formation sandstone-type uranium deposits, 10 representative sandstone samples from the study area were analyzed by using electron microscopy, X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and electron probe microanalysis. Independent uranium minerals in the Yihewusu area of Hangjin Banner were shown for the first time to be composed mainly of coffinite and titanium-uranium oxide, with trace amounts of pitchblende. The major element diagrams of the sandstone and ratios of Sr/Ba, V/Cr, and U/Th and enrichment factors of Mo and U revealed that the source rocks of the Huanhe Formation sandstone in the study area were intermediate-felsic igneous rocks. The tectonic setting is characterized as an active continental margin, with later deposition in brackish-to-marine water environments. The ore-bearing strata indicate a reducing environment, whereas the nonore-bearing strata indicate a weakly oxidizing environment. With reference to previous studies, the sedimentary material primarily originated from the medium-acidic intrusive rocks exposed in the northern portion of the basin, including the Daqing-Wula Mountains, the Yin Mountains, and middle-acidic intrusions along the eastern margin of the Alxa region in the western part of the basin. The uranium-rich granitic pluton of the source area contributed to the preenrichment of uranium in the target sandstone layer. Under oxidizing aqueous conditions, U6+ migration was activated, whereas under reducing aqueous conditions, U6+ was reduced to U4+, resulting in eventual sedimentation of coffinite as ore.

Previously, the ages of U mineralization in sandstone-hosted uranium deposits have not been adequately constrained due to the absence of suitable minerals for precise radiometric dating. To ascertain the mineralogenetic epoch and origin of the ore-forming fluids in the sandstone-hosted uranium deposits within the southern Songliao Basin of northeastern China, we conducted U-Pb dating, major and trace element analyses, and Sr isotope analyses on carbonate minerals taken from the sandstone. In this study, we present a novel U-Pb age of 92.5 +/- 6.9 Ma (MSWD = 0.56) for calcite nodules, which is interpreted as the depositional age of the target formation hosting the ore. The age of the main mineralization stage is constrained by two types of high uranium carbonate minerals: the dolomite coexists with siderite and recrystallized framboidal pyrite, whereascoarse-grained ankerite occurs with dawsonite enveloping dolomite. The dolomite vein yields an age of similar to 60 Ma (62.8 +/- 0.5 Ma, MSWD = 2.7; 60.0 +/- 0.4 Ma, MSWD = 6.4), the coarse-grained ankerite may be contemporaneous with the widely distributed diabase with an age of similar to 40 Ma, which is interpreted two U mineralization ages. The similar to 92 Ma calcite nodules are characterized by low U and U/Th ratios and relatively flat REE distribution patterns, and the high 87 Sr/ 86 Sr ratios (0.7109-0.7327) and the dispersed trace element composition can be attributed to fluid-rock interactions. In contrast, dolomite veins with an age of approximately 60 Ma exhibit elevated MnO and Y/ Ho ratios, as well as patterns enriched in heavy rare earth elements (HREEs); the Sr-87/ Sr-86 ratios range from 0.7066 to 0.7092, indicating their association with hydrocarbon seep-related carbonates of microbial origin. The coarse-grained ankerite, which has high REE + Y values and hump-shaped, MREE-enriched patterns with low Y/ Ho ratios and negligible to positive Eu anomalies, combined with the spatial relationship between the ankeritebearing sandstone sample and diabase, indicates that the ankerite is the product of hydrothermal processes. This similar to 60 Ma dolomite presents initial evidence indicating that the Hulihai deposit is contemporaneous with a significant regional tectonic inversion event and preceded or coincided with hydrocarbon fluid activity in the southern Songliao Basin. Based on the spatial and temporal correlations, it is plausible that both the Palaeocene (similar to 60 Ma) tectonic reversal event and the Eocene hydrothermal event (similar to 40 Ma) were causally linked to sandstone-hosted uranium deposits in the southern Songliao Basin. The present study demonstrates the robustness of in situ carbonate mineral U-Pb dating as a valuable tool for geochronological investigations pertaining to sandstone-hosted uranium deposits.

The Songliao Basin is rich in uranium ores, and the Yaojia Formation, which is dominated by gray fine-grained sandstones, contains the main ore-bearing stratum. Rocks in the formation contain high SiO2, Al2O3, and total alkali, with enrichment in Rb, Th, U, K, and light rare earth elements but are depleted in high field strength elements, similar to upper crustal rocks. U-Pb dating of zircon grains from sandstones in the formation yielded four groups of ages, including 99-182, 202-245, 284-365, and 1800-1900 Ma. These ages combined with the Hf isotope composition, geochemical characteristics, and regional history suggest that the Yaojia Formation rocks are associated with passive and active continental margin settings. These clastic rocks originate principally from felsic rocks in the Zhangguangcailing-Xiao Xing'anling area, and these were deposited in oxic freshwater environments.