The Geology, Geochemistry and Petrogenetic Studies of the Precambrian Basement Rocks around Iworoko, Are and Afao Area, Southwestern Nigeria

Olusiji Samuel Ayodele

doi:10.4172/2381-8719.1000212

Abstract

The geology, geochemistry and petrogenetic studies of the Precambrian basement rocks around Iworoko, Are and Afao Ekiti were carried out to determine their geochemical and petrogenetic characteristics. Three lithologies including migmatite-gneiss, granite gneiss and banded gneiss with a pegmatite dyke that occurred as an intrusion were recognized in the study area. A total of seventeen rock samples were collected from the study area which were described based on their field relationships. Ten fresh rock samples were later selected for geochemical analysis. The result of the geochemical analysis revealed that silica (SiO2) is the most abundant major oxide when compared with other oxides present in all the rock samples analyzed with an average percentage composition of 66.31%. The average percentage composition of other oxides present in all the rock samples are as follows; (16.41%) Al2O3, (3.67%) Fe2O3, (0.25%) CaO, (4.28%) K2O, (3.53%) Na2O, (1.75%) MgO, (0.78%) P2O5, (0.54%) TiO2 and (0.061%) MnO. The results of the trace and rare earth elements analyses revealed that Barium (Ba) is the most abundant with an average value of 328.7 ppm compared to other trace and rare earth elements present in the rock samples. The high concentration of barium in the migmatite-gneisses of the study area revealed the radioactive nature of this lithology. Petrological and chemical data suggests a sedimentary protolith, probably greywacke for the migmatite gneiss, gneiss and banded gneiss in the study area which may have been derived from a continental environment.

Highlights

Nigeria lies to the rest of the West Africa craton in the region of late Precambrian to Early Paleozoic orogenesis
A lot of literatures abound on the study of basement geology of Nigeria and its associated structures which include Geochemical dispersion of gold in stream sediments in Paleoproterozoic Nyong series, southern Cameroon undertaken by Mubfu and Nforba [1] in an attempt to explore for gold using stream sediments collected in the Ngo Vayang area of southern Cameroon, and revealed that the Au-Hf element association from the R-mode factor analysis indicated gold mineralization while U-Th-Pb-W, Nb-Ta-Co-V, Au-Hf-Cu associations reflected lithologic controls
Odeyem et al, [4] suggested that almost all the foliation exhibited by the rocks of southwestern Nigeria excluding the intrusive are tectonic in origin because pre-existing primary structures have been obliterated by subsequent deformation while Anifowose et al, [5] noted that joints ranging from minor to major ones are found in all the rock types, some of which are filled with quartz, feldspars or a combination of both

Summary

Introduction

Nigeria lies to the rest of the West Africa craton in the region of late Precambrian to Early Paleozoic orogenesis. The study area is dominated by granite-gneiss, banded-gneiss and migmatite-gneiss respectively These rocks are mostly metamorphic and belong to the Precambrian basement rocks of southwestern Nigeria, which itself is part of the basement rocks of Nigeria (Figure 2). The migmatite-gneiss-quartzite complex occurs as ridges and highlands at Iworoko and Afao-Ekiti, but as valleys at Are Ekiti Most of these rocks have been subjected to mechanical and chemical weathering. The texture of the migmatite-gneiss-quartzite complex in the study area varies from fine grained to medium grained while the structures observed on the outcrop include folds, joints, cracks and veins. The granite-gneiss in the study area occurs as a hilly outcrop especially around Afao and Iworoko Ekiti. The texture of these rocks varies from fine to medium grained. The present state of the rock is as a result of weathering

Method of Study

Discussion

Findings

Conclusion and Recommendation