Geochemistry and sedimentology of coal seams from the Permian Witbank Coalfield, South Africa; a means of identification

B. Cairncross, R. J. Hart, J. P. Willis

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)

Abstract

Sedimentological investigations of the coal-bearing Vryheid Formation (Karoo Sequence) in the Witbank Coalfield have revealed that coal-peat deposition was associated with both marine and non-marine palaeodepositional events. At the terminal stage of peat accumulation, swamps were inundated by marine transgressions which deposited mud and silt above the peat (coal) and these overlying sediments contain typical marine features: glauconite associated with marine ichnofossil assemblages. In similar stratigraphic positions elsewhere in the basin, the peat swamps were invaded by basinward-prograding non-marine fluvial systems which deposited coarse sand and gravel over the peat. These overlying sediments are coarse-grained arkosic strata. Geochemical analysis of the No. 2, No. 4 and No. 5 coal seems in the region were undertaken using instrumental neutron activation analysis (INAA) and X-ray fluorescence spectrometry (XRFS). These analyses show that the geochemistry of the coal compliments the sedimentological interpretations. Elements which tend to be more concentrated in marine-derived sediments, e.g. boron, chlorine, lithium and bromine, occur in greater concentrations in the top of coals overlain by marine strata than in coals overlain by non-marine fluvial sequences. The latter do not show enrichments of these elements. Trace-element composition of the coal seams was further utilized as means of identifying the seams using multivariant discriminant analysis. Each coal seam plot in a specific field thereby permitting its identification based on the trace-element content. If unknown areas of the coalfield are being explored, a knowledge of the palaeodepositional stratigraphic sequences together with quantitative geochemical analyses could permit rapid identification of the coals concerned.

Original languageEnglish
Pages (from-to)309-325
Number of pages17
JournalInternational Journal of Coal Geology
Volume16
Issue number4
DOIs
Publication statusPublished - 30 Dec 1990
Externally publishedYes

ASJC Scopus subject areas

  • Fuel Technology
  • Geology
  • Economic Geology
  • Stratigraphy

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