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.
|Number of pages||15|
|Publication status||Published - 1984|