Preliminary Risk Assessment of Lead-Zinc Mining in Part of the Benue Trough, Nigeria

The Cretaceous Asu river group pay host to certain economic minerals; chiefly among this is the Pb-Zn mineralization that has attracted both skilled and artisan miners to the basin in the last few decades. This study investigated possible environmental hazards that may be connected with this unregulated mining and prospecting in the zone. Field work was done. A total of 48 and 29 soil and water samples were selectively collected from abandoned mine pits, tailings, nearby farm lands, streams, hand-dug wells and boreholes. These were subjected to Atomic Absorption Spectrometry (AAS) and X-ray fluorescence analyses. X-ray diffraction and permeability tests were also carried out on some of the samples using standard procedures. Potential and observable risks in the area include artificial ponds, which developed as a result of failures of miners to conform to existing mining laws in the nation. Concentrations of potentially harmful elements (PHEs) in analyzed water are generally below the 2010 acceptable limits set by the World Health Organization. Contrariwise substantial contamination and pollution of soils, stream sediments and tailings with PHEs was revealed. Consequently, the customary use of these soils for construction purpose by inhabitants has possible health hazards. Similarly, the high concentrations of PHEs recorded in farm lands, suggest direct contamination of the cereals grown in this area; thus endangering the life of its final consumers. The shaly lithology underlying the area is increasingly affected by weathering and lateritization, thus improving the easiness with which PHEs can be leached to the water table. Regular monitoring and assessment is recommended by relevant mining and environmental agencies to ensure adherence of miners operating in the basin to existing mining laws.