Abstract

The Ellisras Basin, with very large coal resources, is fault-bounded along its southern and northern margins and is a graben-type depository. The study area is situated in the south-western part of the Limpopo Province of the Republic of South Africa, where the basin is influenced by three major fault zones, the Eenzaamheid Fault delineating its southern limit, the Zoetfontein Fault near its northern limit and the Daarby Fault, with a down-throw of approximately 350 m towards the north-east. Sedimentological facies changes also influence the continuity of the coal zones, with deterioration in coal development.

The use of slimline geophysical methods to log lithologies is a technique which has been tried and tested in industry over a long time. In the study area the correlation between the measured densities derived from the traditional method of air and water measurement and those derived from Vectar processed derived densities from geophysical logging is better than 95%. As a method of “fingerprinting” the various coal zones and samples it was decided to calculate the distribution of relative densities in the chosen geological intersection. The data were then used to portray geophysically derived relative density cumulative distribution line diagrams (GDCDD) of the various lithotypes on either a sample-by-sample or zone-by-zone basis. Using the classification method proposed, the various coal seams and zones can be correlated to a high degree and discrepancies easily identified. The lateral correlation between lithologies can be described accurately and substantiated, thereby providing a competent evaluator with an invaluable method in classifying coal resources in the Ellisras Basin.

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