Alkaline Rocks and Carbonatites of the World

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Chaumbwi Vent


Occurrence number: 
Chilwa Province
Longitude: 34.8, Latitude: -15.05

This is a small agglomerate vent the full size of which is obscured by debris, but it is probably several hundreds of metres long. The gneisses in the vicinity of the vent are fractured with ramifying veins filled with aegirine. The fragments in the vent are up to 20 cm across and heavily fenitized with replacement by aegirine and albite. The matrix to the fragments contains phenocrysts of altered olivine and augite, which in areas adjacent to carbonate has aegirine-augite rims, and microphenocrysts of barkevikite and pyroxene in a groundmass of barkevikite, augite, orthoclase, albite, titanomagnetite, vug-like areas of carbonate, and fluorite. The matrix is in places cut by ramifying veins of albite, orthoclase and aegirine.

GARSON, M.S. 1965d. The geology of the area west of Lake Malombe, Fort Johnston District. Records, Geological Survey of Malawi, 3: 35-48.
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