ZORTMAN-LANDUSKY: CHALLENGES IN A DECADE OF CLOSURE

The adjacent Zortman and Landusky mines in Montana, USA, produced gold and silver from a mineralized syenite intrusion. Although mining in the area began over 100 years ago, the most extensive production was from open pit mining and heap leach cyanide processing that occurred from 1977 until 1998 when the operator declared bankruptcy and the site was taken over by the U.S. Bureau of Land Management and the Montana Department of Environmental Quality. This paper details the history and management of mine drainage issues at the site from the first recognition that acidic drainage was a problem, through initial characterization and prediction work, to final reclamation and water treatment. Closure costs to date include approximately US$42M for material handling, grading, soil placement and vegetation, and approximately US$15M for construction, operation, and maintenance of water treatment facilities. Work continues on residual impacts many of which were not fully recognized until well into the closure phase. These include characterization and treatment strategies for acid mine drainage in Swift Gulch, a small stream whose headwaters originate on the mine property and which eventually flows onto adjacent tribal lands