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Naturally occurring granular uranium particles are typically fine and are often found as accessory minerals. However, reports of megacrystalline uraninite are rare. The discovery of megacrystalline uraninite is a significant achievement in uranium prospecting and mineralogy in the Kangdian region and China. Our team's research and review of previous studies have led to a systematic summary of the formation age, genetic types, relationship with migmatization, and metallogenic dynamic background of megacrystalline uraninite in the Kangdian region. The key findings are as follows: (1) the formation age of megacrystalline uraninite is Neoproterozoic (790–770 Ma); (2) migmatization preceded uranium mineralization; (3) the formation of megacrystalline uraninite is linked to high-temperature, low-pressure metamorphism caused by partial melting; (4) and the formation of megacrystalline uraninite may be associated with the Rodinia rifting event. This review aims to enhance our understanding of uranium mineralization during the Neoproterozoic in China and worldwide. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Baimadong U deposit is hosted by carbonate rocks and is associated with black and red alterations. • Black alteration is characterized by exogenous graphite and bitumen. • Red alteration is marked by precipitation of hematite and goethite. • Black alteration provides reducing agents for, and red alteration results from, U mineralization. The Baimadong uranium deposit is hosted in carbonate rocks that were subjected to extensive black and red alterations, silicification and argillization, and is assigned to the carbonaceous-siliceous-pelitic rock-type uranium deposits in the Chinese literature. However, the nature of the mineralization, especially the black and red alterations and their relationship with uranium mineralization, remains poorly understood. Petrographic and Raman spectroscopic studies indicate that the black material are organic matter mainly composed of graphite and bitumen, whereas the red-altered rocks are characterized by abundant iron oxides. Crosscutting relationships suggest that the black alteration occurred before the red alteration. Comparison of whole-rock geochemistry between the different types of rocks suggests that total organic carbon (TOC), U and total organic sulfur (TOS) were gained through the black alteration, and FeOT was gained through the red alteration, whereas total inorganic carbon (TIC), CaO and MgO were lost in both types of alterations. The δ13C org (PDB) values and biomarker characteristics of the black-altered rocks suggest that the organic matter was derived from the black shale of the Niutitang Formation underneath the deposit. U enrichment is associated with both the black and red alterations, and shows positive correlations with Al 2 O 3 , K 2 O, TiO 2 , SiO 2 , TOC and TOS. It is proposed that the uranium mineralization at Baimadong resulted from superposition of two fluid events controlled by a common structural system. First, petroleum generated in the black shales of the Niutitang Formation and hydrothermal fluids migrated along cross-formational faults to the carbonate rocks of the Qingxudong and Shilengshui formations, causing the black alteration and preliminary uranium enrichment. Second, an oxidizing, U-bearing fluid flowed through the same structure and precipitated uraninite through reaction with the black-altered rocks, accompanied by precipitation of hematite and goethite as marked by the red alteration. The combination of black and red alterations with major faults may be used as a mineralization indicator in the exploration of this type of U deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-existing pyrite and calcite with uranium minerals play a significant role in ISL of uranium. • Gypsum produced by pyrite and calcite in CO 2 + O 2 environment disadvantages the leaching of uranium. • Secondary hexavalent uranium minerals will be produced in the ore layer of a neutral environment. Oxidative weathering of pyrite, a widespread iron sulfide mineral, is crucial for the uranium mineralization in sandstone-hosted uranium deposits and the ore utilization leaching under manual intervention. To understand the behavior of pyrite under CO 2 + O 2 leaching conditions in sandstone-hosted uranium deposits, samples of uranium ore from the mineralized zone of the Qianjiadian IV uranium deposit located in the lower section of the Yaojia Formation were collected for this study. The stirring leaching experiment was carried out through the processes of the pyrite-bearing uranium ore samples thinned before and after the reaction, followed by an optical microscopic study and the TESCAN Integrated Mineral Analyzer analysis, and finally, the thermodynamic simulation by making use of PHREEQC3.0. The results revealed the following: (1) The dissolution particles of pyrite become smaller, which may increase the porosity of the ore layer and the exposure ratio of uranium minerals. And more soluble pyrite with a high free surface will be more competitive with uranium minerals for the consumption of O 2. (2) The ion (Fe2+) produced by the dissolution of pyrite will be oxidized to Fe3+ by excess O 2 (4 mol), which provides an oxidant for the oxidation of uranium minerals, and the generated SO 4 2- will combine with the Ca2+ released from calcite to form a permanent precipitate of gypsum, which may block pores and cover the uranium ore. (3) Pyrite and calcite will consume O 2 and CO 2 in the injection system, thus jointly inhibiting the leaching of uranium minerals. After the injection of excessive CO 2 and O 2 , the concentration of Ca2+, SO 4 2-, Fe3+, UO 2 2+, and HCO 3 – in the system will continue to accumulate, resulting in the secondary precipitation of calcite, co-precipitation of gypsum, iron minerals, colloids, and hexavalent uranium minerals, resulting in plugging pores and seriously affecting the effective leaching of uranium. This study contributes to the understanding of the behavior of pyrite during uranium recovery through CO 2 + O 2 leaching. It also contributes to the understanding of quantitative uranium mineralization in sandstone-hosted uranium deposits and process parameters in in-situ leaching (ISL) of uranium. [ABSTRACT FROM AUTHOR]

• Elevated U concentrations (up to 266 ppm) were found in the Lala IOCG ores. • Uraninite, uranothorite, polycrase and coffinite were recognized. • Uranium was initially enriched with Cu, Mo, Th and REE at ca. 1086 to 1053 Ma. • U and Mo were remobilized and re-enriched together at ca. 888 to 828 Ma. Elevated uranium concentrations have been reported in many IOCG deposits, but detailed information about the occurrences of uranium minerals and their relationships with other minerals remains scarce, which hinders understanding of the mineralization mechanisms and the nature of the association of these metals. This paper reports a new case of uranium enrichment in an IOCG system, the Lala Cu-Fe deposit in the Kangdian region, SW China. Whole-rock analyses of ores and barren rocks yielded highly variable U concentrations ranging from 0.76 to 266 ppm. Uranium shows a strong positive correlation with Mo, broadly positive correlations with Cu and ΣREE, and a vague, negative correlation with Th. Four uranium minerals, uraninite [UO 2 , uranothorite [(Th,U)SiO 4 , polycrase [(Y,Ca,Ce,U,Th)(Ti,Nb,Ta) 2 O 6 , and coffinite [U(SiO 4) 1-x (OH) 4x , were identified. The uraninite is divided into two phases: phase 1 (Ur1) characterized by corroded or irregular crystal shapes, and phase 2 (Ur2) showing well-developed, subhedral to euhedral crystal shapes. Ur1 is interpreted to be formed in the primary Cu – Fe – Mo – REE – U mineralization, together with the bulk of Cu and other metal sulfides, as well as other U and REE minerals, including uranothorite, polycrase, bastnäsite and xenotime, and accompanied by K-alteration (K-feldspar and biotite). Ur2 is interpreted to be formed in a secondary hydrothermal event characterized by introduction of fluorite and carbonates, in which U and Mo, and to lesser extent Cu and REE, were remobilized, while Th remained relatively stable. The primary mineralization is inferred to have taken place in a period from ca. 1086 to 1053 Ma based on previous Re-Os geochronology, and the secondary mineralization (remobilization) likely took place from ca. 888 to 828 Ma, as suggested by uraninite chemical ages obtained in this study and other published geochronological data. These ages correspond to tectonomagmatic events taking place in generally extensional environments, in the western margin of the Yangtze Block during the Meso- to Neoproterozoic time. The Lala Cu-Fe deposit represents a new case of IOCG deposits with U (and REE) enrichment, the economic potential of which warrants further examination. [ABSTRACT FROM AUTHOR]

[Display omitted] • Uranium enrichment mainly occurs at the transition zone between Neogene and Quaternary sandstones. • The C-O isotopes of carbonates associated with U suggest involvement of hydrocarbons. • Disseminated uranyl silicates (coffinite) are major constituents of ore. There are several sandstone-type uraniferous basins around Tibetan Plateau. The Qaidam Basin is the largest sedimentary basin in the internal Tibetan Plateau, hosting important oil and coal resources, and has good potential for sandstone-hosted uranium resources. In this study, we examine the petrographic and mineralogical characteristics of a uranium mineralization interval at the Neogene-Quaternary transition (NQT) in the western Qaidam Basin using optical microscopy and electron probe microanalyzer (EPMA), including back scattered electron (BSE) imaging and energy-dispersive spectroscopy (EDS). The sedimentary lithofacies features and C-O stable isotopes of carbonate cement from two boreholes were analyzed, especially for the uraniferous interval. Whole-rock analyses of ores and barren rocks yielded highly variable U concentrations ranging from 1.5 to 2548 ppm. The main uranium minerals are coffinite and uraninite. The co-occurrence of uranium minerals with calcite indicates that uranium mineralization and calcite cementation were coeval. Coffinite mainly occurs at the interface between calcite cement and other minerals. The carbonates have δ13C V-PDB ranging from −29.67 to +3.93‰, suggesting involvement of organic carbon during uranium mineralization. This is also supported by the general trend of decreasing δ13C V-PDB and increasing U content from the conglomerate/coarse sandstone to the mudstone samples, and the overlap of δ13C V-PDB values between the calcite cement and organic matter in sedimentary rocks. The organic carbon may have been derived from hydrocarbons sourced from the deeper part of the basin and/or biogenic gases at shallow depths. The unconformity at the NQT may represent a favorable interval where oxidizing fluids carrying uranium met with reducing fluids carrying hydrocarbons and resulted in uranium mineralization. Thus, the NQT may serve as a guide for uranium exploration in this basin. [ABSTRACT FROM AUTHOR]