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.
The No. 1, No. 2, No. 3 and No. 4 Coal Seams are present at Elandspruit.
No. 1 Coal Seam
The No. 1 Coal Seam increases in thickness from less than 1 m along the eastern boundary where the seam pinches out, to over 4m in the western sector. In the opencast area, the seam averages 4 m in thickness whereas in the underground area in averages 2.9 m. The depth to roof of the No. 1 Coal Seam ranges from less than 10 m along the eastern boundary, to around 72 m at its deepest along the southern boundary (underground area). The gently dipping seam generally ranges in elevation from about 1 520mamsl to 1 540 mamsl.
No. 2 Lower Coal Seam
The No. 2 Lower Coal Seam ranges in thickness from less than 1m in the area of the washout, to up to 6.5 m in the north, where it has been mined out. The average seam thickness across the remaining opencast area is 2.64 m. The No. 2 Lower Coal Seam is usually separated from the underlying No. 1 Coal Seam by less than 1 m of sediments, but the interval thickness increases to over 11 m in the southern-eastern corner of the property.
In the southeast of the property, the seam is absent along a north-south trending zone approximately 400 to 500 m in width. It is assumed that the seam was washed-out by a syn- or post-depositional fluvial channel. On either side of the wash-out, the seam is relatively thin and exhibits elevated ash contents. The depth to seam roof ranges from 10-20 m along the eastern boundary, to over 60m in the south. The floor elevation is relatively constant, between 1530 and 1550 mamsl across the licence area, with the exception of the southwestern corner where is drops below 1520 mamsl.
No. 2 Upper Coal Seam
The No. 2 Upper Coal Seam thickness averages around 1.8 m in thickness across the remaining resource area. The interval between the No. 2 Upper and No. 2 Lower Coal Seams ranges from non-existent in the north to over 11 m in the south. The depth to roof of the No. 2 Upper Coal Seam ranges from less than 10 m along the eastern boundary to over 50 m in the south. The seam floor elevation is relatively constant around 1546 mamsl, however this does drop to less than 1530 mamsl in the southwestern corner of the licence area.
No. 3 Coal Seam
The presence of the No. 3 Coal Seam is dictated by its proximity to the limit of weathering, as it is eroded in areas of lower topographic elevation. It is the thinnest of the four seams, averaging 0.4 m across the entire licence area, and never attaining thicknesses of greater than 0.6 m. The interval between the No. 2 Upper and No. 3 Coal Seams is consistent across the property ranging from 12.0 to 15.5 m. The depth to seam roof ranges from 10 – 20 m in approaching the sub-crop to around 45 m in the south. The No. 3 Seam accounts for approximately 4% of the total opencast resources at Elandspruit.
No. 4 Lower Coal Seam
The No. 4 Lower Coal Seam is present only in areas of elevated topography; elsewhere it has been eroded. It ranges in thickness from less than 1 m as the seam approaches the sub-crop, up to 2 – 3 m. Within the remaining resource area, the seam averages 1.5 m in thickness. The 4L Seam is on average 6 – 7 m above the No. 3 Coal Seam. The depth to roof ranges from less than 10 m up to 35 m in the southwest. The floor elevation ranges from 1550 – 1580 mamsl, indicating a gentle dip towards the south-west. The No 4 Lower Seam accounts for approximately 8% of the total opencast resources at Elandspruit.
Examination of the geological model noted that there are no major structural disturbances such as dolerite displacements or faults. The major structural irregularity present is noted in the underground sections and is the area where the No. 2 Lower Coal Seam is absent, due to a suspected washout. No dolerite or faulting has been encountered during mining, and it is not envisaged that it will affect mining operations in the future either.