Management of High Stress and Seismicity at Vale Inco Creighton Mine

Abstract

At Creighton Mine, most of the seismicity occurs at depth and in close proximity to excavations. Seismic events are generally caused by mining induced stress fracturing of the surrounding rockmass and are typically triggered by blasting. Some significant seismic events, however, occur away from active mining areas, along major geological structures such as faults and shear zones and are characterized by low event densities and large magnitudes. These events have a direct link to the mining activity yet they do not always occur immediately or soon after production blasts. They are the result of fault slip movement along pre- existing, well-known sub-vertical geological shear zones. Slippage occurs when mining-induced stresses reduce the clamping stress on the fault or cause the shear stress to exceed the shear strength of the respective structure. In some cases, intact rock failure may occur if the shear zone is locked-up by asperities or by healing. The on-echelon fractures, when crushed, can lead to slips and major seismic events. These events represent risk to major infrastructure such as the haulage ramp and footwall accesses where the shear zones cross the excavations. This study summarizes the evolution and implementation of appropriate geotechnical design and practices for the management of the high stress and seismicity. It describes the overall ground control concepts used for the strategic enhanced support placement required to manage the high stress and seismicity at depth. Meanwhile, the analysis includes a case study for the understanding of the mechanism of major events that occur remotely from active mining areas.