Determining the most suitable mining method for block 2 at Auptism Underground Mine

Abstract

Auptism Underground Mine (AUM) currently employs longhole open stoping as the main method for its underground gold mining operations. The mine adopted longhole open stoping in 2009 to replace shrinkage stoping, which had been used since 2005. Being a vein-hosted deposit, mineralization at AUM is hardly continuous. Discontinuities separate the orebody into several zones. One such mineralized zone is Block 2. Block 2 is about 500 m long on strike and 600 m high with an average width of 3.5 m, varying between 1.5 m and 10 m. Block 2 is about 300 m below ground level, strikes approximately north south and dips approximately 60°. Block 2 contains 41,867 ounces of gold with an average grade of 12.17grams/tonne (g/t) contained in 106,987 tonnes of gold ore. Based on experience and literature, these characteristics of Block 2 might pose operational challenges for longhole open stoping and ultimately, the economic potential of the zone might not be fully realized. This project seeks to determine the most appropriate mining method that would guarantee the optimum operational efficiency and maximum economic return for Block 2. The mining method selection process involved two main phases: the preliminary phase and the final phase. In the preliminary phase, the geologic and geometric characteristics of Block 2 were subjected to the University of British Columbia (UBC) mining method selection system. Three mining methods: sublevel stoping, shrinkage stoping and cut-and-fill were considered applicable based on the UBC test. Given that shrinkage stoping was discontinued at AUM for safety reasons in the past, it was considered undesirable for further evaluation. Therefore, open stoping and cut-and-fill were the two mining methods considered for further analysis in the final phase. Comparison of the economic outcomes of both methods revealed that cut-and-fill generates 30% more net profit than open stoping. Furthermore, cut-and-fill proved to be more economically efficient with a lower unit operating cost of $337/t compared to that of open stoping of $473/t. Based on this study, cut-and-fill was deemed the most favourable technique for mining Block 2.