Extending over 66,000 square kilometres, the Bushveld Igneous Complex is the world's largest known deposit of platinum group metals (PGMs). The PGMs – namely platinum, palladium, rhodium, ruthenium, osmium and iridium – occur with small amounts of gold, nickel, copper and cobalt, mainly in the UG2 and Merensky horizons. The Bushveld Igneous Complex also boasts the largest resources of chromium and vanadium in the world.

The complex is a 2 billion year-old igneous intrusion with outcrop extremities approximately 450 Km east-west and 300 kilometres north-south, with a thickness of between 7 and 9 kilometres. The complex contains diverse igneous rocks which vary from plutonic to volcanic, with compositions ranging from ultramafic to felsic. The lateral persistence and regularity of its layers is notable.

It is understood that the Bushveld Igneous Complex was formed by the ongoing injection of magma into a sub-volcanic chamber. As the volumes of magma were considerable, cooling and crystallisation were slow processes. Different minerals were formed as the magma cooled and these accumulated into sub-horizontal layers, building from the base of the chamber. Such processes were repeated by the intermittent replenishment of magma, and so the mineral layering built up.

While the Merensky reef was the source of most of South Africa's PGMs in the past, approximately 76% of current South African production comes from the UG2 reef. The UG2, although of slightly lower grade than the Merensky reef, is more consistent throughout the Bushveld Igneous Complex and contains approximately 75% of its known remaining PGM resource.