The Bushveld Complex is an extremely large (65 000km²), two billion-year-old layered igneous intrusion occurring in the northern part of South Africa. Rock types range in composition from ultramafic to felsic. The complex is not only unique in size, but also in the range and economic significance of its contained mineral wealth. In addition to the PGMs and associated base metals, vast quantities of chromium, vanadium, tin, fluorine and dimension stone are also produced.

The accompanying map (page 21) and schematic diagram (page 19) show the extent of the Bushveld Complex. The layered sequence, the Rustenburg Layered Suite, comprises five major sub-divisions. These are, from the bottom upwards, the marginal, lower, critical, main and upper zones as indicated in the generalised stratigraphic column below. Two horizons within the critical zone, namely the Merensky Reef and the Upper Group 2 (UG2) Reef, host extensive economically exploitable quantities of PGMs. These two horizons, along with other layers, which can be traced for hundreds of kilometres around the complex, are the focus of Implats’ operations. The PGMs – platinum, palladium, rhodium, ruthenium and iridium – as well as the associated gold, copper, nickel, cobalt, chromium and other minor metals and compounds, are mined concurrently, but recovered by different processes. Chromitite layers present below the UG2 Reef contain little to no PGM mineralisation and are mined by other operators for their chromium content.

Implats’ operations on the Bushveld Complex comprise Impala Mine north of Rustenburg, Marula Mine north-west of Burgersfort and the Two Rivers Mine, a joint venture between Implats and African Rainbow Minerals Limited (ARM) situated south-west of Steelpoort.

A detailed geological description of the various reef types is provided in the relevant operational sections. Examples of different Merensky Reef vertical grade profiles are shown above. It is clear that the grade distribution varies materially from area to area. The UG2 Reef morphology and associated vertical grade distribution also differs significantly between regions (see above), specifically in terms of the width of the main platinum bearing chromitite layer and in the number of layers. In general the grade increases if the chromitite layer width becomes thinner.

The Great Dyke is a 2.5 billion-year-old layered maficultramafic body intruded into Archaean granites and greenstone belts. It is highly elongated, slightly sinuous, 550km long, north-northeast trending with a maximum width of 12km. It bisects Zimbabwe in a northnortheasterly trend and is divided vertically into a lower ultramafic sequence, comprising cyclic repetitions of pyroxenite, harzburgite, dunite and chromitite, and an upper mafic sequence consisting mainly of norite, gabbronorite and olivine gabbro. The accompanying schematic diagram and map show the extent of the Great Dyke. It is U-shaped in section with layers dipping and flattening towards the axis of the intrusion. Much of the mafic sequence has been removed by erosion and at the present plane of erosion the Dyke is exposed as a series of narrow, contiguous layered complexes or chambers. These are, from north to south, Musengezi, Hartley (comprising the Darwendele and Sebakwe sub-chambers) and a southern chamber comprising the Selukwe and Wedza sub-chambers.

The Main Sulphide Zone (MSZ), host to economically exploitable PGMs and associated base metal mineralisation, is located 10m to 50m below the ultramafic/ mafic contact in the P1 pyroxenite. The PGMs, along with gold, copper and nickel, occur in the MSZ. A detailed description of the MSZ and the value distributions is provided in the relevant operations sections. Examples comparing different areas indicate that the grade profiles vary between areas and that the platinum and palladium peaks are somewhat offset. Typically, the MSZ consists of a 2m to 10m-thick zone containing 2% to 8% of ironnickel- copper sulphides disseminated in pyroxenite. The base of this nickel-copper-rich layer is straddled by a 1m to 5m-thick zone of elevated precious metals (Pt, Pd, Rh and Au). The base metal zone contains up to 5% sulphides, while the sulphide content of the PGM zone is less than 0.5%. This change in sulphide content is related to the metal distribution in a consistent manner and is used as a mining marker. It can normally be located visually in borehole core and with careful observation it can also be located underground, therefore careful monitoring supported by channel sampling and XRF scanning is required to guide mining.

Chromitite layers present below the MSZ contain little to no PGM mineralisation and are mined by other operators for their chromium content only.

Implats’ Operations on the Great Dyke comprise Zimplats’ Ngezi Mine south-west of Harare and the Mimosa Mine, a joint venture between Implats and Sibanye-Stillwater situated east of Bulawayo.