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MICRO-ANALYTICAL INSTRUMENTS FOR INVESTIGATION OF ELEMENTAL AND MINERAL DISTRIBUTION IN URANIUM-BEARING SANDSTONES

M.Sc. Petr Mikysek, Assoc. Prof. Dr. Marek Slobodnik, M.Sc. Marek Dosbaba, Assoc. Prof. Dr. Tomas Trojek

Abstract

Innovative methods in the investigation of low-grade uranium ores were tested. As the individual ore components in the rock are optically undetectable, we focused on the detection of selected elements (U, Zr, Fe, Nb), their possible associations and distribution. For this purpose, mineral mapping of sample surface was used. The studied samples are uranium-bearing sandstones with remarkable elemental and mineral compositions. Low concentrations of the main ore elements and the small size of mineral phases (in microns) require a sophisticated approach. X-ray fluorescence (XRF) was used to obtain elemental maps. The XRF analyzer was equipped with two changeable X-ray tubes and a semiconductor Si-PiN detector. The X-ray source was operated at a voltage of 35 kV and a current of 0.11 mA. Lateral resolution of scanned samples was 2 mm per image point and the acquisition time was 20 s per spot. Mineralogical analysis was performed using automated mineralogy systems (TIMA3) that included a FEG-SEM with three EDS detectors. The samples were analysed in the modal analysis mode under these operating conditions: accelerating voltage 25 kV and beam current 6 nA. The sample surface was scanned at a high resolution using a 3 ?m and 1 ?m pixel spacing, respectively. Data from the automated mineralogy systems were verified by X-ray powder diffraction (XRD) analyses. XRD data were collected in the 2? range of 4пїЅ80пїЅ with a step size of 0.014пїЅ and a counting time of 1 second at each step. XRF analyses allowed to detect accumulations of the elements of interest across maximum possible surface areas. The resulting elemental maps showed a strong association of UпїЅZr and a high variability in the distribution of other elements. Furthermore, this micro-analytical technique represents a fast and effective tool for an effective selection of ore material in the preparation of thin sections and other types of samples. The mineral maps were used to establish modal mineralogy and confirm the bulk rock chemical composition. Hydrozircon was identified as the main uranium phase, and the other determined ore minerals included rutile, pyrite and magnetite. Mineral maps show two styles of mineralisation: hydrozircon as cement and hydrozircon in micro-grains dispersed in clay matter. XRD phase analyses verified the mineral composition and match well with the XRF-based elemental maps. The applied micro-analytical instruments and their combination proved to be efficient in the investigation of the given type of samples.

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DOI resolver: doi.org/10.5593/sgem2017h/63/s24.006

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