Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Assessment of the impact of mining and processing of ores on the environment in mining districts of Namibia: Results of the Czech project of development cooperation in 2006
Abstract
During the last year of the project the impact of mining and processing of ore was evaluated at the Rosh Pinah mining district, South Namibia. It was found that the main source of pollution is dust blown out from ore crushers, ore concentrate dumping grounds and tailings dam. Contamination halo around the tailings dam and processing plant exceeds 39 km2. The shape of the contaminated area is elongated northwestward according to the prevailing direction of winds during the summer season. The northeastern district of the town of Rosh Pinah suffer from the fallout tail. The concentrations of Stot in the uppermost part of the soil horizon in this part of the Rosh Pinah equal 0.09 to 03 wt. %, Mn 0,07 to 0,23 wt. %, As 6 to 25 ppm, Cd 20 to 30ppm, Hg 0.1 to 0.2 ppm, Pb 1000 to 3000 ppm and Zn 5000 to 10,000 ppm. However, the contamination affects only the uppermost part of the soil profile which is favourable from the viewpoint of future soil reclamation. The contamination of stream sediments by heavy metals and sulphur swiftly decreases downstream, and does not show any specific pattern at a distance of over 1 km from the tailings impoundment. The highest contents of metals in grasses were found in the immediate vicinity of the tailings dam (Cd: 5 ppm, Cu: 80 ppm, Mn: 260 ppm, Zn: 1070 ppm and Pb: 825 ppm). Monitoring of the dust-fallout in Rosh Pinah revealed that the total amount of dust decreases from the tailings dam across the observation point located in the ore dressing plant and the hostel in the city center to the observation point situated in the local school in the southwestern quarter of the town. The results of meteorological modelling also confirmed that the northeastern part of the Rosh Pinah town has been most affected by the dust-fallout. The results revealed that while the whole surface of the tailings dam was dry in the past, the amount of dust in the Rosh Pinah town corresponded to 40 to 300 |g . m-3 of normalized air. The present moistening of the large part of the tailings dam resulted in a decrease in dust down to 20-100 |g . m-3 of the air.
