Nooitgedacht (Gelukshoek, Nooitgedagt)

The Nooitgedacht carbonatite complex lies just 4 km north of Kruidfontein (No. 151-00-013) and these two occurrences are situated with Tweerivier (No. 151-00-014), Buffelskraal (No. 151-00-011), Bulhoekkop and Bulhoek South (No. 151-00-015), Welgevonden (No. 151-00-016) and Keikamspoort (No. 151-00-017) precisely along a north-south line. Much of the eastern part of the complex is obscured by flats along the Crocodile River while elsewhere the soil cover is extensive. Although the precise outline of the mass is not clear, because of want of exposure, it appears to be an ovoid body 3.2 km long orientated in a northwesterly direction. An isolated outcrop of carbonatite northeast of the main body may be a subsidiary intrusion. Carbonatite is by far the most abundant rock outcropping but there is also a little nepheline syenite and there are marginal fenites as well as an extensive area of fenite within the complex. Sovite, the earliest and most abundant carbonatite, has a concentric flow structure, generally with vertical or steep inward dips. Calcite is the only carbonate present and the planar structure is generally defined by layers of magnetite and apatite; phlogopite, pyrite, pyrochlore, chondrodite and fluorite are also present. Conspicuous outcrops near the centre of the complex are sovites bearing quartz and ankerite which form dykes cutting across the flow banding of the sovite. The proportions of calcite and ankerite are variable and Verwoerd (1967) cites textural evidence for replacement of the former by the latter. Pyrochlore is an accessory within calcite areas, whereas monazite and pyrite are mostly embedded in quartz which is associated with the ankerite; quartz may form 50% of some rocks. Beforsite is found as intrusions up to 500 m long and 2 m wide, which may be conformable to the sovite banding or cut across it. The principal constituents are ankerite, dolomite, apatite and quartz with a little monazite and pyrite; calcite may form microscopic veinlets. Limestone of the Transvaal sequence adjacent to the contact shows no contact effects, but at a number of places quartzites have been fenitized. The fenites contain aegirine-augite and feldspar including orthoclase, turbid perthite and subordinate plagioclase. One type of fenite has a migmatitic structure with alternating pyroxene-rich and feldspathic streaks. In some fenitized quartzite xenoliths sodic amphibole and pyroxene and alkali feldspar have developed. Nepheline syenite outcrops are found in four areas, although all of them are small, three of which are just outside the main complex. In all examples they consist of alkali feldspar, nepheline and aegirine or aegirine-augite with accessory titanite and apatite and some alteration of nepheline to cancrinite. At two of the localities the paucity of feldspar classifies the rocks as ijolite or urtite. A tinguaite dyke of similar mineralogy has also been located. Ba and Sr data for three carbonatites are given by Verwoerd (1967).