Open pit optimisation, design and production scheduling – a case study

Abstract

Iron ore mining operations started declining in 2012 due to falling concentrate prices. Some mining operations in Sierra Leone had to shut down totally or go under care and maintenance owing to the falling concentrate prices. Most operating mines and those intending to resume operations have had to implement strategic plans with the objective of maximising profits to keep the project running. Sierra Leone (SL) Mining Plc acquired the rights to the Marampa deposit and plans to resume operations with the intention to maximise profits at the prevailing world market conditions. With iron ore price on the world market relatively low, there was the need to determine the feasibility and profitability of the project. In this work, GEOVIA Surpac was used to validate and generate the block model of the Marampa deposit. Whittle software was used for optimisation and the optimal pit selected using the highest Net Present Value (NPV) criteria. GEOVIA Mineshed was used to generate a long-term mining schedule to meet the annual processing plant throughput and was again used to design the optimised pit. The optimal pit produced 174 836 920 t of ore at an average grade of 33.89 %Fe. An NPV of US$ 184 665 345 for 29 years of mining was obtained at a stripping ratio of 0.34:1. The project is sensitive to iron ore price, mining recovery and dilution. The designed pit contains 171 393 104 t of ore at an average grade of 34.42 %Fe at an NPV of US$ 155 437 194 to be mined for 27.6 years.