Summary:
Khwezela North is located in the Witbank Coalfield where five coal seams are present. These consist of, from the bottom upwards, the No 1 Seam sequentially to the No 5 Seam at the top, and all contribute to the resource and reserve base. At the Navigation pit, all seams, with the exception of the No 3 Seam, to a greater or lesser extent, have previously been mined underground, with the select portion of the No 2 Seam mined most extensively. The No 4 Seam, No 2 Seam, and No 1 Seam currently contribute to the colliery’s export product, with the No 5 Seam reported as a resource.
Washouts have been intersected in the north where the coal seams have been eroded by palaeo-rivers, with the resultant channels filled with clastic sediments. The edges of the washouts are irregular due to differential compaction. Northeast – southwest trending floor rolls are also encountered.
Both the No 1 and the No 2 Seam occur, separated by the No 1 Seam parting (P1). The floor to the No 1 Seam consists of a thin carbonaceous shale band, which conformably overlies a reworked tillite of the Dwyka Formation. The No 1 Seam is present over the majority of the Navigation area and has been previously mined via underground workings (bord and pillar). It averages 1.27 m thick but reaches a maximum thickness of 2.63 m.
The P1 is variable in thickness, ranging from zero to 4.20 m with an average thickness of 1.74 m.
The No 2 Seam is present across the entire Navigation area; the select portion of the seam ( the Number 2 Seam Select, S2S) has been previously mined by underground mining. The No 2 Seam is generally 7.12 m thick (varying from 4.63 to 9.60 m) and consists of a number of distinct quality zones or sub-seams with the better quality coal occurring in the lower portions of the seam. The uppermost zone, the Number 2 Seam Roof Coal (S2RC), is generally poorer in quality with shaley partings. The underlying Number 2 Seam Top Coal (S2TC) has a maximum thickness of 1.08 m, only averaging 0.21 m, and consists of dull coal. The S2TC is occasionally separated from the S2S by a gritty, carbonaceous shale parting (P2S). The S2S occurs at the base of the No 2 Seam and has a high proportion of bright coal.
The No 3 Seam consists of good quality coal but is thin (average thickness of 0.30 m) and is therefore not currently economic.
The No 4 Seam is present across most of the Navigation area, but due to a regional erosional event, it is truncated to the west of the Navigation Pit. It averages 3.99 m thick and is subdivided into the Number 4 Seam Top (S4T) and Number 4 Seam Select (S4S) sub-seams. The S4T is on average, 0.95 m thick and the S4S is 1.59 m thick. The S4U is separated from the No 4 Seam by a shaley parting that ranges between 0.15 and 3.86 m thick. The S4U has an average thickness of 1.63 m and consists of virgin coal with a relatively low Calorific Value (CV1) of 19 MJ/kg and is therefore not considered economic.
The No 5 Seam has been affected by weathering and erosion and, as a result, is poorly preserved in the Navigation area. It is generally present in the south and south-eastern portion of the area (as both virgin blocks and pillars in previously mined areas) These previously mined areas have extraction rates of up to 67%. It averages approximately 1.75 m thick.