PT Freeport Indonesia has undertaken the task of designing the Grasberg Block Cave mine below the open-pit, scheduled to be completed in 2015. The Grasberg Block Cave will be one of the largest single block caves in the world, with a planned production rate of about 160,000 tonnes per day. Geotechnical characterization of the area of the proposed block cave has commenced and preliminary design works are in hand. The design and layout of infrastructural facilities for the mine are also in progress and the geotechnical data are being collected at site. The development of the block cave will be started well before the completion of the Grasberg Pit so that the block cave can be ramped up soon after the pit is exhausted. Planning the transition from the pit to the block cave raises additional geotechnical issues such as stability of the steep slopes and the waste dumps and the possible sterilization of ore in the block cave due to migration of fine grained waste material. These issues are being addressed through different kinds of models. This paper presents some of the critical geotechnical issues identified in the transition between the Pit and the Block Cave and the efforts being made to resolve these issues so that the transition can be successful.
PT Freeport Indonesia (PTFI) is mining copper and gold deposits in the province of Papua, Indonesia in one of the world’s most geographically remote and challenging locations. The district is in rugged mountainous terrain from 2,900 to 4,200 meters in elevation, with annual rainfall exceeding 400 cm. The district has reserves exceeding 2.6 billion tonnes in eight surface and underground deposits that contain recoverable metal of about 54 billion pounds of copper and 66 million ounces of gold.