Hydrogeochemical evaluation of groundwater in the lower Offin basin,Ghana |
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| Authors: | Benony K Kortatsi Collins K Tay Geophrey Anornu Ebenezer Hayford Grace A Dartey |
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| Institution: | (1) CSIR-Water Research Institute, P. O. Box M32, Accra, Ghana;(2) Civil Engineering Department, KNUST, Kumasi, Ghana;(3) Geology Department, University of Ghana, Legon, Accra, Ghana |
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| Abstract: | Alumino-silicate mineral dissolution, cation exchange, reductive dissolution of hematite and goethite, oxidation of pyrite
and arsenopyrite are processes that influence groundwater quality in the Offin Basin. The main aim of this study was to characterise
groundwater and delineate relevant water–rock interactions that control the evolution of water quality in Offin Basin, a major
gold mining area in Ghana. Boreholes, dug wells, springs and mine drainage samples were analysed for major ions, minor and
trace elements. Major ion study results show that the groundwater is, principally, Ca–Mg–HCO3 or Na–Mg–Ca–HCO3 in character, mildly acidic and low in conductivity. Groundwater acidification is principally due to natural biogeochemical
processes. Though acidic, the groundwater has positive acid neutralising potential provided by the dissolution of alumino-silicates
and mafic rocks. Trace elements’ loading (except arsenic and iron) of groundwater is generally low. Reductive dissolution
of iron minerals in the presence of organic matter is responsible for high-iron concentration in areas underlain by granitoids.
Elsewhere pyrite and arsenopyrite oxidation is the plausible process for iron and arsenic mobilisation. Approximately 19 and
46% of the boreholes have arsenic and iron concentrations exceeding the WHO’s (Guidelines for drinking water quality. Final
task group meeting. WHO Press, World Health Organization, Geneva, 2004) maximum acceptable limits of 10 μg l−1 and 0.3 mg l−1, for drinking water. |
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| Keywords: | Cation exchange Ghana Offin basin Silicate weathering Pyrite and arsenopyrite Oxidation |
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