AMD Characterization of Surfacewater and Groundwater in Jos-Bukuru Rayfield Area of Plateau State, Nigeria.

Abstract

Extensive mining of cassiterite and columbite ores in the Jos-Bukuru parts of Plateau State, Nigeria have precipitated conditions for the formation of acid mine drainage (AMD) in the area. To check for contamination of water sources, geological, hydrogeological and hydrochemical investigations were carried out. This is to improve the current status of knowledge on the occurrence of AMD in the Plateau. The Rayfield area of Jos-Bukuru is underlain by pink, medium to coarse grained biotite granites. The upper 5m of the rock is highly weathered, jointed and fractured. This forms a shallow unconfined aquifer which is tapped by hand-dug wells and small streams. A total of sixteen water samples drawn from hand-dug wells, mine ponds and streams were analysed for major element chemistry and heavy metals. All the samples (except two) have pH values which range from 5.1 to 6.9 which indicate acidic conditions. The two samples which indicate alkaline conditions were drawn from a river and an industrial discharge pond. The value of sodium (Na⁺ ) concentration range from 2.5mg/l to 43.9mg/l while calcium (Ca²⁺) is from 0.31mg/l to 7.6mg/l. Values for potassium (K⁺) range from 0.67mg/l to 108.85mg/l. Magnesium ion concentration is rather low (0.02mg/l to 1.13mg/l). Concentration values for major anions are very low especially in the case of bicarbonate (HC0^-₃). Its concentration in most of the samples was below detection levels. It could be detected only in 4 samples where it ranges from 6.10mg/l to 24.40mg/L. Chloride (Cl^-) values range from BDL(Below detention level) to 198.52mg/l (a river sample). For sulphate (S04^2-), the range is 3.21mg/l to 6.31mg/l.  The values for iron concentration range from 0.16mg/l to 10.27mg/l which certainly exceed all guidelines for iron in water. The geochemical qualities of acid mine drainage include low pH, high fe and sulphates. Whilst the waters of Rayfield area show low pH and high Fe values, the concentration values for sulphate are low but lead (Pb) concentrations exceeds W.H.O.

Key words: AMD (acid mine drainage); Jos-Bukuru; Rayfield; Lead; Iron)