Acid mine drainage from the historic Mt Morgan gold mine : devastating to river water quality, and fish

Abstract

Contaminative drainage waters from the historic abandoned Mount Morgan gold mine (central Queensland) are acidic, contain high levels of heavy metals and sulphate and have leached into the adjacent Dee River basin over 100 years. This paper reviews a current study which quantifies the discharge impacts on the water quality and fish inhabitants at a number of sites both upstream and downstream of the mine site with emphasis on distribution of contaminants during summer 2006. Pollutants discharged into the Dee River greatly diminished the water quality, and also negatively affected aquatic life, especially fish. The water is very acidic (pH 2.8) and concentrations of metals and sulphates are much higher in samples close to the mine compared with other sites. Results for most sites in the Dee River indicated that metal concentrations in the water generally exceeded ANZECC (2000) trigger levels for Al, Cu, and Zn. For Cd, the highest value observed (0.0592mg/L) was at Kenbula (closest to the mine i.e. 5km from the mine).Subsequent analysis of concentrations of heavy metals in five species of fish – Rainbow Fish (Melanotaenia splendid), Fly Specked Hardihead (Craterocephalus stercusmuscaru), Glass Perchlet (Ambassis agassizii), Spangled Perch (Leiopotherapon unicolour) and Purple Spotted Gudgeon (Mogurnda adspersa) – revealed that metal concentrations generally declined with distance from the mine but not a single fish was caught at the site closest to the mine. Al (1100mg/L), and Cu (61.6 mg/L) concentrations in fish species at Penny Royal (22.2 km from the mine) exceeded ANZFA (2000) maximum permitted levels for human consumption whereas Cd (0.05 to 0.3 mg/L), and Zn (100 to 195 mg/L) were also high, but below ANZFA levels. These results demonstrate clearly that, even though the Mt Morgan mine is no longer operational, the plume of contaminated acidic water originating from the mine continues to enter the Dee River and presents a significant threat to the environment