stripes
Near the village of Sutherland, 20 km northwest of Saltpeterkop (No. 151-00-041), there are numerous outcrops of olivine melilitite (Verwoerd et al., 1990, Fig. 14) that Rogers and du Toit (1904) interpreted as a series of necks together with semi-circular dykes, but Taljaard (1937) considered represented sheets intruded into Karoo sandstones. Verwoerd et al. (1990) indicate that there are dykes which also feed a number of sills that are probably no more than 3 m thick. Both grey and green melilitites are distinguished by Verwoerd et al. (1990) who consider that the grey is younger as it contains small xenoliths of the green. The green melilitites contain olivine, partly replaced by phlogopite, in an altered groundmass which includes opaque spinel, perovskite, apatite, garnet, zeolites, carbonate, bleached phlogopite, chlorite, serpentine and clay minerals. Nepheline, melilite and clinopyroxene may have been present formerly. The grey melilitite is characterised by the presence of plentiful olivine and magnetite phenocrysts up to 1 cm in diameter in a fine-grained groundmass dominated by monticellite. Melilite, perovskite, spinel, nepheline and minor apatite and phlogopite are also present. Rock and mineral analyses are given by Duncan et al. (1978), McIver and Ferguson (1979), and Boctor and Yoder (1986), mineral analyses by Dawson et al. (1985) and there are modes in Verwoerd et al. (1990).
BOCTOR, N.Z. and YODER, H.S. 1986. Petrology of some melilite-bearing rocks from Cape Province, Republic of South Africa: relationship to kimberlite. American Journal of Science, 286: 513-39.DAWSON, J.B., SMITH, J.V. and JONES, A.P. 1985. A comparative study of bulk rock and mineral chemistry of olivine melilitites and associated rocks from East and South Africa. Neues Jahrbuch für Mineralogie, Abhandlungen, 152: 143-75.DUNCAN, R.A., HARGRAVES, R.B. and BREY, G.P. 1978. Age, palaeomagnetism and chemistry of melilite basalts in the southern Cape, South Africa. Geological Magazine, 115: 317-27.MCIVER, J.R. and FERGUSON, J. 1979. Kimberlitic, melilitic, trachytic and carbonatite eruptives at Saltpetre Kop, Sutherland, South Africa. Proceedings of the Second International Kimberlite Conference, American Geophysical Union, 1: 111-28.ROGERS, A.W. and DU TOUT, A.L. 1904. The Sutherland volcanic pipes and their relationship to other vents in South Africa. Transactions of the South African Philosophical Society, 15: 61-83.TALJAARD, M.S. 1937. South African melilite basalts and their relations. Transactions and Proceedings of the Geological Society of South Africa, 39: 281-316.VERWOERD, W.J., VILJOEN, J.H.A. and VILJOEN, K.S. 1990. Olivine melilitites and associated intrusives of the southwestern Cape province. Guidebook Geocongress ’90, Geological Society of South Africa, PR3: 1-60.