MINERALOGICAL STUDIES OF WEATHERED PEGMATITE AROUND KITIBI-IWOYE, SOUTHWESTERN NIGERIA

Abstract

Weathering profile of pegmatite around Kitibi-Iwoye and Awo mining sites is heterogeneously composed of primary and secondary mineral constituents. Weathered materials obtained from nine dug pits and pegmatite samples were studied with a view to gaining insight into the mineral assemblages constituting the weathered materials. This was achieved by describing the field, petrographic and mineralogical features of the pegmatite and its weathered components. Effect of weathering on the pegmatitic parent rock leading to the evolution of secondary minerals was as well investigated. The authors are not aware of any previous investigation existing in these aspects in the study area.

This study involved geological mapping of the study area. Representative samples of pegmatite were collected for microscopic examination. Unconsolidated weathered mass obtained from the Saprolite and B-horizon was air dried. The loosened mass was sieved and screened to remove organic components and detrital quartz. The pulverized samples were analysed using X-Ray Diffractometry (XRD) technique in the Department of Geological Sciences, University of Cape Town, South Africa.

The Northeastern-Southwestern (NE-SW) trending pegmatites intruded into migmatite gneiss, banded gneiss, diorite and granite. Petrographic studies revealed primary constituent minerals such as K-feldspar, quartz, plagioclase, muscovite, biotite and opaque minerals in the pegmatite. Secondary minerals obtained are illite, kaolinite and goethite. Occurrence of ordered and well crystalline kaolinite was facilitated by weathering of feldspathic, micaceous and accessory minerals as shown by X-Ray Diffractometric studies. Kaolinite was the main secondary mineral while illite and goethite occurred in subordinate amount. This study generally showed moderate to intense degree of weathering.