Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences



Occurrence number: 
Longitude: 15.95, Latitude: -12.15

A circular pattern of hills of fenite define a 6 km-diameter ring in the centre of which is a complex of carbonatites of lower relief. The country rocks are poorly exposed Precambrian granites. Apart from the central carbonatite and the ring of fenite hills most of the complex is obscured by a mantle of Recent sediments and soils. The carbonatites, the true extent of which is not known because of overlying sediments, comprise a central oval body of 1.3x1.0 km which is enriched in iron oxides, barite and apatite, and a surrounding calcite carbonatite. A smaller area of carbonatite lies on the northern side of this central outcrop and numerous areas of calcite carbonatite cut the fenite ring, notably on the eastern and southern sides. The carbonate of the central carbonatite is dominantly calcite but dolomite and ankerite are also plentiful. Apatite is abundant, but patchy in distribution, and barite is almost universally present; magnetite, bastnasite, parisite/synchysite, rare earth phosphates, pyrochlore, hollandite and strontianite have also been identified. The calcite carbonatite contains abundant magnetite, which may be concentrated in streaks, a little barite, tetraferriphlogopite, in some areas zoned pyrochlore and may be silicified, particularly in the carbonatites within the fenites. The fenites have been variably feldspathized with replacement of quartz and development of sodic pyroxene and amphibole. Some palaeomagnetic data for carbonatites are given by Allsopp and Hargraves (1985). Alberti et al. (2000) give analyses, including REE and C, O, Sr and Nd isotope data, for three carbonatites, a phoscorite and an apatite cumulate.

Small-scale mining of magnetite from the central carbonatite was formerly undertaken and preliminary assessment made for exploiting the superficial deposits and the central carbonatite. Accessories in these deposits include pyrochlore, apatite and barite.

ALBERTI, A., CASTORINA, F., CENSI, P., COMIN-CHIARAMONTI, P. and GOMES, C.B. 2000. Geochemical characteristics of Cretaceous carbonatites from Angola. Journal of African Earth Sciences, 29: (in press).ALLSOPP, H.L. and HARGRAVES, R.B. 1985. Rb-Sr ages and palaeomagnetic data for some Angolan alkaline intrusives. Transactions of the Geological Society of South Africa, 88: 295-99.ISSA, A., DOS SANTOS, A.B.R.M.D., RIFFEL, B.F., LAPIDO-LOUREIRO, F.E.V. and MCREATH, I. 1991. Aspects of the geology, petrology and chemistry of some Angolan carbonatites. Journal of Geochemical Exploration, 40: 205-26.LAPIDO-LOUREIRO, F.E. 1973. Carbonatitos de Angola. Memórias e Trabalhos do Instituto de Investigação Científica de Angola, 11: 1-242.

Fig. 3_10 Bailundo (after Lapido-Loureiro, 1973, p. 126).
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