Sedimentological and Geochemical Appraisal of Stream Sediments of Part of Igangan Sheet 240 South Western Nigeria

Abstract

An integrated sedimentological and geochemical evaluation was carried out on the sediments sampled from part of Igangan sheet 240 (1:100,000) SW Nigeria, covering Lanlate and its environs. This study is to characterize the provenance and depositional processes prevalent in the area. Twenty-nine stream sediment samples were collected after the confluence points of two or more rivers at a depth of 20-25cm, along with rock samples for further analyses in the laboratory. The techniques involved using standard sedimentological methods involving field descriptions, textural parameters, and petrographic analysis methods. The geochemical studies involved the determination of major elemental composition using Heavy Mineral analyses. Granulometric analysis was carried out on twenty-nine (29) stream sediments samples, while five (5) representative samples were systematically picked and analyzed for their mineralogical maturity using ZTR index. The rock samples were cut into thin section and analysed under the microscope for mineral composition. The results of the geochemical analysis were thereafter subjected to multivariate statistical analysis. The statistical plot shows that the sands are poorly sorted, medium to coarse grained and sub rounded to sub angular in shape. The sands which are medium to coarse grained suggests that the sands were deposited under a moderately energy condition. The field investigations and petrographic studies show that most of the study area has undergone an episode of metamorphism. Migmatite gneiss (80%), Biotite Hornblede Gneiss, quartzite (5%), muscovite hornblende biotite granite (10%) and biotite hornblende granite (5%) are the major rock in the area, while biotite, feldspar, quartz, hornblende and accessory minerals were observed in hand and thin sections. The calculated ZTR index for the sandstones ranges from 51.3% to 57.9 %, with an average of 54.6 %. This suggests that the sandstones of the formation are mineralogical mature. The conclusion drawn from the integration of the geochemical and multivariate analyses revealed that the study area is mineralized and the sediments were deposited under a moderate energy condition.

Keywords: Igangan, Nigeria, Sedimentological, Stream sediments, Geochemical, Statistics