Diagenesis of paleodrainages in Lake Way and Lake Maitland, Western Australia, and the role of authigenic Mg-clays and dolomite in the genesis of channel and playa uranium deposits

ABSTRACT This study integrates mineralogical and hydrogeochemical analysis of channel and playa uranium deposits to characterize aquifer evolution and the physico-chemical mechanisms that result in the accumulation of uranium into potentially economic deposits. This subset of surficial U deposits occur in Tertiary to Recent calcrete and dolomitic, clay-rich fluvial paleochannel and palustrine sediments, wherein uranium is largely bound in the potassium-uranyl-vanadate mineral carnotite [K2(UO2)2(VO4)2·3H2O]. Scanning electron microanalysis indicates that the carnotite mineralization is part of a late-diagenetic mineral assemblage that critically includes Mg-clays (sepiolite and stevensite), amorphous magnesium silicate, and synsedimentary dolomite. This authigenic mineral assemblage is observed concentrated in fractures and pores in groundwater calcrete and silty salt marsh “palustrine” sediments. Drill-hole gamma ray and conductivity data from the Centipede-Millipede uranium deposit indicate that the locus of uranium mineralization occurs near the present-day water table where oxidizing fresh-to-brackish groundwater interacts with playa brine, forming a hypopycnal groundwater estuary beneath the clay pan and salt marsh. It is interpreted that effective U fixing occurs in areas where groundwater, near-saturated with respect to carnotite, is hydrologically focused upward and into the zone of evaporation. The appreciable precipitation deficit in the Northern Yilgarn is interpreted to produce an evaporation-driven positive feedback mechanism that results in the co-precipitation of Mg-clays, dolomite, and carnotite. The presence of vanadium-rich Mn-oxide phases in high-grade U ore zones indicates that Mn-redox cycling may serve an important role in increasing the local activity of V, and thus carnotite saturation. Mineralogical comparison of other channel and playa uranium deposits throughout Western Australia and Namibia have identified a similar mineral association and paragenetic trend, suggesting that contemporaneous evaporative precipitation of Mg-clays and dolomite are integral in achieving carnotite saturation and precipitation.

Rare-Metal (In, Bi, Te, Se, Be) Mineralization of Skarn Ores in the Pitkäranta Mining District, Ladoga Karelia, Russia

The results of the study of rare-metal (Bi, Te, Se. Be, In) mineralization of skarn deposits (Sn, Zn) in the Pitkäranta Mining District, genetically related to the Salmi anorthosite-rapakivi granite batholiths of Early Riphean age are reported. Minerals and their chemical composition were identified on the base of optical microscopy as well as electron microanalysis. The diversity of rare-metal ore mineralization (native metals, oxides, and hydroxides, carbonates, tellurides, selenides, sulfides, sulphosalts, borates, and silicates) in Pitkäranta Mining District ores is indicative of considerable variations in the physicochemical conditions of their formation controlled by the discrete-pulse-like supply of fluids. Bismuth, wittichenite, and matildite are the most common rare-metal minerals. Sulfosalts of the bismuthinite-aikinite series are represented only by its end-members. The absence of solid solution exsolution structures in sulfobismuthides suggests that they crystallized from hydrothermal solutions at low temperatures. Be (>10 minerals) and In (roquesite) minerals occur mainly in aposkarn greisens. Roquesite in Pitkäranta Mining District ores formed upon greisen alteration of skarns with In released upon the alteration of In-bearing solid sphalerite (Cu1+ In3+) ↔ (Zn2+, Fe2+) and chalcopyrite In3+ ↔ Fe3+ and 2Fe3+ ↔ (Fe2+, Zn2+) Sn4+ solutions. Sphalerite with an average In concentration of 2001 ppm, is a major In-bearing mineral in the ores.

Spin and valence dependence of iron partitioning in Earth’s deep mantle

We performed laser-heated diamond anvil cell experiments combined with state-of-the-art electron microanalysis (focused ion beam and aberration-corrected transmission electron microscopy) to study the distribution and valence of iron in Earth’s lower mantle as a function of depth and composition. Our data reconcile the apparently discrepant existing dataset, by clarifying the effects of spin (high/low) and valence (ferrous/ferric) states on iron partitioning in the deep mantle. In aluminum-bearing compositions relevant to Earth’s mantle, iron concentration in silicates drops above 70 GPa before increasing up to 110 GPa with a minimum at 85 GPa; it then dramatically drops in the postperovskite stability field above 116 GPa. This compositional variation should strengthen the lowermost mantle between 1,800 km depth and 2,000 km depth, and weaken it between 2,000 km depth and the D” layer. The succession of layers could dynamically decouple the mantle above 2,000 km from the lowermost mantle, and provide a rheological basis for the stabilization and nonentrainment of large low-shear-velocity provinces below that depth.

Plaster Pigments in Traditional Folk Architecture - A Case Study from Moravia (Czech Republic)

The results of analyses of coloured plasters are given in the paper. The samples come from traditional folk earth houses from SE and Central Moravia and were chosen so as all of the most common colours of the Central European folk architecture are present among them: red, yellow, blue, green, and black. The analyses were conducted by the means of light microscopy, which is also a powerful tool for stratigraphical analyses, X-ray diffractometry, Raman spectrometry, end electron microanalysis. Hematite of industrial origin was identified as the red pigment, the yellow one was formed by yellow earth, which also may be a precursor for traditional production of red dye. The widest used blue pigment was ultramarine in the 19th and the first half of 20th century in Moravia. The analysed green pigments were formed by an organic dye of green earth and the black one consisted of soot. Based on the sort and composition of pigment and plaster, the age of the material is also discussed.

Effect of Methyl Cellulose on Apatite Formation of a Sol-Gel Derived Bioactive Glass/Titania Nanostructure Composite

In order to widen the application range of bioactive glass (BG), we prepared a bioactive glass as a composite matrix, strengthened by titania nanoparticles. The prepared composites had different amounts of both bioactive glass (49S) and titania in the weight percents of 1:3, 1:1 and 3:1, respectively. Bioactive glass sols (49S) in the system (SiO2CaOP2O5) were prepared following the solgel technique, then a solution of 2 wt% methylcellulose was added and stirred at room temperature. Precalcinated TiO2 nanopowder was dispersed in the sol and the prepared mixture was fired at 600 °C. The inhomogeneity problem in preparation of composite powder was overcome by using methylcellulose (MC) as a dispersant. The nanostructure composites were characterized using X-ray diffraction (XRD) and Fourier transforms infrared spectroscopy (FT-IR). The microstructure of the surfaces of the different composites was examined by scanning electron microanalysis (SEM) to verify the apatite formation. The results led us to the conclusion that the addition of MC reinforces the composites and increases the formation of an apatite layer in the presence of BG and titania content.

Sectioning of Individual Hematite Pseudocubes with Focused Ion Beam Enables Quantitative Structural Characterization at Nanometer Length Scales

A dual-beam focused ion beam microscope equipped with a nanomanipulator was used to fabricate slices from within individual hematite (α-Fe2O3) pseudocubes with selected orientations with respect to the original pseudocubes. Transmission electron microanalysis through selected area electron diffraction enabled assignment of each thin section to a particular zone of the hematite lattice. While the pseudocubes are composed of numerous crystallites, 25–50 nm in size, they are not simply polycrystalline particles. Electron diffraction of thin sections showed that while the pseudocubic hematite particles are composed of numerous coherent domains, the individual thin sections display a net crystallographic orientation to the underlying hematite lattice. Quantitative analysis of the lattice misorientation between coherent domains was calculated from the azimuthal spread of electron diffraction peaks and is consistent with a structure that contains small-angle grain boundaries. Based upon this analysis, we conclude that the pseudocubic hematite particles are mosaic crystals, composed of highly oriented coherent domains.

Influence of Preparation Parameters on Properties of Belite Clinker

Low-lime saturated belite clinkers were prepared under different regimes of burning in the laboratory. Development of compressive strengths of the obtained belite clinkers was evaluated in relation to the reactivity of raw meals, burning temperature and time, and degree of lime saturation. Electron and optical microscopy, X-ray diffraction analysis and high-temperature microphotometry were the methods used for characterization of belite clinkers. It was discovered that the quickly-burnt belite clinker has unexpectedly lower hydraulic activity with respect to the longer-time burnt, recrystallized clinker. The reason could be little contamination of its crystal lattice by secondary oxides as determined by electron microanalysis.