The oxide minerals of the Wesselton mine kimberlite, Kimberley, South Africa

The compositions of the constituent spinels, ilmenites, rutiles and perovskites have been determined in six kimberlite intrusions at Wesselton. Groundmass spinels show a normal magmatic trend of Cr-rich, Ti-poor chromite cores and Ti-rich, Cr-poor titanomagnetite rims. Spinels from peridotite xenoliths are compositionally distinct from groundmass spinels. Ilmenites occur as: 1) macrocrysts; 2) in metasomatized peridotites; 3) as inclusions in olivine phenocrysts; and 4) as groundmass grains in the kimberlite. Despite some overlap they can be distinguished compositionally. The origin and crystallization sequence of oxide minerals at Wesselton is pre-intrusion: chromite (xenocrysts), rutile macrocrysts (xenocrysts), ilmenite macrocrysts (phenocrysts or xenocrysts?), groundmass chromite, rutile and ilmenite inclusions in olivine phenocrysts, groundmass ilmenite (microphenocrysts); and post-intrusion: groundmass titanomagnetites, perovskites and magnetites (microphenocrysts). -J.M.H.