Secondary Uranium Research Articles

Using stable oxygen isotope dual-inlet isotope-ratio mass spectrometry to elucidate uranium transport and mixed 230Th/U calcite formation ages at the seminal Devils Hole, Nevada, natural laboratory.

Vein calcite in Devils Hole has been precipitating continuously in oxygen-isotope equilibrium at a constant temperature for over 500 000years, providing an unmatched δ18O paleoclimate time series. A substantial issue is that coeval calcite (based on matching δ18O values) has uranium-series ages differing by 12 000years. An unparalleled high-accuracy δ18O chronology series from continuously submerged calcite was used to correct the published uranium-series ages of non-continuously formed calcite in two cores, cyclically exposed by water-table decline during glacial-interglacial transitions. This method relies on the premise that the δ18O values of coevally precipitated calcite are identical, allowing matching calcite δ18O values to establish formation ages. Exposed calcite can have apparent ages that are 12 000years too young due to unrecognized uranium mobility and resulting mixed ages identified in over 50 mixed uranium-series ages from previous studies. Secondary uranium in fluids, sourced from the formation or dissolution of porous carbonate deposits (folia) with high uranium-238 (238U) concentrations, has migrated up to 10mm into vein calcite. The continuously submerged Devils Hole δ18O chronology is not explained by orbital forcing. Rather, this chronology represents a regional climate record in the southern Great Basin of sea-surface-temperature (SST) variations off California, variations that preceded the last and penultimate deglaciations by 5000 to approximately 10 000years. Temporal discrepancies between the continuously submerged Devils Hole chronology and other regional δ18O records (e.g., the Leviathan chronology) can be explained by unrecognized cryptic, pernicious uranium mobility, leading to model estimations that may be thousands of years younger than actual ages. Consequently, paleo-moisture availability, water-table, and groundwater recharge models based on these mixed uranium-series ages are too young by as much as 12 000years. The potential for post-formation uranium addition in subaerial cores and speleothems underscores the need for caution in uranium-series dating, highlighting δ18O time-series comparisons as a method for identifying mixed ages.

Studies of radioactive minerals and geochemistry of uranium at the granitic rocks of Wadi Um Shillman Area, South Eastern Desert, Egypt

The northwestern part of Gabal Um Ara granitic pluton is represents a good example for uranium occurrence in the southeastern desert of Egypt. Among the different lithologies in the study area, the granitic rocks attract attention for more detailed geological, geochemical and radiometrical studies. Um Ara granitic masses cover an oval outline area of about 300 km2, which is characterised by moderate topography. The granitic rocks are classified as monzogranite and alkali feldspar granite. Both of them belong to the post-orogenic younger granite magmatic activity that intruded the Egyptian shield between 620 and 530 Ma. The intrusion of Um Ara monzogranite and alkali feldspar granite appears to have been controlled by deep-seated tectonic zones and block faulting. The studied area lies at southeast of Aswan City between 22ͦ 38′ 12˝–22ͦ 38′ 34˝ N and 33ͦ 47′ 27˝–33ͦ 48′ 14˝ E. Geochemically, the average concentration of the elements in North Um Ara granite shows that the relative abundance decreases gradually with decreasing incompatibility from Rb to Y. The common features are enrichment in more mobile elements Rb, Th and U. The monzogranite shows the lowest U and Th content, whereas the alkali-feldspar shows an enhanced contents of both elements, with average Th/U ratio = 3.0. the alkali-feldspar exhibits an expanded enrichment of Th relative to U. The U of the alkali-feldspar may be included within the structure of the refractory accessory minerals. The northern part of the Um Ara granitoids has subjected to different types of alterations. The radiometric survey of the northwestern part of Gabal Um area granitic pluton revealed the presence of several radioactive anomalies near the contact with the Dokhan volcanic and metavolcanic rocks in the north. Some visible uranium mineralisation of uranium minerals occur mainly along the NW, NE, E-W and N-S joints, of a highly sheared alkali feldspar-granite. Uranophane is visible secondary uranium mineral, characterised by bright yellow lemon colours and occurs mainly as filling fractures and joints associated with violet fluorite, iron and manganese oxides. The radioactive and accessory minerals studying and X-ray diffraction analysis that of the mineralised alkali feldspar-granite granite in the northwestern part of Gabal Um Ara granitic pluton revealed include the presence of fluorite, zircon, columbite, spessartine garnet whereas, the secondary uranium minerals are represented by uranophane, β-uranophane and kasolite. The hydrothermal origin was proposed as two possible alternatives for this uranium mineralisation.

Interpretation of vertical electrical soundings by means of ISM, PHT and C-N, case of a ditch in Al-Sharquieh phosphate mine in Syria

The main objective of this paper is basically to calibrate and compare the different geoelectrical results obtained by the three interpretative techniques of the inverse slope method (ISM), Pichgin and Habibuleav (PHT) and concentration-number (C-N) fractal modeling with the well lithology of an existing known ditch in the Al-Sharquieh phosphate mine in Syria. Those interpretative techniques are applied herein to interpret the vertical electrical soundings (VES) points measured along a parallel profile to the ditch. ISM reveals the presence of four to five geoelectrical layers in the study region. The PHT allows the determination of the tectonic subsurface features of the study region, by analyzing the non homogeneity points and their distributions along a given geoelectrical profile. The fractal C-N modeling provides the different apparent resistivity ranges dominating in the study region. Good agreements are obtained between the direct observed field lithological descriptions of both wall sides of this ditch, and the results obtained by those three interpretative geoelectrical techniques. The high radioactive readings exceeding four hundred count per second (cps) are due to the presence of secondary uranium accompanied with fractures, cracks and joints. The secondary uranium occurrences accompanied by phosphate deposits are found in the study area in the fractured zones, as determined by the geoelectrical PHT technique. The three mentioned geoelectrical methodologies are therefore used as indirect techniques for delineating the radioactive zones related to uranium prospecting. It is a successful application of the joint use of those three techniques, that could be applied in mining to delimit the subsurface geological structure. The reliability and efficacy of (ISM), (PHT), and (C-N) fractal modeling techniques are consequently well confirmed, and it is therefore recommended to use and apply them for characterizing and describing similar lithological phosphatic sequences, and for several shallow mining, environmental and civil engineering applications.

Multiproxy provenance analyses in the Devonian Villavicencio Formation of the Mendoza Precordillera, Argentina: correlation and geotectonic implications for the SW Gondwana margin

Abstract This work focuses on the sedimentary provenance of the Villavicencio Formation of the Mendoza Precordillera and integrates the information obtained with previous work on other coeval units of the Precordillera Central of San Juan province (Gualilán Group: Talacasto and Punta Negra formations) in western Argentina. Multiproxy provenance analyses are carried out from different applied methodologies (petrography, geochemistry, morphological, and cathodoluminescence studies of detrital zircon grains, and analysis of U-Pb and Lu-Hf isotopes). The Villavicencio Formation is mostly composed of pelites and very fine-grained psammites. The major components are quartz, both monocrystalline and polycrystalline, and metamorphic lithics that associate this unit with a recycled orogen. Regarding geochemistry, the Chemical Index of Alteration (CIA) values are similar to the Post-Archean Australian Shales (PAAS), indicating a null to incipient degree of weathering. The ratios between different trace elements and rare earth elements (REEs) suggest the felsic composition of the source area. Th/U ratios differ, but a secondary uranium enrichment is inferred. The morphological analysis of the zircon grains reveals their mainly plutonic origin. The integration of U-Pb data with Lu-Hf data shows a juvenile-mantle origin in which the populations are dominantly Mesoproterozoic and ɛHf of positive values (up to 12), indicating poor differentiation. The Villavicencio Formation would be the product of deltaic deposits in which its components are dominantly from the Western Pampean Sierras associated with the Grenville orogen, assuming exhumation and erosion of the Mesoproterozoic basement. The data support the hypothesis of equivalence and correlation with the Punta Negra Formation in the Devonian depocenters of the south-central region of the San Juan Precordillera.

Petrochemistry, rare metals-bearing minerals and spectrometric exploration in Khour Abalea, Abu Rusheid area, Eastern Desert, Egypt

On the Red Sea coast, Abu Rusheid area is located south Marsa Alam City (90 km) in the south Eastern Desert. Khour Abalea as a part of the Abu Rusheid area extends for about 1.0 km in E-W direction. It is subdivided into two main branches; the first one (the longest) extends about 0.7 km in E-W direction with 10–30 m in passing through mylonites, whereas the second branch extends about 0.5 km in ENE-WSW with about 5–20 m in width and passing through mylonites and ultra-mylonites. Microscopically, this rock is composed mainly of k-feldspars, plagioclases, biotite, and quartz as the main minerals, while the accessories include fluorite, allanite, secondary uranium (kasolite), and zircon. The hydrothermal alteration that occurs during the interaction of hydrothermal fluid and rock results in an M-W type tetrad effect range of 1.72–3.66 in the normalized REE chondrite patterns of the Khour Abalea mylonite rocks. The identified heavy minerals associated with Khour Abalea mylonite rocks can be categorized as a) radioactive minerals (soddyite, kasolite, thorite and uranothorite), b) rare earth minerals (monazite, xenotime and rare earth silicate), c) Nb–Ta minerals (columbite, fergusonite, ishikawaite and aeschynite), d) precious metals (gold, silver minerals (argentite, arcubisite and matildit), e) base metals (cassiterite, wolframite, chalcocite, galena, sphalerite pyrite and Bi minerals (bismite, bismuthinite and perite) and f) accessory mineral (zircon). According to the uranium mobilization equations, there are uranium enrichment in Khour Abalea mylonite.

Distinguishing secondary uranium mineralizations in uranium ore using LIBS imaging

The main aim of this work is to demonstrate the potential of LIBS as a complementary technique to electron probe microanalysis (EPMA) for distinguishing and characterizing uranium mineralizations. Combining both methods can help estimate uranium oxidation states and monitor the possible mobilization of uranium in the environment by detecting oxygen and hydrogen using LIBS. It was confirmed that the LIBS signal of oxygen is proportional to oxygen content and that the strength of the oxygen signal is closely related to the oxidation state of uranium. The second assumption that the hydrogen signal is closely related to water (or hydroxyl group) content was also confirmed by detecting a stronger hydrogen signal from the presumed secondary mineralization. In contrast, hydrogen was not found in uraninite and quartz.When superimposed, images obtained with LIBS and EPMA show a clearly visible contrast between primary and secondary uranium mineralizations. Images of uranium obtained with the two techniques match perfectly, while the LIBS image of oxygen confirms the presence of an oxidized form of secondary uranium minerals (uranophane). The LIBS image of hydrogen clearly shows mineral phases containing water or a hydroxyl group, confirming that uranophane and other associated minerals contain greater amounts of hydrogen (water).

X-Ray Diffraction in Mineralogical Research

A brief account of role of X-ray diffraction (XRD) in mineralogical research with special reference to radioactive and atomic minerals is given. Aspects of research methodology such as sample preparation, analysis time, limitations, search match methods for identification, and complimentary techniques are also given. The most common applications of XRD in mineralogical researches related to radioactive/atomic minerals include identification of primary and secondary uranium and associated ore and gangue minerals, determination of the oxidation grade of uraninites, identification of Th, Nb, Ta, Sn, Be, Li, Zr, Hf, Ti, rare-earth elements (REE) minerals, investigations on degree of structural disordering in Nb-Ta minerals, X-ray crystallographic and substitutional solid solution studies, clay minerals, triclinicity of K-feldspar, metamict minerals and influence of the degree of metamictisation on uranium beneficiation, characterisation of leached residue, beneficiated, heat-treated products, metallurgical slags and other mineralogical studies. The results of mineralogical research are used for elucidating physicochemical conditions and geologic processes that prevailed during mineral formation

X-Ray Diffraction in Mineralogical Research

A brief account of role of X-ray diffraction (XRD) in mineralogical research with special reference to radioactive and atomic minerals is given. Aspects of research methodology such as sample preparation, analysis time, limitations, search match methods for identification, and complimentary techniques are also given. The most common applications of XRD in mineralogical researches related to radioactive/atomic minerals include identification of primary and secondary uranium and associated ore and gangue minerals, determination of the oxidation grade of uraninites, identification of Th, Nb, Ta, Sn, Be, Li, Zr, Hf, Ti, rare-earth elements (REE) minerals, investigations on degree of structural disordering in Nb-Ta minerals, X-ray crystallographic and substitutional solid solution studies, clay minerals, triclinicity of K-feldspar, metamict minerals and influence of the degree of metamictisation on uranium beneficiation, characterisation of leached residue, beneficiated, heat-treated products, metallurgical slags and other mineralogical studies. The results of mineralogical research are used for elucidating physicochemical conditions and geologic processes that prevailed during mineral formation

Single-Well Push–Pull Tracer Test Analyses to Determine Aquifer Reactive Transport Parameters at a Former Uranium Mill Site (Grand Junction, Colorado)

At a former uranium mill site where tailings have been removed, prior work has determined several potential ongoing secondary uranium sources. These include locations with uranium sorbed to organic carbon, uranium in the unsaturated zone, and uranium associated with the presence of gypsum. To better understand uranium mobility controls at the site, four single-well push–pull tests (with a drift phase) were completed with the goal of deriving aquifer flow and contaminant transport parameters for inclusion in a future sitewide reactive transport model. This goes beyond the traditional use of a constant sorption distribution coefficient (Kd) and allows for the evaluation of alternative remedial injection fluids, which can produce variable Kd values. Dispersion was first removed from the resulting data to determine possible reactions before conducting reactive transport simulations. These initial analyses indicated the potential need to include cation exchange, uranium sorption, and gypsum dissolution. A reactive transport model using multiple layers to account for partially penetrating wells was completed using the PHT-USG reactive transport modeling code and calibrated using PEST. The model results quantify the hydraulic conductivity and dispersion parameters using the injected tracer concentrations. Uranium sorption, cation exchange, and gypsum dissolution parameters were quantified by comparing the simulated versus observed geochemistry. All simulations required some cation exchange and calcite equilibrium, and one simulation required gypsum dissolution to improve the model fit for calcium and sulfate. Uranium sorption parameters were not strongly influenced by the other parameter values but were highly influenced by uranium concentrations during the drift phase, with possible kinetic rate limitations. Thus, a future recommendation for such push–pull tests is to collect more geochemical data during the drift phase. The final uranium sorption parameters were within the range of values determined from prior column testing. The flow and transport parameters derived from these single-well push–pull tests will provide initial parameters for any future sitewide reactive transport model.

Filling the gaps of uranium oxide hydrates with magnesium(II) ions: unique layered structures and the role of additional sodium(I) ions.

Alkaline earth metal ions play an important role in the formation of secondary uranium minerals due to their abundance in the Earth's crust. Although uranium oxide hydrate (UOH) minerals and synthetic phases with calcium, strontium and barium ions have been investigated, their counterparts with magnesium ions are much less studied. In this work, synthetic UOH materials with magnesium ions have been investigated with three new compounds being synthesised and characterised. Compound Mg2(H3O)2(H2O)6[(UO2)3O4(OH)]2 (U-Mg1 with a U : Mg ratio of 3 : 1) crystallises in the monoclinic P21/c space group having a layered crystal structure, constructed by β-U3O8 layers with 6-fold coordinated Mg2+ ions as interlayer cations. Compound Na2Mg(H2O)4[(UO2)3O3(OH)2]2 (U-Mg2p with U : Mg : Na ratios of 6 : 1 : 2) crystallises in the triclinic P1̄ space group having a layered structure, constructed by a unique type of uranium oxide hydroxide layer containing both α-U3O8 and β-U3O8 features, with alternating layers of 6-fold coordinated Mg2+ and 6-/8-fold coordinated Na+ interlayer cations. Compound Na2Mg(H2O)4[(UO2)4O3(OH)4]2 (U-Mg2n with U : Mg : Na ratios of 8 : 1 : 2) crystallises in the triclinic P1̄ space group having a corrugated layer structure, constructed by a unique type of uranium oxide hydroxide layer with mixed 6-fold coordinated Mg2+ and 7-fold coordinated Na+ interlayer cations. The structural diversity in the UOH-Mg system was achieved by adjusting the solution pH using NaOH, highlighting the importance of solution pH control and the additional Na+ ions in the formation of UOH phases. The extra structural flexibility offered by the Na+ ions emphasizes the opportunity for synthesising UOHs with dual-cations to further improve our understanding of the alteration products of spent nuclear fuel under geological disposal.

Overview on Uranium with Emphasis on Surficial Uranium Deposits in Egypt

This overview addresses uranium ore deposition and classification, mining and refining of uranium are briefly given. The main properties of primary and secondary uranium minerals are reported. The surficial uranium deposits account for approximately 4% of world uranium resources, defined as young uraniferous sediments and soils - Tertiary to Recent - near surface. The major controlling factors effect the world distribution of surficial uranium deposits are reported in details such as : climate, source, Tectonic as controlling factor led difference in relief topography and basin configuration, morphology, stratigraphy, permeability and porosity, tectonics, source and transport, mineralogy and geochemistry, evaporation processes and the interaction between basement source carrying waters and evaporative vertical. Micro- organisms which play an important roles and responsible for predominance of anaerobic bacteria controlling and enriching the U- bearing minerals (Bio- enrich). Finally, comprehensive outline on surficial depositions in Egypt is given, reviewed examples in Egypt, suggest the strong probability of surficial uranium existence (Bahariya, Sitra lakes, Fayium, Tushki basins and Ras Shukeir), moreover the Siwa oasis can represent indicative recent simulator for formation processes. Presence of carnotite in Sinai support the prevalence of similar controlling factors governs the Australia examples

Crystal Chemistry and Structural Complexity of the Uranyl Carbonate Minerals and Synthetic Compounds

Uranyl carbonates are one of the largest groups of secondary uranium(VI)-bearing natural phases being represented by 40 minerals approved by the International Mineralogical Association, overtaken only by uranyl phosphates and uranyl sulfates. Uranyl carbonate phases form during the direct alteration of primary U ores on contact with groundwaters enriched by CO2, thus playing an important role in the release of U to the environment. The presence of uranyl carbonate phases has also been detected on the surface of “lavas” that were formed during the Chernobyl accident. It is of interest that with all the importance and prevalence of these phases, about a quarter of approved minerals still have undetermined crystal structures, and the number of synthetic phases for which the structures were determined is significantly inferior to structurally characterized natural uranyl carbonates. In this work, we review the crystal chemistry of natural and synthetic uranyl carbonate phases. The majority of synthetic analogs of minerals were obtained from aqueous solutions at room temperature, which directly points to the absence of specific environmental conditions (increased P or T) for the formation of natural uranyl carbonates. Uranyl carbonates do not have excellent topological diversity and are mainly composed of finite clusters with rigid structures. Thus the structural architecture of uranyl carbonates is largely governed by the interstitial cations and the hydration state of the compounds. The information content is usually higher for minerals than for synthetic compounds of similar or close chemical composition, which likely points to the higher stability and preferred architectures of natural compounds.

Uraniferous Leucogranites in the Rössing Area, Namibia: New Insights from Geologic Mapping and Airborne Hyperspectral Imagery

Abstract This study combines historical exploration data with new mapping, underpinned by airborne hyperspectral imagery, to provide a detailed camp-scale geologic view of the Rössing uranium mine area in the Damara orogen, Namibia. The Neoproterozoic Damaran metasedimentary host rocks to uranium deposits of the Rössing area structurally overlie Paleoproterozoic basement rock. Both units were subjected to polyphase deformation and upper amphibolite to lower granulite facies metamorphism during Pan-African orogenesis. The sequence was voluminously intruded by leucogranites, where younger phases may contain ore-grade uranium as magmatic uraninite and traces of betafite, together with secondary uranium minerals. Early, postdepositional modifications to the Damaran sequence included partial dolomitization of marble units and development of evaporite dissolution and diapiric breccias. Major pre-D3 extensional structures developed in conjunction with recumbent, isoclinal folding and acted to focus the intrusion of early, mostly barren leucogranites generated primarily through anatexis of Damaran metasediments. Syn-D4 leucogranites overprint complex interference fold geometries that resulted from D3 deformation. D4 leucogranites were emplaced under predominantly ductile, transtensional conditions, into NNE-trending zones oriented highly oblique to all preexisting structures. These steeply dipping zones provided the prerequisite conditions for partial melt material to be derived from uraniferous basement lithologies. The concentration of magmatic uranium was promoted where leucogranite melt material interacted with carbonates and sulfide-bearing Damaran metasedimentary units. In the Rössing area these horizons occur at the Khan-Rössing Formation contact zone for the SJ, SK, SH, Z20, and Husab deposits and within and above the Arandis Formation for the Z19 deposit leucogranites.

Natural radioactivity and geochemical aspects of radioactive mineralisation in El Sela, South Eastern Desert, Egypt

ABSTRACT The natural radioactivity data revealed that eU reached up to 157.4, 1625 and 178 ppm in microgranite and dolerite dikes as well as japer vein, respectively, whereas the two-mica granite possesses the higher eTh-contents up to 53.8 ppm. Mineralogically, the two-mica granite is enriched in thorite, brockite and uranothorite, whereas uraninite and coffinite are recorded in dolerite, and the latter one is recorded in microgranite, bostonite and jasper. Primary uranium minerals as uraninite and coffinite could be a source for uranium enrichment and the formation of secondary uranium mineralisation. Uranium mobilisation was active towards the two perpendicular shear zones having NNW-SSE and ENE-WSW rejuvenated trends. Successive hydrothermal alterations play their role in the formation of uranium ore deposits to be trapped in post-granitic dikes.

Stable isotope signatures of hydration water in secondary mineralization on UO2

Hydrated secondary mineralization readily forms on the surface of UO2 particles exposed to humidity in an oxidizing environment. The oxygen stable isotope composition of the secondary uranium oxide may reflect that of the water vapor, as well as the hydrogen and oxygen stable isotopic composition of the mineral hydration water. The geospatial organization of δ2H and δ18O values of atmospheric humidity and precipitation is increasingly well understood, which suggests that the hydrogen and oxygen stable isotopes in secondary mineral hydration water may yield information on the environment in which the mineralization formed. UO2 powders were exposed to air with constant 30%, 61%, and 91% relative humidity, and constant H and O stable isotope composition. Aliquots were sampled from the UO2 materials at intervals of 1–10 days through the total humidity exposure duration of 180 days. Scanning electron microscopy, transmission electron microscopy, and x-ray diffraction analysis of the humidity-exposed UO2 indicates that schoepite/metaschoepite [(UO3)•2H2O] secondary phases had formed on the underlying UO2. The δ2H and δ18O values of mineral hydration waters were determined by thermogravimetry-enabled isotope ratio infrared spectroscopy (TGA-IRIS). Results indicate that hydrogen in the surface sorbed and mineral hydration waters is exchangeable and thus their δ2H values are difficult to interpret. However, oxygen in these waters is less exchangeable, and thus the oxygen stable isotope composition of the schoepite/metaschoepite hydration water is likely to be related to that of the exposure water vapor. After formation of schoepite/metaschoepite, the δ18O values of the hydration water in schoepite/metaschoepite does not change in response to changes in exposure vapor δ18O values, which suggests that the δ18O values of the hydration water is relatively durable. These findings suggest that information about the origin and storage history of a UO2 sample may be discernable from δ18O values of schoepite/metaschoepite hydration water.

Interpretation of aerospectrometric, aeromagnetic and geochemical data, Um-Alhuweitat basin area, Central Eastern Desert, Egypt

This study presents the analysis of airborne gamma-ray spectrometry and aeromagnetic data to delineate the distribution of the radioactive elements and determine their anomalous zones, subsurface structures controlled mineralized zones, and 3D magnetic inversion to give a full view of basement relief. According to statistical treatment of airborne gamma-ray spectrometry measurements, the highest values of potassium and equivalent thorium associated with Nakhiel Formation are 3.2% and 12.8 ppm respectively. Meanwhile, the equivalent uranium associated with phosphate beds attains 19.1 ppm. The spatial distribution of the relatively high concentrations of eU, eU/K and eU/eTh are recorded in adjacent areas in Upper Cretaceous deposits as > 12, 25 ppm and 5 ppm for eU, eU/K and eU/eTh, respectively.According to field measurements, the highest values of eU associated with phosphate beds and black Shale are 117 ppm and 20 ppm respectively. Meanwhile, the highest value of potassium associated with Quaternary sediments is 2.9%. Moreover, the highest value of eTh associated with Taref Formation is 16.2 ppm. The geochemical studies of collected samples from the anomalous zones showed the presence of secondary uranium in addition to rare earth elements. Meanwhile, the black shale trace elements are measured and showed high concentrations of tungsten. The magnetic data analysis is performed using tilt derivative and 3D magnetic modeling methods. Most of the deduced structures are trending in NW–SE, and NE–SW directions. The depths to the basement rocks are ranged from 0.475 km to 1.07 km below the ground surface.

Bio-sorption of uranium by saragassum detifolium from the trachytic sills of Wadi El Atshan area, central eastern desert, Egypt

In wadi El Atshan area, Central Eastern Desert of Egypt, the main rock types exposed in that area are the older granites, Hammamat sedimentary rocks, younger granites, trachytic sills and dikes. The Field studies and radiometric survey indicate that the trachytic sills are the main rock type in the investigated area which contain secondary uranium minerals. Sargassum detifolium is used to capture uranium from the trachytic sills. The analysis indicates that this alga absorbs the uranium content by 100% in two samples where happened in the other samples as well as, it changes the chemical composition of some minerals content, while some elements changed while other elements are decreased, Sargassum detifolium has the ability to biosorbe uranium content about 75% as in uranotile mineral {CaU2 (SiO4)2(OH)6.3H2O}.

Characteristics of Uranium Mineralization in Red Clastic Formations in the Southwestern Margin of the Ordos Basin

AbstractIn the southwestern margin of the Ordos Basin, uranium mineralization is primarily hosted by predominantly oxidative red clastic formations in the Lower Cretaceous. The main target layers for uranium exploration are the Madongshan and Liwaxia formations of the Liupanshan Group, followed by the Jingchuan Formation of the Zhidan Group. The host rocks (medium‐fine feldspar quartz sandstone), which are bleached to a light grayish white color, contain a minor organic matter component and pyrite. Uranium mineralization changes from surficial infiltration or phreatic oxidation in the upper part to interlayer oxidation in the lower part. Uranium ore bodies are mostly lenticular or tabular in shape, locally shaped like crescent rolls. Individual ore bodies are typically small and shallow. Uranium predominantly manifests as pitchblende and coffinite. Coffinite is usually short and columnar or granular in habit, whereas pitchblende occurs as an irregular colloidal covering on the surface or in fissures of ferric oxide, silicate, clay or carbonate. Secondary uranium minerals are torbernite, uranophane, and uranopilite. Minerals associated with uranium are mainly pyrite, chalcopyrite and, to a minor extent, arsenopyrite and fluorite. The associated elements are Mo, V, Se, Co, Ni, and Mn, the host sandstone being high in Cu and Ba. Overall, the red clastic formations in the southwestern margin of the Ordos Basin are characterized by ‘five multiples but one low’ which means multiple target layers, multiple stages of mineralization, multiple ore body shapes, multiple kinds of uranium minerals, multiple associated elements, but low organic matter. This implies an overall complex uranium metallogenic environment and mineralization process. It is recommended that future uranium exploration should take into consideration regional metallogenic conditions and mineralization features, with target layers in the wide‐smooth synclinal slope being focused on. Most uranium deposits are small to medium in size, and the main type of uranium mineralization can vary by target layer.

Hydrochemical evolution of high uranium, fluoride and nitrate groundwaters of Namakwaland, South Africa

Water quality globally suffers from overuse and pollution, but desert areas with high evaporation rates and groundwater as the only water source have additional challenges. Namakwaland in the Northern Cape is an arid region with a sparse human population dependent largely upon stock farming, with minor mining and tourism. The complex Proterozoic metamorphic geology is overlain by Cenozoic deposits known for containing secondary uranium mineralisation in places. 86 samples of groundwater were taken over an area of 25 000 km2 and analysed for various parameters in the field and laboratory. The salinity of the water varies from fresh to sea water, averaging 2500 mg/L, with pH in the 7–9 range. Major ion abundances indicate marine aerosol as the main source of Cl, Na, Mg and K, with rock weathering being more responsible for Ca and HCO3. Irrigation water quality tests give mixed results, suggesting careful use of groundwater is possible in some locations. Nitrate is occasionally high, the random distribution indicating farm animals as the source. Fluoride averages 2.4 mg/L and is strongly geologically controlled, but also enriched through evaporation. Uranium, averaging 0.155 mg/L (5 times the guideline), has a complex distribution, poorly correlated to bedrock geology and shows two enrichment trends, one in tandem with other ions and one independent. These two trends are proposed to reflect enrichment through evaporation (other ions also increasing) or precipitation of secondary uranium minerals (limited correlation with other ions). These three parameters are uncorrelated, which emphasizes the variety and complexity of hydrochemical processes taking place. Given the U and other water quality risks, further work into cumulative exposure for plants, animals and humans is warranted.

Factors controlling in the concentration of gold and uranium in the Lower Carboniferous marl at Wadi El Kharig area, Southwestern Sinai, Egypt

The Lower Carboniferous middle member of Um Bogma Formation at Wadi El Kharig composed mainly of marl and interbedded dolostone with pockets of gibbsite and marly gibbsite. The organic carbon (related to the presence of organic matter) reaches 2.31%, 6.39%, and 1.36% in the marly gibbsite, black gibbsite, and marl, respectively. The black gibbsite and marly gibbsite have high concentrations of some metals such as Zn, Cu, Ba, and Ni than that in the marl. New detection of high radioactive anomalies was recorded at Wadi El Kharig in the marly gibbsite, black gibbsite, and marl of the middle member of Um Bogma Formation with an average of U-content reaches 342, 726.3, and 229 ppm, respectively. Metatorbernite, carnotite, and autunite are the main secondary uranium minerals recorded in the radioactive facies. Also, new occurrences of gold were recorded at Wadi El Kharig in the marl (1.2 ppm) and its interbedded dolostone (1.4 ppm) of the middle member of Um Bogma Formation. Carbonaceous material and/or organic matter in addition to the presence of iron oxides are playing important roles in the concentration of Au and U and some metals in the studied facies.