Mickberg

The Mickberg occurrence forms a 100 m high double-crested hill of gneiss that is brecciated in places and intruded by several bodies of ankeritic beforsite, the largest of which is about 160x110 m. The carbonatite contains numerous inclusions of gneiss, grit and quartzite some of the last being blue in colour owing to fenitization which has generated tufts of crossite and a mosaic of alkali feldspar. The carbonatite comprises ankerite, ferroan calcite, apatite, magnetite, biotite, chlorite and, in places, a blue sodic amphibole; there is minor malachite and chrysocolla. Verwoerd (1993) describes the presence in the largest carbonatite body of spheroidal inclusions up to 15 cm in diameter consisting of shells of fine-grained ankerite and angular fragments around lithic nuclei 1-7 cm across. He suggests generation by accretion in a fluidized system.