The Bushveld layered sequence around Modikwa strikes northnorthwest to south-southeast and dips to the southwest at 10º to 12º, with local variations in the dip resulting in gradients of nearly 20º. There are several instances where some gentle ‘rolling’ of the reef horizons have been recorded, and normally steeper dips are noted nearer the outcrop (as opposed to at depth).

The outcrop positions of the Merensky Reef and the UG2 normally occur within the areas of low relief, and much of the outcrop is masked by extensive development of black turf, as well as, in places, transported sediments. On the farms Maandagshoek 254 KT, Onverwacht 292 KT and Winterveld 293 KT; however, the UG2 (and occasionally the Merensky Reef) outcrops in a series of elongated hills. Although frequently covered with scree material, much of this outcrop has been marked by a series of trenches and pits, many of which date from early pioneer prospecting.

Both the UG2 and Merensky Reefs are present at Modikwa. The UG2 occurs as a chromitite layer with an average thickness of approximately 60 centimetres. Three leader chromitites occur above the main seam. Gentle undulations of the UG2 with amplitudes of less than 2 metres are developed across the mine area. Potholes are randomly distributed within the North Shaft area but are less abundant in the South Shaft area. The Onverwacht Hill area in the southern portion of the mine is characterised by the presence of several large ultramafic pegmatoid intrusions that disrupt, and locally replace, the UG2.

Mining consists of mechanised development and conventional stoping. The UG2 is accessed via two primary declines from the surface, and South 2 shaft. Run-of-mine tonnage is processed at the Modikwa concentrator and the PGE-rich concentrate is transported to Anglo Platinum’s Polokwane smelter and refining facilities.

Froth flotation is the primary mineral processing separation step employed in the beneficiation of PGM ore bodies. Anglo Platinum operates a significant portion of the total installed flotation capacity in the PGM industry, which is installed at 20 operating plants across the Bushveld.

Anglo Platinum has 20 operating concentrators sited around the Eastern, Northern and Western limbs of the Bushveld complex. The concentrators treat mainly Merensky and UG-2 ores, with Potgietersrust (PPL, Sandsloot) and PPRust North being the only two plants designed to treat the Platreef ore.

For typical UG2 ores, for example, the finer natural PGM grain size in the in situ ore and the relative performance of PGM flotation plants indicate that the ‘watershed’ size where flotation drops off significantly must be relatively fine. This is indicated in, where data collected from a UG2 concentrator illustrate the relative recovery by size fraction in the mainstream roughers and scaven ........