The Pamour mine, one of Newmont’s Porcupine gold mines, is situated in Timmins, northern Ontario, Canada. Discovered in the early 1900s, the development of the Dome, Hollinger and Pamour mines, among others, established the hard rock mining industry in the region. Before 1930, shrinkage mining was used, followed by cut-and-fill stoping (backfilled with unconsolidated sand) of the quartz vein hosted gold mineralisation. Underground mining at Pamour started in 1936 and ended in 1996, yielding more than 4 Moz. Stopes were accessed through relatively small dimension drifts and drives connected to two shafts. Surface mining of crown pillars occurred between 1976 and 1996. Large-scale open pit mining of peripheral veins and disseminated mineralisation started in 2004, which was put on hold in 2009 and partially backfilled in 2012. The pit has been allowed to flood in the last decade. The existing Pamour pit (12 km northeast of the Dome mine) is elongated along an azimuth of 075°, is 1.3 km long, 0.5 km wide, and 280 m deep. Once the water level is lowered, the interconnected underground mine workings will be used to underdrain the rock mass. The excavation will advance an additional 1.1 km towards the east-northeast, will widen by 300m, and will increase in depth to about 530 m. A feasibility level investigation in 2020-2021 found that even though the three mines are separated by tens of kilometres, the lithologies are essentially the same, and the rock masses are mostly FAIR to GOOD. Structurally, there are relatively narrow damage zones of V-POOR ground associated with regional scale brittle deformation, and the alteration effects can be accounted for in the geotechnical domain models. Rock mass foliation (72/155° on Hollinger’s North Wall and 70/335° on Pamour’s footwall) kinematically limit the achievable bench face angles. Beyond kinematics, the dominant open pit design constraint in the Timmins area pre-mined rock masses are the size, shape and induced excavation damage associated with the voids, relative to the slope geometry and the ramp positions. When mining through the older narrow stopes like at Hollinger, where the voids are sub-parallel to the rock mass fabric, the void detection and caving, filling and wall control is done on a bench by bench basis. Where the stopes are larger, like at Dome, and there are weakened intact rock halos around the mineralisation, inter-ramp scale slope design adjustments and the use of waste rock buttresses are more appropriate. The situation seen at Pamour, however, poses more of a challenge because it is a ‘hybrid’ situation. It has several large open voids along the ‘keel’ of the pit, and some steeply dipping narrow stopes in weaker intact rock at mid-height within the hangingwall slopes.
