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Mining activities have been undertaken for over 95 years in Enyigba area of southeastern Nigeria. In this area, thirty-six (36) trace metals including those that are essential for plant and animal nutrition have been analyzed from forty-nine (49) soil samples that were collected from three Pb-Zn mines. The aim of the analysis is to assess the level of contamination of the soils caused by mining activities. Potentially harmful elements which are commonly associated with Pb-Zn mines were of special interest. Such elements included Pb, Zn, As, Cd, Mn, Fe, Se, Sb, Cu and Bi. Generally, the samples analyzed showed elevated concentrations of Pb, Zn, Cd, Cu and Cr when compared with concentrations documented in the international agricultural soil standards. Geo-accumulation indices of soils that occur closer to the mines indicate moderate to extreme level of contamination in Pb and moderate levels in Cd. Enrichment factor (EF) showed very high enrichment to extremely high enrichment in Pb. Cd and Zn enrichment were found to be significant and moderate respectively. Conversely, the geo-accumulation indices for soil samples located away from the mines indicate moderate to heavy contamination in Pb but had moderate to significant enrichment in Cd and moderate in Bi and Cr. In general, soil quality all around the mines were found to have deteriorated as revealed by the pollution load index. Thus the results of this study call for immediate remedial measures to be initiated. In addition, miners and local communities living around the mines need to be enlightened about the dangers of exposure to these heavy metal contaminants.

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IntroductionThe Lower Benue rift is the southern part of the intracontinental Benue rift-basin, which extends from the Niger Delta northeast towards the southern part of Cameroun, a distance of about 1000 km long and 80 km wide. Its evolutionary history was traced to the opening of the Gulf of Guinea and the South Atlantic during the separation of the South American plate from the African plate in the Mesozoic era (Burke et al., 1971;Grant, 1971) (Figure 1), accompanied by magmatic activities that span the Jurassic (Bajocian) to the Tertiary (Umeji, 2000).The first report of the existence of intrusive rocks in the Lower Benue rift was by Wilson and Bain (1928), who described the rocks exposed at Lokpanta during the construction of the Port Harcourt-Enugu railway line as intrusions (Obiora and Charan, 2010). The intrusive and volcanic rocks in the Lower Benue rift have been described as intermediate to basic in composition and associated with lead-zinc mineralization (Farrington, 1952;Gunthert and Richards, 1960;Cratchley and Jones, 1965; Nwachukwu, 1972), as cited by Obiora and Charan (2010). Burke et al. (1971) described the rocks (volcanic and intrusive) around the Abakaliki area (Figure 1) as andesite lavas and tuffs and proposed a subduction origin for the rocks in the Benue rift. However, Olade (1978, 1979) reported alkali basalts and tuffs with spilite using petrographic and geochemical data and concluded that the rocks were within plate 'hotspot' basalts. Some others