CONVECTIVE SCAVENGING AND CASCADE ENRICHMENT IN BUSHVELD COMPLEX MELTS - POSSIBLE MECHANISM FOR CONCENTRATION OF PLATINUM-GROUP ELEMENTS AND CHROMITE IN MINERALIZED LAYERS

The shear-driven aggregation of suspended particulate matter in fluids is a common industrial method of concentration and separation. Such p rocesses must be associated with convecting systems, in which boundary layers are of primary importance in securing concentration. A conside ration of this mechanism indicates that ore-grade concentrations of pl atinum-group elements (PGE) may be secured from a primary melt of Bush veld composition within accepted lifetimes of a Bushveld magma chamber . In addition, convective scavenging systems are capable of producing the observed peculiarities of concentration profiles in the Bushveld C omplex. Crystalline precipitates from the immiscible sulphide liquid i n the cooler, upper reaches of the magma cascade downwards into unders aturated, hotter regions; there they are resorbed, enriching the lower layers until further cooling secures high levels of concentrates in z ones of high shear.