Stability and access implications of open pit mining through old underground mine workings

Increasingly, mining operations are looking at developing large open pits down through old, abandoned underground workings in order to extract remnant ore left within pillar zones. Maintaining pit wall stability while mining through major scale underground stoping zones presents both a risk and challenge that can have significant impact on overall pit economics and viability. Potential operational problems associated with the interactions between the stopes and the pit walls may occur, necessitating pit wall redesign, ground support installation and operational rescheduling. In addition, anticipated interactions of the pit shell with underground mine workings must be closely evaluated to maintain a safe working environment. Using illustrative examples, this paper discusses how operational hazards and risks to pit wall stability can be assessed and mitigated.