Petrochemical Evaluations of the Pan African Pegmatites of Apomu Area, Southwestern Nigeria

Akintola A I,Sanni O G,Ikhane P R,Oduneye O A,Akintola G O

doi:10.5539/enrr.v2n4p8

Akintola A I, Sanni O G + Show 3 more

Open Access

https://doi.org/10.5539/enrr.v2n4p8

Copy DOI

Abstract

Pan African pegmatites occurring as near vertical dykes and striking mainly in the NNW-SSE direction have been studied in Apomu area with a view to evaluate their petrochemical features and possible economic potentials. These pegmatites intrude into the older lithology of granite around Apomu area Southwestern Nigeria. Petrographic determinations show they are composed of microcline, quartz and to a lesser extent plagioclase albite with interstitial muscovite, biotite and accessory minerals under transmitted light. A total of eleven samples comprising whole rock pegmatites were analyzed for major and trace elements using Inductively Coupled Plasma-Atomic Emission Spectrometry analytical technique (ICP-AES). From the geochemical results, the whole rock pegmatite is considerably siliceous, with an average value of 69.31%, while, MnO with a range of (0.01-0.23%), TiO2 with a range of (0.01-0.69%), P2O5 with a range of (0.02-0.23%) has values that are generally low. Mean contents of major oxides, Al2O3 (14.34% ), Na2O (3.31%), Fe2O3 (2.61%), MgO (0.78%), CaO (1.63%), and K2O (4.80%) for the Apomu pegmatites compare favorably with the Ipetu Ijesha barren pegmatites , Kafin Maiyaki barren pegmatites and Ago-Iwoye barren pegmatites. Apomu pegmatites are fairly enriched in Rb, Sr, Zr but comparatively, poor in the rare metals Ta, Nb, Cs and Sn. Rare metal mineralization enrichment indices mainly, Ta vs Nb, Ta vs K/Cs, plots, suggests the Apomu pegmatites to be barren in rare-metal mineralization when compared with other rare-metal pegmatites across the world.

Highlights

Pegmatites are known worldwide to host economically important mineral deposits such as gem stones and rare metals such as tantalum, niobium, tin and tungsten
Precambrian pegmatites of Nigeria occur mostly as dyke like intrusions which vary from few meters to several kilometers in length and few centimeters to meters in width and have been hitherto thought to be confined to a broad 400km long NW-SE trending belt stretching from Wamba area in central Nigeria to Abeokuta area south western Nigeria (Figure 1a)
Major element distribution show that the pegmatites are siliceous; with SiO2 content ranging between 46.03% and 73.54% with an average value of 69.31%; this is marginally lower than average values of rare metal Ta-Nb pegmatite of Nigeria (Okunlola, 2005) but comparable to the Ipetu ijesha barren pegmatites (Elueze, 1982), and Ago-Iwoye barren pegmatites (Akintola et al, 2011)

Summary

Introduction

Pegmatites are known worldwide to host economically important mineral deposits such as gem stones and rare metals such as tantalum, niobium, tin and tungsten. There has been the resurgence of interest in the study of these pegmatites occurrences because of its associated economic rare metal and gem mineralization. This has led to concentration of study on discrimination of the pegmatites into the rare metal mineralized and barren ones in order to elucidate modes and features of mineralization (Matheis, 1981; Matheis et al, 1982; Kuster, 1990; Garba, 2003). Okunlola, (2005) defined the metallogeny of the rare metal Ta-Nb pegmatites of Nigeria outlining 7 broad fields namely Kabba-Isanlu, Ijero-Aramoko, Keffi-Nasarawa, Lema-Ndeji, Oke Ogun, Ibadan-Osogbo, Kushaka-Birnin Gwari. General geology of Nigeria showing the location of the pegmatite zone (after Kinnaird 1984)

Regional Geological Setting

Lithological Association and Petrography

Petrochemical Features

Results and Interpretation

Summary and Conclusion