Summary:
The Elandspruit, Khanyisa, Vanggatfontein and Moabsvelden Collieries are located within the Witbank Coalfield. The northern extent of the Coalfield is defined by the limit of coal-bearing sediments of the Vryheid Formation which abut against pre-Karoo basement rocks of the Transvaal Sequence, the Waterberg Group and Bushveld Complex. The southern limit of the central sector of the Coalfield is marked by a series of Bushveld Complex inliers known as the Smithfield Ridge while in the east and west sectors, the boundary between the Witbank Coalfield and the Highveld Coalfield to the south is somewhat arbitrary.
The five major coal seams of the coalfield are contained within a stratigraphic interval averaging approximately 70m in thickness. The seams are numbered, from the base upwards and include the No. 1 Coal Seam, the No. 2 Coal Seam (split into the No. 2 Lower Coal Seam and No. 2 Upper Coal Seam), the No. 3 Coal Seam, the No. 4 Coal Seam (split into the No. 4 Lower Coal Seam and No. 4 Upper Coal Seam) and the uppermost No. 5 Coal Seam.
Five principal seams are developed at Khanyisa, namely the No. 1, No. 2, No. 3 and the No. 4 Lower and No. 4 Upper Coal Seams. The No. 5 Coal Seam is not present at all. The No. 1 Coal Seam is not considered economic as it is either very thin (~1 m thick) or not developed. Similarly, the No. 3 Coal Seam is also not considered economic as it is on average only around 0.3 m in thickness.
No. 1 Coal Seam
The No. 1 Coal Seam occurs directly on top of the Dwyka Group sediments in both the Triangle and Catwalk Project areas. Undulations in the paleo-topography at the time of peat accumulation resulted in zones where the No. 1 Coal Seam did not develop. The coal is highly variable in nature, ranging from shaley to dull-lustrous. Due to the fact that the seam is thin with relatively poor qualities, it is not considered economic. The depth of weathering across the Catwalk and Triangle Areas averages 17 m. It has been modelled and considered when estimating resources.
No. 2 Coal Seam
The No. 2 Coal Seam is the main economic target. It is present in the Triangle Area as in situ coal, and in the Catwalk area as pillar and roof coal, as well as a small portion of in situ coal. Within Triangle 1, the No. 2 Seam is considered mined out, and within Triangle 2, only a small portion in the north remains. The Catwalk resource area is also considered mined out as at FY21.
Triangle Mining Area
The No. 2 Coal Seam is present as in situ coal in the Triangle Resource Area and is on average 5.90 m thick. The average depth to the No. 2 Coal Seam roof is 40.9 m, ranging from 38 m to 43 m. The coal is dull to lustrous in nature with an average CV of 20.90 MJ/kg. The No 2 Seam is separated from the No. 4 Lower Seam above by a parting ranging in thickness from 9.92 m to 12.22 m (average 10.84 m).
Catwalk Project Area
The No. 2 Coal Seam has been historically mined using underground board and pillar methods in the Catwalk area and therefore the majority of the resource area comprises roof and pillar coal. The average pillar height is 2.7 m, while the remaining roof coal ranges in thickness from 1.5 to 2.3 m. The depth to seam roof ranges from 21 to 27 m. The CV for both the roof and pillar coal is in the region of 22.5 MJ/kg. The No. 2 Seam is considered mined out at Catwalk; any remaining peripheral coal has been removed from the coal resource estimation.
No. 4 Lower Coal Seam
The No. 4 Lower Coal Seam occurs across the majority of the Triangle Area, with the exception of a few areas to the South where it has been eroded. The No. 4 Lower Coal Seam is not present in either Catwalk North or South. The No. 4 Lower Coal Seam lies on average 0.6m above the No. 3 Coal Seam, where it is separated by a sandstone band. The seam thickness is relatively constant, ranging in thickness from 3.7 to 4 m, averaging 3.84 m in thickness. The average coal quality is good; raw ash content around 25% and a raw CV of 22.7 MJ//kg. The seam is unaffected by either faulting or dolerite.
No. 4 Upper Coal Seam
The No. 4 Upper Coal Seam occurs over the majority of the Triangle Project Area, with the exception of a few areas in the south, where the seam has been removed by erosion. The seam is on average 4.10 m thick and occurs directly above the No. 4 Lower Coal Seam. The coal quality is considerably poorer than the No. 4 Lower Coal Seam. The ash content is in the region of 39.70% and the CV is on average 17.20 MJ/kg.
Dolerite and Faulting
The majority of the holes in the Catwalk Project area intersected dolerite, which has affected both the quality and distribution of the coal measures. However, during the historical mining, the area where the No. 2 Coal Seam was mined out underground, was limited to those areas where the coal was unaffected by the dolerite. As the current Catwalk Project is a roof and pillar reclamation project of the existing mined out areas, this remaining coal is unaffected as well.
Within the Triangle Project area, only 2 boreholes in the south-western corner of the licence area intersected dolerite, and this had no effect on the coal qualities in that area. The No. 4 Upper Coal Seam to the east is however devolatilised and a large portion removed from resources. Within triangle North, the seams are totally unaffected. No faulting or dolerite has been encountered in any of the boreholes, or during the mining process.