Mineral Uraninite Research Articles

Newly identified uranyl vanadate mineral formation in the Thrace Basin, NW Türkiye: Insights into identification and origin of carnotite and tyuyamunite minerals

The Thrace Basin is located in the northwest of Türkiye, bounded by the Rhodope Zones to the west, the Strandja (Istranca, Strandzha) Massif to the North, and the İstanbul Zone to the east. The Stranja Massif’s basement is composed of the Tekedere Group, which includes Paleozoic gneisses and schists, as well as the Şeytandere Metagranite, consisting of altered and unaltered metagranites. Unaltered metagranites are characterized by large feldspar crystals and are typically white and pink in color, while altered metagranites are typically yellow color. The subject of this study Şeytandere metagranites which the uraninite mineral, for the first time, was identified in unaltered metagranite samples, while carnotite and tyuyamunite minerals were identified in altered meta-granite samples. The morphologies and elemental compositions of these minerals were identified by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The SEM-EDS analyses revealed that the major elements of carnotite [K2(UO2)2(V2O8)(H2O)3] and tyuyamunite [Ca(UO2)2(V2O8)(H2O)8] are of K, U and V and Ca, U and V, respectively. In the investigated samples carnotite has a plate-like morphology, whereas tyuyamunite shows a fibrous apperance. This investigation shows that carnotite and tyuyamunite are epigentically formed from uranyl vanadate minerals in the Şeytandere metagranite. These minerals indicate uranium leaching from granitic materials and re-deposition as fine specks in open pores by circulating meteoric water. The leached uranyl ions, combined with vanadate ions, form carnotite and tyuyamunite under weathering conditions.

Extent and significance of the Racklan–Forward Orogen in Canada: far-field interior reactivation during Nuna assembly

Abstract Mesoproterozoic orogenesis is well established on the western and southern flanks of Laurentia in the well-known Racklan–Forward and Mazatzal orogens, but its significance within the previously assembled interior of the supercontinent Nuna has not been established. We examine regional isotopic and structural evidence for Mesoproterozoic deformation in the c. 1.7–1.63 Ga Hornby Bay, Elu, Thelon and Athabasca intracontinental basins, and present evidence for Mesoproterozoic reactivation of Paleoproterozoic structures in the Wopmay and Trans-Hudson orogens. The Racklan–Forward Orogeny in the interior of north Laurentia comprises north–south-trending, high-angle, east-vergent folds and thrusts that occur across a region 1660 km wide and over 1000 km long, stretching from the Yukon to near Hudson Bay and from Banks Island to below the Western Canada Sedimentary Basin. The structures progress from ductile amphibolite and greenschist facies in the Racklan type area to sub-greenschist facies and ultimately brittle or brittle-ductile in the far foreland, showing a predominant thick-skinned style typical of many intracontinental orogens. We present compiled low-temperature thermochronological data, including ages of spatially associated uraninite mineralization, to characterize the scope of reactivation of basement structures in the Archean Rae craton in Nuna's interior. We compare the nature of widespread far-field reactivation in the Racklan–Forward Orogen with other orogens of Nuna's assembly to show it is unusual for Nuna's peripheral margin. We suggest that c. 1.6 Ga continent–continent collision of North Australia with NW Laurentia propagated stresses far into the interior as a result of combined favourable pre-existing structural grain and a weak subcontinental lithospheric mantle in the Rae craton due to repeated episodes of refertilization across 500 Ma of accretion and intrusion. Cratons that experience the complex, two-sided collision and protracted upper plate setting during supercontinent assembly noted herein may be particularly susceptible to extensive foreland propagation of peripheral orogens.

Magnetite‐fluorapatite geochemistry and monazite U–Pb geochronology of the Mohuldih uranium deposit, Singhbhum Shear Zone, eastern India

In this study, textural relations coupled with mineral chemistry of hydrothermal magnetite, fluorapatite, monazite and allanite from the Mohuldih uranium deposit in the Singhbhum Shear Zone (SSZ) is used to characterize the nature of the fluid during various events of alteration and uranium precipitation. These minerals have two distinct textural types, the earlier of which are coeval with the uraninite mineralization. The later type formed during subsequent hydrothermal overprint as a result of coupled dissolution‐reprecipitation of earlier fluorapatite and mobilization of light rare earth elements. Uranium‐lead dating of texturally‐constrained hydrothermal monazite grains yields two major concordant age clusters at 1855 ± 7 Ma and 963 ± 10 Ma and several discordant analyses. Two spot analyses furnish concordant ages of 1656 ± 33 Ma and 1438 ± 35 Ma that are identical within error of the 207Pb/206Pb ages (1628–1643 Ma and ca. 1392 Ma) of several discordant data points. Similar ages have been reported by other studies from the rocks of the SSZ and are therefore considered to be geologically meaningful. The oldest age of ca. 1855 Ma obtained from the texturally early core regions of monazite corresponds to the earliest stage of uraninite mineralization. The two main alteration types can be interpreted based on the known metamorphic events in the SSZ. A combination of high‐temperature calcic iron ± sodic and high‐temperature potassic iron alteration accompanied the M1 metamorphic event and the low‐temperature silicification/K‐Al alteration during the M2 metamorphic event. A comparative study between our data on magnetite and fluorapatite compositions with those from global iron oxide‐Cu‐gold (IOCG) and iron oxide‐apatite deposits classifies Mohuldih as an IOCG‐type deposit.

Toxic uranium contamination in groundwater of Thoothukudi district, India: Evaluation of health risks using the geochemical and statistical approach

The present investigation aims to determine the health risks of toxic uranium contamination in the drinking water of the Thoothukudi district. Two hundred and eighty-six samples were examined during the pre- and post-monsoon seasons and found the uranium concentration ranges from <0.2 to 167 ppb (mean 12, Standard deviation 21) (pre-monsoon) and <02 to 190 ppb (mean 13, Standard deviation 24) (post-monsoon). Geochemical modeling studies and the reducing nature of samples reveal that the uraninite mineral is under saturated conditions, and the least soluble U4O9 mineral species is predominantly distributed during both seasons. Statistical analysis provides that applying nitrogen and phosphate fertilizers may induce the dissolution of uranium minerals, which is responsible for elevated uranium in the collected samples. The calculated noncarcinogenic risk of uranium range from 0.005 to 8.09 (pre-monsoon) and 0.005 to 9.18 (post-monsoon). 15% (pre-monsoon) and 17% (post-monsoon) of the samples show a higher noncarcinogenic risk. The calculated cancer mortality and morbidity are within the permissible limit of 10−3, and the present health risk assessment of uranium is evident that the people from this district have the chemical toxicity of uranium than the carcinogenic risk due to drinking water.

Application of GIS technique to address the uranium contamination in groundwater of a hard rock aquifer, South India

The present research aims to determine the sources and concentration of uranium in the groundwater of the hard rock aquifer. Two hundred and fifty-four groundwater samples were collected, and the analysis shows the uranium concentrations range from 0.5 to 113 ppb (pre-monsoon) and 0.5 to 120 ppb (post-monsoon). Factor analysis illustrates that the lower concentrations of uranium in the study region may be due to the poor dissolution of minerals in the subsurface. Saturation Index values confirm that the Uraninite mineral is undersaturated, and the U4O9 has dominant distribution during both seasons. During both seasons, four samples have a uranium concentration of more than 60 ppb, which might be due to the fertilizer usage in the agricultural activities in the study area. The GIS technique highlights the uranium-contaminated location and polluted water quality parameters using the Inverse Distance Weighted spatial interpolation plots.

Hydrogeochemical characteristics of the sandstone-hosted uranium mineralization in northern Ordos Basin, China

The northern Ordos Basin is one of the biggest uranium resource production areas in China. However, the hydrogeochemical mechanism for the formation of uranium deposits remains poorly understood, despite that interlayer oxidation, hydrothermal fluid mineralization and gas reduction were proposed. In order to provide a more comprehensive knowledge on their formation mechanism, the investigation was carried out by analyzing hydrogeochemistry and environmental isotopes of waters from river, lakes, shallow private wells, boreholes over the period from 2015 to 2016. The results showed that the analysed samples exhibited a hydrochemical heterogeneity confirmed by a large range of pH, Eh, main cation and anion concentrations, and uranium concentration in surface water, Quaternary shallow groundwater, Cretaceous confined water and Jurassic confined water. The Piper and Durov diagrams highlighted that hydrochemical facies changed with groundwater flow from shallow to deep, with HCO3–Ca•Mg and HCO3–Ca in Quaternary shallow groundwater, HCO3•Cl–Ca•Na in Cretaceous confined water and Cl–Na and HCO3–Na in Jurassic confined water. Aqueous geochemistry indicated that the Jurassic ore-bearing confined waters originated from the Cretaceous confined waters, involving both leaching processes and desulfidation. Nonetheless, the Cretaceous confined waters originated from Quaternary shallow groundwater and mainly have experienced leaching processes. Gibbs plot indicated that, with an accumulation of ions in the groundwater during runoff, calcite and uraninite minerals would be oversaturated and precipitation tended to occur. The variation of TDS along depth indicated desulfurization occurrence in ore-bearing aquifer and a decrease in migrating ability of UO22−, leading to U precipitation. Isotopic results showed that the ore-bearing confined waters were depleted in 18O and D and were located along the global meteoric water line (GMWL). Most ore-bearing confined waters plotted on or near the meteoricwater line, showing their deep-circulating meteoric origin. Uranium species study indicated that dissolved uranium was dominated by UO2(OH)3− and UO2(CO3)34−, which have a high migrating ability. Saturation index of uraninite in all water samples were determined to be below 0, indicating that this uranium deposit was currently not under mineralization. The pH and Eh values of the samples were located in the migration area, suggesting that uranium is in a migration state under current groundwater conditions, only when pH = 5 ~ 8 and Eh < − 200 mV uranium precipitation will occur.

Late Cretaceous age of the Crucea uranium ore deposit, East Carpathians, Romania

U-Th-Pb chemical dating is a suitable technique for determining ages of minerals (e.g., uraninite, monazite) that have large amounts of U and/or Th such that the radiogenic Pb can be measured. We investigate the chemical age of bitumen-supported uraninite from the vein-type Crucea uranium deposit, which is located in the Tulghes Series basement of the East Carpathians. We find that uraninite has a crystallization age of 88.8 ± 4.9 Ma, much younger than the Paleozoic age of magmatic emplacement and metamorphism of the host rock. The age of uraninite mineralization corresponds well with the timing of Mid-to-Late Cretaceous thrust faulting in the East Carpathians fold and thrust belt, during which the Tulghes Series was thrust over organic carbon-rich black shales of the Ceahlau and Moldavides nappes. These thrust faults likely acted as conduits through which U-rich carbonaceous matter, extracted from the black shales, migrated upward to be emplaced as veins.

Lead Isotopes in Exploration for Basement-Hosted Structurally Controlled Unconformity-Related Uranium Deposits: Kiggavik Project (Nunavut, Canada)

Pb-isotopes have been proposed as pathfinders for sandstone-hosted unconformity-related U deposits, with isotope ratios providing information on mineralization timing and element remobilization and migration. Pb-isotopes proximal to mineralization display radiogenic signatures, often with ‘excess Pb’ suggestive of derivation from greater U concentrations than are currently present. The U deposits in the Kiggavik project area (west of Baker Lake, NU, Canada) are basement-hosted, contain several generations of pitchblende mineralization, display a strong structural control, and are located in fault-related fracture systems and foliation-parallel veinlets. Drill core samples were analysed by Inductively-Coupled Plasma-Mass Spectrometer (ICP-MS) for Pb isotopes following multi-acid total-digestion, reverse Aqua Regia partial-digestion, and weak-acid-leach attacks, to evaluate the utility of the respective dissolution methods in Pb-isotope pathfinder geochemistry. Partial-digestion results are similar to weak-acid-leach results, indicating that interpretation of Pb-isotope signatures can be carried out from partial-digestion data if weak-acid-leach data are unavailable. Application of this pathfinder method at Kiggavik shows that Pb-isotope ratios display systematic trends useful for exploration vectoring. Uranium-content-adjusted 206Pb/204Pb ratios and 206Pb/204Pb ‘excess-lead’ data highlight anomalous isotopic values. 207Pb/206Pb ratios display downhole trends complementary to location of mineralization. Three-dimensional (3D) distributions of Pb-isotope data at the Contact U prospect show systematic trends and form halos around the mineralization. Isotopic footprints are limited to &lt;50 m from the mineralization outline, reflecting host-rock and structural control, but indicate areas with elevated potential for U mineralization and provide vectoring information within basement lithologies.

Uranium Mineralization of Fossil Wood

Uraniferous sandstone deposits commonly resulted when uranium in groundwater precipitated in reducing environments caused by degradation of ancient wood and organic debris. However, the mineralogy of uranium in fossil wood has received relatively little study. Previous microscopic observations of petrified wood from a few uranium mines have demonstrated that uranium in fossil wood primarily involves the oxide mineral uraninite or the silicate mineral coffinite, often in association with metal sulfides such as chalcopyrite. These observations are applicable to primary ore zones that are located below the water table, where oxidation is inhibited. New analyses utilizing scanning electron microscopy and X-ray fluorescence (SEM/EDS) reveal that fossil wood from oxidized ore zones may contain a diverse variety of uranium minerals, including carnotite, tyuyamunite, and zippeite, as well as various vanadate and sulfate minerals. Uranium-bearing common opalized wood and stratiform common opal from two prospects in Nevada, USA, contain no identifiable uranium minerals. Instead, the element is dispersed in trace amounts within the opal.

Effect of Aging on the Stability of Microbially Reduced Uranium in Natural Sediment.

Reductive immobilization of uranium has been explored as a remediation strategy for the U-contaminated subsurface. Via the in situ biostimulation of microbial processes, hexavalent U is reduced to less soluble tetravalent species, which are immobilized within the sediment. Although the mineral uraninite (UO2) was initially considered the dominant product of biological reduction, non-crystalline U(IV) species (NCU(IV)) are found to be abundant in the environment despite their greater susceptibility to oxidation and remobilization. However, it has been recently proposed that, through aging, NCU(IV) might transform into UO2, which would potentially enhance the stability of the reduced U pool. In this study, we performed column experiments to produce NCU(IV) species in natural sediment mimicking the environmental conditions during bioremediation. Bioreduced sediment retrieved from the columns and harboring NCU(IV) was incubated in static microcosms under anoxic conditions to allow the systematic monitoring of U coordination by X-ray absorption spectroscopy (XAS) over 12 months. XAS revealed that, under the investigated conditions, the speciation of U(IV) does not change over time. Thus, because NCU(IV) is the dominant species in the sediment, bioreduced U(IV) species remain vulnerable to oxidation and remobilization in the aqueous phase even after a 12-month aging period.

Oxidation state and coordination environment of Pb in U-bearing minerals

This study examines the oxidation and coordination of lead (Pb) in the uranium (U) minerals uraninite (UO2), coffinite (USiO4), and brannerite (UTi2O6), and minerals that have U as a minor constituent, zircon (ZrSiO4) and titanite (CaTiSiO5). The characterization of Pb was conducted through a combination of micro-synchrotron X-ray fluorescence mapping (µSXRF) and micro-X-ray absorption spectroscopy (µXAS), collected at the Pb LII and LIII edge on characterized grains (electron microscopy and X-ray diffraction) from a range of geological settings and ages.For all minerals considered in this study, Pb LII and LIII X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data indicate that Pb exists as Pb2+. In the case of uraninite, DFT structure optimization calculations suggest that the substitution of Pb2+ for U4+ is facilitated by the stereochemically active electron lone pair indicative of Pb2+, which effectively takes the place of an oxygen vacancy (coupled substitution Pb2+ + □ = U4+ + O2−). In detail, however, the EXAFS and XANES data, supported by first principle calculations of the XANES associated with Pb2+ replacing U4+ in the crystal lattice of uraninite, indicate that Pb2+ is present in a less distorted coordination than suggested by DFT, which may reflect a yet to be characterized link between interstitial oxygen defects and Pb2+ incorporation, rather than a simple oxygen vacancy. For coffinite, the XANES data demonstrate that Pb exists mainly as Pb2+ in the form of galena, indicating limited stability of the isomorphous substitution in coffinite. In contrast, Pb is homogeneously distributed in the metamict mineral brannerite, which displays a distinct XANES spectrum suggestive of Pb2+ bonded to oxygens in a highly distorted coordination environment. Pb LII XANES indicate that radiogenic Pb exists predominantly as Pb2+ within the crystal lattice of zircon and as distinct mineral PbO nano-scale inclusions or domains. Additionally, Pb LII XANES measurements also indicate that Pb2+ exists within titanite although the coordination environment is unclear.Overall, these data suggest that the previous indications of the presence of Pb4+ in radioactive minerals need to be reconsidered. The nature of radiogenic Pb2+ incorporation in U-bearing minerals controls the mobilization of Pb in hydrothermal fluids and the utility of a mineral as a geochronometer. The Pb valence and coordination data presented in this study provide fundamental constraints imperative for our understanding of the controls governing the mobilization of radiogenic Pb during water-rock interaction and metamorphism.

Syntheses, Crystal Structures, and Spectroscopic Studies of Uranyl Oxide Hydrate Phases with La(III)/Nd(III) Ions.

We have synthesized two uranyl oxide hydrate (UOH) phases incorporating La(III) or Nd(III) ions under hydrothermal conditions. Investigations with scanning electron microscopy and transmission electron microscopy (TEM) revealed thin-plate morphologies with a U-to-Ln atomic ratio of 2:1 (Ln = La or Nd), while single-crystal X-ray diffraction and TEM electron diffraction studies confirmed that both UOH phases crystallized in the trigonal P31m space group with uranyl oxide layered structures incorporating La(III)/Nd(III) ions as interlayer species. Vibrational spectroscopic studies revealed typical vibrational modes for U ions, with the derived U═O bond lengths being comparable to the values reported on other UOH phases. Bond-valence-sum calculations suggest hexavalent uranium in the uranyl form, which was confirmed by the results of diffuse-reflectance and X-ray absorption near-edge structure spectroscopies. This work reports the first single-crystal structural investigation of UOH phases with Ln ions, which has significant implications in the weathering products of uraninite mineral in nature as well as the alteration products of spent nuclear fuels during interim storage and safe disposal over geological timespans.

Kocuria Bacterial Isolates from Radioactive Springs of Jáchymov spa (Joachimsthal) as Sources of Polyunsaturated Fatty Acids.

Four bacterial isolates, which produced polyunsaturated fatty acids (PUFA), were isolated from water samples of radioactive springs collected from Jáchymov spa. Jáchymov (Sankt Joachimsthal) is a city in northwestern Bohemia, where Marie and Pierre Curie isolated radium in 1898 from the mineral uraninite. To date, four springs (Agricola, Behounek, C1, and Curie) have been used for spa purposes, that is for the treatment of nervous and rheumatic disorders by constantly produced radioactive gas radon (222 Rn) dissolved in the water. The radioactivity reaches 24 kBq/L. Using 16S rRNA gene sequence analysis, all four isolates were identified as members of the genus Kocuria, with two isolates designated 208 and 401 affiliated with Kocuria kristinae, while isolates 101 and 301 most likely with K. rhizophila. The content of fatty acids in polar lipids was determined by gas chromatography-mass spectrometry (GC-MS) and two PUFA, that is arachidonic and eicosapentaenoic, were identified. The position of double bonds was confirmed by GC-MS of 3-pyridylcarbinol (formerly picolinyl) esters. We assume that all four isolates of Kocuria produce PUFA to increase the stability of cell membranes, which may be impaired by the reaction of the reactive oxygen species. These can arise, for example, because of α radiation during 222 Rn decay.

In-situ U–Th–Pb geochronometry with submicron-scale resolution: low-voltage electron-beam dating of complexly zoned polygenetic uraninite microcrystals

Abstract Complexly zoned microcrystals of uraninite were encountered in orthogneiss from the central Tauern Window in Austria (K1 gneiss, Felbertal scheelite mine) and analysed in-situ for U, Th and Pb with state-of-the-art FE-SEM/EDX techniques. A three times finer spatial resolution was achieved using an acceleration voltage of 8 kV, compared to the classic 15–20 kV set-up of U–Th–total Pb electron microprobe dating. The lower voltage allows a spheroid of material with a diameter of only 0.3 µm to be selectively analysed. Careful tests on three uraninite reference materials show that the low-voltage method yields sufficient precision and accuracy for U–Th–total Pb uraninite dating, with errors on individual spot ages in the order of 10–30 Ma. By means of this innovative analysis technique, small-scale age zoning patterns could be resolved and dated in the uraninite microcrystals from the orthogneiss. Based on microstructures observed in backscattered electron images we interpret that an older uraninite generation in the rock, with a late Permian formation age (~260 Ma), was recycled two times through a coupled dissolution–reprecipitation process at ~210 Ma and at ~30 Ma. The younger dissolution–reprecipitation phase at ~30 Ma coincides with the Alpine regional metamorphism (lower amphibolite facies). The two older ages (~210 Ma and ~260 Ma) have been previously recognized in rocks from the Tauern Window by uraninite dating, but it is the first time here that both are recorded in the same rock and even the same uraninite grain. The present study shows that recrystallized accessory uraninite can provide a sensitive geological “hard disk” where several discrete thermal events of an area are stored. In addition, our work attests that the mineral uraninite has an unexpected geochronological robustness, even on the microcrystal scale.

Early uranium mobilization in late Variscan strike-slip shear zones affecting leucogranites of central western Spain

Mineralization related to the post-collisional reorganization in Iberia occurs along strike-slip shear zones (Sn, Au, ± U), in extremely differentiated leucogranites and pegmatites (Sn, Nb, Ta, Be, Li), in skarns (W, ± Au, ± U), and in quartz-veins with greisen (W, Sn, ± Au, ± U). Episyenites/albitites with uraninite mineralization in strike-slip shear zones yield U–Pb ages of 304 ± 6 Ma (2σ) that are identical within error with the 40Ar/39Ar age of micas grown during fabric development (306 ± 3 Ma, 2σ), suggesting shearing and formation of episyenite/albitite and uraninite mineralization are directly related. Mineral chemistry of uraninite from episyenite and deformed muscovite-rich leucogranite host are indistinguishable and has immobile element signatures typical for uraninite that formed from a hydrothermal or metamorphic fluid. The mineral chemistry of uraninite hosted in the deformed muscovite-rich leucogranite, together with the large time span between granite emplacement (347.6 ± 1.9 Ma, U–Pb zircon) and uraninite (chemical age 300 ± 3 Ma) excludes a magmatic origin of uraninite. Mass balance indicates that leaching of rock-forming minerals (especially muscovite and monazite) of the muscovite-rich leucogranite during extensive metasomatism (e.g. albitite or episyenite formation) could provide most uraninite-hosted U. The precipitation of the uraninite-pyrite association with carbonaceous matter in episyenite/albitite was related to local reducing conditions and/or fluid unmixing processes, analogue to hydrothermal uraninite from retrograde scheelite skarn and W ± Au quartz veins in the Iberian Massif. Chemical ages of uraninite from episyenite and muscovite-rich deformed granite demonstrate that episyenitization is not a late-stage Variscan process, but a post-orogenic one. Metal mobilization is structurally controlled. Chemical dating of uraninite may provide a first-order age constraint in unravelling the post-Variscan tectonic history.

Kinetics of uranium extraction from coffinite—A comparison with other common uranium minerals

Abstract A synthetic coffinite was hydrothermally prepared and characterized before conducting a series of acid sulfate leach tests under conditions of relevance to uranium extraction. The results were then compared with similar studies on synthetic versions of the related U4+ minerals uraninite (UO2) and brannerite (UTi2O6) to identify and differentiate the rate and U extraction among these important uranium minerals. Tests examining the influence of residence time on uranium dissolution from synthetic coffinite, uraninite and brannerite showed that under similar experimental conditions, complete dissolution of uranium from coffinite was obtained between 36 and 48 h. The activation energy for this reaction was calculated to be 38.4 kJ/mol. This represented a significantly slower rate of dissolution than that indicated for uraninite which dissolved in 3 h (Ea=15.2 kJ/mol). The synthetic brannerite was leached at a much slower rate than the coffinite and reached a maximum dissolution of ∼18% U in 144 h (Ea=42–84 kJ/mol). The clear differentiation in rates and U extraction among the three minerals is consistent with previous literatures which suggest that in terms of leachability, uraninite>coffinite>brannerite. It is expected that the presence of impurities in natural coffinites would further inhibit leachability.

Optical and Chemical Characterization of Uranium Dioxide (UO2) and Uraninite Mineral: Calculation of the Fundamental Optical Constants.

Uranium dioxide (UO2) is a material with historical and emerging applications in numerous areas such as photonics, nuclear energy, and aerospace electronics. While often grown synthetically as single-crystal UO2, the mineralogical form of UO2 called uraninite is of interest as a precursor to various chemical processes involving uranium-bearing chemicals. Here, we investigate the optical and chemical properties of a series of three UO2 specimens: synthetic single-crystal UO2, uraninite ore of relatively high purity, and massive uraninite mineral containing numerous impurities. An optical technique called single-angle reflectance spectroscopy was used to derive the optical constants n and k of these uranium specimens by measuring the specular reflectance spectra of a polished surface across the mid- and far-infrared spectral domains (ca. 7000-50 cm-1). X-ray diffractometry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were further used to analyze the surface composition of the mineralogical forms of UO2. Most notably, the massive uraninite mineral was observed to contain significant deposits of calcite and quartz in addition to UO2 (as well as other metal oxides and radioactive decay products). Knowledge of the infrared optical constants for this series of uranium chemicals facilitates nondestructive, noncontact detection of UO2 under a variety of conditions.

Spatial investigation of some uranium minerals using nuclear microprobe

In this work, several individual grains of uranium minerals—uraninite with high content of Ca, Ca-rich boltwoodite, growths of uranophane with β-uranophane, and weeksite—from different uranium deposits were studied by a scanning nuclear microprobe. Particle-induced X-ray emission technique provided by the microprobe (µ-PIXE) was carried out to obtain a concentration and 2D distribution of elements in these minerals. In addition, energy dispersive X-ray spectrometry (SEM-EDS) provided by a scanning electron microscope was used. The types of minerals were determined by X-ray diffraction methods. Results of this study improved the understanding of trace elemental composition of the uranium minerals depending on their origin. Obtained signatures could be linked then to the sample provenance. Such data are important for nuclear forensics to identify the ore types and even specific ore bodies, when only small samples may be available for analysis. In this study, the µ-PIXE technique was used for obtaining the 2D distribution of trace elements that are not commonly measured by SEM-EDS at the relevant concentrations. The detected levels and precisions of elements determination by µ-PIXE were also defined. Using µ-PIXE, several micro mineral inclusions such as phosphate with high level of V and Si were identified. The age of the uranium minerals was estimated due to a significant content of radiogenic Pb that provides an additional parameter for determination of the main attributive characteristics of the minerals. This work also showed that due to its high elemental sensitivity the nuclear microprobe can be a new analytical tool for creating a nuclear forensic database from the known uranium deposits and a subsequent analysis of the intercepted illicit materials.

Geochemical anomaly recognition of rare earth elements using multi-fractal modeling correlated with geological features, Central Iran

The aim of this paper is the geological studies and delineation of geochemical anomalies of lanthanum (La), cerium (Ce) and yttrium (Y) rare earth elements (REEs) in Saghand area, Central Iran. In order to recognize the mineralization zones considering their concentrations, the results of the sampled litho-geochemical data were processed by concentration–area (C–A) fractal model. The C–A log-log plots of the elements were generated and their thresholds were identified. Therefore, the high intensive geochemical anomalies of the studied elements were discriminated. A part of their high intensive geochemical anomalies are situated in the west of the study area occurred within the metasomatic, porphyry microdioritic and acidic volcanic rocks associated with epidotic alterations. The other high intensive geochemical anomalies of Ce and Y are located in the center of the study area. In addition, the moderate anomalies of La and Ce were located in the metasomatic units associated with epidote and chlorite alterations in the central part of the study area. The SE parts of the Ce moderate anomalies are probably related to basic dykes associating with epidotic alterations which are situated between metasomatic and microdioritic units. Based on the results obtained from multi-fractal modeling, the locations of the main anomalies of La, Ce and Y were recognized which all are in the western, central, southern, and SE parts of the study area. Several high and moderate concentration anomalies obtained from the C–A model were confirmed by ground surveying and compared with the achieved result from remote sensing investigation. According to the correlation between geological particulars and obtained REEs anomalies, it has been proved that the proper and promising areas are in metasomatite rock units, chlorite and epidote alterations in the western and central part of the study area. By Scanning Electron Microscope (SEM) studies of davidite and uraninite minerals, it was determined that the REEs mineralization in this area have taken place mostly in the form of replacement in radioactive elements uranium (U) and thorium (Th). The combination of the field observations and mineralogical studies based on the type of REEs mineralization in the study area revealed that one of the main factors controlling the mineralization is related to metasomatism.

New data on REE and rare-metal mineralization in pegmatites of the Slyudyanogorsk muscovite deposit in the Southern Urals

The Slyudyangorsk muscovite deposit in the southern Urals was explored and mined in 1926–1957. By the mid-1950s, 104 veins of quartz–feldspar pegmatites including 21 muscovite-bearing veins have been found. Pegmatites with giant black Y-bearing epidote crystals are crosscut by veins with giant muscovite crystals, which, in turn, are intersected by veins of two-mica–quartz–two-feldspar pegmatites with rare-metal and REE mineralization. Microprobe data on compositions of complex Ti–Ta–Nb oxides [fergusonite-(Y), samarskite-(Y), euxenite-(Y), polycrase-(Y), columbite-(Fe), pyrochlore supergroup] are characterized, as well as of uraninite, ilmenorutile, scheelite, Y-bearing epidote, certain sulfides and rock-forming minerals from the Slyudyanogorsk deposit. The morphology and interrelation of minerals indicate that they are the result of crystal growth in cavities rather than of metasomatic replacement of gneisses, as has been suggested earlier. Thus, it is more promising for rare-metal and REE minerals in the Slyudorudnik area to be found in igneous rocks (granitic muscovite–quartz–feldspar pegmatites with the Nb–Ta–Ti–Y–U–W–Mo mineralization) than in metasomatic rocks.