Obuasi gold mine

Gold has been mined at Obuasi, 60 km south-west of Kumasi, since 1897. The underground mine was once among the ten largest in the world; since 2004 it has belonged to AngloGold Ashanti, formed by the merger with Ashanti Goldfields. It closed in late 2014, with more than 5,000 lay-offs, and during the shutdown the concessions were occupied by illegal miners; production resumed in 2020.

A 2018 study sampled surface soils in commercial and residential areas and on the tailings dams. Mean concentrations followed the order As > Cu > Zn > Cr > Ni > Pb > Co > Hg > Cd. The highest mean arsenic, 598 ± 132 mg/kg, was on the tailings dam of the Pompora treatment plant; the lowest, 89.7 ± 58.2 mg/kg at Sanso, was still above the 40 mg/kg the authors give as the threshold for toxicological risk. The maps show two hot spots, at the sulphide treatment plant and Pompora tailings dams; the centre of the area is also polluted with lead, zinc and copper.

Illegal mining has added to the historical discharges: a 2026 study of the Kwabrafoso, Pompom and Diewuo rivers describes Obuasi as one of the hotspots of the phenomenon in Ghana. In groundwater at Sanso mean total arsenic was 15.5 µg/L, above the WHO guideline value of 10 µg/L (Ankapong et al. 2025).