Ondurakorume (Kameelberg)

The Ondurakorume carbonatite complex forms a prominent hill rising to 275 m, is approximately circular in outline and has a diameter of 1.4 km. Silicate rocks are minor within the carbonatite complex but form a substantial intrusion immediately to the south. The country rocks are Damara System marbles, quartzites, greywackes and schists invaded by granite. The marbles are in contact with sovite in places and, although a range of contact metamorphic minerals developed, there is no indication of fenitization. Granites and quartzites, however, are shattered and fenitized up to 300 m from contacts with the development of sodic pyroxene and amphibole. Breccia bodies on the northern and western margins consist of country rock fragments up to 30 cm in diameter in a matrix of comminuted rock and feldspar grains and patchy calcite, aegirine and sodic amphibole. They are enveloped and penetrated by carbonatite dykes. The principal carbonatite is a micaceous sovite in which the fine-grained biotite is generally altered to chlorite or vermiculite, and in which there are patches of glimmerite. Nodular structures of 3 mm to 5 cm diameter occur in places, these having diameters and consist of biotite, calcite and apatite. Aegirine, magnetite and zircon are also present. Sovite forms five major bodies and a number of smaller ones, some in the form of arcuate ring-dykes. This rock consists of calcite, with some replacement by parankerite, apatite and accessory magnetite, which often defines a banding, strontianite, green monazite, pyrite, biotite and sodic amphibole. The last major period of carbonatite emplacement is represented by a complex system of arcuate ring dykes of beforsite, some of which cut the country rocks. They consist of parankerite, a little calcite, apatite, which may be abundant, and accessory quartz, ancylite, monazite, galena and pyrite. Parts of some beforsite dykes are characterised by abundant blue sodic amphibole. Veins and dykes, up to several metres wide, of oxidised iron ore occur in micaceous sovite and beforsite. The carbonatite is traversed by a number of olivine dolerite dykes. An irregular semicircular body of nepheline syenite lies to the south of the carbonatite complex. It comprises microperthite, nepheline, which is largely replaced by cancrinite, aegirine, biotite and accessory magnetite, apatite and calcite. Analyses of the major rock types are given by Verwoerd (1967) and of carbonatites, including some trace elements, by Prins (1981). Whole rock chemical analyses and Sr, Nd and Pb isotope data for three rocks are in le Roex and Lanyon (1998).