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.