Environmental Impact of Mining Activities in the Shakiso Area

ABSTRACT

Shakisso is one of the localities where intensive mining of primary and placer gold is taking place for many decades in Ethiopia. This research is focused on the identification and description of environmental problems occurred due to mining activities in the area. A number of field works were conducted to investigate the environmental impacts in the area. Chemical analyses of water, soil and plants were conducted to know the concentration of some elements in the samples collected from the area. Residents of the area were interviewed to assess their observations and inspect changes that might have occurred in the past two years. The environmental impacts identified in the area are found to be land degradation; contamination/pollution; health, safety and socio-economic problems. Contamination/Pollution/ is related to a relatively high concentration of some heavy metals in sediments, plants and water. From the analytical results it has been possible to see that most metals in stream sediments are more than the normal concentration in the Upper Crust. Especially As, Cu, Ni, and Se are concentrated as 5 to 50 times the normal crustal abundance. Such trend will end up in degrading the soil fertility and polluting the plants/crops growing in the region. As, Co, Ni, Pb, Sb, Cr, and other metals exceeded the recommended (WHO, 1993) concentrations in drinking water. Waters in active placer mining areas like Hayadima show high metal contents (as much as 95 ppm, of As). The concentrations of the metals are related to unlocking from minerals and rocks and subsequent remobilization due to crushing, washing and dissolution by chemicals like cyanide to separate gold, the effects of these toxic metals do not seem severe at the present time. However, with a decrease in pH and on set of acidic condition, their effect will be aggravated. Now, the Lega Dembi primary gold processing plants uses high dose of alkaline materials like Ca(OH)2 to maintain high pH. In the absence of such condition, the pH significantly changes. Even now around placer mining areas far from the processing plant, trees are observed dried which most probably is due to loss of fertility in topsoil or toxicity due to heavy metals. The most alarming environmental problems in the area of investigation are thus the land degradation and deterioration of the water quality. The land degradation can easily be mitigated by aforestation, back filling, etc. The heavy metals contamination needs more detailed investigation regarding their speciation, bio-availability, etc. The most likely solution is water treatment, at least, for human consumption. The environmental problems of mining in the Adola area do not seem to be out of control. If proper environmental monitoring, subsequent adjustments and well planned final reclamations are conducted, it will not create much negative impacts. However, it seems that there is no close observation and control except the self-initiative by MIDROC Gold, which routinely checks the cyanide concentration of the effluents from the processing plant.

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