Secondary Uranium Research Articles

Tensile stress and related Th-U-REE mineralizations in the granite of Wadi Ras Abda, North Eastern Desert, Egypt

The main rock types exposed at Wadi Ras Abda area are subduction-related older granite intruded by fine-grained alkali feldspar granite (microgranite intrusions). These rock types are dissected by acidic dykes (rhyolite) and basic dykes (basalt and dolerite) with their associated pegmatites and quartz veins. Ras Abda microgranite is highly radioactive and this radioactivity is structurally related. The thorium, uranium, and rare metal mineralization are distinguished within the microgranite intrusions along fault zones that are trending N40° E with high dipping angle reaching to 86°. It shows radioactive measurements ranging from 500 to 9500 ppm and showing visible secondary uranium and thorium minerals in addition to the deposition of black rare metal minerals. Uranothorite, thorite, and secondary uranium minerals (uranophane) are the main radioactive minerals at Wadi Ras Abda area, in addition to the rare earth–bearing mineral (REE) fergusonite. Six events are affected in W. Ras Abda area. Each event begins with compression (CP) and then extensional (EXT) phase of deformation. These events were arranged chronologically basing on field relations from the oldest to the youngest as following: WNW-ESE (CP), NNE-SSW (EXT), E-W (CP), N-S (EXT), NE-SW (CP), NW-SE (EXT), NNE-SSW to N-S (CP), WNW-ESE to E-W (EXT), NW-SE to NNW-SSE (CP), ENE-WSW to NE-SW (EXT) and ENE-WSW (CP), and NNW-SSE (EXT). The WNW-ESE to E-W–directed tensile stress reactivated faults and induced new faults along which the mineralized fluids flow. It is recognized that the low-stress regions in the vicinity of faults and their associated tension joints, along contacts between microgranite and older granite, are favorable locations for alterations and Th-U and REE mineralization.

Laboratory core investigations of sandstone-hosted uranium for in situ recovery

ABSTRACTSeveral core plugs from a 1243 m-deep borehole penetrating the Westwater Canyon Member of the Morrison Formation in New Mexico (USA) have been investigated by various petrophysical methods to evaluate the potential of extracting deeply buried sandstone-hosted uranium deposits by in situ recovery (ISR). Petrophysics and mineralization patterns of the host rock in the target aquifer are crucial parameters for ISR amenability and were determined according to the ISR feasibility criteria. Mineralogical investigations revealed a secondary uranium mineralization mainly coating the silica grains of the arkosic sandstone and some interstitial pore fillings. The differences between mineralized and non-mineralized sandstone plugs are highlighted by nuclear magnetic resonance (NMR), X-ray microcomputed tomography, and spectral induced polarization (SIP). The NMR results show a doubling of the clay- and capillary-bound water and a decease of free-fluid porosity of mineralized samples. A correlation of mineralization grade and polarization is observed through the SIP investigations.

Autunite-Group Minerals and Their Paragenesis from the Sheared Granite of Gabal El Sela, South Eastern Desert, Egypt

G. El Sela is located in the Southern Eastern Desert of Egypt cropping as two parts, occupied by monzogranites that were categorized as biotite granite, muscovite granite and two mica granites. The northern part is more significant according its high concentrations of uranium that controlled by complicated structure regime; faulting, infrastructures and shearing are the most common structural criteria of this part. The Egyptian Nuclear Materials Authority (NMA) mined this part to produce the uranium ore. The previous mineralogical studies indicated that this granite was dominated by primary uranium minerals (pitchblende and coffinite) and secondary minerals belong to the autunite group (autunite, metautunite, phurcalite) in addition to uranophane. In the present work, petrographic and mineralogical studies are applied for the granites using the polarized and stereo microscopes and followed by electron microscope and XRD. The result of the microscopic examinations revealed the tectonic regime controlling the radioactivity and recognized the sodic autunite (meta-natroautunite) beside the pre-mentioned autunite group minerals completing the paragenetic sequrnce of these minerals. In this study, it is concluded that the sheared biotite granite is monzogranite originated during the episode of the continental plate collision (syncollision). The study finished to presence of two main types of the alteration corresponding to the two high levels of radioactivity (moderate and anomalous). The first is the thermal alteration (saussiritization, sericitization, kaolinization, silicification and hematization) and the second is the chemical transformation (oxidation, dehydration, ion substitutions and confusion) responsible for formation of the secondary uranium minerals. The temperature needed for the thermal alteration is sourced by the hydrothermal solutions, while the temperature needed for the uranium minerals transformation may be generated during the episode of the continental plate collision (syncollision). Paragenesis of these minerals indicates that they represent a series of uranyl phosphate minerals (autunite group) with paragenetic sequence starting by autunite (calcic uranyl phosphate) and ends by meta-natroautunite (sodic uranyl phosphate). An advanced process of dehydration accompanies the process of mineral transformation from autunite to meta-natroautunite leading to formation of the anhydrous uranyl mineral (phurcalite) formed by oxidation and dehydration of autunite. Meta-autunite is recorded as a transitional mineral composed of sodic-calcic uranyl phosphate. Uranophane is created by thermal confusion of autunite with the silica.

Laboratory simulation of uranium metal corrosion in different soil moisture regimes

A novel laboratory simulation system has been developed for the study of the corrosion of uranium metal in soils. Corrosion and transportation of depleted uranium (DU) as the metal undergoes weathering as a buried material within the soil environment. The corrosion of uranium metal in soil was not well understood due to the gas-liquid-solid phase of the soil. This study presents a novel method to investigate the change of uranium species during the process of process of oxidation of metallic uranium in these environments. Compared with other techniques used for the study of environmental corrosion of metals in soils, this method has the advantage of low secondary uranium pollution, no energy consumption, and ease of operation. The simulation system has been used for the following studies:•Simultaneously simulate the corrosion of uranium metal in different soil moisture regimes•Study the influence of biogeochemical factors on the corrosion of uranium metal•Investigate the change of uranium species during oxidation

Hydrogen and oxygen stable isotope composition of water in metaschoepite mineralization on U3O8

When exposed to humidity in an oxidizing atmosphere hydrated uranium oxide grows as a secondary mineral on aged U3O8 and may incorporate the oxygen stable isotope signature of the water vapor into the secondary uranium oxide, as well as hydrogen and oxygen stable isotopes into any mineral hydration water. Because geospatial variation in δ2H and δ18O values of atmospheric humidity and precipitation is well understood, the H and O stable isotope composition of mineral hydration waters can give information on the environment of mineral formation. We exposed powdered U3O8 to humidity with known H and O stable isotope composition at constant 30%, 61% and 91% relative humidity. We sampled and analyzed the U3O8 powders along with any secondary hydrated minerals that had formed on the particle surfaces at various intervals from 1 to 10 days throughout the 180-day humidity exposures. We present stable H and O isotope results of mineral hydration waters in uranium oxide materials analyzed by thermogravimetry-enabled isotope ratio infrared spectroscopy (TGA-IRIS), which uses precise heating by thermogravimetric analyzer to liberate water vapor for subsequent online isotope analysis via a laser-based isotope ratio infrared spectroscopy instrument (Picarro L-2130i). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray diffraction (XRD) analysis of humidity-exposed U3O8 heated to 350 °C indicates that the U3O8 had a measurable metaschoepite ((UO3)•2H2O) phase along with α-U3O8. After heating to 350 °C, the metaschoepite is eliminated but the α-U3O8 is retained, meaning that the heating successfully extracted the water in the metaschoepite but did not disturb the crystalline structure of the U3O8. Analysis of the bulk oxygen isotope composition by fluorination of these samples before and after heating, indicates that the oxygen isotope value of the U3O8 is also not affected by heating to 350 °C. Precision for δ2H and δ18O values of metaschoepite mineral hydration water stable isotope values yielded by the TGA-IRIS method on metaschoepite are 5.86‰ for δ2H, and 0.34‰ for δ18O. Hydrogen in the various water reservoirs is highly exchangeable and thus the δ2H values of these waters is not easily interpreted. However, oxygen in the separate water reservoirs is much less exchangeable, and thus δ18O values of the metaschoepite mineral hydration water is likely to reflect that of the water vapor the sample was exposed to. Once metaschoepite is formed on the surface of U3O8 particles, the oxygen isotope signature of the mineral hydration water in metaschoepite does not respond to changes in exposure vapor isotopic composition, and thus appears to be fairly durable in this regard. These results suggest that it may be possible to discern information about the provenance and history of an oxidized U3O8 sample from oxygen stable isotope measurements of metaschoepite mineral hydration water.

Geology and fluid geochemistry of the Na-metasomatism U deposits in the Longshoushan uranium metallogenic belt, NW China: Constraints on the ore-forming process

The Longshoushan belt in Gansu Province is a very important uranium metallogenic belt in Northwest China and contains a series of different types (magmatic, Na-metasomatism, supergenetic) of uranium deposits and occurrences. Of all these mineralization types, the Na-metasomatism type is the most predominant with great potential, represented by two Na-metasomatism uranium deposits (Xinshuijing and Jiling). Different from the fluorite-, illite-, quartz-dominated alteration minerals in other hydrothermal uranium mineralization system, the Na-metasomatism type uranium deposits are characterized by the unique albite-dominated (up to 90 vol%) alteration mineral assemblage, which is referred to albitite in many literatures. All the uranium orebodies in both the Xinshuijing and Jiling deposits are hosted within the metasomatic albitites, and controlled by the subsidiary faults of the regional Malugou Fault. The mineralization process in both deposits can be divided into four stages, namely: the Na-metasomatism stage, U mineralization stage, post-mineralization stage and supergene mineralization stage. The Na-metasomatism stage is predominantly composed of albite (with hematite staining), with minor chlorite and anatase, while the U mineralization stage is characterized by the occurrence of uranium minerals (mostly pitchblende), intergrown with some tiny albite, calcite, chlorite, pyrite, apatite, REE-minerals and sometimes hydrothermal zircons. The mineral assemblages of the Na-metasomatism stage and U mineralization stage are too intimately related to each other and might be the products of the evolution from the same ore-forming fluids. The post-mineralization stage is mainly the calcite-quartz veinlets or occur as aggregate clusters, while the supergene mineralization stage includes mineral assemblage of secondary uranium mineralization-clay minerals (e.g. kaolinite)-limonite. Mineralogical studies and comparison of major and trace elements assay results between fresh biotite granite (predominate host rocks), albitite and uranium ores suggest that the ore-forming fluids resulting in the formation of the Na-metasomatism alteration are oxidized and rich in Na, Sc, V, Cr, Co, Ni, U, Th, while the ore-forming fluids of the U mineralization stage are relatively reduced and rich in heavy rare earth elements, U, Th, PO34-. Fluid inclusion and calcite C-O isotope studies indicate that the ore-forming fluids are meteoric water-dominated, which circulated at depth (~8 km, by fluid inclusion geobarometer) and scavenged uranium from the host biotite granites and metamorphic rocks of the Longshoushan Group. The ore precipitation is mainly attributed to physicochemical changes (fO2, temperature, fluid composition) from fluid-rock interaction and further temperature decrease of the ore-forming fluids, while fluid boiling and fluid mixing processes are limited. The proposed ore-forming process is not only important for the understanding of the ore genesis for the Na-metasomatism mineralization systems in Longshoushan, but also highlights the significance of albite alteration, which could be used as an important indicator during further uranium exploration.

P2O5 – F- U Characterization and Depositional Environment of Phosphatic Rocks for the Duwi Formation, Qussier- Safaga Region, Red Sea Coast, Egypt.

Abstract The Duwi Formation in Qusseir-Safaga region is conformably overlain by the Qusseir variegated shales and underlain by the Dakhla shales. The studied phosphatic rocks in the Duwi Formation, is an attractive rock unit for it’s enrichment in heavy metals and U content. Mineralogically, phosphatic rocks in the Duwi Formation are mainly composed mainly of fluorapatite, in addition to minor occurrence of calcite, dolomite, gypsum, quartz, and pyrite. Geochemical data reveal that the rocks of the Duwi Formation were deposited under anoxic environments. The present study used the statistical result of the interrelation between P2O5, F and U concentrations on Egyptian phosphate samples and compared to the measured data. Uranium mostly occurs in an oxidized U 6+ state. It could be fixed with the phosphatic ion, forming secondary uranium phosphate minerals such as phosphuranylite and belovite in Qusseir region. In addition to Uranyl phosphates, uranium minerals in Safaga region contain also Uranyl carbonates and Uranyl sulfates, which had been attributed to the post-depositional U enrichment. The chemical data and index show that the phosphatic rocks in Safaga region are more enriched in the majority trace and rare earth elements, and are subjected to high chemical weathering than those in Qusseir region.

Uranium Mineralization in Leucogranite of Mastipuram Area, Wanaparti District, Telangana – A New Find

ABSTRACT The NNW-SSE trending leucogranites in and around Mastipuram, Wanaparthi district, Telangana are intrusive into Peninsular Gneissic complex. The leucogranite is metaluminous to mildly peraluminous, alkali-feldspar granite with I-type signatures, probably formed from a fractionated melt involving crustal component. Magmatic and hydrothermal contributions are supported by wide range of U/Th ratios in mineralized samples, which also show Na-enrichment as compared to non-mineralized leucogranites. Average U and Th contents and U/Th ratio in mineralized leucogranite is 541ppm, 147 ppm and 2.85, respectively. Main ore mineral is uraninite and its altered form - gummite, while secondary uranium minerals such as schoepite, uranophane and haiweeite are also identified in leucogranite by XRD. Reconnoitory drilling of ten boreholes have confirmed sub-surface continuation of uranium mineralization with varying width of 1m to 31m at vertical depth of about 50m. Thus, the leucogranites bordering Gadwal schist belt around Mastipuram forms a very potential target.

Characteristic and Significant of Uraninite in Danfeng Uranium Ore-fields

Development of nuclear energy needs the support of considerable uranium reserves. Danfeng uranium ore-fields was the unique pegmatite-type uranium deposits been found in China. Characteristic, mineral paragenesis, alteration and secondary-mineral-assemble of uraninite in this area been studied by Microscope, SEM and EPMA. The results revealed: 1) Uraninite was the only primary uranium mineral, displayed in automorphic-hypautomorpuic granular texture, disseminated embedded within gangue minerals or among their grains. 2) U, Th and Pb were the major elements,Y, Ca, Si, Na, Hf, Fe, Zr, Mg, P, Mn were the minor elements in uraninite. 3) Uraninite subjected to hydrothermal alteration and some of it were surrounded by secondary minerals included secondary uranium minerals, sulfide, oxides and other silicate minerals. 4) Mineralization of uranium was mainly controlled by crystallization differentiation of primary pegmatitic magma, later hydrothermal alteration and/or supergenetic oxidation had influence on it.

El Seboah peralkaline A-type magmatism, South Western Desert, Egypt: evidences for the HFSE and REE enrichment

El Seboah peralkaline A-type magmatism is one of the numerous alkaline plutonic and volcanic (trachyte, rhyolite, and basalt)/subvolcanic rocks, which are occurring in the South West of Egypt along the Guinean-Nubian lineament. El Seboah magmatic rocks include fresh peralkaline granite and rhyolite dikes (pantellerite). The fresh peralkaline granite intruded the Late Cretaceous Nubia sandstones, and furthermore, the pantelleritic dikes cut it. The fresh peralkaline granite and the pantelleritic dikes show common features of the A-type granites. They contain alkalic mafic minerals such as aegirine and riebeckite in the peralkaline granite or aegirine in the pantelleritic dikes; they also have high alkalis and HFSE (e.g., Zr, Nb, REE, Th, and U) with high ratios of FeOt (total iron)/MgO and Ga/Al, and strong depletions in Ba, Sr, Eu, Ti, and P. Both of the fresh peralkaline granite and the pantelleritic dikes have peralkaline, ferroan, and fertile character, and belong to subgroup A1-type magmas. Additionally, these rocks were formed as separated batches, emplaced within the African plate along the volcanic zone of the Guinean-Nubian lineament, and the source for both rock types is suggested as the ocean island basaltic magmas. Moreover, the pantelleritic magma displays more enrichment in the HFSE than the alkaline granitic magma, suggesting highly fractionated and alkalinity association. The peralkaline granite was subjected to different degrees of hydrothermal alterations along the fault zones. The hydrothermally altered peralkaline granite shows a strong enrichment in the HFSE that occur in minerals such as zircon, bastnaesite-(Ce), monazite-(Ce), percleveite-(Ce), pyrochlore, fergusonite-(Ce), columbite-(Mn), thorite, uranothorite, and amorphous secondary uranium. In addition, it shows a strong increase in the FeOt and CaO and a depletion in Al2O3, MgO, Na2O, and TiO2 with a slight increase in K2O and a slight decrease in SiO2 compared to the fresh peralkaline granite. Consequently, I suggest that the hydrothermally altered peralkaline A-type granite within the El Seboah area as a potential source for the rare metal deposits, but further detailed studies are needed.

Geochemical Characteristics and Radioactive Elements Estimation along Trenches of Um Ara area, South Eastern Desert, Egypt

Um Ara area is located in the extreme south Eastern Desert of Egypt between 581400mE-584900mE and 2503000mN-2504600mN. The area comprises distinct tectono-stratigraphic units beginning with the oldest as follows: Dokhan volcanic and post-collision granitoids (monzogranite, and alkali feldspar granite), and associated with dykes and quartz veins. The granite affected by deuteric K-metasomatism (microclinization) followed by Na-metasomatism (albitization) causing zonation in this part of the pluton. The high radioactivity in the anomalous sites is structurally controlled (strong shearing, fracturing and jointing). The intensity of mineralization is especially significant along joint sets striking NNW-SSE, NNESSW and NE-SW trending. The spacing among these joints ranges from few mm up to about 5 cm. locally, the joints are filled with kaolinite and other alteration products including hematite and Mnoxides. Geochemically, Um Ara granites trenches and core samples show a relative enrichment in K2O compositions due to plagioclase destruction and formation of muscovite/sericitization. Um Ara granites trenches and core samples have variable total REEs contents 117.41 to 308.28 and 256.51 to 397.22 ppm respectively. ΣLREEs in trenches and core samples range from 108.47 to 298.41ppm and from 236.84 to 384.78 ppm respectively, whereas ΣHREEs range from 5.48 to 14.01 ppm and from 12.44 to 19.67 ppm respectively. The lowest concentration of total REEs in core samples is at 100m depth, while the highest values at 145m depth. Um Ara granites trenches, U contents vary from 154 to 506 ppm with an average of 245.7 ppm, and Th contents vary from 47 to 415 ppm with an average of 165.4 ppm. Core samples granite, U contents vary from 128 to 349 ppm with an average of 237.3 ppm, and Th contents vary from 45 to 146 ppm with an average 107.4 ppm. Visible secondary uranium mineralization is represented mainly by uranophane and β-uranophane. Uranium is also contained within a range of U-bearing accessory minerals, mainly fluorite, monazite, xenotime, allanite and zircon. The secondary processes played a main role in uranium enrichment (uranium added to these granitic sites post-magmatically). Um Ara altered granites trenches and core samples rocks are an abnormal radiation and have an extension. So, these anomalies are suitable to be a place for uranium extraction. The result is the continuous of its mining work besides leachability experiments.

Hydrothermal Fracture Controlled Vein Type Uranium Mineralization in the Paleoproterozoic Bijawar Group of Rocks, Sonrai Basin, Lalitpur District, U.P. – Fresh Findings from Subsurface Borehole Data

ABSTRACT Sonrai basin, located along the southwestern margin of Bundelkhand Granite-Gneiss Complex (BGC) is known for its base metal and phosphorite mineralization. Uranium mineralization of appreciable grade and thickness was reported in Pisnari block in the northern part of this basin during sub-surface exploration activity in 1976-97. This was in the form of uranium-bitumin association within fractures in the carbonate-terrigenous sediments of Gorakalan shale, Rohini carbonate and Bandai sandstone of Sonrai Formation of Bijawar Group. Similar mineralization was also noted within the lower chloritic shale member of Solda Formation of the same Group. During subsequent drilling activity at a later phase (2005-09), uranium rich zones within Rohini carbonate and chloritic shale members were corroborated by the interception of mineralized bands in two boreholes drilled near Pisnari. Petrographic study of radioactive core samples reveal that uranium mineralization is closely associated with globular carbonaceous matter and sulphides along the fractures. Uranium is either adsorbed in carbonaceous matter or occurs as ultrafine inclusions of coffinite within carbonaceous matter. An additional phase of secondary uranium mineral (uranophane) is also noted in one of the boreholes. The uranium minerals, in association with sulphides, fill up moderately dipping fractures (approximately 15° towards North) which are oblique to the core axis of the inclined borehole and thus, the mineralization is characterized as hydrothermal fracture-controlled vein type mineralisation. C-H-N-S analysis of carbonaceous matter occurring in close association with the uranium minerals reveal heterogeneity in composition with respect to carbon and sulfur. The present paper aims at discussing the geological, petrological and radiometric aspects of this mineralization, so as to enhance the understanding of the same.

The Uranium Prospects in Mika Region, Northeastern Nigeria

Uranium exploration especially in currently non-producing countries like Nigeria possesses high economic prospect. This study investigates a new uranium prospect in Mika, Northeastern Nigeria. The Mika uranium mineralization is located in Mika, Taraba State. Two lodes were identified and additional nine (9) trenches were added. The main lode in the west extends about 10 m, ore vein strikes 348°, inclination 42° and the strike of the lode 306° with average uranium content of 18%. The eastern trench is about 8 × 4 × 6 m which exposes a veinlet of pitchblende. From the petrography, one can deduce that the granitic host rock has suffered deformation resulting in crushing of quartz crystals and stretching of plagioclase. The uraninite and chalcedony in the late phase filled up the fractures along the crystal grain boundaries as veinlets. The laboratory gamma ray analysis of the samples showed that the secondary uranium content is 0.1%, while the primary uranium ore grade is 1.5%. Radiometric in situ measurements showed that Th and K ranges from 47.3 - 3654 ppm and 4.26% - 6.26% respectively. From the survey, a strong radiometric zone extends 800 × 35 m in an NW-SE direction and has highest radiation content of 1200 cpm against the background count rate of 30 cpm. Generally, the uranium concentrations in the ores in Mika area range from 0.03% - 0.12%. Since only the surface occurrences have been explored, the study area is a good prospect for future development when properly explored. The North-eastern Nigeria has been roughly explored by Nigeria Uranium Mining Company (NUMCO) in 1980, but no formal exploration had been followed after that, especially near the site of this article. The company (ACE Mines, Ltd) of the first author was among the few uranium mining companies approved in the list of Nigerian Geological Survey agency of Abuja in Nigeria. The authors determined the coordinates of the site in their first survey which formed the prospect area in the licence.

Rare-earth element fractionation in uranium ore and its U(VI) alteration minerals

A cation exchange chromatography method employing sulfonated polysterene cation resin (DOWEX AG50-X8) was developed in order to separate rare-earth elements (REEs) from uranium-rich materials. The chemical separation scheme is designed to reduce matrix effects and consequently yield enhanced ionization efficiencies for concentration determinations of REEs without significant fractionation using solution mode-inductively coupled plasma mass spectrometry (ICP-MS) analysis. The method was applied to determine REE abundances in four uraninite (ideally UO2) samples and their associated U(VI) alteration minerals. In three of the samples analyzed, the concentration of REEs for primary uraninite are higher than those for their corresponding secondary uranium alteration phases. The results for U(VI) alteration minerals of two samples indicate enrichment of the light REEs (LREEs) over the heavy REEs (HREEs). This differential mobilization is attributed to differences in the mineralogical composition of the U(VI) alteration. There is a lack of fractionation of the LREEs in the uraninite alteration rind that is composed of U(VI) minerals containing Ca2+ as the interlayer cation (uranophane and bequerelite); contrarily, U(VI) alteration minerals containing K+ and Pb2+ as interlayer cations (fourmarierite, dumontite) indicate fractionation (enrichment) of the LREEs. Our results have implications for nuclear forensic analyses since a comparison is reported between the REE abundances for the CUP-2 (processed uranium ore) certified reference material and previously determined values for uranium ore concentrate (UOC) produced from the same U deposit (Blind River/Elliott Lake, Canada). UOCs represent the most common form of interdicted nuclear material and consequently is material frequently targeted for forensic analysis. The comparison reveals similar chondrite normalized REE signatures but variable absolute abundances. Based on the results reported here, the latter may be attributed to the differing REE abundances between primary ore and associated alteration phases, and/or is related to varying fabrication processes adopted during production of UOC.

Leószilárdite, the first Na,Mg-containing uranyl carbonate from the Markey Mine, San Juan County, Utah, USA

AbstractLeószilárdite (IMA2015-128), Na6Mg(UO2)2(CO3)6·6H2O, was found in the Markey Mine, Red Canyon, White Canyon District, San Juan County, Utah, USA, in areas with abundant andersonite, natrozippeite, gypsum, anhydrite, and probable hydromagnesite along with other secondary uranium minerals bayleyite, čejkaite and johannite. The new mineral occurs as aggregates of pale yellow bladed crystals flattened on ﹛001﹜ and elongated along [010], individually reaching up to 0.2 mmlong. More commonly it occurs as pale yellow pearlescent masses to 2 mm consisting of very small plates. Leószilárdite fluoresces green under both longwave and shortwave ultraviolet light, and is translucent with a white streak, hardness of 2 (Mohs), and brittle tenacity with uneven fracture. The new mineral is readily soluble in room temperature H2O. Crystals have perfect cleavage along ﹛001﹜, and exhibit the forms ﹛110﹜,﹛001﹜,﹛100﹜,﹛101﹜ and ﹛101﹜. Optically, leószilárdite is biaxial (-), α= 1.504(1), β= 1.597(1), γ= 1.628(1) (white light); 2V (meas.) = 57(1)°, 2V (calc.) = 57.1°; dispersion r > v, slight. Pleochroism: X= colourless, Y and Z= light yellow; X<Y ≈ Z The average of six wavelength dispersive spectroscopic analyses provided Na2O 14.54, MgO 3.05, UO3 47.95, CO2 22.13, H2O 9.51, total 97.18 wt.%. The empirical formula is Na5.60Mg0.90U2O28C6H12.60, based on 28 O apfu. Leószilárdite is monoclinic, C2/m, a = 11.6093(21), b = 6.7843(13), c = 15.1058(28) Å, β = 91.378(3)°, V= 1189.4(4) Å3 and Z = 2. The crystal structure (R1 = 0.0387 for 1394 reflections with Iobs > 4σI), consists of uranyl tricarbonate anion clusters [(UO2)(CO3)3]4- held together in part by irregular chains of NaO5(H2O) polyhedra sub parallel to [010]. Individual uranyl tricarbonate clusters are also linked together by three-octahedron units consisting of two Na-centred octahedra that share the opposite faces of a Mg-centred octahedron at the centre (Na–Mg–Na), and have the composition Na2MgO12(H2O)4. The name of the new mineral honours the Hungarian-American physicist, inventor and biologist Dr. Leó Szilárd (1898–1964).

Modelling of the dissolution and reprecipitation of uranium under oxidising conditions in the zone of shallow groundwater circulation

Generic hydrochemical modelling of a grantoid-groundwater system, using the Russian software “HydroGeo”, has been carried out with an emphasis on simulating the accumulation of uranium in the aqueous phase. The baseline model run simulates shallow granitoid aquifers (U content 5 ppm) under conditions broadly representative of southern Norway and southwestern Siberia: i.e. temperature 10 °C, equilibrated with a soil gas partial CO2 pressure (PCO2, open system) of 10−2.5 atm. and a mildly oxidising redox environment (Eh = +50 mV). Modelling indicates that aqueous uranium accumulates in parallel with total dissolved solids (or groundwater mineralisation M – regarded as an indicator of degree of hydrochemical evolution), accumulating most rapidly when M = 550–1000 mg L−1. Accumulation slows at the onset of saturation and precipitation of secondary uranium minerals at M = c. 1000 mg L−1 (which, under baseline modelling conditions, also corresponds approximately to calcite saturation and transition to Na-HCO3 hydrofacies). The secondary minerals are typically “black” uranium oxides of mixed oxidation state (e.g. U3O7 and U4O9). For rock U content of 5–50 ppm, it is possible to generate a wide variety of aqueous uranium concentrations, up to a maximum of just over 1 mg L−1, but with typical concentrations of up to 10 μg L−1 for modest degrees of hydrochemical maturity (as indicated by M). These observations correspond extremely well with real groundwater analyses from the Altai-Sayan region of Russia and Norwegian crystalline bedrock aquifers. The timing (with respect to M) and degree of aqueous uranium accumulation are also sensitive to Eh (greater mobilisation at higher Eh), uranium content of rocks (aqueous concentration increases as rock content increases) and PCO2 (low PCO2 favours higher pH, rapid accumulation of aqueous U and earlier saturation with respect to uranium minerals).

Geochemistry and chemical dating of uraninite in the Samarkiya area, central Rajasthan, northwestern India – Implication for geochemical and temporal evolution of uranium mineralization

In the Samarkiya area, located at the central part of the Aravalli-Delhi Fold Belt (ADFB), uranium mineralization is hosted both by the basement Mangalwar Complex and the overlying supracrustal rocks of the Pur-Banera belt. The present study aims to appraise the geochemical and temporal evolution of uranium mineralization from the basement and the adjoining supracrustals in the Samarkiya area integrating textural features, geochemistry, and in situ U-Th-PbTotal dating of uraninite.Uraninite occurs as inclusions in the major rock forming minerals, viz. plagioclase, quartz, biotite, and chlorite. Based on the shape, location in the host mineral (well inside/at the grain boundary/along or connected to micro-cracks etc.) and association with other secondary uranium minerals, uraninites are classified into different groups, which are compositionally distinct, barring some exceptions. Integrating texture, geochemistry and in situ electron probe dating we propose that in addition to an old event at ∼1.88Ga in the basement rocks, there are two major events of uraninite formation at ∼1.24–1.20Ga and ∼1.01–0.96Ga in both the basement and supracrustal rocks. Although none of the pristine, unaltered uraninites that formed during the above mentioned events contain significant intrinsic minor or rare earth elements, the basement uraninites are consistently much enriched in thorium compared to those from the supracrustal. Based on the compositions, we propose that the basement uraninites formed from a high temperature magmatic/metamorphic fluid, whereas those in the supracrustal rocks crystallized from a low temperature, presumably oxidized fluid. Back-scattered electron images, X-ray elemental mapping of selected elements and EPMA spot analysis of large uraninite grains (both from the basement and the supracrustals) collectively demonstrate that subsequent to the major mineralizing event at ∼1.24–1.20Ga, the mineralized rocks were subjected to fluid-mediated alteration, which resulted in ∑REE+Y- and Si (Ca)-enrichment of existing ∼1.24–1.20Ga uraninites in the basement and supracrustal rocks, respectively. We cannot constrain the exact timing of this alteration event. However, as this event altered the ∼1.24–1.20Ga uraninites and as spot ages of the altered grains yield ages largely between ∼1.24 and 0.96Ga, it is reasonable to place this event between the second and third stages of uranium mineralization/mobilization at ∼1.20Ga and ∼1.01Ga, respectively. The last event that took place at ∼1.01–0.96Ga most likely represent an episode of recrystallization/alteration of existing uraninite leading to complete Pb-loss and resetting of the isotopic clock. However, we do not entirely reject the possibility of neo-mineralization.The discrete events deciphered from uraninite in the Samarkiya area can also be broadly linked to some major magmatic-metamorphic events, identified from other independent studies, in the ADFB. For example, the earliest ∼1.88Ga event displayed by basement uraninite is most likely related to a pervasive magmatic-metamorphic event (∼1.86–1.82Ga) that affected the basement, whereas the last/latest event ∼1.01–0.96Ga can be linked to a pervasive metamorphic event that affected perhaps the entire ADFB. This last episode can also be linked to the tectono-thermal event related to the Rodinian amalgamation. The ∼1.24–1.20Ga event appears to be somewhat enigmatic in the context of well-known geological events in the area. However, based on some very recently published data, we interpret this to be a post-peak metamorphic (∼1.37–1.35Ga) hydrothermal event or even a new metamorphic event, hitherto unknown.

Who's Who in Mineral Names: Rodney C. Ewing (b. 1946)

Ewingite, Mg8Ca8(UO2)24(CO3)30O4(OH)12·138(H2O), is a rare secondary uranium mineral. It was named in honor of Rodney C. Ewing, professor of geological sciences, Frank Stanton Professor in Nuclear ...

Laboratory column experiments and transport modeling to evaluate retardation of uranium in an aquifer downgradient of a uranium in-situ recovery site

The purpose of this study was to determine the attenuation potential and retardation of uranium in sediments taken from boreholes at the Smith-Ranch Highland in-situ recovery (ISR) site. Five column experiments with four different sediments were conducted to study the effects of variable mineralogy and alkalinity on uranium breakthrough. Uranium transport was modeled with PHREEQC using a generalized composite surface complexation model (GC SCM) with one, two, and, three generic surfaces, respectively. Reactive surface areas were approximated with PEST using BET derived surface areas to constrain fitting parameters. Uranium breakthrough was delayed by a factor of 1.68, 1.69 and 1.47 relative to the non-reactive tracer for three of the 5 experiments at an alkalinity of 540 mg/l. A sediment containing smectite and kaolinite retained uranium by a factor of 2.80 despite a lower measured BET surface area. Decreasing alkalinity to 360 mg/l from 540 mg/l increased retardation by a factor of 4.26. Model fits correlated well to overall BET surface area in the three columns where clay content was less than 1%. For the sediment with clay, models consistently understated uranium retardation when reactive surface sites were restricted by BET results. Calcite saturation was shown to be a controlling factor for uranium desorption as the pH of the system changes. A pH of 6 during a secondary background water flush remobilized previously sorbed uranium resulting in a secondary uranium peak at twice the influent concentrations. This study demonstrates the potential of GC SCM models to predict uranium transport in sediments with homogenous mineral composition, but highlights the need for further research to understand the role of sediment clay composition and calcite saturation in uranium transport.

Time delay and profit accumulation effect on a mine-based uranium market clearing model

The mining industry faces a number of challenges such as market volatility, investment safety, issues surrounding employment and productivity. Therefore, computer simulations are highly relevant in order to reduce financial risks associated with these challenges. In the mining industry, each firm must compete with other mines and the basic target is profit maximization. The aim of this paper is to evaluate the world uranium (U) supply by simulating financial management challenges faced by an individual U mine that are caused by a variety of regulation issues.In this paper front-end nuclear fuel cycle tool is used to simulate market conditions and the effects they have on the stability of U supply. An individual U mine’s exit or entry in the market might cause changes in the U supply side which can increase or decrease the market price. In this paper we offer a more advanced version of a mine-based U market clearing model. The existing U market model incorporates the market of primary U from uranium mines with secondary uranium (depleted uranium DU), enriched uranium (HEU) and enrichment services. In the model each uranium mine acts as an independent agent that is able to make operational decisions based on the market price. This paper introduces a more realistic decision making algorithm of individual U mine that adds constraints to production decisions. The authors added an accumulated profit model, which allows for the profits accumulated to cover any possible future economic losses and the time-delay algorithm to simulate delayed process of reopening a U mine. The U market simulation covers time period 2010–2030 in order to illustrate the evolution of the front end markets under increased demand conditions for nuclear fuel. The offered conception is applicable for other nuclear fuel cycle simulators which contains front-end U market model or can be used with reactor models as a separate model. The model can be used to evaluate economic shocks in U supply or demand.