The Bushveld magmas were strongly sulfide undersaturated during emplacement, leading to accumulation of S-poor ultramafic cumulates of the Lower and Lower Critical zones. The magmas in the chamber eventually reached sulfide saturation in response to differentiation, forming sulfide-bearing noritic cumulates of the Upper Critical Zone and gabbonoritic cumulates of the Upper Zone. Prior to complete solidification of the rocks, the Main Zone was injected as the last major magma addition into the pile of cumulate mushes. This caused subsidence of the chamber, mobilization and mixing of semi-consolidated cumulate mushes and, in places, gravity-driven, mechanical un-mixing of crystals and liquid leading to the formation of distinct layers, plugs and pipes enriched in olivine, pyroxene, plagioclase, chromite, magnetite, and sulfides, particularly in more centrally located portions of the Bushveld Igneous Complex
