Abstract

Three major sulfide zones containing platinum group elements (PGE) have been identified in the upper part of the ultramafic sequence of the Great Dyke. The PGE are at the bases of the sulfide zones; the lower two have sparse sulfide mineralization over a thick interval; the upper zone contains higher grade in a thinner stratigraphic layer. None of the current models for the formation of stratabound sulfide deposits in layered intrusions adequately accounts for the mineralization. The two lower sulfide zones are interpreted as resulting from progressive fractional segregation of sulfide from the silicate magma, whereas the upper zone may have resulted from mixing of a relatively primitive magma at the base of the chamber with an evolved liquid derived from near the roof.

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