Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Longitude: 8.87, Latitude: 10.8

Approximately circular and 6 km in diameter, Gamawa consists of a broad ring-dyke of amphibole-aegirine granite which was succeeded by a boss of pyroxene-fayalite-quartz syenite. An early volcanic phase is represented by a narrow zone of breccia along the inner contact of the ring-dyke in the southeast, which is made up almost entirely of fragments of basement granite, and two diatremes within areas of basement granite enclosed within the ring-dyke. The granite of the ring-dyke consists of quartz, perthite, albite, arfvedsonite, aegirine, aenigmatite and accessory zircon and fluorite. The rock of the syenite boss is variable between localities and consists of perthite, a little quartz and aegirine-augite, while fayalite, aenigmatite, amphibole and biotite may or may not be present. A small intrusion of aegirine-riebeckite granite cuts the syenite and late felsite dykes, in which needles of blue sodic amphibole and aegirine are abundant, cut all rock types.

JACOBSON, R.R.E. and MACLEOD, W.N. 1977. Geology of the Liruei, Banke and adjacent younger granite ring-complexes. Bulletin, Geological Survey of Nigeria, 33: 1-117.
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