Bulhoekkop And Bulhoek South

The volcanic vent of Bulhoekkop is situated 3.5 km west of Tweerivier South (No. 151-00-014) and forms a hill rising to about 250 m above the plain immediately north of the Elands River. Another centre Bulhoek South, which is of similar extent but with little topographic expression, lies 3 km to the south. Bulhoekkop consists of red fenitized granite which is cut by two areas of volcanic breccia, both rock types being traversed by dykes and large, irregular bodies of beforsite. Varying degrees of fenitization are often closely juxtaposed, relatively unaltered granites with abundant quartz lying close to almost pure feldspar rocks. The principal new mafic mineral is chlorite but remnants of acicular pyroxene also occur. The volcanic breccias consist of gabbro fragments which are traversed by numerous calcite-filled fractures, sericitised feldspar and pyroxene replaced by chlorite. Although apatite, calcite, biotite and opaque oxides appear to have been added to the gabbro there is no aegirine or sodic amphibole. The beforsite contains blocks of fenite and vent breccia and a chemical analysis is given by Verwoerd (1967), which indicates that chemically this rock is a ferrocarbonatite. The Bulhoek South occurrence consists of the same rock types as Bulhoekkop.