Dago (Dogo Dutse)

This approximately circular 60 km2 peralkaline granite intrusion has a discontinuous, peripheral ring-dyke which post-dates sparsely preserved volcanic rocks (Ike and Sakoma, 1985). The volcanics, which are preserved only in the south close to the ring-dyke, are predominantly crystal-rich ignimbrites with 40-50% alkali feldspar and quartz phenocrysts, lithic fragments and fiamme with evidence of strong welding. The ring-dyke is preserved on the eastern and southwestern margins of the intrusion, elsewhere apparently having been obliterated by later granite. It is a quartz porphyry with a similar abundance of phenocrysts to the volcanic rocks, but with addition of arfvedsonite and aegirine. The granite consists of perthite, quartz, arfvedsonite and aegirine.