OVERVIEW OF THE IMPACT OF MINING ON THE ... - IIED pubs

• Antimony, cadmium and tin contamination of surface waters in Greenstone Formations mined for these
metals, or as contaminants in gold mining operations located in Greenstone rock formations in South Africa
and Zimbabwe. Specific examples are the Murchison and Giyani Greenstone Formations in South Africa.
• Copper contamination of various levels arising from copper mines and smelters on the Zambian Copperbelt,
the areas close to the Great Dyke in Zimbabwe, the Selibe-Phikwe copper-nickel mine in eastern Botswana
and the Phalaborwa area in South Africa.
• Iron and manganese contamination of surface streams, either in solution or as unsightly oxy-hydroxide
precipitates, caused by aeration of iron-rich acidic solutions associated with pyrite oxidation and AMD.
Specific examples occur in several iron ore mines and in gold and coalmines in South Africa and Zimbabwe.
• Zinc and lead contamination associated with AMD of low-grade ore stockpiles at Kabwe in Zambia and the
Letaba Mine in South Africa.
• Antimony contamination associated with mines located on the Murchison Greenstone Formation in South
Africa.
6.1.3 Impacts due to the release of potentially toxic substances
The most important issues here relates to the potential for contamination posed by organics and solvents used
to separate metals from their ores during the processing phases. Most attention has been paid to cyanide used
in gold mining because of the very large volumes of cyanide that are used and its toxicity to most forms of life.
Importantly, cyanide can exist in numerous different forms and not all of these forms are equally toxic. In
addition, cyanide is rapidly photo-oxidized to harmless carbon dioxide and nitrogen gas in sunlight, thereby
greatly reducing the potential toxicity risk; the general public seldom appreciates this feature.
Discussions with stakeholders have revealed that their specific areas of concern around potentially toxic
substances relate entirely to issues associated with cyanide and are seldom attributable to any specific mine or
mining operation:
• The discharge of cyanide-rich tailings to tailings dams at most gold mines and their subsequent seepage
from these sites into the aquatic environment.
• Inadequate control maintained over cyanide processes on gold mines such that spillages occur and
contamination results.
• Occasional spillages caused by rupturing of cyanide storage tanks at gold mines, resulting in localized
contamination.
• The potential for the release of toxic hydrocyanic acid (HCN) gas from cyanide-rich tailings at most gold
mines.
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