Coal measures of the Highveld and Witbank coalfields are hosted in the Ecca Group, which includes the Vryheid and Volksrust coal-bearing formations. All coal seams in the ECC area are hosted in the Vryheid formation which ranges in thickness from 80m to 300m. There are five major coal seams present in the area, named from the base upwards as S1, S2, S3, S4 and S5.

A granitic basement high, which forms part of the Smithfield Ridge and is referred to below as the Central plateau, divides the DCM complex into two separate geological domains and the western and eastern limbs can be found on either side of this plateau. S1 is only developed in the central portions of the paleo-valleys, ranging in thickness from 0.1m to 2.5m. Underground extraction of this seam is considered uneconomic due to its highly variable thickness, inferior quality, isolated occurrence and coal devolatilisation. In the DCM complex, seam splitting is generally a provenance of detrital material resulting largely from the proximity of the seam to the Smithfield Ridge and, as a result, the S2 and S4 are further subdivided into S2L, S2U and S4L and S4U, respectively.

S2L is thinnest over palaeo-highs and thickest over troughs of palaeo-valleys. Two S2L thickness domains exist in the complex. In the west (DCMW), seam thickness ranges from 0.1m to 5m and, in the east (DCME) from 0.2m to 6.0m. In the north of DCMW, the S2L exists as a single coal horizon, generally devoid of stone partings. ........

The complex covers a total rights area of 7 892ha comprising the underground Dorstfontein West mine and opencast and newly developed underground mine at Dorstfontein East mine. Seams being exploited are mainly S4 divided into S4 upper (U) and S4 lower (L) and S2 divided into S2U and S2L. The Dorstfontein West operation is exploiting the S4L through an incline development from the historical S2 workings with three production sections. A new development at Dorstfontein East is the implementation of an underground mine exploiting S2 through two adits accessed from one of the open pits. Dorstfontein East is the only opencast mine in the ECC stable targeting primarily S2 and S4. However, where thicker than 1.0m S5, S3 and S1 are present, they are also extracted. Mining activities use a truck-and-shovel method to expose and extract coal.

Front-End Material Handling.
Raw coal with a top size of – 50 mm discharges to a ~7400 tone surge stockpile. Material is withdrawn from the stockpile via three feeders (two fixed and one variable speed) and is conveyed to a plant feed bin. The plant feed bin distributes the coal vial two independent vibrating feeders and conveyors to the two modules. A weightometer and variable speed feeders maintain a constant feed rate for each plant feed (Exxaro Coal Central (Pty) Ltd B, 2017).

Dense Medium Pant.
A conventional dense medium cyclone plant is used for single stage washing. As the two modules are identical, the process explained below is for one module. The raw coal is deslimed at 1 mm prior to being introduced into the plant, with the 50 x 1 mm fraction reporting to the dense medium plant and the 1 mm to a spiral plant.

The desliming screen discharge combines with circulating medium from the head box and is pumped to the DM cyclone for separation. The c ........