Alkaline Intrusive and Extrusive Rock from Areas West of the Anyim River, South-Eastern Benue Though

ABSTRACT

Twenty-one outcrops of igneous bodies were studied in a small area (ca. 335 sq. km) of folded sediments west of Anyim River in the

Lower Benue Rift. The extrusives occur mainly as basaltic to trachybasaltic tuffs and lapilli tuffs. The minor intrusives are found as basaltic

and dolerite sills composed essentially of plagioclase (An,,), augite, with or without olivine. The major intrusives are dioritic small

bodies considing of sodic plagioclase (An,,), biotite andor hornblende, and rarely nepheline. Common accessory minerals in these rocks

are magnetite, pyrite, apatite, sphene and quartz. Calcite appears to be secondpry, and biotite, in some cases, is a pseudomorph after

hornblende.

The rocks are mostlyalkalic, total alkali ranges from 3.21 to 9.92% with Na,0,2.62 to 6.55% and K,O