EMPLACEMENT AGES OF KIMBERLITE OCCURRENCES IN THE PRIESKA REGION, SOUTHWEST BORDER OF THE KAAPVAAL CRATON, SOUTH-AFRICA

Rb-Sr (mica) and U-Pb (perovskite) emplacement ages for kimberlites from the southwest part of the Kaapvaal Craton, near Prieska, South Africa, vary from as old as 170 Ma to as young as 74 Ma, similar to ages elsewhere in southern Africa. Isotopically defined Group-I and -II kimberlites are found on the Kaapvaal Craton northeast of the Doomberg and Brakbos lineaments (Domains I and II as defined by Skinner et al., 1992), with ages of 74, 108 and 118-125 Ma. Kimberlites in the craton margin area bounded by the two lineaments (Domain III) are exclusively Group II, with ages of 116-119 Ma. Kimberlites in Domain IV, to the south of the craton boundary, are of Group-I affinity emplaced in two episodes at 74 and 100-103 Ma. Southernmost Domain V is dominated by kimberlites petrographically, chemically and isotopically transitional between Group-I and -II types, but with the oldest ages at 140 and possibly 170 Ma. Phlogopite from a peridotite xenolith from the Sanddrift kimberlite has retained an age of 2250 Ma, presumably the enrichment age of the nodule.