Abstract. The Zortman 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. Zortman Landusky is where valley-fill-heap-leach cyanide processing was first used for gold production and is the first large-scale gold mine where unexpected consequences of acid rock drainage occurred. Neither the mining industry nor the agencies anticipated the problems, which developed at the mine. Subsequently Zortman/Landusky is where many of the best management practices for mining and new reclamation techniques were developed. In 1998, 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 of acid rock 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 site reclamation and approximately US$15M for 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 Some of the lessons that Zortman/Landusky are that detailed characterization and closure planning before and throughout the mine life are critical. This project also highlights the importance of having adequate financial guarantee mechanisms available to support both the anticipated reclamation throughout the project life and any potential water treatment.

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Following a complex legal history after a permit expansion in 1990, a Montana District Court ruled in 2002 that the Golden Sunlight's reclamation plan must include backfilling the pit in compliance with the Montana State Constitution and the Metal Mine Reclamation Act. The Golden Sunlight Mine submitted a proposed partial pit backfill plan in December of 2002. This presentation will detail the analysis and conclusions of the detailed studies that were undertaken to evaluate the impacts of backfilling the open pit at the mine with 33 million tons of acidic waste rock.

In the late 1980's the Bureau of Land Management came under scrutiny from the environmental community and our Nation's Congress for lax enforcement of operations conducted under the Nation's Mining Laws. This attention often focused on operations utilizing cyanide in the processing of gold ores. In response to this, the Bureau developed a Cyanide Management Policy and Cyanide Advisory Committee to provide guidance and technical assistance to field offices and advise management on related issues. The Bureau's Cyanide Management Policy was released in August 1990. Later the role of the Committee was expanded to include other technical issues related to hard-rock mineral development. During this time period it became apparent to the Bureau that a policy on acid rock drainage was as important as the cyanide policy. The Committee identified the need to develop a Bureau policy for mines with the potential to develop acid rock drainage. Several mines on Bureau managed public lands are extracting mineral deposits that have the potential for developing acid rock drainage. The Bureau Acid Rock Drainage Policy has several major points: 1. All proposals for surface disturbance must be evaluated for acid rock drainage. 2. Mitigating measures addressing acid rock drainage must be applied. 3. Operations that propose active water treatment of acid rock drainage discharge require financial guarantees for water treatment facilities. 4. All portions of the mine facilities that may contain acid-generating materials are to be bonded for 100 percent of the cost to implement the approved reclamation measures.

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