Environmental Geochemistry of Soils and Stream Sediments from the Birnin-Gwari Artisanal Mining Area, North-western Nigeria

Abstract

The geochemistry of surface soils and stream sediments from the Birnin-Gwari area in the north-western Nigeria Schist Belt was studied in order to assess the environmental impact of small-scale artisanal mining of quartz-gold-sulfide mineralization. Total elemental concentration was measured using X-ray fluorescence spectrometry. The results show elevated concentrations of silica, zirconium and paucity of base cations due to intense tropical weathering, accompanied by removal of fine labile fractions by wet season flooding and dry directional winds. This has implication for water chemistry in the area, especially with respect to pH due to low buffering capacity. The results further show that artisanal mining has not caused severe potentially toxic elements contamination. The consistently higher arsenic concentrations, relative to baseline values, were found not to vary between the mine-impacted and background areas. It is therefore interpreted to have been contributed by the use of agrochemicals in the area. The study has not found a significant human health risk associated with potentially toxic element uptake from mine wastes. It is however recommended that the distribution of arsenic in the soils, sediments and surface water in the area should be further studied in order to ascertain the sources and possible human health implications.