A GEOCHEMICAL PROFILE THROUGH THE UITKOMST COMPLEX ON THE FARM SLAAIHOEK, SOUTH AFRICA, WITH REFERENCE TO THE PLATINUM GROUP ELEMENTS AND SM-ND ISOTOPES
A detailed petrographic and geochemical investigation of borehole core SH176 shows that the Complex may have crystallized in a dynamic conduit setting. The whole rock geochemical trends indicate that there is a reversed fractionation in the basal portion of the Complex and a lack of fractionation in much of the MHZBG. Trace and Rare Earth Element variations show a decrease in concentration with height, contrary to what is expected of a progressively differentiating magma in a closed system. Further, the PGE concentration of the four basal units show no depletion with increasing height, suggesting that the individual units are not related to each other by means of in situ fractionation. Instead, a model whereby the individual units crystallized from distinct pulses of magma best explains the data.
By comparing Nd isotopes and ratios of highly incompatible trace elements like [Th/La]n and [Sm/Ta]n from the Uitkomst and the Bushveld Complex it is seen that the Uitkomst magmas are of a similar lineage as the B1 magma of the Bushveld Complex, supporting a genetic link between the two complexes. The upper portion of the Uitkomst Complex shows values more akin to B3 magmas indicating the possible presence of more than one type of magma. The relatively low Cu/Ni ratios of the sulphides in the LHZBG, PCR and MHZBG (Cu/Ni 0.03 to 0.8) may be modelled by segregation from B1 magma and not from fractionation of sulphides that were later entrained in the streaming magma.