Grain-size and Heavy Mineral Analysis of River Osun Sediments

In river sediments the whole range of known minerals can be found: salt minerals in very restricted areas, carbonates, heavy minerals; feldspars, quartz and clay minerals. In this paper we report the grain size and heavy minerals analysis of Osun River sediments. The heavy mineral analysis involved separation of sand grains into different sizes; density separation of heavy minerals using heavy liquid and counting the number of grains of each mineral using transmitted light microscope. Results show that the sediments with 250p,m grain size dominate in all the samples. The average graphic mean, inclusive graphic skewness and measure of kurtosis determined from the grain size data are 1.14, 1.69 and -2.61 respectively. The heavy mineral assemblage indicates the presence of opaque and non-opaque minerals. The non-opaque minerals fall into three groups: Ultra stable (Zircon, Tourmaline, Rutile), Stable (Staurolite, Garnet) and moderately stable (Sillimanite, Epidote). The most abundance is Staurolite with 43.92%. The calculated Zircon, Tourmaline and Rutile (ZTR)% values varied between 21.1% in Ekiti to 56.7% in Lagos State. The maximum ZTR index of 56.7% obtained shows that the sediments are mineralogically immature