Search

The luminescence of the uranyl cation UO22+ depends on the local crystalline environment and is sensitive to structural influences. Steady-state photoluminescence emission spectra of the related uranyl silicates uranophane-α, uranophane-β, sklodowskite and haiweeite from various locations are presented and discussed in the light of structure–property relation. The four mineral species were chosen for their close relationships: uranophane-α and uranophane-β are polymorphs and share the underlaying topology with sklodowskite. Haiweeite, with different topology, shares the composing elements Ca, U, Si, O with uranophane, while in sklodowskite Mg replaces Ca. All species show some variability in their spectra, parameterized as a variation of the centroid wavelength. Those variations are linked to defects and structural disorder, relevant in studies of uranyl speciation and migration. We present empiric spectra of the four mineral species with the least influence of structural disorder. As an unexpected feature, a prominent—partly dominating—double peak structure occurs in the case of uranophane-α only, while it is absent in the spectra of the other species. Considering a model of luminescent transitions in the uranyl ion in more detail, this observation is discussed in the light of the polymorphism of uranophane. We show evidence that variable amounts of uranophane-β phase embedded in uranophane-α are possibly at the origin of this spectral signature. Growth of those uranophane-β clusters might be induced by defects in the uranophane-α lattice and further promoted by the polymorphism of uranophane. [ABSTRACT FROM AUTHOR]

The article discusses problems of migration, sorption, and redistribution of uranium in felsic volcanic rocks (ignimbrites) and volcanic glasses of different compositions from the Tulukuev and Novogodnee deposits, located at the upper structural level (the cover of volcano-sedimentary rocks) of the Streltsovka caldera, which hosts Russia's largest Streltsovka uranium ore field (SOF). The research covers the entire sorption series of rocks and minerals: from abnormally high uranium contents in felsic volcanic rocks and volcanic glasses of the Novogodnee deposit, located in a reducing geochemical environment, to complete uranium removal from mineral concentrators in an oxidizing environment in the Tulukuevsky open pit deposit. The uranium distribution and variations in its content were studied using f-radiography in different zones of metasomatic aureoles, minerals, rock fragments, the matrix and fiamme of ignimbrites, elements of deformational alterations, including mineralized and open fractures of different morphology, as well as in cataclasis, microbrecciation, and veinlet zones, etc. Integrated geological-structural, mineralogical-geochemical, and petrophysical studies and hydrogeochemical and isotope-geochemical monitoring studies of fracture-vein and atmospheric waters have been conducted since 2000 and continue at present. It is shown that the Tulukuev and Novogodnee deposits are unique objects, which can be used for studying the conditions, migration paths, migration mechanisms, and accumulation of uranium in different structural settings under varying redox conditions. It was established that the most important mechanism of uranium retardation is sorption processes on permeable reaction barriers under reducing conditions, formed currently within hydraulically active faults, crosscutting blocks of oxidized rocks. At these natural physicochemical barriers, U(VI) is effectively retained and transformed into insoluble U(IV) form due to the reactivity of Fe–Mn oxyhydroxides, impregnated carbonaceous matter, and vital activity products of microorganisms (ferrihydrides). Comparing the sorption capacity of minerals with respect to uranium allowed us to develop a comparative series of minerals and mineral aggregates in descending order from amorphous Fe and Ti oxides to feldspar and quartz. The above studies can be used when substantiating the search, exploration, and mining of uranium ores at uranium-ore deposits and when considering possible sources of ore matter. The radiogeoecological aspect of surveys involved with substantiating the long-term isolation of radioactive materials and remediation of radionuclide-polluted areas and groundwater horizons is also crucial. [ABSTRACT FROM AUTHOR]

Kaolinitization, ferrugination, silicification, and illitization hematitization are the main alteration types recorded in the Gabal (G.) El Sela area, South Eastern Desert, Egypt. These altration zones occur in successive manar as supergene events along faults plane causing mineral redistribution. Uranium mineralization observed in the northern part of Gabal El Sela is mainly controlled by complicated structure regime: faulting, infrastructures, and shearing. So, the northern part of Gabal El Sela area is considered as the most significant and U-fertile part in the studied area. Visible secondary uranium minerals (uranophane and autunite) have been identified and are found to be related mainly to kaolinitized and ferruginated altered samples. Also, pyrite and chalcopyrite can be recorded as reduced Fe bearing minerals in fewer amounts than in hematite and goethite minerals. Finally, the present work confirms that G. El Sela granite is considered as one of the most promising granite plutons in Egypt. The fertility parts are mostly related to the extent of the overlap between the magmatic uranium enrichment, hydrothermal reworking through open fracture system, and suitable reservoir for the leached mineral. The U mineralization may be the result of all these reactions between the granite and the successive fluids. [ABSTRACT FROM AUTHOR]

Heterogeneous equilibria in the system Ca(HSiUO6)2 · 5H2O(c)-aqueous solution were studied over broad ranges of pH, ionic strength, and ionic composition of the solution, and the pH range of stability of Ca uranyl silicate is determined. Hydrolysis products of Ca uranyl silicate are identified, and their solubility is determined. The equilibrium constant of the dissolution reaction and the standard Gibbs function of formation of Ca(HSiUO6)2 · 5H2O are calculated from experimental data, and solubility curves of uranophane and equilibrium speciation diagrams for U(VI), Si(IV), and Ca(II) in coexisting aqueous solutions and solid phases are calculated. [ABSTRACT FROM AUTHOR]

Quartz-diorite, gneissose granodiorites, two-mica granite and perthite leucogranie are the main rock units cropping out in the Wadi Ghadir area, South Eastern Desert of Egypt. Along the NNE-SSW mega-faults, a broad brittle shear zone is developed in the Ghadir two-mica granite. Brittle deformation is manifested by severe mylonitization and alteration of these granites. These sheared altered granites are characterized by the presence of radioactive mineralization, associated with alteration features such as silicification, hematization and kaolinitization. Radioelement measurements revealed that the unaltered and altered two-mica granites are considered as uraniferous granites. The average uranium and thorium contents in the unaltered two-mica granites are 12.29×10 and 19.81×10, respectively, and the average Th/U ratio is 1.62. The altered granites exhibit higher concentrations of U (averaging 97.949), but have lower Th and Th/U ratios (13.83 and 0.16, respectively), which indicates uranium enrichment in the granites. Binary relations of eTh/eU against either eU or eTh and eU with eTh in the studied granites suggest that the distribution of radioactive elements not only magmatic (positive correlation between eU and eTh), but also due to hydrothermal redistribution of radioelements (weak correlation between eU and eTh/eU). The magmatic U and Th are indicated by the presence of uraninite, thorite, zircon and monazite whereas the evidence of hydrothermal mineralization is the alteration of rock-forming minerals such as feldspar and the formation of secondary minerals such as uranophane and pyrite. Microscopic, XRD and scanning electron microscopic studies revealed the presence of uraninite, uranophane, thorite, Ce-monazite and zircon, in addition to phlogopite-fluor mica in the studied altered granites of the Wadi Ghadir shear zone. [ABSTRACT FROM AUTHOR]

This study is concerned with the radioactivity and mineralogy of the younger granites and pegmatites in the Wadi Haleifiya area, southeastern Sinai Peninsula, Egypt. The area is occupied by metasediments, migmatites, older and younger granites. Most of these rocks, especially granites, are dissected by mafic and felsic dykes as well as pegmatites. The younger granites are represented by three main varieties: monzogranites, syenogranites and alkali feldspar granites. The monzogranite consists essentially of quartz, plagioclase, potash feldspar and biotite with minor muscovite. Iron oxide, titanite, zircon and allanite are the main accessory minerals. Syenogranite is massive, medium- to coarse-grained and commonly exhibits equigranular and hypidiomorphic textures. It is made up essentially of potash feldspar, quartz, plagioclase and biotite. Iron oxides, allanite, epidote, titanite, and zircon are accessory minerals. The alkali feldspar granite consists mainly of perthite, quartz, alkali amphibole (arfvedsonite and riebekite), biotite, subordinate plagioclase and aegirine. Iron oxide, zircon and apatite are accessory minerals, whereas chlorite and sassurite are secondary minerals. The altered monzogranite and pegmatite recorded high radioelement contents. The eU reaches up to 120 (av.=82×10) in the altered monzogranite and up to 55 (av.=27×10) in the pegmatites. The high radioactivity in the altered monzogranite is due to the presence of thorite, uranothorite and metamict zircon. In the pegmatites, it is related to the presence of uranophane, uranothorite, thorite, zircon, samarskite, monazite, xenotime, magnetite, ilmenite, hematite and rutile. [ABSTRACT FROM AUTHOR]