Search Results (8)

Near the Segura pluton, hyper-differentiated magmas enriched in F, P, and Li migrated through shallowly dipping fractures, which were sub-perpendicular to the schistosity of the host Neoproterozoic to Lower Cambrian metasedimentary series, to form two swarms of low-plunging aplite–pegmatite dykes. The high enrichment factors for the fluxing elements (F, P, and Li) compared with peraluminous granites are of the order of 1.5 to 5 and are a consequence of the extraction of low-viscosity magma from the crystallising melt. With magmatic differentiation, increased P and Li activity yielded the crystallisation of the primary amblygonite–montebrasite series and Fe-Mn phosphates. The high activity of sodium during the formation of the albite–topaz assemblage in pegmatites led to the replacement of the primary phosphates by lacroixite. The influx of external, post-magmatic, and Ca-Sr-rich hydrothermal fluids replaced the initial Li-Na phosphates with phosphates of the goyazite–crandallite series and was followed by apatite formation. Dyke emplacement in metasediments took place nearby the main injection site of the muscovite granite, which plausibly occurred during a late major compression event. Full article

The Kolijan bauxite deposit (southeast Mahabad, northwestern Iran) mainly contains aluminum-bearing iron ores and was deposited in karstic depressions and sinkholes of the middle Permian carbonate rocks of the Ruteh Formation. Based on microscopic observations, the aluminum-bearing iron ores were allogenic in origin. According to XRD and SEM-EDS analyses, hematite and goethite are their main constituents, accompanied by lesser amounts of kaolinite, illite, amesite, boehmite, rutile, anatase, calcite, pyrolusite, crandallite, and parisite-(Ce). Chondrite-normalized REE patterns are indicative of fractionation and enrichment of LREE (La–Eu) compared to HREE (Gd–Lu), along with positive Eu and Ce anomalies (Eu/Eu* = 2.29–5.65; Ce/Ce* = 3.63–5.22). Positive Ce anomalies can be attributed to the role of carbonate bedrock as a geochemical barrier and the precipitation of parisite-(Ce). A strong positive correlation between Eu/Eu* and Ce/Ce* (r = 0.84) indicates that Eu anomalies, similar to Ce anomalies, are closely dependent on an alkaline pH. The distribution and fractionation of elements in the iron ores were controlled by a number of factors, including the pH of the environment in which they formed, wet climatic conditions, adsorption, isomorphic substitution, scavenging, co-precipitation, fluctuations of the groundwater table level, and the role of carbonate bedrock as a geochemical barrier. This research indicates that the aluminum-bearing iron ores were probably generated from the weathering of basaltic protolith. Full article

Citric acid has been identified as an environmentally sustainable organic acid capable of leaching up to ~30% of easily accessible REEs from underclay material. An analysis of the leaching profiles was performed to discern the reaction rates, extraction efficiencies, and potential leaching mechanisms of REEs and cations of interest from ion-adsorbed underclays. The initial leaching stage follows a slow intraparticle diffusion mechanism followed by a second stage controlled by a mixed diffusion regime. The leaching profiles of Ca and P were similar to those of REEs, suggesting that REEs are most likely derived from mineral surfaces such as hydroxyapatite or crandallite rather than predominately from underclays. Fitting to a modified diffusion control model found diffusion-controlled leaching to be the primary mechanism whereas non-diffusive mechanisms made up about 22% of the extracted REEs. Gangue cations associated with underclays had less non-diffusive leaching than REE species, indicating that their leaching kinetics may be dominated by diffusion from within the material or potentially from product layer formation. Fitting to Boyd plots further indicated that REEs were leached following intraparticle diffusion control. These results have important implications for the development of more efficient and sustainable methods for extracting REEs or critical minerals from alternative feedstocks. Full article

In the Neolithic Gavà mines, variscite and turquoise were exploited for ornaments manufacturing, although some prospective pits and tunnels were dug on other similar greenish minerals such as smectite or kandite. A 3D study of the distribution of mineral phases allows us to determine the parameters involved in variscite colours. Methods are comprised of quantitative colourimetry, thin section petrography, SEM-BSE-EDS, EMPA, XRD, Raman spectroscopy, and ⁵⁷Fe Mössbauer spectrometry. Mapping of the mines indicates that colour is not directly dependent on depth. Although variscite from Gavà is poor in Cr³⁺ and V⁺³ compared with gemmy variscite from other localities, the deep green samples content has the highest values of Cr³⁺. In the case of cryptocrystalline mixtures with jarosite, phosphosiderite, or goethite, variscite tends to acquire a greenish brown to olivaceous hue. If white minerals such as quartz, kandite, crandallite, or alunite are involved in the mixtures, variscite and turquoise colours become paler. Full article

The search for a reliable U.S. domestic source of rare earth elements (REE) is necessary to support the demand of advanced energy applications (e.g., catalysts, electronics, magnets). Sedimentary deposits may be sources for selectively recovering REE and critical metals—specifically the interbedded seat rock, or underclay, that underlies or forms the floor of a coal seam. This material is often a major component of coal waste fines and refuse and thus readily available. This study examines several Appalachian Basin underclays associated with actively mined coal seams as potential feedstocks for the REE. Multimodal microanalytical electron microscopy (SEM, FIB-SEM, EMPA) synchrotron-based µXRF, and image processing techniques are coupled with detailed elemental and mineral data to classify the 2D and 3D petrophysical properties of the materials. The REE contents of Appalachian Basin underclays were measured from 235–399 ppm and predominantly observed as discrete REE-bearing minerals such as monazite and xenotime on the order of 10–100 µm in size. These REE-bearing minerals typically accounted for less than 1% of the scanned areas and volumes under SEM and FIB-SEM analysis, with the exception of regions enriched in crandallite. Synchrotron-based µXRF elemental maps further identified several REE deposition environments in different underclays, including micro-scale (10–100 µm) light REEs co-localizing with Ca and P, micro-scale heavy REEs with Fe, and large-scale light REEs (>200 µm) co-localizing with Sr, Ba, Ca and P. Full article

In sedimentary rocks, Fe-Al phosphate minerals occur in different rocks and depositional environments. Herein, we present microcrystals of wavellite, crandallite, and cacoxenite from pedogenic goethite pisoliths and nodules. Pisoliths and nodules are generally dominated by Fe oxides and oxihydroxides. Frequently, pisoliths and nodules demonstrate high phosphatization and a substantial contribution of allogenic detritus. The aim of our study is to present these remarkable crystals found in goethites. We describe the geochemistry and mineralogy of the pisoliths and try to interpret the possible paragenesis of the minerals. Loose ferruginous pisoliths and nodules are separated from the red paleosol and analyzed using field emission scanning electron microscope (FE-SEM) coupled with the energy dispersive X-ray detector (EDS), X-ray fluorescence spectroscopy (XRF), and X-ray powder diffraction (XRD) methods. The studied paleosols are weathered in a subtropical climate and the newly formed precipitation products, such as crandallite, wavellite, cacoxenite, and goethite, accumulate during the weathering of apatite. Full article

The essential role of Critical Elements (CE) in 21st century economy has led to an increasing demand of these metals and promotes the exploration of non-conventional deposits such as weathering profiles. The present work is focused on the study of a weathering profile located at the Archaeological Park of the Gavà Neolithic Mines, Barcelona, Catalonia, Spain. In the Gavà deposit, acid and oxidising meteoric fluids generated intense weathering during the early Pleistocene, affecting series of Llandoverian black shales and associated syn-sedimentary phosphates. The circulation of these acid fluids at deeper levels of the profile generated supergene vein-like mineralisations comprised of secondary phosphates (e.g., variscite, perhamite, crandallite, phosphosiderite) and sulphates (e.g., jarosite, alunite). This supergene mineralisation is significantly enriched in certain CE (e.g., Ga, Sc, REE, In, Co and Sb) that were mobilised from host rock components and later hosted in the crystal lattice of supergene minerals. Weathering processes and corresponding supergene enrichment of CE at the Gavà deposit could be used as an example to determine exploration guidelines of CE in weathering profiles and associated supergene phosphates worldwide. Full article

The mining industry of Poland is based mostly on coal and copper ores. Strict carbon emissions and the depletion of deposits will slowly phase out coal. Therefore, metallic ores and other mineral raw materials will dominate the extractive industry of Poland. Current measured resources of the largest deposits of halloysite and diatomaceous earth in Poland are over 0.5 Mt and 10 Mt, respectively. Halloysite and diatomaceous earth samples from halloysite Dunino deposits and Jawornik diatomaceous earth deposits (composed mostly of diatomaceous skeletons (frustules)) were subjected to mineralogical analysis, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDS) nanostructural, chemical, elemental, and mineral content analysis. Both these minerals have similar properties, i.e., sorption capacity and cation exchange capacity, and are used mostly for the same purposes, e.g., adsorbents, filler material, and filtration. Samples of Dunino halloysite consist of minerals such as halloysite, kaolinite, hematite, magnetite, quartz, magnesioferrite, rutile, ilmenite, geikielite, goyazite, gorceixite, and crandallite, with little impurities in the form of iron oxides. Occasionally, halloysite nanoplates (HNP) nanotubes (HNT) were found. Diatomaceous earth is composed mainly of silica-containing phases (quartz, opal) and clay minerals (illite and kaolinite). The frustules of diatoms are mostly centric (discoid) and have radius values of approximately 50–60 μm. Large resources of these minerals could be used in the future either for manufacturing composite materials or highly advanced adsorbents. Full article