RECONNAISANCE GEOCHEMICAL STREAM SEDIMENT SURVEY OF AKURE-ODA-IDANRE AREA, ONDO-STATE NIGERIA

Abstract

Seventy stream sediment samples were collected from an area of approximately four hundred square kilometers, located in Akure-Oda-Idanre area, Southwestern Nigeria. The study aims at providing a baseline geochemical data for the area and also to identify and isolate areas of possible metallic mineralization. All the samples were air dried and sieved with minus 80 mesh fractions; it was later treated with hot aqua regia digestion. The solution were analyzed for Ag, As, Au, Ba, Ce, Co, Cu, Fe, Mn, Nb, Ni, Pb, Rb, Sr, Ta, Ti, U, V and Zn using Varian Spectra AA Flame Atomic Absorption Spectrometer. The resulting data were analyzed using univariate and multivariate statistical techniques. Frequency distribution plots of the raw data showed that Cu, Y and Ta are positively skewed, while all the remaining elements are less skewed. Ba, Pb, Rb and Fe show approximately normal distribution while all other elements are log-normally distributed after log-transformation. The histograms showed an obvious break in distribution for all the elements except Co, Rb, Cu and Mn. The cumulative probability plot of the elements reveals multiple populations, except for Co, which has only one population. Plots of As, Ce, Mn, Nb, Pb, Rb, Sr and V show two populations. Ag, Au, Ba, Ni, Ta, Ti, U, Y, Zn and Fe have three populations while Cu has four populations. The Pearson’s correlation study of the raw data shows that there is strong positive correlation between Au/U, Ce/Fe, Nb/Ni, Ni/Sr, Pb/Rb, Zn/Rb, Sr/Y and Ti/V. Fairly moderate correlation exist between Ba/Ag, As/Ag, Ba/Cu, Ba/Zn, Ce/Rb, Ce/Zn, Ni/Rb, Sr/V and V/Y, while a weak correlation exist between Fe/Ag, Ag/Sr, As/Ce, Sr/As, Ba/Ta, Ce/Co, Mn/V, U/Zn and Ni/Ti. The R-mode quartimax rotated factor analysis for the log-transformed data revealed six factors which accounted for 87.9% of the data variability after nine iterations. The factors are: Pb,Ce,Rb,Zn,Fe,Au,Ba,pH; Nb,Y,Ni,V,Ta,Au,Sr; Cu,As,Ag,Ta; U,Sr,Rb,Zn; Ti,Mn and Co,Ba,Au,Fe which accounted for 28.80%, 16.34%, 13.80%, 11.82%,8.94% and 8.16% of data variability respectively. These were interpreted in terms of underlying rock lithology, potential mineralization and environmental factors. Contamination as result of the prolonged use of fertilizer, pesticides and herbicides in the area had an effect on the elemental association. The pH of the stream sediment range from 5.94 to 7.45 and it contributed to the geochemical distribution pattern of metals and trace elements in the study area. The geochemical maps show the distribution pattern of the metals and trace elements in the study area. However, factor 2 ,Nb,Y,Ni,V,Ta,Au and Sr may probably be the major mineralization factor. Nb and Ta are the ore elements found together in the theoretical end member of solid solution series called columbite-tantalite. These minerals may probably exist in the pegmatite and possibly in the pegmatitic veins of the migmatite and granites