Gibeon

Among the kimberlite occurrences of the Gibeon province are a number of carbonate-rich rocks that may be carbonatites, as well as a rather altered rock which could be a melilite basalt (Janse, 1975). On the farm 'Hatzium 2' a 110 m-diameter circular pipe consists of a carbonate-rich rock with garnet and ilmenite megacrysts and a core consisting of rock containing magnetite octahedra set in a groundmass composed principally of apatite. A 2 m-wide dyke of carbonate rock enters the pipe. This is the ‘Hatzium’ locality of Verwoerd (1993). Some 2 km south of this pipe a vein of calcite and barite about 2 m wide has been found. A similar carbonate-rich dyke occurs on the Mukorob' farm. Apart from carbonate there are inclusions of country rock together with nodules of diopside-ilmenite and diopside-garnet with even more numerous nodules of serpentinized olivine with concentric shells of ilmenite. Frankel (1956) identified melilite pseudomorphs in this rock which he considered to be an olivine melilitite. A further carbonate dyke, connecting two kimberlites, is found on the farm 'Amalia' for which an analysis is given by Janse (1975), while similar dykes are also found in the Ovas area (see Janse, 1975, Fig. 2).