The New Vaal colliery coal reserves are located in the northernmost part of the Vereeniging – Sasolburg coalfield in an area locally referred to as the Cornelia coalfield. The coalfield field occurs on the northern edge of the Karoo basin.

The Permian age Ecca Series are part of the Karoo System. The Vryheid Formation of the Ecca Series contains three major coal seams, the Top, Middle and Bottom seams. The Dwyka Series, a sequence of glacial and fluvio-glacial sediments occurs below the coal measures and lie unconformably on the Transvaal System. In the New Vaal area the Transvaal Dolomite underlies the Karoo except for a narrow strip of Black Reef Quartzite that occurs along the eastern edge of the New Vaal mine area.

The Dwyka series is not continuous across the whole area and, in places the coal measures lie on the Dolomite. The contact between the Dolomite and the overlying Karoo rocks is a glaciated surface that was previously affected by structural features of the Dolomite such as doline structures.

Quaternary age river alluvium consisting of unconsolidated basal river gravels, sands, silts and clays were deposited onto the eroded Karoo surface. Wind blown, (aeolian) sand occurs in the upper few metres of this Quaternary sequence that ranges from 4 to 30 metres in thickness.

The New Vaal mine floor is undulating but the overall dip of the coal bearing Ecca Series is 2 to 3 degrees to the south. Two major geological features occur and are significant in the geohydrological regime of the area. These are:
- A dolerite dyke swarm that strikes east west through the northern part of the New Vaal reserves. The swarm zone is up to 60 metres wide and in places individual dykes are greater than 20 metres in width.
- The Viljoensdrift fault, also locally called the Valley fault, is a graben structure that strikes east west and forms the southern boundary of the New Vaal mine and separates it from the old Cornelia Colliery to the south. It has downthrown the Karoo rocks 60 to 100 metres below their original elevation. This graben varies between 1,3 and 2 kilometres in width.

The New Vaal coalfield contains three main coal seams, termed the top (9.7m), middle (6.0m), and bottom (4.9m) seams. Although all three seams had been mined previously, most of the old workings are in the middle seam.

The New Vaal utilises opencast strip mining methods to mine the remnant coal pillars that was a result of the underground extraction mining methods practiced in the area in the 1960’s. The colliery has three different pits: namely North, South, and West pit with a dragline in each pit. The draglines remove the hard overburden from the pit and place it on the spoil heap. The mining operation at New Vaal Colliery is divided into three sections: namely Sand Stripping, Draglines, and Coaling.