Alkaline Rocks and Carbonatites of the World

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Upper Bua Area


Occurrence number: 
The North Nyasa Alkaline Province
Longitude: 33.22, Latitude: -13.68

Aegirine-bearing quartzo-feldspathic granulites and gneisses are thinly, but widely, spread over a large area drained by the upper reaches of the Bua River (Thatcher and Wilderspin, 1968) and extend northwards into the area south of Kasungu (Peters, 1969). The most continuous outcrop forms the Bhumi, Chafisi and Chikumba hills where an arcuate body of aegirine-bearing rocks extends over 12 km and is up to 700 m wide. The rocks have a banded gneissic structure and a colour index of 25 to 45. Aegirine forms upto 20% and is generally associated with prisms of riebeckite, some of which may have grown at the expense of the pyroxene. Microcline and oligoclase are equally abundant, quartz is of approximately the same volume as the feldspar and accessories include ilmenite, magnetite, anatase, zircon, biotite and titanite. Thatcher and Wilderspin (1968) give two whole rock analyses.

PETERS, E.R. 1969. The geology of the Kasungu area. Bulletin, Geological Survey of Malawi, 25: 1-55. THATCHER, E.C. and WILDERSPIN, K.E. 1968. The geology of the Mchinji-Upper Bua area. Bulletin, Geological Survey of Malawi, 24: 1-72.
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