Summary:
Goedehoop colliery is located in the Witbank Coalfield where generally five coal seams are present. These consist of, from bottom, the No 1 Seam sequentially to the No 5 Seam at the top, with inter-seam partings consisting of mainly siltstone and sandstone, with thicknesses ranging between 1 m and 30 m. The No 4 Seam and No 2 Seam are the only contributors to the GHN colliery’s export product.
The Goedehoop area has been intruded by transgressive Karoo dolerites in the form of sills and dykes and stringers. Minor faulting occurs infrequently.
The Ogies Dyke, a major west-east trending intrusion of up to 20m thick and over 100km in length, sub-divides GHN into two domains.
Surface material at Goedehoop consists of weathering products of the sandstones, siltstones and mudstones of the Vryheid Formation, with isolated patches of dolerite. The top layer consists of reddish-brown sandy soil, with clayey-sandy subsoil below.
Weathering generally does not extend deeper than approximately 10 m at Goedehoop, although isolated areas display weathering to depths of around 40 m. Weathering negatively affects the mineable Coal Resource, but rarely has an impact of the physical mining operation in terms of mining method and design.
Strata at Goedehoop are typical of the Witbank Coalfield, with all five coal seams being present on both properties. Underlying the coal sequence of the Vryheid Formation are glacial deposits of the Dwyka Group, which accumulated on the erosional pre-Karoo basement surface. The distribution of the lower seams (No 1 and No 2 Seams) is controlled by the underlying palaeotopography while that of the uppermost No 5 Seam is controlled by the level of the present-day erosion. The seams are generally flat lying and gently undulating.
Goedehoop North
Both the No 1 and the No 2 Seams occur in this sequence and are described from the base of the sequence upwards. The Vryheid Formation of the Ecca Group conformably overlies the Dwyka Group, with the No 1 Seam conformably overlying these glacial sediments.
The No 1 Seam is present over 70% of the Goedehoop North area. It is highly variable with respect to both quality and thickness (increasing to the west). Although the No 2 Seam is the primary mining seam, there are areas where the No 1 Seam can be mined in a “Bottom Coaling” operation, if the safety factor allows. The remaining No 1 Seam Coal Resources (the majority of which lie under the current Goedehoop North MRD) are on average 3.25 m thick and host two erratic, gritty sandstone in-seam partings ranging in thickness from 0.22 to 0.70 m. Mining of the No 1 Seam is constrained by the cuttability challenges presented by these intra-seam partings.
The No 2 Seam is developed over the entire mine area, has an average thickness of six metres and varies in depth from 20 to 140 m below surface. Thicker coal (up to 10 m) occurs mainly to the south of the Ogies Dyke.
Although often of good quality, the No 3 Seam is poorly developed throughout the coalfield and is not exploited at Goedehoop.
The No 4 Seam Coal Resources underlie most of the Goedehoop area, except in the northeastern part, where the distribution is patchy. The seam thickness is generally between 2.00 and 3.00 m. The expected practical Steam Coal yield (at 26.40 MJ/kg) is 30 to 40 percent in the north and east, increasing to 50 to 65% in the south and west. The seam is also shallowest in the area immediately to the north and east of the Simunye Shaft complex and rapidly deepens to the south and west. Opencast potential exists to the north of the shaft area, where the No 4 Seam is on average 25 m below surface.
There is no recognisable vertical quality variation in the No 4 Seam. The coal is dull lustrous to lustrous with occasional bright bands and in certain areas, intra-seam partings (comprising limestone, siltstone, shale and occasionally sandstone) occur.
The No 5 Seam is present in the western, southern and southeastern parts of Goedehoop North. In the resource area, the seam is generally between 1.30 and 1.80 m thick, with the depth below surface ranging between 20 and 50 m.
Several dykes, with wide zones of burnt coal, have been encountered. Dolerite sills have also displaced the seam into blocks at different elevations and burnt substantial areas. Dolerite intrusions in the vicinity of the East Shaft have caused severe burning.
Goedehoop North MRD
Lower quality discard material from previously mined and beneficiated coal (both the No 5, No 4, No 2 and No 1 Seams) has been placed on the MRD. The deposit is heterogenous in character, due to the deposition of discard material from different mining areas and different seams being placed at similar times. A raw product coal is currently being sold to a third party under contract.
Goedehoop South
Both the No 1 and the No 2 Seams occur in this sequence and are described from the base of the sequence upwards.
The No 2 Seam averages 6.50 m in thickness (but ranges from 5.00 to 7.50 m). The average depth below surface is 75 m, ranging from subcrop in topographic lows (such as along the Olifants River in the south), to a maximum of 130 m (in the eastern area of the Hope Shaft). The No 2 Seam shows well-defined zoning, with up to six zones of differing quality. It is mined to a maximum height of 4.5 m.
The No 4 Seam at Goedehoop South varies in thickness from 2.20 to 3.30m, averaging 2.80 m. The average depth to the seam floor is 40 m, ranging from a subcrop (in the far northern extent of Vlaklaagte and in Koornspruit), to a maximum of 80 m (in the eastern part of the Hope area).
The No 5 Seam has been extensively eroded and is therefore restricted in distribution. The seam ranges in thickness from 0.98 to 2.10 m with an average of 1.42 m. Overburden depth ranges from sub-outcrop to 58 m, with an average depth of 40 m. The seam comprises mixed, mainly bright, banded coal with a thin intermittent mudstone parting of 0.05 to 0.10 m thickness, located 0.20 to 0.30 m above the floor.
Goedehoop South MRD
Lower quality discard material from previously mined and beneficiated coal (both the No 5, No 4 and No 2 Seams) has been placed on the MRD. The deposits are heterogenous in character, due to the deposition of discard material from different mining areas and different seams being placed at similar times. A beneficiated product coal can be produced for an export grade product of 20.10 MJ/kg.