The Platreef in the northern limb of the Bushveld Complex comprises pyroxenites and gabbros that contain enormous quantities of Ni, Cu and platinum-group elements (PGE) concentrated from a larger volume of magma than represented by the Platreef itself. Chill zones and cross-cutting relationships between the Platreef pyroxenites and hanging wall norites show that the Platreef was originally a relatively thin, sill-like, intrusion or sill network without an overlying magma column. Lower Zone cumulates pre-date the Platreef and show depletion in Ni and Cu compared with similar rocks elsewhere in the Bushveld, suggesting that they interacted with sulphides in a sub-chamber or conduit. In order to overcome the mass balance paradox imposed by the absence of an overlying magma a new model for the development of the Platreef is proposed whereby Ni, Cu and PGE were concentrated in conduits that fed magma chambers of the Lower Zone and that these sulphides were transported by a later magma into the Platreef.

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