Mineralogy and geochemistry of the Ngaoundaba Crater Lake sediments, northern Cameroon: implications for provenance and trace metals status

Abstract

This study was conducted on the Ngaoundaba Crater Lake sediments to infer provenance, weathering conditions, organic matter accumulation, and trace metal concentrations. Ngaoundaba Lake sediments were collected using a manual core sampler at 5 to 8 m water depth. Two sediment cores from the littoral and center of the lake were analyzed for grain size distribution, water content (WC), organic matter content, mineralogy, and major and trace element concentrations. The Ngaoundaba sediments were classified as silt and sandy silt. Sediments show high content in organic matter, which is more to the littoral than to the center of the lake, varying from 14.6% to 24% and 21.2% to 40.8%, respectively. The grain surface features identified by Scanning Electron Microscopy (SEM) show both chemical and mechanical microtextures with sub-rounded to angular shape suggesting both proximal and distal sources. The lake sediments are composed of quartz, kaolinite, and hematite, with low amounts of feldspars, rutile, calcite, illite, and ilmenite. Weathering indices such as the chemical index of alteration (CIA), chemical index of weathering (CIW), and index of compositional variability (ICV) indicate moderate to intense chemical weathering in the source area and immature to mature sediments. The geochemical composition indicates that the sediments were derived from felsic to intermediate igneous rocks, such as granitoids, and mafic alkali lavas like basanites. The environmental risk assessment of trace metals obtained by enrichment factor (EF) and geo-accumulation index (I-geo) shows low contamination of the lake sediments.