Study on the Impact of Trolley Assisted Haul Trucks on Strategic Mine Planning in Open Pit Mines

Abstract

Trolley assist is a system in which haul trucks in open pit mines are propelled by electric energy along a designated haul road segment. This can lead to high savings on fuel costs, productivity, CO2 emission and engine life, but is associated with limitations on mine planning. The purpose of this thesis is to determine how trolley assist can be accommodated into strategic mine planning, in view of optimizing the Net Present Value (NPV). This was investigated by assessing the impact of relocating the trolley infrastructure on the mine schedule and NPV, using GEOVIA Whittle for a theoretical case study concerning a Ghanaian gold mine. The outcome of the case study was that a diesel only scenario yielded the highest NPV, meaning that the operational savings of trolley assist were not high enough to offset the required capital investment. The comparison between two trolley assist scenarios with a different time period of trolley line relocation resulted in a slightly higher NPV for the scenario with a delay in movement of one period, relative to the original trolley assist scenario. To account for the trolley infrastructure in the scheduling process, increased mining cost adjustment factors (MCAF) were used on the trolley line locations. This methodology was found adequate for the Ghana Gold case, but it requires detailed knowledge on the planned (re)location of the trolley infrastructure. It was found that delaying the trolley line relocation by one period only caused minor changes in the mine schedule and operating costs of the Ghana Gold case, justifying the slightly increased NPV for the delayed trolley assist scenario. However, considering the proportion of the total project value, the difference between the NPV's of the assessed scenarios was negligible. The results of the case study did not deliver enough support for the hypothesis that incorporating trolley assist in the long-term mine plan is key in achieving an increased NPV with trolley assist. Nevertheless, it is clear that the feasibility of trolley assist is not a simple offset between capital investment and operational savings. Most limitations of this research resulted from the complexity of the Ghana Gold block model and the poor availability of detailed cost data.