J. van Duijn

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Master thesis (1)

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Mining method selection based on cost modelling and stability analysis for Mine 2 of the Stjernøy mine in Norway

Master thesis (2020) - Jaap van Duijn , M.W.N. Buxton , A. Barnhoorn , M. Keersemaker , Robrecht Schmitz

To optimise mining in a safe, geotechnically controlled and economical most beneficial way in Mine 2 of the Stjernøy mine, a choice has been made to review the current mining method, sublevel open stoping, and a different mining method, vertical crater retreat. The Stjernøy mine is an open pit and underground mine for Nepheline Syenite and this thesis focuses on Mine 2, the underground mine which is partially completed. The stopes of Mine 2 are closely located to old stopes, which can cause stability issues. Between the new and old stopes is a barrier pillar which is a key element in the stability of the underground mine and the infrastructure for the open pit operation as well. This project consists of field work and laboratory testing to create a basis for the numerical stability analysis of the mine and the creation of a cost model for the two different mining methods. The results of the cost modeling show that the use of sublevel open stoping will result in a cost per tonne of 9.86 NOK and the use of vertical crater retreat will result in a cost per tonne of 10.39 NOK. The use of sublevel open stoping as mining method is the most economically beneficial option for the mining operation. It is less expensive as a mining method and it is a proven method at this mine site. The vertical crater retreat method uses a more expensive blasting method, with the same burden and spacing parameters as the sublevel open stoping. The results of the field work and the laboratory testing provided important parameters for the numerical modelling, such as the strength of the material. Based on these results the numerical modelling also showed that it is beneficial for the stability of the pillar if some stopes near the barrier pillar are not extracted. The extraction of these stopes will decrease the factor of safety of certain areas of the barrier pillar to one or for some areas below one. The stope size has also been reviewed. To make sure that the stopes are well connected to drawpoints, it is important to keep them the same size, which is a stable stope size for the roof. Smaller stope sizes are found to be a bit more stable, however the effect of the increasing amount of pillars is not known on the overall stability.