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.

Only underground mining methods are employed. The coal seam is accessed by means of three shaft systems (Central Shaft, North Shaft and Okhozini Shaft). The following underground mining methods are presently employed and are envisaged to continue until the end of the life of the mine.

Continuous miner mechanised mining is used to develop the bord and pillar primary, secondary and tertiary developments. The coal seam is mined to its full thickness. This method of development was selected on the grounds of productivity, requiring less equipment and less manpower than conventional mechanisation. The primary development is the main development on the mine. It offers primary access to the coal seam. The number of roadways is determined by the ventilation requirements. The centre set of roadways carry intake air and is flanked by two further sets of roadways, that carry return air. The secondary development is developed off the primary access to give access to mining reserve blocks. These developments also consist of central intake airways flanked by two return airways that are separated by a solid pillar. The number of roadways is also determined by the ventilation requirements.

The tertiary development is developed off the secondary developments to give access to each individual block. The number of roadways is also dependent on the ventilation requirements. Three road chain developments are developed off the tertiary developments to allow access to the total extraction panels. The roadways are at a 25 m square spacing for primary and secondary developments, with 7.0 – 7.5 m bord widths, giving a safety factor of more than two, using the squat pillar formula.

Longwall mining
Two sets of chain roads are driven for 1 500 - 4 000 m to establish the block to be mined. Once the chain roads have reached their extremity, they are joined by two or more roads to form the face line. Faces up to 250 m in length are mined. The longwall equipment is installed on the face line. The roof strata on the face are supported by hydraulically operated 825 tonne capacity two leg chock shield supports. A double-ended ranging drum shearer travels from one end of the face to the other, cutting off approximately 1 m web of coal. All the equipment is moved forward behind the shearer as it cuts.

The coal is transported away from the face by an armoured face conveyor, that discharges the coal at a rate of 1 750 tonnes per hour onto the section belt by means of a stage loader. A longwall face is capable of consistently producing in excess of 300 000 tonnes of coal per month.

Stooping
Stooping operations started at the end of 2018 to increase extraction by mining the pillars remaining in previous bord-and-pillar production panels in the Central Shaft area. Safe stooping operations are achieved by mining according to the approved planning and mining processes and associated standards:
• Benchmarking;
• NEVID method;
• Breaker lines;
• Policeman sticks;
• Risk assessments and inspections;
• Trained and competent workforce;
• Protection of surface structures; and
• Rock Engineering Safety topics.

According to the NDC Pillar extraction memo dated January 2019, pillar extraction will be done as per the Nevid (and/or an adjusted Nevid) extraction method. No extraction will take place on pillars that correspond to D/2.7 distance (where D is the depth below surface) where surface structures are present, and no pillar extraction will be planned underneath surface structures/restrictions. A zone calculated by D/2.7 will be left in situ to protect surface structure / restriction with future mining. Maximum subsidence expected is a 1/3 of the mining height., with actual subsidence between 0.3 – 0.5 m expected.

The coal processing plant is basically comprised of the Crusher Plant. The Crusher Plant is located between the North and Central Shaft areas and adjacent to the Coal Stockyard.

In order to meet the more stringent coal quality requirements of Eskom, NDC proposes to construct a De-Stoning Plant adjacent to the existing Crusher Plant.