Dorstfontein complex is on the northern margin of the Highveld Coalfield between the towns of EMalahleni in the north and Bethal in the south. Dorstfontein complex is on the Smithfield ridge, the boundary between the Highveld and Witbank Coalfields. Basement rocks in the area comprise pre-Karoo rocks, i.e. Transvaal supergroup, the Waterberg group, and intrusives of the Bushveld igneous complex. These are overlain unconformably by diamictites and associated glaciogenic sediments of the Dwyka group of the Karoo supergroup. Dwyka rocks are overlain by sediments of the Vryheid formation of the Ecca group. Coal seams in the area are hosted in the Vryheid formation which ranges in thickness from 80m to 300m.

Five major coal seams are present in the area, named from the base upwards, no 1 seam (S1), no 2 seam (S2 subdivided into S2L and S2U), no 3 seam (S3), no 4 seam (S4 subdivided into S4L and S4U) and no 5 seam (S5).

Numerous Jurassic dolerites (dykes and sills) intruded the Vryheid formation at various stratigraphic levels in the area. These intrusions tend to negatively influence stratigraphy and coal qualities in places. The distribution of the lower coal seams is strongly influenced by basement topography, while the distribution of the upper seams is controlled by present-day topography. Seams often thin and sometimes pinch out over and against palaeo-highs.

The Forzando complex – comprising Forzando North and Forzando South mines and contiguous prospecting right areas – is in the north eastern corner of the Highveld Coalfield, separated from the Witbank Coalfield by the pre Karoo Smithfield ridge. Basement rocks comprise Rooiberg felsites and granites of the Bushveld Lebowa suite. These felsites and granites are often palaeo-weathered to a depth of several metres. Diabase has been recorded in the western end of the complex. Given the proximity of the Forzando complex to the edge of the basin, only an abbreviated Karoo sequence is present. This package comprises the Dwyka, characterised by tillites, diamictites and varvites, and Vryheid formation, consisting of an arenaceous sequence of sandstones and conglomerates with subordinate siltstones and coal seams.

Diverse palaeo-environments including transgressive shorelines, lacustrine, fluvial and deltaic have been recognised. Across the suite of five seams, the thickest and most ubiquitous are the S2, S4 and S5 seams. S1 is restricted to palaeo lows while S3 only occurs on the western side of the mining right. Seam splitting is a common feature. Local Forzando nomenclature recognises the following seams from the base upwards: S1, S1 lower, S2, S2 leader, S3, S4 and S5.

Most exploited is S4, whose internal composition is reasonably consistent. The S2, which presents challenges of rapid seam-width variability, was also mined at Forzando North.

Tumelo mine is in Mpumalanga, 15km north-west of the town of Hendrina and 5km south-east of Hendrina power station. Tumelo’s mining right (116MR) covers an area of 461,9ha over the farm Boschmanskop 154IS and was acquired by TESA in
October 2000.

Tumelo lies north of the Smithfield ridge on the north-eastern edge of the Springs-Witbank Coalfield. The area is part of the Karoo basin with stratigraphy similar to Dorstfontein and Forzando, but with subtle location-induced differences.

Six coal seams are developed in the area, named from the base upwards as S1, S2, S4L, S4U, S4A and S5. S1 is very thin and only developed in the deepest part of the palaeo-valley. The thickest seam is S2 (0,45m to 5,31m), developed mainly in the palaeo-valley. A uniform seam, S2 is either thin or absent over the adjacent palaeo-ridges. This is the seam that has been exploited since Tumelo production started in 2009. S4L is the most persistent and second thickest. S4U is thin and may have been eroded in this area or poorly developed. S4A is thin and patchily developed. S5 is only present in a topographically high area in the south-east.

Dorstfontein complex, illustrated below, lies just north of the town of Kriel, in Mpumalanga, South Africa. The complex comprises the underground Dorstfontein West (DCMW) operation and open-cast Dorstfontein East (DCME) mine.

Opencast techniques are currently employed to mine the DCM reserves. The remainder of the deeper reserves will be mined by conventional mechanised underground bord and pillar mining method. Opencast mining activities currently targets the No. 2 and 4 seam lower reserves, however all seams thicker than 0.5 m are considered during mining operations.

The complex comprises two underground mines, Forzando North (FZON) and Forzando South (FZOS). Forzando complex covers 12 113ha over the farms Weltevreden 193IS, Koppie 228IS, Bankpan 225IS, Geluk 226IS, Halfgewonnen 190IS, Uitgedacht 229IS, Kalabasfontein 232IS, Schurvekop 227IS, Legdaar 78IS, Rensburgshoop 74IS and Kafferstad 79IS. Currently, only FZOS is in operation with FZON under care and maintenance.

A 2002 feasibility study confirmed the presence of economic coal reserves. First coal was recorded in 2009, with Tumelo exploiting S2 using bord-and pillar. Mining was outsourced to SBS Mining Proprietary Limited, a mining contractor.

ROM coal from underground is conveyed from FZOS to the coal-processing and beneficiation plant at FZON to produce an export product of 5 800kcal/kg. The final product is loaded at FZOS via existing rail-loading facilities, and sold free-on-board at Richards Bay Coal Terminal to existing markets in India.

Using one continuous miner, the mine produced some 700kt ROM at its peak. Initially, this was custom washed for an export product at the Shanduka (Glencore-owned) Koornfontein mine washing plant, but would later be carted to Forzando North and washed for a 5 800kcal/kg export product.