Summary:
Khwezela Operation (Landau and Kleinkopje Collieries) consists of two sections, namely the Kromdraai Section and the Navigation Section (Navigation West extention).
Surface material at Khwezela consists of weathering products of the sandstones, siltstones and mudstones of the Vryheid Formation, with a small area of weathered doleritic material found in the southern-most corner of Khwezela North. The top layer consists of reddish-brown sandy soil, with clayey-sandy subsoil below.
The depth of weathering across Navigation and Bokgoni varies between five and twelve metres; the overburden material is therefore likely to be relatively competent. However, deep weathering may be encountered below the wetlands in the SACE Lifex areas.
Navigation
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.
Bokgoni
The No 1 Seam averages 2.0 to 2.5 m in thickness and is generally of good quality, able to produce a steam coal of 27.40 MJ/kg at yields greater than 60%. The Number 1 Seam Roof (S1R) coal is of lower grade with lower yields and is only mined when the No 1 Seam is destined for the local power station market. In places, the seam may be too thin to mine.
The P1 parting between the No 2 and No 1 Seams is between 1.5 and 4.0 m thick and consists of sandstone. The No 2 Seam is developed over almost the entire Bokgoni area, subcropping to the north of the Bokgoni Pit. The seam varies in thickness from five to eight metres, averaging six metres. The seam is subdivided into subseams, generally based on quality. The highest quality coal occurs in the middle of the seam (the S2S), with duller coal above and below it.
The No 3 Seam, although of good quality, is thin (approximately 30 cm) and has not been mined; it is used as a marker horizon. The quality of the No 4 Seam is highly variable across Bokgoni, with poorer quality coal in the west where the P4L parting occurs. The thin, upper portion of the seam (the S4) is of a higher quality, while the lower split below the parting, is of poorer quality. Higher grade coal is found in the east. The average seam thickness is 2.2 m.
The No 5 Seam is on average, 1.5 m thick and is found in the deeper areas of Bokgoni.
SACE Lifex
The seams in the various SACE Lifex areas are very similar to those found at both Navigation and Bokgoni; Table 4-2 adequately represents the seams here. The seams all dip gently to the southwest, with the upper seams subcropping in the northeast.
The No 1 Seam is on average 1.3 m thick. It is separated from the overlying No 2 Seam by the P1 sandstone parting, which attains thicknesses of over six metres in places but is more commonly around two metres thick. The No 2 Seam is on average 6.1 m thick with an average depth of 47.43 m, reaching a maximum of 102.12 m. The interburden between the No 4 Seam and the No 2 Seam varies and is generally between 10 and 20 m thick.
The No 4 Seam is on average 2.9 m thick with a maximum thickness of 7.2 m. The interburden between the No 5 Seam and the No 4 Seam ranges between 3.9 m and 34.2 m in thickness (average is 16.0 m). S4 has an average depth of 37.2 m. The S4A seam ranges in thickness from 0 m to 2 m with an average of 1m thick, while the S4U ranges from 0 m to 6.5 m in thickness with an average thickness of 2.6m.
The No 5 Seam is found over most of the Bokgoni area, except for a small area in the south. It can reach thicknesses of over 3.5 m but is generally around 1.5 m thick.