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1. Potential Uses of Artisanal Gold Mine Tailings, with an Emphasis on the Role of Centrifugal Separation Technique

   https://doi.org/10.3390/su14138130  

   Munganyinka, Jeanne Pauline; Habinshuti, Jean Baptiste; Ndayishimiye, Jean Claude; Mweene, Levie; Ofori-Sarpong, Grace; Mishra, Brajendra; Adetunji, Adelana R.; Tanvar, Himanshu (July 2022, Sustainability)

   Few investigations have focused on the potential uses of artisanal gold (Au) mine tailings, despite the fact that artisanal gold mining activity contributes to environmental issues such as greenhouse gas. Mineralogical characterizations of artisanal gold mine tailings in Miyove gold mine (Baradega and Masogwe) in Rwanda were investigated for potential utilization as a source of valuable gold, using the centrifugal separation technique. Results of X-ray diffraction analysis, energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, inductively coupled plasma–optical emission spectroscopy, and X-ray fluorescence showed that artisanal gold mine tailings samples have significant amounts of gold to justify economical gold extraction opportunity. The gold grades in the ores and artisanal gold mine tailings were in the ranges of 37–152 and 2–7 g t−1, respectively. Quartz was a major phase, with minor impurities in two different types of gold ores and their respective tailings. The beneficiation carried out using centrifugal separation, regarded as an extension of gravity separation, showed gold grades in the range of 535–1515 g t−1 for gold ores and 36–302 g t−1 for artisanal gold mine tailings. The gold recoveries for ores and artisanal gold mine tailings were in the range of 21.8–47.3% and 46.9–63.8%, respectively. The results showed that the centrifugal separation technique was more efficient in boosting gold recovery compared to the present panning approach employed at the site, which sometimes recover as low as 10%. The results suggest that mineralogical characterization of artisanal gold mine tailings allows for the development and design of a suitable methods for improving gold ore beneficiation and artisanal gold mine tailings reprocessing. 

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2. Leveraging automated mineralogy analysis to assess paleosol chemical weathering

   Weislogel, A; Pfaff, K; Knapp, J (July 2025, Goldschmidt 2025)

   Paleosol weathering commonly is characterized by an index of alteration determined from bulk rock elemental abundances. Although a variety of indices exist, they all essentially compare the proportion of immobile major elemental oxides associated with refractory minerals (mainly Al2O3 in phyllosilicate clays) to mobile major elements associated with labile minerals (i.e., CaO, Na2O). Higher proportions of immobile major elemental oxides reflects more intense chemical weathering, which is used to infer warmer, wetter climate conditions. However, bulk rock alteration indices are known to be influenced by variability in particle size, effects of quartz dilution, and authigenic mineralization, which are challenging to account for when destructive analytical approaches are used. We tested a non-destructive method of assessing chemical weathering intensity using automated mineralogy analysis, which relies on SEM BSE imaging and EDS spectrum acquisition with automated matching of whole spectra to reference spectra to generate quantitative mineralogy estimates. Our case study focused on 9 Upper Pennsylvanian Spodosol samples from the Appalachian basin, and the dominant mineralogic group identified by automated mineralogy in all samples were phyllosilicate clays (50-85%). Six samples showed >20% feldspar: however, grain shape analysis indicates often micron-scale clay-sized grains with prismatic crystal habit were assigned a potassium feldspar spectra. This is due to the automated mineralogy algorithm identifying a mixed signal from sub-micron quartz/amorphous silica and illite in the X-ray volume as a feldspar x-ray spectrum. Furthermore, the Chemical Index of Alteration calculated from bulk elemental estimates of automated mineralogy results ranged from ~60-65, and A-CN-K ternary plots indicate samples were influenced by K-metasomatism. Using an algorithm that assigns automated mineral identification on the basis of both whole-spectrum matching and particle morphology attributes (including grain shape/crystal habit and size), we can better constrain mineralogical interpretation of fine-grained sedimentary lithologies. This allows automated mineralogy analysis to be used in a new approach for assessing weathering intensity by analyzing the proportion of mobile versus immobile elements in prismatic grains versus equant grains across a distribution of grain sizes in a way that can mitigate or minimize known limitations to the accuracy of alteration indices (e.g., authigenic skins, K-metasomatism). 

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3. Preliminary insights on evaluating paleosol composition from automated mineralogy analysis

   Weislogel, A; Pfaff, K; Knapp, J (December 2024, American Geophysical Union)

   Advancements in automated mineralogy offer an opportunity to develop new approaches to the study of fine-grained sedimentary lithologies including paleosols and pedogenic minerals that hold valuable paleoclimate information. Automated mineralogy is a non-destructive analytical technique that relies on BSE imaging with spectral data to output multimodal hypermaps. Spatial domains are delineated and assigned mineral phases using whole spectrum best matching to reference spectra, providing quantitative sample composition estimates with high throughput data collection. We targeted a Spodosol in the lower part of the Upper Pennsylvanian Casselman Fm. of the Appalachian basin to evaluate the utility of automated mineralogy in determining paleosol composition. During deposition of the lower Casselman Fm., tropical climate during the Late Paleozoic Ice Age began a return to a more humid regime following the Kasimovian–Gzhelian boundary (~304 Ma) warming event. The Spodosol is a composite paleosol approximately 1.4 m thick that displays redoximorphic mottling, small scale (≤ 3 cm) slickensides and weak angular platy ped development. We performed automated mineralogy analysis on 9 paleosol samples, which were formed into 25 mm polished epoxy mounts of disaggregated peds, and generated complete mineralogical maps of the samples. These results indicate that phyllosilicate clays, mainly illite, formed the dominant mineralogic group (50-85%) with lesser amounts of quartz (~5-23%), feldspar (12-30%), carbonate (0-12%) and Fe-oxides (0-9%). Estimates of Al, Ca, Na and K from were used to determine Chemical Index of Alteration, with values ranging from 59-67. These CIA estimates tend to be quite low compared to CIA estimates determined from previous work using bulk elemental abundances by WDS-XRF (CIA >67). Further interrogation of these preliminary results revealed that interphase quartz-illite analyses were assigned a potassium feldspar interpretation. Ultimately we will combine image analysis (e.g., particle shape/habit) with new reference spectra for paleosol interphase matrix material, which together with WDS-XRF and XRD mineralogy calibration can be used to develop a robust methodology for automated mineralogy analysis of paleosols. 

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4. Genesis and geochronology of the Bayanteeg Li-mineralized pegmatite in the Idermeg terrane, central Mongolia

   https://doi.org/10.1016/j.jseaes.2025.106615  

   Dashtseren, Khashbat; Tunnell, Bolorchimeg N; Boldbaatar, Enkhjargal; Sereenen, Jargalan; Locmelis, Marek; Yang, Yueheng; Yang, Ming; Hames, Willis; Nakano, Nobuhiko; Adachi, Tatsuro (June 2025, Journal of Asian Earth Sciences)

   We present the first petrographic, lithogeochemical, and geochronological study of the Bayanteeg LCT pegmatite located in Idermeg terrane, central Mongolia, and interpret the findings within the geodynamic setting. The pegmatite extends over 140 m with a width of 1.3 m and unknown depth within Neoproterozoic gneiss. The pegmatite contains plagioclase, quartz, and lepidolite with minor K-feldspar, spodumene, muscovite, and topaz, and accessory amounts of cassiterite, amblygonite, columbite-tantalite, monazite, zircon, apatite, and fluorite. Locally, minor secondary quartz and lepidolite occur interstitially between plagioclase and quartz and along the edges of primary lepidolite, respectively, implying late-stage hydrothermal influence. Lithogeochemical data show that the pegmatite contains 0.3–1.12 wt% Li, 256–1285 ppm Cs, and 59–522 ppm Ta. Monazite U-Th-Pb geochronology yielded an age of 144.9 ± 2.8 Ma while cassiterite yielded a U-Pb age of 134.8 ± 1.4 Ma. Lepidolite yielded 40Ar/39Ar plateau age of 131.25 ± 0.3 Ma. These age results fall during the geodynamic evolution of an intracontinental extension accompanied by the exhumation of metamorphic core complexes and extensive magmatism in the eastern Central Asian Orogenic Belt. These events occurred due to a combination of gravitational collapse resulting from lithospheric delamination and asthenospheric upwelling. The geodynamic setting during the pegmatite emplacement implies abnormally hot conditions, ruling out the possibility of anatectic origin. The pegmatite dike with elevated concentrations of Be, Ga, Rb, Nb, Sn, Cs, Ta, and Tl supports a granitic origin with a hidden parental granite at depth. The fact that the Idermeg terrane contains several LCT pegmatites implies an important exploration target for Li exploration. 

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5. Hydrothermal REE partitioning between fluorite and aqueous fluids: insights from experiments and natural fluid inclusions

   https://doi.org/10.7185/gold2021.4834  

   Payne, M.; Gysi, A.P.; Hurtig, N. (July 2021, Goldschmidt)

   Rare earth element (REE) deposits are found in association with carbonatite and alkaline systems, where metasomatism plays a significant role in the late-stage transport and enrichment of REE [1]. Fluorite is a common gangue mineral in these mineral deposits and can incorporate varying REE concentrations by substitutions of REE3+ for Ca2+. Fluorite-hosted fluid inclusions contain significant REE concentrations [2], providing a potential record of the hydrothermal ore-forming fluids. The fluorite-fluid REE partitioning mechanisms, however, are largely unknown. To date, only one study [3] measured the partitioning of REE between fluorite and aqueous fluid at 60 °C. Here, we evaluate these REE partitioning mechanisms by combining laboratory experiments with characteristics of natural fluid inclusions that provide a range of salinities and homogenization temperatures relevant to natural systems. Batch-type experiments will be conducted between 100 and 250 °C in Teflon-lined reactors, in which millimeter-sized natural fluorite crystals (Cooke’s Peak, New Mexico) will be reacted with fluids of varying initial REE concentration, pH, and salinity. Kinetic experiments were carried out at 150 °C to test for attainment of a steady state between the fluorite crystals and the aqueous solutions. The reacted fluorite crystals will be studied using SEM, CL and EMPA. Major cations and anions in the quenched fluids will be analyzed using IC and ICP-OES; REE will be determined using solution ICP-MS. These results will permit deriving REE fluorite-fluid partition coefficients. Fluid inclusions in hydrothermal fluorite veins from the fluorite-bastnäsite REE deposits in the Gallinas Mountains in New Mexico are studied to constrain temperatures, salinities, and REE concentrations of hydrothermal ore-forming fluids in alkaline systems. Fluid inclusion assemblages were identified in growth zones and will be further studied using microthermometry. Previous studies found maximum temperatures of 400 °C in sulfate-rich NaCl-KCl brines [4]. The goal will be to link partition coefficients derived from the experiments to the REE partitioning behavior found in the natural fluorite. [1] Gysi et al. (2016), Econ. Geol. 111, 1241-1276; [2] Vasyukova and Williams-Jones (2018) Chem. Geol. 483, 385-396; [3] van Hinsberg et al. (2010), Geology 38, 847-850; [4] Williams-Jones et al. (2000), Econ. Geol. 95, 327-341. 

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