Summary:
No 1 Seam
The S1 is consistently developed in the western half of the Arnot Project area, while in the eastern portion it only occurs as isolated patches. It is intersected at an average depth of more than 50 m in the underground extents, rendering it not feasible for exploitation in these areas. It does occur at shallower depths of at least 23 m in the opencast areas and remains a good prospect in these resource areas. It is, however, patchily distributed. Where present it is generally 1.2 m thick and consists of a hard, good quality mixed bright and dull banded coal, an average in situ Calorific Value (“CV”) of 25 MJ/kg on an air-dried basis (“adb”).
The inter-seam parting between the S1 and S2 consists of a grey micaceous mudstone unit that is usually between 0.7 m to 1.5 m in thickness, which increases up to 5 m at the fringes of the S1 outcrop area.
No 2 Seam
The S2 is site-specifically subdivided into the Seam 2 Lower (“S2L”), Seam 2 Upper (“S2U”) and Seam 2A (“S2A”) marked by two intra-seam partings, namely parting P2 and P3, respectively. The S2L constitutes the majority of the coal resources in the Arnot area and consists of hard, dull to lustrous coal with several bright coal bands and occasional stone partings. It has a CV of between 22.83 - 23.80 MJ/kg in the underground resource area and between 24.06-24.46 MJ/kg in the opencast resource area.
The S2L is continuous across the Arnot Project. The depth to the top of the S2L depends largely on local surface topography and reaches a maximum depth of 80 m along the eastern boundary of the Project area, pinching and thinning out in the eastern parts of the mining section due to local, pre-Karoo basement palaeo-highs.
No 4 Seam
The S4 occurs erratically across the lease area with an average thickness of 0.7 m. The seam is often split by internal clastic partings into Seam 4 Lower (“S4L”) and Seam 4 Upper (“S4U”). The No. 4 Seam is overlain by interlaminated units of siltstone and shale with the S5 sporadically developed in areas. Neither the S4 nor S5 are included in the coal resource estimates.
Structure and Intrusions
A well-developed dolerite sill is present some 15m–20m above the S2L in the topographically elevated areas in the south-eastern portion of the Arnot Project area. This sill is between 5m–40m thick, with an average of approximately 11 m, and has resulted in devolatilisation and minor resource loss where the volatile matter dropped below 18%. Feeder dykes are expected to occur in the vicinity of the sill. A number of dolerite dykes are also known to have intruded the Karoo Supergroup succession in the area, with six dykes having been intersected in the underground workings to date. The dykes often lack magnetic signature and are not responsive to geophysical methods of detection.
Faults with displacement in excess of 2.5 m are rare and to date only six have been encountered in the underground mine (Sambo and van der Merwe, 2015). A high density of compactional structures (i.e. slips and faults), however, occur in zones adjacent to pre-Karoo palaeo-highs. Similar features are observed on the flanks of relatively large floor rolls, scour and dome structures. The aforementioned geological structures have an adverse effect on underground coal-mine roof and strata-stability as they manifest into roof and side falls, caving of the roof and, more rarely, in subsidence of the ground surface.