This publication presents a study on the mineral chemistry and luminescence properties of quartz samples from pegmatites of the T & oslash;rdal region in Norway. A total of 12 samples were analyzed using Secondary Ion Mass Spectrometry (SIMS), Electron Paramagnetic Resonance Spectroscopy (EPR), and Cathodoluminescence (CL) to gain insights into their trace element concentration and distribution as well as their luminescence behavior. The samples are characterized by different Cl emissions at 450 nm, 500 nm 650 nm and an additional shoulder at 390 nm, which is only partially visible due to the absorption of the glass optics. Of these luminescence bands, the 500 nm band is the most dominant in most samples and it is characterized by an initial blue-green luminescence, which is not stable under electron irradiation. Moreover, it is characterized by a heterogeneous distribution within the samples. This luminescence can be mostly assigned to [AlO4/M+](0) defects, with charge compensation mostly achieved by Li+. Analyses by EPR spectroscopy prove the dominance of structurally bound Al, Li, and Ti ions in the investigated samples. Further analyses using SIMS mapping demonstrate that Na and K are mainly bound to micro fractures or inclusions, suggesting a limited role in the compensation of the luminescence centers. Additionally, the SIMS mappings show that some samples contain Al-rich clusters of 10 to 20 mu m in diameter, whereas other trace elements are characterized by a homogeneous distribution. These clusters correspond to bright luminescence areas in size and shape and could potentially indicate H+ compensated [AlO4/M+](0) defects.

Mineral separation processes operate on properties of individual particle, which can currently be quantified with 2D characterization techniques, namely 2D automated mineralogy. While 2D automated mineralogy data have driven significant developments in particle-based separation models, this data inherently correspond to 2D slices of 3D objects, which leads to stereological bias in the quantification of geometric particle properties. X-ray micro-computed tomography (& mu;CT) is a 3D imaging technique that can quantify particle geometry. However, & mu;CT only collects limited information regarding material composition, making mineral identification quantification a challenge. To overcome this challenge, we present a workflow that utilizes individual particle histograms and corrects image artefacts caused by & mu;CT measurements, such as partial volume effect. We demonstrate the application of the workflow to perform 3D mineral characterisation of a sulfidic gold ore, where mineral phases that are commonly mistaken with & mu;CT could be distinguished: pyrite and chalcopyrite, gold, and galena. Results were verified by comparison with inductively coupled plasma mass spectrometry and 2D automated mineralogy. As a result, the workflow provides the user with a detailed 3D particle dataset containing the modal mineralogy and surface compositions, size, and geometrical properties of each particle in a sample - essential data for modelling mineral separation processes.

Abstract Norilsk sulfide ores are one of the largest known sources of Pd on Earth. Palladium in these ores is presented in platinum-group minerals (PGM) and base metal sulfides (BMS), especially in pentlandite [(Fe,Ni)9S8]. Although several studies demonstrated high concentrations along with heterogeneous distribution of Pd in pentlandites from Norilsk, the form of Pd in pentlandite has not been established. Here, we provide the first evidence for Pd incorporation in the structure of pentlandite from Norilsk ores using X-ray absorption near edge structure (XANES) spectroscopy, synchrotron-based micro-X-ray fluorescence (μXRF), and electron backscatter diffraction (EBSD). We present the first ever measured XANES spectra of Pd in pentlandite and atokite [(Pd,Pt)3Sn] as well as in other common Pd minerals. Divalent Pd in pentlandite was detected by XANES. The Pd spectra in pentlandite show no similarities with Pd spectra in PGM, metallic Pd, PdS, PdCl2, and PdSO4 which signifies that Pd incorporates into the lattice of pentlandite. Substitution of Ni by Pd in the lattice of pentlandite is supported by negative correlations shown by μXRF and electron probe microanalysis (EPMA) and complies with the previous studies. The additional EBSD study demonstrates a resemblance in cell parameters of the Pd-rich and Pd-poor parts of the pentlandite grains and reflects that Pd incorporation into the pentlandite structure does not imply any notable structure distortion. The combination of analytical techniques used in the present study demonstrates the great potential of these methods for understanding the mechanisms of noble metal incorporation into ore minerals.

The Mt. Rudnaya MSS-ISS (monosulfide and intermediate solid solution) fine-grained ores from a NE termination of Norilsk 1 deposit were analyzed using a combination of X-ray computed micro tomography, spectral X-ray computed micro tomography and scanning electron microscopy to achieve both, 2D and 3D data. The ores consist of ISS composed of tiny lamellar intergrowths of cubanite and chalcopyrite solid solutions, which form up to 4-mm distinct globules surrounded by an ISS-MSS matrix. Our X-ray computed micro tomography results may provide 3D textural evidence of a possible natural sulfide-sulfide liquid immiscibility between Cu-rich and Cu-poor sulfide liquids that occurred before MSS and ISS were crystallized. The platinum group minerals (PGM) distribution shows that 20.6 vol% of all PGM occur in the ISS-MSS matrix and 79.4 vol% in the ISS globules. We suggest that this distributional behavior is due to the fact that the platinum group elements (PGE) cannot be dissolved in ISS, which led to the formation of the large PGM grains, which are up to 120 μm on their longest axis. The initial enrichment of ISS in PGE was controlled by differences in the partition coefficients of platinum and palladium between Cu-poor and Cu-rich liquids.

The Witwatersrand Supergroup in South Africa is not only the best-preserved sequence of Archean sedimentary rocks but also hosts the largest gold deposit on earth, yet discovered. The gold is situated in quartz-pebble conglomerates and is generally associated with a wide variety of minerals, including pyrite (FeS 2 ), uraninite (UO 2 ), pyrobitumen, base metal sulfides and phyllosilicates [1]. Despite extensive research over the past 100 years, the origin of the gold is still debated with two models receiving most of the attention: the modified paleoplacer model and the hydrothermal models [2]. The modified paleoplacer model assumes that detrital gold was transported into the host rock by fluvial processes, followed by a short-range mobilization (micrometer-to meter scale) by hydrothermal fluids that infiltrated the host rock [2]. In the hydrothermal model, gold was introduced into the host rock by postdepositional hydrothermal fluids from an external source [2]. To find new evidence for the origin of gold, we present new high-resolution 3-dimensional (3D) data based on the combination of X-ray computed micro tomography (micro-CT) and spectral X-ray computed micro tomography (Sp-CT

We present a new approach to 3-dimensional chemical imaging based on X-ray computed micro tomography (CT), which enables the analysis of the internal elemental chemistry. The method uses a conventional laboratory-based CT scanner equipped with a semiconductor detector (CdTe). Based on the X-ray absorption spectra, elements in a sample can be distinguished by their specific K-edge energy. The capabilities and performance of this new approach are illustrated with different experiments, i.e. single pure element particle measurements, element differentiation in mixtures, and mineral differentiation in a natural rock sample. The results show that the method can distinguish elements with K-edges in the range of 20 to 160 keV, this corresponds to an element range from Ag to U. Furthermore, the spectral information allows a distinction between materials, which show little variation in contrast in the reconstructed CT image.

Image-based analytical tools in geosciences are indispensable for the characterization of minerals, but most of them are limited to the surface of a polished plane in a sample and lack 3D information. X-ray micro computed tomography (micro CT) provides the missing 3D information of the microstructures inside samples. However, a major drawback of micro CT in the characterization of minerals is the lack of chemical information that makes mineral classification challenging. Spectral X-ray micro computed tomography (Sp-CT) is a new and evolving tool in different applications such as medicine, security, material science, and geology. This non-destructive method uses a multi-pixel photon-counting detector (PCD) such as cadmium telluride (CdTe) in combination with a conventional CT scanner (TESCAN CoreTOM) to image a sample and detect its transmitted polychromatic X-ray spectrum. Based on the spectrum, elements in a sample can be identified by an increase in attenuation at specific K-edge energies. Therefore, chemically different particles can be distinguished inside a sample from a single CT scan. The method is able to distinguish elements with K-edges in the range from 25 to 160 keV, which applies to elements with Z > 48 (Sittner et al., 2020). We present results from various sample materials. Different pure elements and element oxides were measured to compare the position of theoretical and measured K-edge energies. All measured K-edge energies are slightly above the theoretical value, but based on the results a correction algorithm could be developed. Furthermore, different monazite grains were investigated, which can be divided into two groups with respect to the content of different RE elements on the basis of the spectrum: La-Ce-rich and La-Ce-poor. In addition, samples from the Au-U Witwatersrand Supergroup demonstrate the potential applications of Sp-CT for geological samples. We measured different drill core samples from the Kalkoenkrans Reef at the Welkom Gold field. Sp-CT can distinguish gold, uraninite and galena grains based on their K-edge energies in the drill core without preparation. Sittner, J., Godinho, J. R. A., Renno, A. D., Cnudde, V., Boone, M., De Schryver, T., Van Loo, D., Merkulova, M., Roine, A., & Liipo, J. (2020). Spectral X-ray computed micro tomography: 3-dimensional chemical imaging. X-Ray Spectrometry, September, 1–14.

Image based analytical tools in geoscience are indispensable for the characterization of minerals but most of them are 2D techniques, limited to the surface of a polished plane in a sample. X-ray micro computed tomography (micro-CT) is becoming a common analysis technique in geoscience and provides direct 3D information of the internal structure of a sample. A major drawback of micro-CT in the characterization of minerals, however, is the lack of chemical information. There have been different approaches to obtain chemical data using micro-CT but most of them are time consuming and difficult to adapt to regular use. Therefore we introduce a potential new analytical tool: Laboratory-based Spectral X-ray Micro Computed Tomography (Sp-CT). Results from a spectral imaging detector prototype, installed inside a TESCAN CoreTOM micro-CT scanner, will be shown. This new analytical technique enables to obtain both high resolution structural and chemical information in 3D. With this information, the mineral distribution inside unbroken rocks and particles can be identified and quantified. Based on the transmitted energy spectrum of a sample, main elements can be distinguished and minerals classified. It is also possible to quantify heavy elements within particles of complex composition and the measured sample volume is significantly larger compared to conventional analytical 2D techniques. Furthermore, Sp-CT is non-destructive and does not require sample preparation. Sp-CT will open exciting new possibilities for mineral analysis. With this new technique, the 3D properties of the particles can now be measured and used for example in process mineralogy simulations. This is a major improvement to current simulations that predominantly use less representative 2D or bulk particle properties. Moreover, the Sp-CT could potentially be used as an alternative technique for regular characterization of ore deposits and processed ores since more representative volumes can be analyzed in a fast manner relative to existing techniques. This research is part of the upscaling project “Resource Characterization: from 2D to 3D microscopy” and has received funding from European Institute of Innovation and Technology (EIT), a body of the European Union, under the Horizon 2020, the EU Framework Programme for Research and Innovation.

Quartz of metamorphic rocks from the Kaoko belt (Namibia) representing metamorphic zones from greenshist to granulite facies were investigated by cathodoluminescence (CL) microscopy and spectroscopy to characterize their CL properties. The samples cover P-T conditions from the garnet zone (500 ± 30 °C, 9 ± 1 kbar) up to the garnet-cordierite-sillimanite-K-feldspar zone (750 ± 30 °C, 4.0–5.5 kbar). Quartz from 10 different localities and metamorphic environments exclusively exhibits blue CL. The observed CL colors and spectra seem to be more or less independent of the metamorphic grade of the host rocks, but are determined by the regional geological conditions. Quartz from different localities of the garnet-cordierite-sillimanite-K-feldspar zone shows a dominant 450 nm emission band similar to quartz from igneous rocks, which might be related to recrystallization processes. In contrast, quartz from different metamorphic zones in the western part of the central Kaoko zone (garnet, staurolite, kyanite, and kyanite-sillimanite-muscovite zone) is characterized by a heterogeneous blue-green CL and a dominant 500 nm emission band that strongly decreases in intensity under electron irradiation. Such CL characteristics are typical for quartz of pegmatitic and/or hydrothermal origin and indicate the participation of fluids during neoformation of quartz during metamorphism.