Sodium Cyanide Hazards to Fish and Other Wildlife from Gold Mining Operations

Abstract

Highly toxic sodium cyanide (NaCN) is used increasingly by the international mining community to extract gold and other precious metals through milling of high grade ores and heap leaching of low grade ores. Of the g8 million kg cyanide (CN) consumed in North America in 1989, about 80% was used in gold mining (Knudson rggo). In Canada, more than go% of the mined gold is extracted from ores with the cyanidation process. This process consists of leaching gold from the ore as a gold-cyanide complex, and gold being recovered by precipitation (Simovic and Snodgrass 1985). Milling and heap leaching require cycling of millions of liters of alkaline water containing high concentrations of potentially toxic NaCN, free cyanide, and metal cyanide compl&s that are frequently accessible to wildlife. Some milling operations result in taihngs ponds of 150 ha and larger. Heap leach operations that spray or drip cyanide solution onto the flattened top of the ore heap require solution processing ponds of about 1 ha in surf&x area. Although not intentional or desired, puddles of various sizes may occur on the top of heaps where the highest concentrations of NaCN are found Exposed solution recov- ery channels are usually constructed at the base,of leach heaps. All of these cyanide- containing water bodies are hazardous to wildlife if not properly managed (Henny et al. 1994). In this account we emphasize hazards of cyanide from mining operations to fish and wildlife species and proposed mitigation to protect them. 5.2