New Denmark Colliery reserves occur within the Vryheid Formation of the Ecca Group within the Karoo Sequence. Sixty boreholes have been drilled by the mine to the base of the Karoo Supergroup in the MRA from which geological information could be derived. The thickness of the sediments underlying the No. 4 coal seam varies between 50 and 300 m. The coal-bearing Ecca Group ranges in thickness from 125 - 360 m and is comprised of an upper shale-like stage, the Volksrust Shale Formation, the mainly sandy coal measure stage, the Vryheid Formation, and a locally developed lower silt to shale stage, the Pietermaritzburg Shale Formation. The Vryheid Formation sediments developed in the NDC area are similar to those occurring elsewhere in the Highveld and Witbank Coalfields and are comprised mainly of sandstone, with lesser amounts of sandstone / siltstone and mudstone.

New Denmark is mined the No. 4 Seam. The No. 4 Seam is comparatively narrow at an average height of 1.8 m, being as low as 1.6 m in places.

New Denmark Colliery (NDC) is an underground mine and has been operational since 1983, extracting coal through both bord-and-pillar and longwall mining methods. The coal mined at NDC is transported via conveyors, from the Central Shaft to the stockyard located at Eskom’s Tutuka Power Station. The mine comprises four main operations areas, namely Central Shaft, North Shaft, Okhozini Shaft and a Crusher Plant. Infrastructure (such as offices, workshops, etc.) has been provided at all three shafts, but the main surface operations are located at Central Shaft. The coal is transported via conveyors, from the Central Shaft and the North Shaft, to the stockyard located at Eskom’s Tutuka Power Station.