Both the Merensky and UG2 Reefs are present but only the UG2 is currently exploited. However, no Merensky Reef is present on Tweefontein and the UG2 Reef only occurs on a small portion of this farm. The UG2 Reef outcrops in the Klein Dwarsrivier valley over a north-south strike of 7.5km and dips to the west at 7° to 10°. The vertical separation between the Merensky and UG2 Reefs is around 140m to 160m. Due to the extreme topography, the Merensky Reef outcrops further up the mountain slope.

The topography also means that the UG2 occurs at 935m below surface on the western boundary. The geological succession is broadly similar to other areas of the eastern limb of the Bushveld Complex. An exception is the presence of the Steelpoortpark granite in the south-western part of the project, which is unique to this area. Three distinct reef types have been defined for the UG2 Reef, namely the “normal” reef with a thick main chromitite layer; a “split” reef characterised by an internal pyroxenite/norite lens within the main chromitite layer; and a “multiple split” reef with numerous pyroxenite/norite lenses occurring within the main chromitite layer. The multiple split reef predominates in the southern portion of the mining area. The Merensky Reef is a pyroxenite layer with a chromitite stringer close to the hangingwall contact and also at the basal contact. Mineralisation is primarily associated with the upper and lower chromitite stringers. The graphical illustration of the profiles is shown overleaf.

The geological structure of the area is dominated by the regional north-northeast to south-southwest trending Kalkfontein fault, which has an apparent vertical displacement of 1 200m down throw to the west. A series of sub-parallel faults occur to the south-east adjacent to the Kalkfontein fault, which affect both the MR and UG2 Reefs. These faults exhibit variable apparent vertical displacements of between 20m and 300m, which increase progressively to the south-west.

The UG2 orebody is accessed via two decline shaft systems situated 3km apart, namely the Main Decline and the North Decline. Reef production is through a fully mechanised bord and pillar stoping method is employed where stoping widths average around 1.8 metres. A mining section consists of eight 8-12m bords, with pillar sizes increasing with depth below surface. In the shallow areas up to 100m below surface, the pillars are 6m x 6m in size. The rooms are mined mainly on strike.

Two Rivers has a concentrator plant on site where initial processing is done. It comprises a standard MF2 design as generally used in the industry. Concentrate is transported by road to Impala Mineral Processes in Rustenburg where further processing takes place in terms of an agreement with IRS.