Carbonatitic Lava from Fort Portal Area in Western Uganda

Abstract

IN an excellent paper Holmes¹ quotes chemical analyses of two spectacular carbonated lavas, one from the Katwe region, the other from Kalyango volcano near Fort Portal. In earlier work, Holmes and Harwood² described a similar carbonated lava from Lake Kyekora, also near Fort Portal. Present examination of a vesicular lava of high carbonate content poured out from Kalyango volcano shows close geochemical affinities with intrusive carbonatites. It must be emphasized that the lavas examined are fresh and unaltered and that the carbonated nature cannot be attributed to alteration after solidification. A proposed investigation of the numerous lavas in the Fort Portal field may elucidate the formation not only of the characteristic ultra-basic potassic volcanics of south-west Uganda and adjoining parts of the Congo, the petrogenesis of which Holmes has presented so admirably, but also the genesis of the carbonatites themselves.