The Mafube Colliery is operated as a 50:50 joint venture between Exxaro Coal Mpumalanga Proprietary Limited, which is a wholly owned subsidiary of Exxaro Resources Ltd., and South Africa Coal Operations Proprietary Limited, a subsidiary of Thungela Resources Limited.
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Summary:
Mafube mine is situated near the northern edge of the Witbank coalfield. The Witbank coalfield has up to five coal seams in the middle Ecca group sediments of the Karoo supergroup. The Karoo sequence in the area is represented by the Dwyka formation and the middle Ecca, with little or no lower Ecca development. Only four of the five main coal seams occur within Mafube, and S5 has been eroded. These consist of, from bottom, the No 1 Seam, sequentially to the No 4 Seam at the top. The No 2 Seam is the main source of the declared Coal Resources and Coal Reserves, with the No 4 Seam and No 1 Seam also contributing.
Surface material at Mafube consists of weathering products of the sandstones, siltstones and mudstones of the Vryheid Formation. The top layer consists of reddish-brown sandy soil, with clayey sandy subsoil below.
Weathering is deepest in the south and west, and shallowest in the north and east, following the general trend of the topographic surface. The average depth is 9.9 m, reaching a maximum of 23.28 m.
The Mafube area is underlain by a sequence of sedimentary rocks of the Dwyka Group and the Vryheid Formation of the Ecca Group (Karoo Supergroup), which rest unconformably on an uneven floor composed of older gabbro and granodiorite (associated with the Bushveld Igneous Complex) as well as felsite of the Transvaal Supergroup.
The generally flat-lying Vryheid Formation consists of sandstone, siltstone, shale and coal seams. Strata at Mafube are typical of the Witbank Coalfield, with four of the five coal seams being present. Underlying the coal sequence of the Vryheid Formation are glacial deposits of the Dwyka Group, which accumulated on the erosional pre-Karoo basement surface.
The palaeotopography of the pre-Karoo basement largely controlled the deposition of the lower coal seams and partings.
The glacial deposits of the Dwyka Group vary within the project area and consist of fine-grained varved siltstone and shale to very coarse, matrix supported tillites. Clasts within the tillite are typically felsite from the Rooiberg Group, or sandstone and quartzite of the Wilge River Formation of the Waterberg Group.
Within the Ecca Group, the Vryheid Formation comprises zones of alternating conglomerates, sandstone and mudstones within which the coal seams are located. At Mafube, the stratigraphy of the Vryheid Formation may be divided into two main sequences: a basal No 2 Seam Sequence, overlain by the No 4 Seam Sequence.
Four of the five major Witbank Coalfield seams exist within the Mafube Nooitgedacht area. These are (from bottom to top), the No 1 Seam, No 2 Seam, No 3 Seam and the No 4 Seam. The No 4 Seam is confined to the deeper parts (northwest) of the mining area.
The No 4 Seam averages 4.68 m thick. It is confined to the extreme northwest of the Mafube area due to erosion and generally consists of several plies of differing coal quality.
The No 3 Seam is thin and of no current economic significance (average thickness of 0.2 m).
The No 2 Lower Seam (S2L) is the main economic seam with an average thickness of 4.23 m. The quality is variable due to interbedded bright and dull coal plies with some shale and carbonaceous shale, mudstone and occasional sandstone bands. An upper sub-seam, designated No 2 Upper Seam (S2U), is sometimes present. The S2U and S2L are separated by a thin but distinctive parting (designated Number 2 Seam Parting (P2) with an average thickness of 0.41 m). The S2U is fairly thin (averaging 0.77 m in thickness) and consists of poorer quality coal and is therefore not economic.
The No 1 Seam (S1) is thin (average thickness of 1.38 m) and continuous throughout the Mafube area. It lies approximately 0.5 m below the S2L. Two minor seam splits of the No 1 Seam (designated S1L and S1LL) occasionally occur. They are, however, of no economic significance.