Integrated Major Oxide Geochemistry, Contamination Factor and Pollution Load Index for Evaluating Geogenic Enrichment in the Ikole–Itapaji Basement Complex, Southwestern Nigeria

DOI: 10.22161/ijeab.115.11

Abstract:
The Ikole–Itapaji Basement Complex, southwestern Nigeria, comprises diverse crystalline rocks that influence both regional geochemical characteristics and environmental quality. This study integrated major oxide geochemistry, sequential extraction, Contamination Factor (CF), and Pollution Load Index (PLI) to evaluate geogenic enrichment and the environmental behaviour of trace elements within the study area. Geological mapping was conducted, during which thirty-five fresh rock samples representing the major lithological units were collected. Following detailed megascopic examination, twenty representative rock samples were selected for whole-rock major oxide geochemical analyses, while seventeen representative soil/sediment samples were analysed for environmental geochemical assessment. Major oxide analyses were carried out using Inductively Coupled Plasma–Mass Spectrometry (ICP–MS) following lithium metaborate fusion combined with multi-acid digestion (HCl–HNO₃–HClO₄), with analytical quality assured through certified reference materials, analytical blanks, duplicate samples, and internal laboratory standards. The soil/sediment samples were subjected to a seven-step modified Tessier sequential extraction procedure to determine trace-element partitioning among water-soluble, exchangeable, carbonate-bound, Fe–Mn oxide-bound, organic-bound, sulfide-bound, and residual fractions. Contamination Factor and Pollution Load Index were subsequently computed using average shale background values to evaluate elemental enrichment and environmental quality. The area is underlain by migmatite, granite gneiss, coarse porphyroblastic gneiss, granite, pegmatite, and charnockite. Major oxide geochemistry indicates predominantly calc-alkaline, magnesian, and metaluminous to weakly peraluminous compositions, reflecting magmatic differentiation and fractional crystallization within the Precambrian Basement Complex. Sequential extraction results reveal that most trace elements are concentrated within the Fe–Mn oxide, sulfide-bound, and residual fractions, indicating strong lithogenic control and generally low environmental mobility. Although CF identifies localized enrichment of Cd and Pb at a few sampling locations, PLI values indicate that most sites remain within the unpolluted to moderately polluted category. Overall, the study demonstrates that the geochemistry of the Ikole–Itapaji Basement Complex is primarily controlled by parent-rock composition, while localized enrichment of Cd and Pb highlights the need for periodic environmental monitoring to safeguard ecosystem integrity and public health.

Keywords:
Ikole–Itapaji Basement Complex, major oxide geochemistry, sequential extraction, contamination factor, pollution load index, geogenic enrichment, environmental assessment.

Article Info:
Received: 29 Jul 2026; Received in revised form: 22 Aug 2026; Accepted: 27 Aug 2026; Available online: 03 Oct 2026

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