Thursday, January 1, 2004
Private File Attachment:
Cyanide extraction of gold through milling of high-grade ores and heap leaching of low-grade ores requires cycling of millions of liters of alkaline water containing high concentrations of potentially toxic sodium cyanide (NaCN), free cya- nide, and metal–cyanide complexes. To prevent flooding in mine open pits, and to enable earth moving on a large scale, it is often necessary to withdraw groundwater and use it for irrigation, discharge it to rapid infiltration basins, or, in some cases, discharge it to surface waters. Surface waters are diverted around surface mining operations. Available for irrigation, stock watering, and domestic, mining and milling, and municipal uses; reduction or loss of vegetation cover for wildlife, with reduced carrying capacity for terrestrial wildlife; loss of aquatic habitat for native fishes and their prey; and disruption of Native American cultural traditions. Surface discharge of excess mine dewatering water and other waters to main waterways may contain excess quantities of arsenic, total dissolved solids, boron, copper, fluoride, and zinc. When mining operations cease, and the water pumps are dismantled, these large open pits may slowly fill with water, forming lakes. The water quality of pit lakes may present a variety of pressing environmental problems.