Pyroxenite and anorthosite of the Critical Zone in the eastern belt of the Bushveld complex are extensively but incompletely replaced by ultramafic pegmatites, some of which are rich in magnetite. Formation of the pegmatites has involved loss of silica and alumina and addition of iron and, locally, magnesia. Water, as a vehicle, is required from an outside source, but products of replacement need represent only a rearrangement of substances available in rocks of the Critical Zone. Mineralogy and textures suggest high temperature.

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