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This study investigates the paleodepositional conditions of the No. 6 Seam of the Madzaringwe Formation in Makhado and Voorburg south area of the Soutpansberg Coalfield (Limpopo Province, South Africa) utilizing organic petrography and inorganic geochemical proxies. The coals are predominantly high-volatile bituminous B-A rank with high ash yields (avg. 36.1 wt%), characterized by high-vitrinite (~ 41.5 vol%), moderate-to-high inertinite (9.8 vol%–33.7 vol%) and low liptinite (~ 2.3 vol%). The distribution of inertinite varies among different coal horizons (from bottom-lower to middle-upper), suggesting differential oxidation conditions and/or paleofire occurrence. Vitrinite-to-inertinite (V/I) ratio, tissue preservation–gelification index (TPI–GI), and groundwater–vegetation index (GWI–VI) plots, indicate that the peat-forming forest-swamp vegetation accumulated under mesotrophic-to-rheotrophic hydrological conditions. The presence of structured macerals (i.e., telinite, collotelinite, fusinite, and semifusinite) suggests well-preserved plant tissues, whereas framboidal pyrite and sulphur content (0.24 wt%–2.16 wt%) point to brackish-water influence at the peat stage. The coals contain quartz, kaolinite, siderite, muscovite, dolomite, calcite, and pyrite minerals, most of which were likely sourced from felsic igneous rocks. The Al/(Al+Fe+Mn) and (Fe+Mn)/Ti ratios for the studied samples range between 0.24–0.97 and 0.57–70.10, respectively. The ratios, Al–Fe–Mn plot, and presence of massive botryoidal-type pyrite imply some influence of meteoric waters or fluids from hydrothermal activity post-deposition. Moreover, the chemical index of alteration (CIA: 98.25–99.67), chemical index of weathering (CIW: 92.04–97.66), and A–CN–K ternary diagram suggest inorganic matter suffered strong chemical weathering, indicating warm paleoclimatic conditions during the coal formation. [ABSTRACT FROM AUTHOR]

The emplacement of igneous intrusions into coal alters both the organic and inorganic components, and may result in the addition of specific components, including rare earth elements (REEs), into the country rock. Previous studies on the intruded coals of the Main Karoo Basin (South Africa) have mainly focused on understanding changes to their organic fraction despite the likelihood that the inorganic composition is also affected, as demonstrated by others studying intruded coals elsewhere in the world. This study reports on the effects of a 0.4 m thick dolerite dyke on the mineralogy and geochemistry of Witbank coals, South Africa. Coal samples were collected at 0.25 m intervals on both sides of the dyke (west and east); in addition to the intruded coals, an unaltered coal from the same seam and a sample of the dolerite were included. The samples were assessed using petrography, X-Ray Diffraction, X-Ray Fluorescence, Scanning Electron Microscopy, and Inductively Coupled Plasma Mass Spectrometry following sequential leaching, focusing on REEs for the latter analysis. Inertinite is the main maceral group in the coal samples; as a result, the impact of the intrusion on the organic fraction is compared using mean random total reflectance (%RoTmr). Total reflectance increases from 1.65 %RoTmr (for the unaltered coal) to 4.17 %RoTmr closer to the dyke on the western side. In contrast, the eastern side reports lower values (max. 1.94 %RoTmr). Similar to reflectance, dolomite is higher in samples from the western side of the dyke. Dolomite is also found in the unaltered coal (4 wt%) and the dolerite sample (15 wt%). Syngenetic dolomite and a weak positive Gd anomaly for the unaltered coal (ΣREE = 83.7 μg/g) suggest the presence of acidic groundwaters during peatification. Subsequently, the coals were also affected by hydrothermal activity, related to the intrusion of the dolerite dyke. For the intruded coals, dolomite (fracture-infilling) and ΣREEs are higher on the western side, at a maximum of 24 wt% and 153.0 μg/g, respectively. Carbonate associated REEs are higher for the intruded coals than the total for the dolerite (ΣREE = 23.3 μg/g). This reflects the incompatibility of REEs with early-formed minerals in the dolerite, concentrating them in the residual melt. Increased reflectance and dolomite (and associated REEs) in coals from the western side suggest pronounced hydrothermal activity, related to the availability of accommodation space (i.e., fractures). [Display omitted] • Two sets of intruded Witbank coals were studied. • Dolomite is a significant epigenetic phase. • A high proportion of REEs is associated with carbonates. • Reflectance, dolomite, and ΣREEs are higher in the west of dyke. [ABSTRACT FROM AUTHOR]

Coal contains a significant concentration of free radicals as a result of the coalification process. One of the experimental methods sensitive to the presence of radicals is electron spin resonance (ESR), and differences in ESR spectra for different macerals may provide insight into coal-forming processes. In this study, ESR data along with the H/C atomic ratio (to infer the aromatic fraction) are used to characterize coal samples with the aim of assessing a fire-origin for dominant inertinite macerals. A medium rank C bituminous Witbank No. 4 Seam Upper coal (the parent) was density-fractionated to create vitrinite-rich and inertinite-rich samples. The parent sample consists of 42 vol% vitrinite and 49 vol% inertinite. The density-fractionated samples comprise of 81 vol% total vitrinite (dominated by collotelinite and collodetrinite), and 63 vol% total inertinite (dominated by fusinite, semifusinite, and inertodetrinite). The H/C ratio is 0.74 for the inertinite-rich sample, and 0.85 for the vitrinite-rich counterpart, suggesting the former sample is more aromatic. The ESR spectra obtained for the three samples were found to fit best using a Lorentzian distribution. The fit is noticeably better for the aromatic inertinite-rich sample, for which the spectrum is symmetric. This is attributed to pronounced electron mobility and exchange interactions. The higher radical content of the inertinite-rich and parent samples is attributed to the presence of specific inertinite macerals, namely: fusinite, semifusinite, and inertodetrinite. And, owing to the greater radical content of the inertinite-rich sample, the dominant inertinite macerals are interpreted to have formed through charring of plant matter. [ABSTRACT FROM AUTHOR]

Petrological and mineralogical features are key for inferring palaeoenvironmental and sedimentary conditions of coal-bearing sediments. Following the logging of a borehole core, this study reports on the organic petrology and mineralogy of the A and B Seams, Ermelo Coalfield, Main Karoo Basin (MKB), South Africa. Seventeen coal samples collected from the core, differentiated based on changes in lithotypes, were assessed using detailed petrography (macerals, microlithotypes, and mean random vitrinite reflectance), quality analyses (proximate, elemental, and gross calorific value), and mineralogy in order to deduce depositional environments for the Ermelo coals. The lithologies present in the core were typical of the MKB, and the coals were inertinite- and mineral matter-rich, apart from samples occurring at the base of the seams. The latter samples also had a higher proportion of structured inertinite macerals (fusinite and semifusinite) and lower ash yields. The rest of the samples had higher inertodetrinite contents, occurring in association with detrital quartz and kaolinite, resulting in higher ash yields. The formation of each coal seam thus commenced with the prevailing conditions conducive to the preservation of structured macerals and concluded with the accumulation of predominantly inertodetrinite. Select samples from the B Seam also had durite, an association of inertodetrinite and liptinite (including alginite). The co-occurrence of inertodetrinite and the detrital minerals alongside alginite suggests two depositional episodes. The first episode relates to the formation of primary inertinite macerals through charring, followed by fragmentation and redeposition as inertodetrinite. This latter process likely also reflects seasonal flooding, resulting in fluctuating water levels within the palaeomire. The second episode was quieter, occurring in deeper waters, and conducive for the growth of algae. An allochthonous origin is thus proposed for inertodetrinite and the associated detrital minerals, whereas alginite deposition was autochthonous. The cyclical upward-fining and upward-coarsening facies of the MKB were observed in the core, indicative of fluvial and deltaic palaeoenvironments, respectively. The fluvial facies were generally associated with the occurrence of structured vitrinite and inertinite macerals, suggesting in-situ formation, and mostly occur at the base of the coal seams. In contrast, the inertodetrinite-rich samples appear to be related to the overlying deltaic deposits. • An Ermelo core intersecting the A and B Seams is described. • Inertinite is common in the coals, though vitrinite is higher at the base of the seams. • In some B Seam samples, alginite occurs with inertodetrinite reflecting autochthonous and allochthonous deposition. • Structured macerals are associated with fluvial facies and inertodetrinite with deltaic facies. [ABSTRACT FROM AUTHOR]

The increased global demand for rare earth elements (REEs) from unconventional sources has led to increased interest and research in coal deposits. South Africa has extensive coal resources, but understanding of the concentration, mode of occurrence, and distribution of REEs in the coals and associated sediments is limited. This study aims to assess selected coal samples obtained from an exploration project underway in the Waterberg Coalfield (South Africa) to determine the concentration and mode of occurrence of REEs, and to gain insight into the behaviour of REEs during density fractionation. Density fractionation of coal is considered a pre-concentration method prior to REE extraction. Samples were selected from zones 8, 7, 4, and 3, spanning the Grootegeluk and Vryheid Formations of the Waterberg Coalfield. Density fractionation was conducted at relative densities (RD) of 1.3 to 1.8, providing float (F) and sink (S) products. Five parent and thirty density-fractionated coal samples were characterized using proximate analysis, petrography, X-ray diffraction (XRD), and the concentration of REEs determined using Inductively Coupled Plasma- Mass Spectrometry (ICP-MS) (after microwave digestion). The samples are classified as medium-rank C bituminous coals with variable maceral composition. The dominant minerals are kaolinite and quartz, occurring as both syngenetic and epigenetic phases. The total REY (REEs + yttrium) concentrations range from 45.1 to 389.2 ppm, higher than for world coals (except sample 8H F1.30, REY = 45.1 ppm), and generally higher than the average for Chinese coals. Float products obtained at 1.40 to 1.80 RD show greater variation of light REY (LREY) compared to medium REY (MREY) and heavy REY (HREY), whereas float fractions at 1.30 and sink fractions at 1.80 RD show no distinct enrichment patterns. Although the results suggest a relationship between the concentration of LREY with float fractions obtained between 1.40 and 1.80 RD, pre-concentration using density fractionation generally shows limited benefits for these coals. Ashing of the coals may be more effective in concentrating the REEs and further investigations are therefore required. • The REY concentrations range from 45.1 to 389.2 ppm, comparable to or higher than that of world coal average values. • Density fractionated 1.4–1.8 float products show a greater variation of light REY (LREY) compared to medium REY (MREY) and heavy REY (HREY). • Pre-concentration by density fractionation may not be the best REY concentration process for these Waterberg coal samples. [ABSTRACT FROM AUTHOR]