Mada

Intruded into basement gneisses, migmatites and amphibolites and in part overlain by Cretaceous sediments, Mada covers 271 km2 and is composed essentially of biotite and hastingsite-biotite granites. There are, however, small remnants of early volcanic rocks including ash fall tuffs, breccias and agglomerates and comenditic ignimbrites. The unwelded volcanics do not appear to be peralkaline, although they are generally weathered and the mafic minerals difficult to determine (Abaa, 1985a). The ignimbrites, in contrast, are fresher and occupy a small area on the eastern side of the complex where the comendite forms a dyke-like body. The rock contains lenticular fiamme and crystals of quartz, perthite, albite, arfvedsonite, with deeper blue rims, aegirine, which generally forms incomplete rims on arfvedsonite, and hedenbergite. Possible catapleite and eudialyte have been identified, although this seems unlikely because of the presence of quartz. Analyses of the major rock types, including the comendite, with trace element data, including REE, are given by Abaa (1985b).