THE KIGOM PERALKALINE GRANITE PLUTON OF THE NIGERIAN YOUNGER GRANITE SUITE

The kigom granites in central Nigeria are alkali amphibole bearing and peralkaline in nature. They are hypersolvus in character and contain mesoperthite in which the albite (Or1-2) and microcline are present in approximately equal proportions. The albite is fully ordered while K-rich feldspar is dominantly microcline. The extreme compositions of these feldspars suggests effective crystallization and ordering by hydrothermal fluids at lower than 3000C. Geochemical data suggest that the fluid involved in the metasomatism was peralkaline in composition and resulted in the enrichment of Nb, Y, and Th, in microgranite, and of Rb, Zn, Li, Sn, and F in the amphibole-bearing units suggesting that the granites underwent long duration of rock-fluid interaction in a peralkaline environment. Keywords: Kigom, Peralkaline granite, Mesoperthite, Arfvedsonite, Riebeckite, [Global Jnl Geol. Sci. Vol.1(1) 2003: 1-12