When closure fails: Uncovering the environmental impact of gold rewashing on abandoned mine sites in Southwestern Nigeria

Gold “Rewashers” are groups of illegal miners who infiltrate closed alluvial gold mine sites to scoop out and wash chunks of mud with the hope of extracting any residual gold deposits in the site. This paper examines the implications of the rewashing operations by these miners on the environment. To achieve this, soil and water samples were collected from selected sites where the operations were being conducted. Physicochemical analyses were then conducted on the samples to determine the level of contamination from the operations. For the soil samples, ordinary (control) samples were collected about 50 m away from the washing sites while samples of the washed soil were also collected to examine the impact of the operations on the soil samples. There is a significant increase of the presence of cyanide and some heavy metals (Cr and Pb) in the washed soils compared with the ordinary soils across all sites investigated. The concentrations of cyanide (mg/kg) in washed soils are significantly higher than in ordinary soils across all sites: site 1 (from 0.7533 to 1.1160), site 2 (from 0.7033 to 1.5188), site 3 (from 1.0363 to 2.0000). The difference in concentration levels between washed and ordinary soils for the two soil samples collected in each site for Cr (mg/kg) are Site 1 (+0.29/+0.1305); Site 2 (+1.321/+0.891); Site 3 (+1.617/+1.541) and for Pb (mg/kg) Site 1 (+0.229/+0.1645); Site 2 (+0.7505/+0.7065); Site 3 (+0.7315/+0.696). There was a general drop in the average pH values of the washed soils as compared with the ordinary soils across all sites: site 1 (from 6.150 to 5.885); site 2 (from 6.455 to 5.518); and at site 3 (from 5.890 soil to 5.010). Such reductions suggest increased soil acidity, potentially due to the leaching of alkaline minerals during the washing process. The findings of the water tests also revealed elevated turbidity in the water samples from the sites with potential health risks and ecological stress. Similarly, the water samples show low level of dissolved oxygen (DO) with potential stress on aquatic life. Qualitative data were also collected from the sites through interviews conducted with the miners and direct observation of the mining methods to identify how the operations pose danger to the environment. Lessons were drawn from these occurrences to examine how mine planners can better protect the environment by efficiently planning for mine closure and reclamation. The paper also justifies the need for effective formalisation effort that capture the needs of the impoverished locals who take succor in this occupation.