Optimization of open pit to underground transition depth: An idea for reducing waste rock contamination while maximizing economic benefits

摘要

As open pit (OP) mines grow downward, more waste rocks are produced. Thus, the waste removal and management costs increase exponentially. On the other hand, waste rocks spoil natural surfaces, water resources, and local biodiversity surrounding mining areas. These reasons motivate the shareholders to shift from their routine mining method toward an underground (UG) operation by which less waste rocks are extracted. The depth of this transition should be determined so as to achieve maximum profit from the entire project (OP & UG). The present study aims to evaluate the amount of waste rock reduction while optimizing the transition depth. To this end, an integer programming (IP) optimization model was executed on a real orebody. The results indicated that waste rock generation decreases up to 7.5 million tons while the net present value (NPV) of the project increases up to 0.28%. In addition, due to this optimization, around 4.5% of natural surfaces, which had been initially allocated to the disposal site, remained uncontaminated. Further, based on acid base accounting (ABA) test, it was concluded that waste rocks do not have acid generation potential and, thus, can be used as backfilled material. (C) 2020 Elsevier Ltd. All rights reserved.