ENVIRONMENTAL GEOCHEMISTRY OF LEAD-ZINC MINING AT ISHIAGU AREA, LOWER BENUE TROUGH, SOUTH EASTERN NIGERIA

AUTHOR: ODIKA, PRECIOUS ONYINYECHI 

DEPARTMENT: GEOLOGICAL SCIENCES

AFFILIATION: NNAMDI AZIKIWE UNIVERSITY, AWKA

The study area is divided into two major zones; Iheututu zone (comprising the Pb-Zn mines) and Ishiagu zone (consisting of the quarries). Water, soil, stream sediment and ore samples were analyzed using atomic absorption spectrophotometer (AAS), in which eight cations namely Pb, Cu, Ni, Zn, Mn, Co, Cd and As were determined. Intrusive igneous rock samples were studied under thin sections with a petrological microscope. Surface water analysis show the following ranges of heavy metal concentrations; Cu (0.4-1.6ppm), Zn (0.07-0.25ppm), As (2.60-3.00ppm), Cd (0.04-0.23ppm), Ni (0.44-1.11ppm), Co(0.01-0.54ppm) and Pb(0.80-3.00ppm), while heavy metal concentrations in groundwater range from; Cu(0.10-1.20ppm), Zn(0.04-0.82ppm), As(0.80-5.20ppm), Cd(0.01-0.19ppm), Ni(0.26-1.70ppm), Co(0.01-0.09ppm) and Pb(0.10-3.40ppm). Soil sample results indicate the following concentrations; Cu(0.10-0.60ppm), Zn(0.07-0.27ppm), Mn(2.28-5.84ppm), Cd(0.01-1.40ppm), Ni(0.15-2.26ppm), Co(0.02-0.10ppm) and Pb(0.10-1.10ppm). Stream sediment results indicate the following concentrations; Cu(1.00-2.80ppm), Zn(0.12-0.41ppm), Mn(0.00), Cd(0.06-0.13ppm), Ni(0.54-1.50ppm), Co(0.02-0.05ppm) and Pb(0.70-1.20ppm). Ore analyses show these ranges of concentrations; Cu(0.10-1.10ppm), Zn(0.06-0.37ppm), As (0.09-0.20ppm), Cd(0.12-0.33ppm), Ni(0.08-0.87ppm), Co(0.0.03-0.08ppm) and Pb(0.50-1.70ppm). In surface water; Pb, Co, Ni and Cd increase towards the Ishiagu zone, Co increases away from the Pb-Zn mine sites while As and Zn are evenly distributed in both zones. Lead, Cu and Ni in groundwater show higher concentrations in the Ishiagu zone, Zn increases in the Iheututu zone, while Co occurs evenly in both zones. In stream sediment medium; Cu, Zn, Cd and Pb increase towards the Ishiagu zone, Ni and Co are evenly distributed, while Mn is conspicuously absent. Soil samples indicate even distribution of Cu in the zones, higher Zn and Ni levels towards the Ishiagu zone, higher Cd and Pb levels towards the Iheututu zone while Mn occurs sparingly in both zones. Distribution and dispersion patterns of the heavy metals indicate concentration elevations towards flow direction. Petrographic studies show mineral assemblages of biotite, plagioclase, hornblende, augite, up to 40% opaque minerals and less than 10% quartz, with vein fillings of calcite within diorite intrusives suggesting; interaction of hydrothermal fluids and connate-brine waters. Lead, Cu, As, Cd, Mn, and Ni concentrations have reached pollutant level based on the WHO standards. Zinc concentration is below pollutant level. Long-term consumption of water resources, soil and agricultural produce from the soils pose environmental hazard. There is a potential risk of poisoning of humans, animals and agricultural produce by these trace elements.

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