Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Longitude: 15.32, Latitude: -21.97

Eureka consists of several curving carbonatite dykes with a maximum thickness of 7 m (Dunai et al., 1989). They intrude feldspathic quartzites which are fenitized for up to 20 m and intensely fenitized along the contacts with the production of 20 cm thick orthoclasite zones. Verwoerd (1967) describes the occurrence as a monazite deposit in which the monazite forms aggregates of platy crystals up to 13 cm across with a chemistry more akin to that of carbonatite monazite than pegmatite monazite. The carbonate rock consists of 30% dolomite, 5% calcite and 5 % of magnetite, graphite and pseudomorphs of serpentine-like minerals, secondary carbonates and goethite. Analyes of four carbonatite samples by Dunai et al. (1989) indicated 24,550 to 30,580 ppm Sr and 87Sr/86 values of 0.70286-0.70318.

A separated sample of monazite dated by the Pb method gave 500±20 Ma (Burger et al., 1965).
BURGER A.J., KNORRING, O.VON and CLIFFORD, T.N. 1965. Mineralogical and radiometric studies of monazite and sphene occurrences in the Namib Desert, South-West Africa. Mineralogical Magazine, 35: 519-28.DUNAI, T., STOESSEL, G.F.U. and ZIEGLER, U.R.F. 1989. Note: a Sr isotope study of the Eureka carbonatite, Damaraland, Namibia. Communications of the Geological Survey of Namibia, 5: 89-90.VERWOERD, W.J. 1967. The carbonatites of South Africa and South West Africa. Handbook, Geological Survey of South Africa, 6: 1-452.
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