Authors: Savage, E; Jordan, L; Hartman, W

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Savage, E, Jordan, L & Hartman, W 2022, 'The planning of a cave reorientation at the Ernest Henry sublevel cave mine ', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 1161-1170,

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The Ernest Henry Operation (EHO) in Queensland (Australia) is developed to a depth of just over 1 km, and current active production cave levels have reached a depth of 800 m, with a pre-feasibility study underway to assess a mine extension to around 1,375 m below surface. The EHO main cave orebody is changing shape with depth, narrowing from east to west and elongating north to south. The narrowing and elongation of the orebody is resulting in the current longitudinal mining layout to consist of a reduced number of ore drives at an extended length, impacting productivity and mining associated risks. The extended ore drives (>400 m) pose a secondary ventilation challenge, ground instability risks in maintaining access crossing a major geological structure and excessive cave loader tramming distances. The intersection of new major geological structures within the cave footprint significantly increases potential unravelling and seismic risk, particularly with the start-ups of new levels and their associated step-outs. These ground related issues are expected to be challenging with depth and therefore necessitate a change in cave orientation. Altering the mine design, to reduce these challenges, is considered an optimal way to de-risk the mine plan at depth. This paper outlines key items within the study process, some mining associated challenges and risks, a decision-making and planning process in rotating the cave layout, proposed control measures to ensure local and regional stability. Thus, the paper outlines the requirements for creating an environment where risk aversion will be the state of play in an increasingly challenging environment.

Keywords: mine planning, caving, sublevel cave, reorientation, cave flow, seismicity, stability

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