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Research Journal of Earth and Planetary Sciences Vol. 3(1) pp.13 – 37 February 2013
Available online http://www.globalresearchjournals.org/?a=journal&id=rjeps
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Full Length Research
HEAVY MINERAL CHARACTERISTICS AND GRAIN-SIZE DISTRIBUTION OF THE SILICICLASTIC SEDIMENTS IN IJEBU-OMU, ILOTI, ITELE AND IJEBU-IFE STUDYAREAS OF EASTERN DAHOMEY BASIN, SOUTHWESTERN NIGERIA
IKHANE, P.R , *AKINTOLA, A. I AND OSINOWO, A.A
Department Of Earth Sciences, Olabisi Onabanjo University, P.M.B 2002, Ago-Iwoye Southwesthern Nigeria.
*Corresponding Authors e-mail: busayoakins@yahoo.com ,Tel: +2348033511485
| Abstract |
The knowledge of particle size distribution and the assemblages of heavy minerals in sedimentary rocks particularly in the earth crust make it possible to effectively locate and use essential minerals to predict their dispersal pattern when they re-enter the natural environment. Particle size distribution of sedimentary outcrop samples exposed around Ijebu-Omu, Iloti, Itele and Ijebu-Ife located within the eastern Dahomey basin were used to study the provenance and to deduce the transportation history, environment of deposition of the sediment.
Twenty four (24) surface samples collected from the study area were subjected to granulometric analysis in order to determine their grain size distribution using the sieve method. The sediment samples were passed through a set of mechanical sieves of 4.75mm diameter screen opening. Thin sections of finer particles from twelve (12) selected samples were also done to describe the heavy mineral make-up.
Results showed that sediments with 0.212mm grain size dominate in all the samples. The average statistical mean (textural maturity), standard deviation (sorting) and kurtosis determined from the grain size data are 0.65, 0.66, and 1.35 respectively. The heavy mineral assemblage shows the presence of opaque and non opaque minerals such as zircon, tourmaline, rutile, staurolite, garnet, apatite and epidote. The calculated zircon, tourmaline, rutile index in percentage (ZTR) varied between 33-56%, average apatite- tourmaline index(ATI), garnet-zircon index(GZI), rutile-zircon index(RuZI) and staurolite-zircon index(SZI) values in all the locations are 27.7%, 30.6%, 46%, and 50% respectively.
The textural study indicates that the sediments are leptokurtic, moderately well sorted coarse sands. The high value of SZI indicates sediments with a fairly short transportation history and the low ATI value is a characteristic of the unstable nature of apatite and tourmaline that has been affected by weathering. The presence of staurolite, garnet and rutile occuring in fairly large quantities is an indication of metamorphic and igneous rock source and the maximum ZTR index of 56% indicates that the sediments are mineralogically immature.
Key words: Sediments, Tourmaline, Kurtosis, Garnet, Zircon.