Buffelskraal

This complex generally does not outcrop but is represented at the surface by scarce scattered boulders over ploughed maize lands. It was discovered by airborne magnetic and gravity mapping and subsequently drilled, the drill core being the source of most of the following information (Frick and Walraven, 1986). The complex consists essentially of alkaline pyroxenite intruded by numerous ijolitic dykes that vary from urtite through to jacupirangite. Two dykes of nepheline syenite and two dykes referred to by Frick and Walraven (1986) as ‘basaltic’ have also been encountered. The pyroxenite is intrusive along steep contacts into dolomite of the Transvaal Sequence, which is altered to calc-silicate hornfelses. The pyroxenites vary from fine-grained to pegmatitic and consist of diopside, magnetite and ilmenite with secondary biotite, titanite and hematite. In the vicinity of ijolite dykes nephelinisation has produced a complete suite of pyroxene-nepheline rocks in which the diopside is partially or wholly altered to aegirine-augite. The ijolite dykes vary from a few centimetres to several metres thick the contacts ranging from sharp to gradational with nephelinisation of the pyroxenite associated with the gradational contacts. The dykes range from urtite to melteigite and are texturally highly variable. They comprise aegirine-augite, which in places is replaced by biotite, nepheline, which is variably altered to cancrinite, and accesory magnetite, ilmenite and apatite. The two ‘basaltic’ dykes contain phenocrysts of diopside which may be rimmed by aegirine-augite, in a matrix of small, acicular aegirine-augites, grains of magnetite and ilmenite, sparse laths of anorthoclase, and masses of zeolites and cancrinite which Frick and Walraven (1986) suggest could be after pseudoleucite. The nepheline syenite dykes comprise perthite, nepheline and diopside rimmed by aegirine-augite. A suite of rocks have been analysed but although these analyses are briefly discussed by Frick and Walraven (1986) the data are not given.