Field occurrence and structural characteristics of basement rocks around Kabba-Bunu Area in part of Kabba-Lokoja-Igarra Schist Belt, southwestern Nigeria

Abstract

Field and structural mapping on a scale of 1:50000 was carried out to determine the lithologic and structural features in the Kabba-Bunu area of the Kabba-Lokoja-Igarra schist belt. The area is underlain predominantly by migmatiteschist suite comprising migmatite gneiss, migmatised schist and a quartz-mica schist-quartzite complex in which quartzite occurs as elongated ridges especially around Aiyegunle-Iluke-Olle and Osomule-Ofere areas. The migmatite-schist suite is interbanded in some places by short lenses of amphibolites. This metamorphic sequence is intruded by north-south trending granite plutons, which form prominent topographic features, and are closely associated with dolerite, pegmatitic and aplitic veins. Polydeformation and polymetamorphism of the rock units produced orientations in different directions. From the field disposition of the competent quartzite bands, the study area has suffered at least two thermotectonic orogenic events: one with E-W fold axis produced by N-S compressional forces assumed to be probably Eburnian in age and the other with N-S fold axis produced by E-W compressional stress usually associated with the Pan-African event. Foliation and lineation in the E-W to NE-SW directions is interpreted to be the ductile and earlier major structures, while minor brittle shear overprinted structures in the NW-SE to N-S directions are filled by quartz veins, dolerites and pegmatite dykes and serve as conduits and pathway of the gold bearing ore fluids.

Keywords: Structures, rocks, schist, N-S trend, polymetamorphsim.