Water quality trends in the Tarkwa gold-mining district, Ghana

A detailed hydrochemical investigation has been undertaken to establish whether mining has adversely affected streams in the Tarkwa gold-mining district and, if so, to what extent. The results show that streams that pass through mining areas and receive mine water exhibit significant spatial and temporal variations in their major ion hydrochemistry. Water analyses of perceived pristine areas reveal that the study area has undergone silicate weathering, but in mining areas, carbonate weathering was inferred. The inconsistency is attributed to the chemistry of mine waters discharging into receiving streams. This is supported by the average pH values of 6.48 for pristine streams and 7.74 for those affected by mine water. Trace element analysis did not show significant changes from the norm except for discharges from a spoil heap, which exhibited hydrochemical characteristics consistent with acid mine drainage. Saturation indices determined for the water samples reflect the sandstone–quartzite–phyllite lithology and intense weathering regime of the area as a result of the humid tropical climate.