The Stillwater Mine, situated in the Stillwater Complex in south central Montana, USA has produced palladium and platinum from the J-M reef since 1987. Mining is primarily done by cut-and-fill methods. Over the past 4 years, however, long-hole stopping practices have been playing a larger role in mine production. This amplified utilization of long-hole mining improves productivity and lowers risk during mining activity. Greater reliance on this mining method, however, results in a potential for decreased hanging wall stability. It therefore becomes very important to quantify sub-level hanging wall stability. Data has been compiled outlining parameters affecting stability. Subjective assessments of the probability of failure have been applied to each stope. From this assessment, a skeletal graph relating probability of failure to rock parameters vs. stope geometry has been proposed. Classes of sub-level hanging wall stability have been identified and presented in matrix form that can be easily communicated.
INRODUCTION
The Stillwater Mine, the largest primary producer of palladium and platinum in the Western Hemisphere is situated in the Stillwater Complex in south central Montana, USA. The Stillwater Complex is a 42-km long layered stratiform lopolith approximately 2.7 b.y. old. It hosts a palladium and platinum rich layer known as the J-M Reef. Stillwater Mining Company has produced palladium and platinum from the J-M reef since 1987. Previous production has primarily been accomplished by variations on cut-and-fill methods. However, over the past 4 years, long-hole stopping practices have been playing an ever increasing role in mine production. This amplified utilization of long hole mining improves productivity and lowers risk of injury to personnel. Greater reliance on this mining method, however, results in a potential for decreased hanging wall stability in the sub-level open stopes. It therefore becomes very important to investigate failure mechanisms for sub-level hanging walls. A desire on the part of Stillwater Mining Company's management to more fully understand hanging wall stability in the sub-level open stopes resulted in the initiation of this project. The project is ongoing thesis research and should, at this point, be considered a progress report. Thirteen case studies have been compiled outlining structure, rockmass quality, stress, stope geometry, and mining sequence. Failure modes are also briefly summarized.
