Petrography and Geochemistry of Rocks of Northern Part of Wonaka Schist Belt, Northwestern Nigeria

Abstract

Systematic mapping and sampling of rocks of northern part of Wonaka schist belt on a scale of 1:50,000 shows that the belt is composed of gneiss, granite gneiss, muscovite-biotite schist, banded iron formation, amphibolite, granite, granodiorite and diorite as major rock types, other rocks are aplite, and pegmatite. Petrographic and geochemical data shows that the there are two types of gneisses in the area: the orthogneiss and the paragneiss. Plots of TiO₂ vs SiO₂ shows that the granite gneiss is paragneiss while the gneiss is an orthogneiss. The granites and the granodiorite are I – Type and the amphibolite is volcaniclastic. The banded iron formation (BIF) is shown to be hematite facies type from a plot of MnO vs FeO(T). It can therefore be said that the orthogneiss represents the original basement rock possibly dating back to the early phase of the Eburnean orogeny. At later stages of the Eburnean, sedimentary deposition and subsequent metamorphism of the sediments might have led to the formation of the paragneiss and the metasediments with the associated BIF as indicated by the REE distribution pattern. The NNE – SSW and the N – S structural trends on the rocks might have been developed by the over printing effects of the Pan- African orogeny

Keywords: orthogneiss, schist belt, paragneiss, banded iron formation, metasediments