Geology and Weathering Indices of the Bedrocks and Sediments in Okemesi -Ijero Area, Southwestern Nigeria

Ayodele Olusiji Samuel

Geological field mapping of the rocks in Okemesi-Ijero area were carried out at a scale of 1:50,000 to determine the underlying lithologic units and petrological characteristics. Also the suitability of the rocks and sediments for geochemical exploration purposes were determined using weathering indices parameters such as chemical index of weathering (CIW), weathering index of Parker (WIP), Plagioclase index of Alteration (PIA) and chemical index of Alteration (CIA). Thirty-five bedrocks and stream sediment samples were collected from various locations within the studied area using grid-controlled sampling techniques. Field studies revealed that the sediments were derived from weathering of the bedrocks such as quartz-biotite-schists, banded gneisses, granite-gneisses, biotite gneisses, calc gneisses, porphyritic granites, charnockites, massive/schistose quartzites and mica schists which are the dominant lithologic units in the studied area. The weathering profiles based on the above parameters showed that sediments from River Elewu and Issa 7c are weakly weathered whereas, sediments from Agbagbara, Ede-1, Ede-2, Effon-Okemesi-2, Esa-Oke-2, Odo-OWa Abidogun, Ofale road, Okemesi-2, 3 and 9 were intensely weathered which makes them unsuitable for geochemical exploration work due to complete weathering of the mineral grains.

okemesi, ijero, lithologic units, sediments, weathering indices

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