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The presence and nature of uranium minerals subject to high leachability is one of the most significant factors in the exploitation of low-grade ores. The detection of these minerals is a challenging task due to their small size and low abundance. This paper presents a novel method of data processing that allows distinguishing and visualization of micron-scale U minerals. For this purpose, core samples of U-bearing sandstones from the Břevniště deposit (Czech Republic) were used. After their study by inductively coupled plasma spectroscopy, optical and scanning electron microscopy (SEM-EDS) and X-ray diffraction analysis, the presence of authigenic grains of U minerals occurring in various associations and their chemical compositions were confirmed by an electron microprobe. However, the use of these conventional instruments for the analysis of heterogeneous ore material with valuable information hidden, showed the necessity for a special data treatment. Matrix transformation of raw SEM-EDS data allowed for even more accurate visualizations such as contour and point maps of elemental distribution. Then, mathematical and visual correlations of transformed data revealed relationships among some measured elements (Ca, P, U, Zr, Nb, Fe, S) and their spectral overlaps. Conditions of ore formation were predicted based on the visualizations, correlations and the paragenesis of ningyoite in uranium ore. Herein suggested approach can help to identify economically significant minerals in complex mineralizations worldwide and increase the mining potential of the deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multi-instrumental approach for study of low-grade U-Zr mineralization was tested. • Mineral identification and distribution was observed by automated mineralogy. • X-ray micro-computed tomography was used for visualization of U-rich domains. • Proportions of U-bearing phases determined by different methods were compared. Multi-level visualization of U-Zr mineralization in sandstones is discussed, aiming at the identification of mineral phases, imaging of their distribution using 2D and 3D projections, and quantification of the presence of U-rich domains. For this purpose, uranium-bearing sediments with anomalous concentrations of Zr, Nb ± Fe, Sr were studied (Břevniště deposit, Czech Republic). The applied multi-instrumental approach included selection of the most suitable areas in core samples (highest U and Zr concentrations) using X-ray fluorescence analysis (XRF). The presence of numerous detrital and authigenic accessories, hardly discernible using optical methods, was confirmed with the use of automated mineralogical analysis (TIMA). Hydrozircon and metacolloidal mixed phases were shown to be the carriers of uranium. Their close relationship to sulfides, Fe oxyhydroxides and clay minerals was documented using phase distribution maps. X-ray micro-computed tomography (μ CT) was used for the visualization of internal structures of uranium-bearing sandstones. Based on a series of thresholding of μ CT data, segmentation of selected samples was performed with subsequent visualization of selected mineral phases. The combination of TIMA and μ CT analysis allowed for an effective discrimination of U-rich areas and quantification of their volume. This approach provides new possibilities in imaging elementary complex disseminated uranium mineralizations. [ABSTRACT FROM AUTHOR]

• Abilities of a unique XRF analyzer for study of low-grade U-sandstone were tested. • Distributions of U–Zr and other elements were observed in large natural samples. • Correlations were used for verification of geochemical coherence among elements. Analytical capabilities of X-ray fluorescence for 2-dimensional elemental analysis were tested on worldwide-unique sandstone-hosted U–Zr mineralization (Bohemian Cretaceous Basin, Czech Republic), and combined with measured spectral data. The applied approach was aimed at the detection of uranium and zirconium, visualization of their distribution across mineralized lithological units and description of their relationships with associated elements (As, Fe, Nb, Pb, Sr, Ti). The studied samples were low-grade uranium-bearing sediments. Experimental work employed laboratory 2D scanning X-ray fluorescence analyzer with the gold target Mini-X X-ray tube. Maps of U–Zr and other identified elements demonstrated their patchy distribution and a frequent association of the elements with mineral fillings (clay matrix, organic matter or Fe sulfides). A correlation-based analysis was used to verify geochemical coherence between the measured elements. This showed an extremely strong linear dependence (R ≥ 0.90) between U and Zr. In addition, a strong correlation (R ≥ 0.85) between U–Zr and some associated elements (As, Nb ± Fe, Pb, Sr) was confirmed. The efficiency and the limits of X-ray fluorescence mapping were tested by comparison with high-resolution techniques. Non-destructive mapping of large natural samples provided relevant data for further mineralogical study with respect to rapid pre-concentration of the ore material. [ABSTRACT FROM AUTHOR]