Abstract
South African Permian coals of the Main Karoo Basin are affected by Triassic-aged dolerite
intrusions associated with the emplacement of the Drakensburg lavas. This study investigates the
effects of a dolerite intrusion on the petrography, mineral, trace, and rare earth element (REE)
compositions of dyke affected, inertinite-rich coals from Manungu Colliery, located in the
western limb of the Witbank Coalfield, South Africa. Coal samples were collected from the No.
2 Seam at 0.25 m intervals (to a cumulative distance of 1.25 m) on either side of a 0.40 m thick
dolerite dyke. An unaltered coal (UN) was included as a control. In addition to the coals, a
sample of the dolerite was also collected. This was done in order to compare the mineralogy and
geochemistry of the intruded coals and the dolerite. The samples were analyzed using: (1) coal
petrography (for maceral group composition and changes in reflectance); (2) coal quality
analyses (proximate, ultimate, and gross calorific value); (3) X-Ray Diffraction (XRD); (4) XRay
Fluorescence (XRF); (5) Inductively Coupled Plasma Mass Spectroscopy (ICP-MS); and (6)
Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDS). Both
petrography and geochemistry appear to vary between the eastern and western side. The intruded
samples were dominated by inertinite (between 54 .2 vol.% and 77.5 vol.%). The unaltered
sample (UN) was also dominated by inertinite (75.5 vol%). Both mean random total reflectance
(%RoTmr) and vitrinite reflectance (%RoVmr) was done. However, due to low content of
vitrinite, %RoTmr was used to compare the maturity of the intruded coal samples. Mean random
total reflectance (%RoTmr) increased from a background value of 1.65 %RoTmr to 3.82
%RoTmr towards the contact of the dolerite dyke on the western side. In comparison, the eastern
side recorded lower %RoTmr values, a finding that was unexpected. The %RoTmr values were
consistent with the %RoVmr values. Similar to published literature, carbonate minerals dominate
the mineralogy of the intruded coals. Specifically, dolomite in the intruded coals occurs as a cleat
and fracture infilling phase, consistent with an epigenetic mode of occurrence, suggesting the
dolerite as the possible source. The western side appears to be more altered compared to the
eastern side, because %RoTmr is higher on the west compared to the east side. Group C
elements, associated with carbonate minerals, were enriched next to the dyke contact on the
western side, indicating a magmatic source. The REE composition of the carbonate fraction was
characterized by M-type enrichment with no distinctive anomaly, consistent with a hydrothermal
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source. Comparable studies in literature did not consider changes occurring to coals on both
sides of a dolerite intrusion; this study focuses on both sides of the intrusion in order to know
how the dolerite has affected both sides.