3.   GEOLOGY

3.3.1  

South African Coalfields

The South African Coaliferous horizons are contained within the late Carboniferous and early Permian Eras. The sediments of this period of the Karoo Sequence are composed of primarily argillaceous and mildly arenaceous sediments that cover, with facies changes towards the distal regions of the basin, the bulk of the Southern African sub-Continent. They are related to the formation of the geosynclinal basin during the Cape Orogeny. Three major depositional regions can be identified within the basin that all have a direct relationship to the deposits being mined or explored by Kumba. They are the Cratonic Paralic basin environment of the Witbank Coalfields, The Cratonic Limnic basin of the Waterberg Coalfield and the Mobile Belt Limnic basin of the Soutpansberg Coalfield.

In general the coal bearing horizons represent the formation of peat accumulations that cap broad scale subsidence and infill of the geosynclinal basin at discrete intervals during the evolution of the Karoo Sequence. The formation of the coals are directly related to the climatic conditions that were prevalent at the time of deposition as the climate was progressing from a glacial through fluvio-glacial and deltaic to fluvial regimes. Peat accumulation and therefore coal formation was directly related to the amount of water available and the slopes of the sediment infill. Although coal was initially mined in the Natal Coalfields for energy generation. in general the exploration and extraction of coal was driven by the need for an energy source to enable deeper level extraction of gold in the Witwatersrand. The primary large-scale coal mining occurred in the Vereeniging area and in the Brakpan/Springs region. Coal production has increased in South Africa from 0.7Mt in the period 1890 - 1894 through to 223.6Mt in 2002 (Minerals Bureau) with a total production of some 6.245Bt until 2002.

As the need increased so the coal exploration extended further east to the Witbank Coalfields and north to the Waterberg and Soutpansberg Coalfields. Mining originally was restricted to internal consumption for steam generation, however with the development of beneficiation techniques and the formation of local steel production the search for coking coal and export of coal to other parts of the world increased coal production to the high of 225Mt p.a. in 2000.

3.3.2  

Waterberg Coalfield

The Waterberg Coalfield is situated some 400kms north west of Johannesburg. Water drilling in the 1920s indicated the presence of a large amount of coal bearing strata in the area. CSO exploration was initially undertaken in 1955 in a joint program by both Iscor and Sasol with Iscor (Kumba) opening Grootegeluk Mine in 1980. This basin is a fault bounded basin with dimensions of approximately 90kms EW x 40kms NS. The faulting plays a distinct role in the preservation and depositional characteristics of the coal occurrences in the region. The two major boundary faults are the Zoetfontein in the north and the Eenzaamheid fault in the south. The presence of post-Karoo faulting has resulted in various portions of the stratigraphy having been preserved. The current weathering surface has a major impact on the relative proportion of the stratigraphy preserved. The major formations of the Karoo Sequence are present within the Waterberg basin but with significant differences in the lithologies and are with the exception of the Lower Ecca all significantly thinner representing much slower rates of subsidence than those encountered in the main Karoo Basin with the progression from glacial through to aeolian and flood basalts being broadly represented.

The major coal bearing horizons of the Ecca Group are the Volksrust Formation (55m of intercalated mudstones and coal) and the Vryheid Formation (three major discrete Seams of approx 3m, 9m and 4m, respectively). The most significant difference to the main Karoo Basin is the fact that the Volksrust Formation is carbonaceous with this formation being represented by intercalated carbonaceous shales and coal. The vitrinite content of the coal plies to the top of the Volksrust Formation result in the upper Zones having a semisoft coking coal yield as well as coal for thermal use. While the remainder of the Volksrust Formation yields low grade thermal coal for power station consumption. The Vryheid Formation coal Seams are composed of predominantly dull coal with minor carbonaceous mudstone intercalations again supplied as thermal coals. The Volksrust Formation coals are classified as a thick interbedded Seam deposit type and the Vryheid Formation as a multiple Seam deposit type.

• Grootegeluk Mine (six farms) occurs within the Waterberg Coalfield

  Grootegeluk Mine is situated some 17kms to the west of Lephalale in the Limpopo Province. Kumba has developed a system of nomenclature that reflects the cyclical nature of the peat formation within the two Formations of the Ecca Group. Kumba has substituted the names zone and sample as opposed to Seam and ply. This has been accepted by the Coal sub-committee of SAMREC. In this regard Kumba has defined 12 major zones to represent all the coal bearing lithologies numbered from 11 at top in the full succession area and number 1 being the deepest, and zone 4 having been sub-divided. The company also takes pre-defined samples from within these zones that are determined by a specific configuration of shale and coal and the system has been rigorously applied over time with only minor evolutionary changes to the principle. The total thickness of the coal measures is in the order of 120m. The general dip of the strata is in the order of 2° to 4° to the southeast.

  The Volksrust Formation from the top of Zone 4 through to zone 11 is characterised by an increasing ratio of bright coal to dull coal and the proportion of semi-soft coking coal is greater in zones 6 to 11. The Volksrust zones typically start with bright coal at the base and the ratio of coal:shale decreases from the base of the zone in an upward direction. The basal zone (zone 5) is the exception because the coal is more evenly distributed throughout the zone.

  The Vryheid Formation (±55m thick), forms the lower part of the coal deposit and consists of carbonaceous shale and sandstone with five dull coal Seams varying in thickness between 1.5m to 9.0m.

  These five coal Seams or zones consist predominantly of dull coal with some bright coal developed at the base of zones 2, 3 and 4. Due to lateral facies changes and changes in the depositional environment, these zones are characterised by a large variation in thickness and quality.

  Zone 3 is the best-developed dull coal zone within the mine lease area and reaches a maximum thickness of 8.9m. The basal portion yields a small fraction with semi-soft coking coal properties. Zone 2 is on average 4m thick and reaches a maximum thickness of 6m in the mine lease area. The basal portion also yields a fraction with semi-soft coking coal properties. Zone 1, the basal Vryheid coal zone, has an average thickness of 1.5m.

  Of the major bounding faults of the Waterberg Basin, the only one that impacts on the resources at Grootegeluk Mine is the east-west striking Eenzaamheid Fault which forms the southern boundary of the mining lease area. There is however a relatively complex structural regime that is related to the pre, syn-and post-depositional faulting within the mine. The major structural discontinuities are therefore the Eenzaamheid in the south, and the Daarby fault also forming the north-eastern boundary of the resources. The Daarby fault (200m downthrown to the north) has a strike in the west of northwest to southeast with a major trend change as it approaches the Eenzaamheid fault to southwest to northeast. At the point of inflection of the fault strike there are a number of minor sympathetic fault structures that have had an influence on the post depositional attitude of the coal resource. However due to the mining method and the bulk nature of the deposit, the minor faulting results in minor losses that are accounted for in the geological loss factors applied. The increase in depth of weathering associated with such faulting does produce problems because of the clay (weathered shale and decomposed coal) remnants in such areas. A substantial area in the 40-year pit is affected by the depth of oxidation that extends into the coal of the Volksrust Formation and this also reflects the dip of the strata to the southeast.

3.3.3  

Soutpansberg Coalfield

The Soutpansberg Coalfield is situated north of the Soutpansberg mountain range in the Limpopo Province (Figure 3.1). The Coalfield has a strike length of ±190km and extends from Waterpoort in the west to the Kruger National Park in the east.

The Karoo Sequence rocks in the Tshikondeni Mine area unconformably overlie rocks of the ±1,750Ma Soutpansberg Group. The Soutpansberg Group is situated on the three-point coupling zone between the Limpopo mobile belt, the Sabi monocline and the Lebombo monocline.

The north-eastern margin of the Kaapvaal craton was down-faulted into a graben structure, in which this pre-Karoo Soutpansberg Group was deposited. This faulting, which controlled graben formation, continued during the deposition of the Karoo sediments and was reactivated in post-Karoo times, resulting in a very complex structural setting. Generally the Karoo Sequence rocks dip to the north at 3° to 20° and are almost always terminated against east/west trending strike faults on the northern margins. The Soutpansberg coal Seams are thick interbedded Seam coal and mudstones in the west and grade to a multiple Seam type consisting of two discrete Seams in the Tshikondeni area. The coal, where developed, is generally bright and high in vitrinite and the coal rank increases to the east.

In the Eastern area two major coal Seams are developed, the Main Coal Seam and the Lower Coal Seam, the Main Seam has been the only economic Seam due to its coking properties and medium phosphorous content. The lower coal Seam also has coking properties but the high phosphorus content is not acceptable to the steelworks.

• Tshikondeni Mine occurs within the Soutpansberg Coalfield

  The mine is situated on the north eastern edge of the Soutpansberg Coalfield. The Karoo rocks in the Tshikondeni Mine mining area unconformably overlie rocks of the ±1,750Ma Soutpansberg Group. The Soutpansberg Group is situated on the three-point coupling zone between the Limpopo mobile belt, the Sabi monocline and the Lebombo monocline. The north-eastern margin of the Kaapvaal craton was down-faulted into a graben structure, in which this pre-Karoo Soutpansberg Group was deposited. This faulting, which controlled graben formation, continued during the deposition of the Karoo sediments and was reactivated in post-Karoo times, resulting in a very complex structural setting (ex-Kumba Geology Department). Generally the Karoo Sequence rocks dip to the north at 3° to 20° and are almost always terminated against east/west trending strike faults on the northern margins.

  Locally two major coal Seams are developed, the Main Coal Seam and the Lower Coal Seam, the Main Seam has been the only economic Seam due to its coking properties and medium phosphorous content. These coal Seams occur in the Madzaringwe Formation which is roughly correlatable to the Vryheid Formation. The Main Coal Seam is situated in the stratigraphic centre of the Formation and the Lower Coal Seam at the base. As is the Kumba standard in the Northern Limpopo Province specific samples are taken at specific stratigraphic intervals and a great emphasis is placed on the correlation of the individual samples. A selected mining horizon is determined at the boundaries of the samples 7B and 7C. The selected Seam thicknesses are generally in the order of 2.6 to 2.7m thick and consist of a very high vitrinite content of approximately 80% and a free swelling index of nine. Generally the coal qualities are consistent across the mine area.

  Structurally the mine is very complex with faulting and intrusives having a significant impact on mining with both displacement and devolatilisation of the coal. Major faults in the area tend to be listric normal faults forming steps and grabens which delineate the different mining blocks. Intrusives occur in the form of dolerite dykes and sills with thicknesses of up to 15 – 30m, respectively. The intrusives result in a devolatilisation halo which is related to the thickness and/or dip of the intrusive.

  The Mutale sill in the northern areas of the mining authorisation has devolatilised large areas of the coal as it closely follows the dip of the coal Seam. Strata control problems are encountered in close proximity to faults and dykes due to brecciation and fracturing.

  The Lower Coal Seam is located at the base of the Madzaringwe Formation some 100m below the Main Seam. It has an average thickness of 2.5m and is characterised by lower vitrinite content (69%) and lower yields at a 16% ash. Recent investigations into the viability of mining this coal Seam are dependant on the ability to find a market that will accept coal with a medium to high phosphorous content. All exploration drilling has ceased at the mine and only in-fill structure drilling is done in areas of complex geology.

3.3.4  

Witbank Coalfield

The Witbank Coalfield is a basin like feature that extends from Brakpan in the West through to Belfast in the East. The northern boundary is the sub-crop against the pre-Karoo basement rocks of predominantly the Waterberg sandstones and the south is a prominent pre-Karoo basement ridge called the Smithfield ridge. The basin was formed in the shallow cratonic paralic environment with slow but consistent subsidence during the late Carboniferous and early Permian. This basin was first exploited before the beginning of the 20th Century in the Brakpan (Apex Mines region) and has been the focus of concerted exploration and exploitation since. The basin is the type area for the multiple Seam deposit type with the development of five major Seam horizons which may in places be composite Seams. The major controls on the development of the coal are proximity to undulations of the “basement” topography, through erosion channeling and sediment influx into swamp beds and finally erosion of the current erosion surface. The primarily economic coal Seams have been the No. 2 Seam, The No. 4 and No. 4 Lower Seam and in places the No. 5 Seam. Structurally the coal horizons are undeformed with each displaying a very slight dip to the south east of less than a degree and minor discrete faulting events that have a southwest to northeast trend of graben features and other minor faulting events. The most distinctive post-depositional feature is the intrusion of dolerites related to the Lesotho Basalts that have resulted in a variety of sills and dykes of various ages. The most prominent of the dykes in the area is the Ogies dyke a 12 to 20m thick essentially vertical intrusion with an east-west strike. The No. 4 Dolerite sill, a 20 to 70m thick multiple flow event, has a preferential intrusion horizon above the No. 5 coal Seam, but in places it transgresses through the coal bearing strata to the pre-Karoo basement and forms in other places a barrier to erosion. The large amount of exploitation in the region has resulted in the development of an efficient coal transportation infrastructure that is now resulting in previously uneconomic coal Seams such as the No. 1 and No. 2 Lower coal Seams becoming economic propositions.

Operations and Projects within the Witbank Coalfield include:

• Leeuwpan Mine

  Leeuwpan Mine is situated on the western edge of the Witbank Coalfield. The mine is unique in this area as it is located in the region of the Palaeo-outcrop of the Malmani dolomites of the Transvaal Sequence. This has resulted in a Palaeo-karst topography on which the Karoo Sequence sediments were deposited. Thus the primary control on the development of the peat was this highly variable topographic surface. The Karoo Sequence in the area is represented by the Dwyka Formation and the Middle Ecca with little or no lower Ecca Development. The Middle Ecca sequence of coal horizons interbedded with sediments is highly truncated with limited sediment deposition between the major peat development events. This resulted in a very sheltered environment in which the peat accumulated but with highly variable coal thicknesses due to the irregular floor topography. Subsequent intrusion of the No. 4 Dolerite Sill very close to the pre-Karoo contact has resulted in large areas of the Bottom Coal being devolatilised although this has not resulted, in the majority of the resource areas, in a physical burning of the coal. Associated with the sill are a number of thin dolerite dyke like structures that crosscut the stratigraphy.

  The dolerite sill appears to break through the coal horizons to the south of the Mining Authorisation area and this is supported by information from the other mines in the region. In general the dolerite sill appears to have a thickness of 10 to 20m. The coal measures are approximately 16m thick and are divided on site into a Bottom Coal Seam (±8m thick, max 20m) and a Top Coal Zone (±8m thick, max 17m). The Bottom Coal Seam is correlated with No. 2 Seam of the Witbank Coalfield (Snyman 1998) and is a lower ash higher yield coal with higher vitrinite contents towards the base. The Top Coal Zone can be correlated with the No. 4 Lower Seam, No. 4 Upper Seam and No. 5 Seam of the Witbank Coalfield and tends to be a higher ash content lower yield coal, but substantially higher in volatile content. The Seam has a vitrinite band close to the top of the Seam in a layer that is higher in sulphur. In the Top Coal sequence a number of correlateable partings are encountered at specific levels, although they are not always developed (ex-Kumba). The lowermost shale parting is named the “O” parting and the upper the “X” parting. The identified coal resource blocks in the area have been well-delineated.

• Arnot Colliery

  The Arnot Colliery coal Seams occur within Karoo-aged strata of the Karoo Supergroup, comprising, in this area, the basal Dwyka Group, conformably overlain by the Vryheid Formation of the Ecca Group. Sediments of the Karoo Supergroup were deposited unconformably over an undulating pre-Karoo basement. The pre-Karoo consists of both felsite and diabase intrusives associated with the Transvaal Supergroup and the Bushveld Igneous Complex, respectively. The felsites are pink, finely crystalline and occur in isolated patches. The diabase is greyish-green, medium to coarse crystalline and occurs over most of the area as “dyke” and “plug” like bodies. The top of the pre-Karoo is undulating forming palaeo-valleys and palaeo-highs and a gentle regional dip from the northeast to southwest is noted. The Dwyka Group is a conglomerate with the matrix ranging from sandstone to shale. The clasts are generally of pre-Karoo origin with sizes ranging from angular fragments to boulders. The Dwyka Group attains a maximum thickness of 2m and is generally absent over palaeo-highs. The Vryheid Formation consists of a number of depositional sequences (culminating in a Peat formation) and is overlain by a number of transgressive events. The Vryheid Formation conformably overlies the Dwyka Group, with the conglomerates grading into a gritty sandstone and minor shale lenses capped by the No. 1 Seam. The depth to the top of the No. 2 Seam depends largely on local surface topography and reaches a maximum depth of 80m along the eastern boundary of the lease area. Incision by the Klein Olifants River and associated tributaries has eroded significant areas of the original extent of the upper coal Seams. In general, the No. 2 Seam sub-outcrops along all the deeply incised valleys. The depth to the top of coal in the sub-outcrop areas is typically 10 metres, but varies between 4m and 20m in depth. In the topographically elevated areas the No. 5 Seam and No. 4 Seam are present some 30m above the No. 2 Seam. The No. 1 Seam is generally 1.1m thick and consists of a hard, good quality mixed bright and dull banded coal with an average calorific value of 25MJ/kg to 29 MJ/kg (dry contaminated). The P1 Parting between the No. 2 Lower Seam and the No. 1 Seam consists of a shale unit between 0.7m and 1.5m in thickness, increasing up to 5m on the fringes of the No. 1 Seam outcrop area. The No. 1 Seam is consistently developed in the western half of the Arnot Coalfield whilst in the eastern portion only occurs as isolated patches.

  The No. 2 Seam is continuous across the Arnot Mining Authorisation area. The Seam has been subdivided into the S2L, S2U and S2A Seams by a number of internal partings termed P2 and P3, respectively. The No. 2 Lower Seam varies from less than 1.0m to 4.5m in thickness, with an average of 3.1m. The No. 2 Lower Seam constitutes more than two-thirds of the coal reserves in the Arnot area. The No. 2 Lower Seam consists of hard, dull to lustrous coal with several bright coal bands and occasional stone partings. The average calorific value of the No. 2 Lower Seam varies between 22 MJ/kg and 26 MJ/kg (dry contaminated). The No. 2 Lower Seam is often split into two different sub-Seams, the No. 2 Lower Upper Seam and the No. 2 Lower Lower Seam. The PL Parting between these two sub-Seams consists of siltstone and shale and is typically 1.0m in thickness. In the underground mining area the PL Parting delineates the extent of the mining operations where the parting thickness exceeds 0.3m.

  The No. 4 Seam occurs erratically across the lease area with an average thickness of 0.4m. The Seam is often split by internal clastic partings into S4L and S4U Seams. The No. 4 Seam is overlain by interlaminated units of siltstone and shale with the No. 5 Seam sporadically developed in areas.

  A limited number of dolerite dykes are known to have intruded the Karoo sediments in the area, with only six dykes having been intersected in the U3 underground workings to date. Dykes lack magnetic signature and are not responsive to geophysical method of detection.

  A well-developed dolerite sill is present some 15m to 20m above the No. 2 Lower Seam in the topographically elevated areas in the south-eastern portion of the Coalfield. This feature is 5 – 40 metres thick and has resulted in devolatilisation and minor reserve loss where volatiles <18%. Feeder dykes are expected to occur in the vicinity of the sill.

  Faults with displacement in excess of 2.5m are rare and to date only six have been encountered in the underground mine. A high density of compactional structures (i.e. slips and faults) occur in zones adjacent to pre-Karoo highs. Similar features are observed on flanks of relatively large floor rolls, scour and dome structures.

• New Clydesdale Colliery

  The coal succession occurs within the Permian-age Vryheid Formation of the Ecca Group, which overlies the Dwyka Group. The two stratigraphic units occur within the Karoo Supergroup. The sediments of the Karoo Supergroup were deposited on an irregular Pre-Karoo basement, which to some extent influenced the distribution of the overlying lithologies. The pre-Karoo basement rocks generally comprise gabbros, diabases and felsites associated with the Bushveld Igneous Complex. The generally flat-lying Vryheid formation sedimentary rocks consist of sandstones, thinly laminated siltstones and mudstones and coal Seams. The Sequence in the area consists of three well-developed Seams, i.e. the upper most No. 2 Seam, the No. 2A Seam and the basal No. 1 Seam. The coal reserves are limited mainly by the fluvial system of the Olifants River and its tributaries. The No. 2 Seam has been further divided into an upper zone referred to as No. 2 Seam Top Coal and the lower zone No. 2 Seam Select. The overburden comprises massive sandstones with laminated mudstones closer to the top coal. The limit of weathering varies from 1.2m to 8m below surface.

  Due to the erosive basal contact the No. 1 Seam has a varying thickness, from 1.05m to 4.57m, with an average of 2.90m. The upper 1.0m is typically a bright-banded coal with calcite cleats. The lower ±2.0m is a dull lustrous coal with mudstone bands very common.

  The No. 2A Seam has a thickness range from 0.52m to 1.80m with an average of 1.2m, however the Seam pinches out in the eastern portion of the reserve area. The mudstone parting that separates the Nos. 2A and 2 Seams is as little as 0.20m to 1.20m and in some cases pinches out completely. Typically the Seam is a mixed coal with alternating dull and bright bands, with only the lower 0.30m with bright coal. The basal contact of the Seam is a typical gritty sandstone.

  The No. 2 Seam has been divided into two zones based on the different inherent qualities. There are no marker bands distinguishing the two zones referred to as the No. 2 Seam Top Coal and the No. 2 Seam Select. Currently the top coal with an average thickness of 2.0m will be discarded due to the poor qualities, i.e. an average volatile matter of 19.0 %, with a raw Calorific value of 19.5MJ/kg dry base. The No. 2 Seam Select has an average thickness of 3.2m. The range here does not vary significantly with an exception to the areas close to the basin edges.

  The Nos. 4 and 5 Seams are limited to the topographically elevated areas. Typically, the No. 4 Seam is characterised by a number of intra-Seam sandstone/siltstone partings, which divide the Seam into the No. 4a, No. 4 Upper and No. 4 Lower Seams.

  The No. 4 Seam at New Clydesdale Colliery is of poor quality but requires further economic evaluation. In certain areas however, the quality of the No. 4 Lower Seam is good enough to satisfy most of the domestic market or as a blend to the higher quality coal Seams.

  The No. 5 Seam also exists at New Clydesdale Colliery, but due to the in Seam parting and average Seam thickness of 1.0m, it has been excluded from the current New Clydesdale Colliery reserves. However, this Seam is of a good quality and still to be fully evaluated.

  The episodic intrusion of dolerite dykes and sills have further complicated the geology, causing minor faults, where the displacement is less than the Seam thickness. However the current mining area is surrounded by dolerite dykes, with only one major sill on average 0.8m thick below the No. 1 Seam in the eastern part of the reserve area. The effect of the sill intrusion on the volatile matter of the coal Seam has been confined to the lower most part of the Seam and in some cases very little effect on the volatile matter. An aeromagnetic survey revealed the dolerites on the margins of the reserve area, therefore an extensive surface drilling program of about 110 boreholes within the 85Ha reserve area was completed.

• North Block Complex

  The coal succession occurs within the Permian-age Vryheid Formation of the Ecca Group, which overlies the Dwyka Group. The two stratigraphic units occur within the Karoo Supergroup. The sediments of the Karoo Supergroup were deposited on an irregular pre-Karoo basement, which to some extent influenced the distribution of the overlying strata and coal Seams.

  The pre-Karoo basement rocks generally comprise gabbros, diabases and felsites associated with the Bushveld Igneous Complex. The generally flat-lying Vryheid formation sedimentary rocks consist of sandstones, thinly laminated siltstones and mudstones and coal Seams.

  The Eerstelingsfontein block is composed of gently sloping topography. The coal reserve at Eerstelingsfontein is contained in a single Seam, the No. 2 Seam. The No. 2 Seam occurs as an erosional remnant on high ground at shallow depths, suitable for opencast mining. The thickness of coal ranges from 0.46m to 3.10m (this is inferred from borehole data) with an average thickness of 2.29m. The coal Seam is overlain by a medium to fine-grained sandstone with shaly bands. On top of the whole succession is the overburden material made of sandy soil and regolith.

  The average total depth to coal is relatively shallow at 10.69m. The maximum depth to top of coal in the area is 17.79m.

• Inyanda Coal Project

  Coal bearing strata of the Vryheid Formation occurs in two areas on the farm Kalbasfontein 284JS, Witbank district 14km north of Witbank. Both areas can be described as outliers unaffected by weathering.

  The southern area ±137Ha in extent, contains the majority of the Coal Reserves. The northern area (16.44Ha) straddles the Kalbasfontein/Geluk boundary. No coal occurs between these two areas. Two well-developed coal Seams are present. The bottom coal Seam is called the No. 1 Seam and the top Seam the No. 2 Seam.

  In the southern area both the No. 1 Seam and No. 2 Seam are well-developed. The sub-outcrop of both Seams is defined by weathering. The coal Seams are close to horizontal, but gently dipping in a southerly direction. No structural disturbances such as faulting or folding have to date been encountered. Although no dolerite dykes or sills have been intersected in any borehole in the mine area, water boreholes intersected a dolerite sill, at least 100m thick indicating the extent of the sill to be confined to the southern area. Airborne magnetic data indicates the presence of such a sill underneath the southern coal deposit. The borehole intersection indicates that the sill occurs stratigraphically below the diamictite (Dwyka Formation). And has not had a negative effect on the volatile content of the coal. The bottom coal Seam (No. 1 Seam) has an average thickness of 3.48m, extending over an area of ±137Ha. The sandstone parting separating the No. 1 and No. 2 coal varies in thickness from 0.30m to 1.13m and averages 0.49m. The top coal Seam (No. 2 Seam) has an average thickness of 4.66m and due to weathering occurs over a smaller area (118Ha) than the No. 1 Seam. The overburden above No. 2 Seam has a maximum thickness of 29.87m in the central part of the mine area but diminishes to between 10 – 14m towards the sub outcrop of the No. 2 Seam. The No. 2 Seam has an average 87% yield at a 14% ash product and the No. 1 Seam an average 80% yield at a 14% ash product.

• Mafube JV Phase II Project

  The primary control on the development of the peat in this area is the pre-Karoo basement palaeotopography of the Bushveld Igneous Complex lithologies and the current weathering induced by the current erosion surface. The Karoo Sequence in the area is represented by the Dwyka Formation and the Middle Ecca with little or no lower Ecca Development. The Middle Ecca sequence of coal horizons interbedded with sediments is highly truncated due to erosion with only very minor areas where the full sequence is developed. Subsequent intrusion of a Dolerite Sill very close to the pre-Karoo contact has resulted in an area in the southwest of the project area being heat affected and faulted.

  The coal horizons developed consist of the lowermost No. 1 Seam (±0.75m) separated from the No. 2 Lower Seam by a ±1m argillaceous parting, the No. 2 Lower Seam (±4.6m) which has an upper ply in certain discrete areas called the No. 2 Lower Upper Seam separated from the lower ply by a moderately arenaceous sandstone (±0.24m). The No. 3 and the No. 4 Seams are sporadically preserved especially in the north due to the current erosion surface. The No. 2 Lower Seam (2L and 2LU) are considered to be the economic horizon on which the resources have been determined.

  The project consists of three discrete peat accumulation areas that are separated by palaeotopographic highs. Two of these areas (named for the farms on which they occur), Springboklaagte and Nooitgedacht, form the project area. The coal is a sub-bituminous coal with an average A grade yield of 41.6% and a secondary 20.5 MJ/kg yield of 32.9%. The overburden thickness varies in the Springboklaagte area from ± 10m to ± 30m and in the Nooitgedacht area from ±10m to ±50m. All mining within this resource area is scheduled to be undertaken by truck and shovel opencast mining methods.

• Belfast Project

  The primary coal Seam development is on the No. 2 Seam. Due to the proximity to the northern edge of the Witbank Basin, the primary control on the coal development is the current weathering surface. Therefore the deposit is divided by a perennial stream into two resource blocks under two distinct spurs in the surface topography. The Karoo Sequence in the area is represented by the Dwyka Formation and the Middle Ecca with little or no lower Ecca Development. The Middle Ecca sequence of coal horizons interbedded with sediments is highly truncated due to erosion with only very minor areas where the full sequence is developed. The No. 2 Seam dips gently to the south. The limit of weathering intersection with the top of the No. 2 Seam has been taken as the limit of potential. Although there is no indication of any faulting from the borehole information, there are potential intrusions of dolerite dykes that are indicated by the airborne magnetics that were done over the area. In addition the regional aero-magnetic compilation done for Coaltech 2020 indicates that there is a regional North-South dyke trend in the region. This is borne out by the dry ash free volatile content which is low in some three boreholes in the centre of the project area; 48 of the 381 boreholes predominantly in the far south west of the project area have dolerite logged in the borehole descriptions. This is generally the No. 4 Dolerite sill which forms a cap in most of the high lying areas.
  

  The coal horizons developed consist of the No. 1 Seam which is sporadically developed occurring in 65 boreholes with an average thickness of 0.48m at an average depth of 35m. The No. 2 Seam is consistently developed except in the areas where it has been eroded and has an average thickness of 2.79m at an average depth of 30.41m. The No. 3 Seam is also sporadically developed due to erosion and has an average thickness of 0.60m at an average depth of 18.05m.

  The No. 2 Seam is a sub-bituminous to bituminous coal with an average A grade practical yield of 53% and middlings yield of 21 MJ/kg product of 28%.

3.3.5  

Ermelo Coalfield

The Ermelo Coalfield is situated in south east Mpumalanga Province between Carolina in the north and Dirkiesdorp in the south, Morgenzon in the west and Amsterdam in the east. The northern and eastern boundaries are defined by the sub-outcrop of the coal-bearing strata against pre-Karoo rocks. The western and southern boundaries are rather arbitrarily defined as straight lines forming the western boundary with the Highveld Coalfield and the southern boundary with the Coalfields of KwaZulu-Natal.

All of the coal Seams occur within the Vryheid Formation of the Ecca Group (Karoo Supergroup). The Karoo Supergroup comprises the following Groups (decreasing age): Dwyka; Ecca; Beaufort; Stormberg and Drakensberg. The Ecca Group comprises the following Formations (decreasing age): Pietermaritzburg; Vryheid and Volksrust.

Within the Ermelo Coalfield, only the Pietermaritzburg and Vryheid Formations are present with the Volksrust Formation having been eroded away. The Pietermaritzburg Formation, however, is only well-developed in the southern parts of the Coalfield. There are five major coal Seams developed in the Ermelo Coalfield, named from the base up: the E Seam; the D Seam; the C Seam; the B Seam and the A Seam.

The B and C Seams have previously been described as coal zones since these Seams are often locally split by clastic partings resulting in several coal “Seams” separated by thin sand and siltstone partings. These Seams are then renamed as the B Upper and B Lower Seams, or C Upper and C Lower Seams.

Basement topography and the present-day erosional surface control the distribution of the coal Seams and not all five Seams may be present at any one locality. The D and E Seams are thin to absent over much of the Coalfield and only the E Seam reaches mineable thicknesses in isolated patches in the northern parts of the Coalfield. The B and C Seams are most widely developed, and to mineable thicknesses, in the Coalfield. The A Seam has, over large areas of the northern and central areas of the Coalfield, been removed by erosion. Although to a lesser extent, the B and C Seams have also been removed by erosion.

Locally, fluvial channels cause erosion resulting in the non-deposition and thinning of coal Seams. The effects of channelling are evident in the central parts of the Coalfield where thick channel sandstones have been delineated which affect the C and C Lowers Seams.

The coal Seams are generally flat-lying to gently undulating with a regional dip to the south-west. The Seams are relatively unaffected by folding although faulting and associated dolerite (igneous) intrusions are common throughout the Coalfield. Dolerite intrusions take the form of vertical to near vertical dykes, often intruding existing faults, and sills, which are parallel to bedding planes. Sills are also often transgressive resulting in the relative displacement of strata. The number of sills increase to the south and up to eight major sills have been identified. An additional effect of dolerite intrusions is the burning or devolatilisation of coal in close proximity to the dolerites. Large areas of coal in the south have either been completely destroyed (burnt) or devolatilised by numerous dykes ranging in thickness from 3 – 5m. Dolerite intrusions not only sterilise available resources but also disrupt mining activities.

• The Incgambu Project occurs within the Ermelo Coalfield

  The surface topography is the primary controlling factor on the preservation of the various coal horizons. The Karoo Sequence is represented in this region by the Lower and Middle Ecca Formations. Almost the entire sequence of the Middle Ecca Formation is preserved in areas in the region as the surface topography is highly dissected due to the proximity to the Gondwanaland Escarpment. On portion 26 of the Farm Uitgevallen, both the C Lower and Upper Seams sub-outcrop against the surface weathering horizon and are quite rapidly covered by overburden as the topography rises to the northeast. Although the topography suggests and reconnaissance drilling on the remainder of Uitgevallen indicates that there are coal resources available this has not been included in this report as the only drilling that has sufficient confidence occurs on portion 26. The C Lower Seam is a high quality coal Seam with good wash characteristics and high yields at an A grade and consists primarily of mixed coal. The Seam is generally thin with and average thickness of 1.3m. The C Upper Seam is generally of a lower quality than the C Lower it does satisfy the coal requirements for Camden Power station as a raw product. The C Upper has an average thickness of 1.4m. The parting between the two coal Seams is generally in the order of 3m to 5m.
  

3.3.6  

Highveld Coalfield

The Highveld Coalfield is located in south-eastern Mpumalanga Province, immediately south of the Witbank Coalfield. The width of the coalfield is some 95km, stretching from Nigel and Greylingstad in the west to Davel in the east, and is about 90km long, from just north of Kriel to beyond Standerton in the south and covers an area of approximately 7,000km². After the Witbank Coalfield, the Highveld Coalfield is the next largest producing coalfield, on a tonnage basis, in South Africa.

The coalfield is host to up to five coal Seams contained within the middle Ecca Group sediments of the Karoo Supergroup. The Karoo Supergroup comprises sediments ascribed to deposition in glacial to fluvio-glacial and from shallow marine to fluvio-deltaic environments. The Karoo Supergroup comprises the following Groups (in decreasing age), although not all Groups are completely represented in the Highveld Coalfield to the present day erosion surface: Dwyka; Ecca; Beaufort; Stormberg and Drakensberg.

The Ecca Group comprises sediments from the following formations (in decreasing age): Pietermaritzburg; Vryheid and Volksrust.

The five identified coal Seams contained in the Vryheid Formation (middle Ecca Group) are named, from the base up, as follows: Number 1 Seam (No. 1 Seam, S1); Number 2 Seam (No. 2 Seam, S2); Number 3 Seam (No. 3 Seam, S3); Number 4 Seam (No. 4 Seam, S4) and Number 5 Seam (No. 5 Seam, S5).

In certain areas of the coalfield, the No. 4 and No. 2 Seams are split by clastic partings and in those areas the Seams are called the No. 4 Upper and Lower Seams and the No. 2 Upper and Lower Seams.

The coalfield is characterised by the fact that in the northern regions, all the coal Seams, with the exception of the No. 3 Seam, attain mineable thicknesses with economic potential, while in the southern regions, only the No. 4 Seam, and in very localised areas the No. 2 Seam, attain mineable dimensions of economic importance.

The depth to the coal Seams increases in a southerly direction, e.g. the No. 4 Seam can be mined by opencast in the Kriel (northern) district, while it occurs at a depth of around 200m in the Standerton (southern) district. The coal Seams are generally flat-lying to gently undulating with a slight regional dip to the south.

Structurally, the coalfield is relatively undeformed with no prominent folding having been identified. Small-scale faulting (less than 1m) is not uncommon although large-scale faulting is. The only large-scale displacements identified are almost always associated with transgressive dolerite sills, intruded during the waning stages of the Karoo times. These intrusive dolerite sills and dykes are related to the Drakensberg Formation flood basalts. The dolerite intrusions adversely affect the coal Seams in the vicinity of the intrusions in terms of coal quality by devolatilising and burning the coal. Large areas of coal have been rendered uneconomical due to the effects of dolerite intrusions.

The most important economic coal Seams are the No. 4 Seam and the No. 2 Seam. The No. 4 Seam accounts for approximately 80% of the economically recoverable coal within the Highveld Coalfield. The No. 2 and No. 4 Seams are mined in the northern parts of the coalfield while only the No. 4 Seam is mined in the southern parts. The bulk of the coal produced is consumed in power stations and for the production of syn-fuels. A very limited quantity is exported.

• Matla Colliery

  The coal deposit at Matla Colliery forms part of the Highveld Coalfield. The coal Seams are found within the Vryheid Formation of the Karoo Supergroup and date at approximately 280 million years in age. The stratigraphic sequence within the Matla area includes five coal Seams that can be easily correlated with the Seams found within the Witbank Coalfield.

  The principal economic Seams currently exploited are the No. 2 and No. 4 Seams. The mining of the No. 5 Seam was terminated as a Power Station feedstock during May 1998 because of high levels of contamination that resulted in an excessively high overall abrasive content.

  The Matla Colliery mining-area is characterised by two distinct dolerite types, namely the B8 (porphyritic) and B4 (olivine-rich) types, which have varying effects on Seam displacements and coal burning and devolatilisation. Floor rolls have been encountered in the No. 2 Seam workings and have created problems in the mining sections. The floor rolls strike NE-SW, vary in width from 50m – 200m, and have amplitudes up to 1.5m. Sandstone lenses encountered are generally less than 0.5m in width, but can reach up to a 1.0m in thickness. Structural information has been collected from borehole sections, horizontal drilling, aeromagnetic surveys and extrapolations from intercepted dykes in mined out areas. A dolerite sill, which has an average thickness of 10 metres, is generally found above the No. 5 Seam in the No. 2 Mine and No. 3 Mine areas, but intersects the coal Seams and underlies the No. 2 Seam at No. 1 Mine. The intrusive activity in the No. 1 Mine area caused extensive devolatilisation of the overlying No. 2 Seam, resulting in the exclusion of this Seam from the mineable reserves at No.1 Mine.

  Economic No. 5 Seam is mainly expressed in the No. 2 Mine and No. 3 Mine areas, and to a limited extent, in the western limb of the Southern Reserve area. The roof consists of 0.25m to 0.70m thick sandy micaceous shale at No. 2 Mine that thickens up to 1,60m at No. 3 Mine. Above this is competent sandstone, which, in some areas, is saturated with water. Due to this, the parting between the two sequences is highly weathered. Consequently, this shale is difficult to support and is removed with the product in development sections.

  The average mineable horizon, when described from bottom to top, consists of approximately 0.50m to 1.00m of mixed coal, 0.10m to 0.17m of torbanitic material and 0.35m to 0.60m of mixed coal, resulting in an average thickness of 1,50m. At No. 2 Mine, the floor is made up of competent sandstone over 80% of the area. Over the greater part of the No. 3 Mine area, the floor is generally a 0.10m to 0.25m fine-grained and micaceous sandstone. Underlying the sandstone is a 0.30m to 0.50m thick shale to sandy shale.

  Economic No. 4 Seam is strongly expressed in the No. 1 Mine, No. 2 Mine and Southern Reserve areas, and to a limited extent in the No. 3 Mine area. At No. 3 Mine, the Seam splits into two thin, poor quality horizons towards the west, so it has been necessary to exclude this coal from the mineable reserves. In general terms, calorific value decreases from east to west, and from No. 1. Mine moving north toward No. 2 Mine and south toward the Southern Reserve. Thus the best quality No. 4 Seam may be found at No 1. Mine and at the eastern edges of No. 2 Mine.

  Over the total mining area, it is often necessary to leave a beam of dull to shaly coal, with inter-bedded shale bands, in the roof. This is done mainly because of quality constraints. This coal in the roof has been found to form a competent beam resulting in good roof conditions.

  The mineable coal horizon is restricted to the upper portion of the Seam in areas where the in-Seam parting in the lower portion exceeds 0.30m or where the sandstone band exceeds 0.10m in thickness. In such areas, the bottom part of the Seam is excluded from the reserves. The occurrence of shale bands complicates horizon and floor control.

  In some areas of No. 2 Mine and No. 3 Mine, coal is left in the roof or floor due to mining height constraints. Where coal is not left in the roof, the roof consists of fine-grained sandstone or sandy, micaceous shale.

  Seam thickness varies between 1.2m and 5.5m (mining height limit). The Seam generally consists of homogeneous, dull lustrous coal, interspersed with bright coal bands. In-Seam partings typically consist of discontinuous lenses of shales and siltstones less than 0.1 metres thick, but these may thicken locally to 0.3 metres. Carbonaceous limestone lenses are also prevalent within the central portion of the No. 2 Mine area.

  In areas where coal has been left in the floor at No. 3 Mine, the floor is not competent and tends to disintegrate under tramming operations. The coal Seam floor generally consists of competent medium to coarse-grained sandstone.

3.3.7  

Bowen Basin (Australia)

There are numerous Coalfields on the east coast of Australia of which the only Coalfield in which Kumba has an interest is the Bowen Basin in Central Queensland and specifically the western limb of the Bowen Basin. The Bowen Basin has a number of distinct coal measures of late Permian age. They range from the older Blenheim Coal measures through to the Rangal coal measures. The Bowen basin is a structurally complex compressional basin with thrusting repeating the coal sequences to the east. All the coal measures dip gently to the east with thrust faulting having a general north south trend and extensional normal faulting having a general east west trend. The Bowen Basin extends from Collinsville in the north to Emerald in the south a distance of some 250kms. Recent modeling by the CSIRO has indicated that folding can be divided into broad flexures with a 4 – 5km wavelength and that a major anticline extends from Goonyella in the north to Moranbah in the south with extensive Seam splitting occurring to the north and south of the regional anticline. In general the Moranbah coal measures, which are in the region of 320m thick, are defined by the three most correlateable coal Seams, the Goonyella Lower (Dysart) at the base. The Goonyella Middle Seam (Harrow Creek) in the centre and the Goonyella Upper Coal Seam at the top (Q upper). In general medium to low phosphorous low ash coking coal with acceptable yields can be expected from the primary coal Seams with lower quality coals occurring at the top of each of the principal Seams.

• The Moranbah South Project occurs within the Bowen Basin

  The Moranbah South coking coal project is located roughly 15km south-east of the town of Moranbah. The principal coal mining sequence in the Moranbah South area is the Moranbah Coal Measures, which are extensively mined for prime quality coking coal in the northern Bowen Basin. The Moranbah Coal Measures contains seven major coal Seams of which, only the P Seam and Harrow Creek are considered prospective underground mining targets. The P Seam, which is equivalent to the Goonyella Upper Seam, ranges from 2.13 to 3.87m thick. However, acceptable yields of +70% product can only be obtained if a product ash of 12% or higher is marketed. Thickness of the Harrow Creek Seam, including partings, ranges from 2.50m to 4.47m and averages 3.51m across the Moranbah South area. A shale band up to 50cm thick occurs in the north and west, thinning gradually to the east with a marked increase in recovery. This Seam contains high grade coking coal which can be produced at either 8.5% or 9.5% ash. The Harrow Creek (“HCK”) Seam represents the target Seam in Moranbah South. It is the equivalent of the well-known Goonyella Middle Seam. Depth of cover to the HCK Seam, based on boreholes, ranges from 60 to 200m on the western boundary and with a dip of 1° to 5° against the eastern boundary the depth is greater than 500m. The HCK Seam does not subcrop within the controlled bounds of the property. Only in the north-west corner of the EPC (north of the Moranbah air strip) does the HCK Seam come close enough to the surface to be mined by open cut methods. The structure is partially determined due to the wide borehole spacing and is confined to the three major structures, two normal extensional faults with variable throws (Watonga and Grovenor) and a compressional thrust fault (Cherwell).

  A number of igneous intrusions have been encountered in the stratigraphy above and below the HCK in a number of boreholes, indicating that the possibility of intrusions exists.