Improvements to void hazard management for an active open pit mining through an old underground mine

McArthur River Mine (MRM) in the Northern Territory, Australia is one of the largest Zn-Pb deposits in the world. The ore body was initially mined with an expansive underground network of room and pillar and stopes, many of which remain open. The operation transitioned to open pit mining in 2006. Due to the extent and location of underground workings under the pit floor, void hazard interaction and management is an important part of the day-to-day pit operations.

The Void Management Procedure and Plans provide a framework to manage the risks to personnel and equipment from interaction with underground workings. More specifically, Void Management Plans provide a review and operational management plan for a particular void hazard area, considering the cost, timing and equipment access prior to works commencing. Due to variation in ground conditions and void geometry, management solutions are often not a straightforward problem. Prioritisation of safe management options may cause delays or changes to mine schedule.

This paper presents an overview of the operational strategies as well as recent improvements to void management, which involve a focus on a more rigorous and robust review of ground and void conditions. These improvements include a grid based Catastrophic Failure Analysis (CFA) check, which was developed to provide a rapid assessment of areas that require targeted investigation. The development of specific Q values to refine Scaled Span Analysis (SSA) results are also presented. The paper also presents an updated probe and monitor approach for stope management.