The Bushveld Complex consists of three roughly coeval components, namely the Lebowa Granite Suite, the Rashoop Granophyre, and the Rustenburrg Layered Suite (RLS), the latter being the only economically important unit. The RLS underlies an area of ∼65,000 km2 in the northeast sector of South Africa, and is the oldest and largest mafic-layered complex in the world (Figure 1). It is also the largest repository of magmatic ore deposits and hosts, inter alia, 80% of the world's platinum-group-metal (PGM) resources and most of the chromitite resources. Over an east-west distance of roughly 350 km, the RLS outcrops as three apparently discrete, crescent-shaped lobes (the Western, Eastern and Northern limbs) and lies below cover rocks along the southeastern limb. The far Western Limb is currently not of economic significance. Lithologies range across mafic and ultramafic cumulates plus anorthosites. Pseudo-stratigraphic layering exhibits dips of 8–20° toward the center of the complex. The UG2 and Merensky “reefs” constitute the major PGM-bearing horizons of mining interest and fall close to the top of the 1500-m thick Critical Zone, an assemblage of alternating leuconorite, anorthosite, and pyroxene rocks outcropping midway through the RLS succession.

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