The mining method currently in use is long hole longitudinal retreat sub level open stoping (the Avoca method) with the following parameters:
- Sills are driven on 15 m (sublevel) spacing approximately 4.5 m high;
- Longhole stopes (panels) are drilled using parallel or fan drill holes between the sublevels (approximately 11 m);
- A slot is drilled and blasted first to create a void to shoot to if one does not exist;
- Multiple rings are blasted into the void (exact number of rings blasted is dependent on production requirements and regulations);
- Stopes are filled with waste rock backfill as production advances, typically leaving only 20 m of void to reduce dilution and hanging wall failure;
- The production cycle is repeated until the level is completed;
- Temporary sill pillars are left between mining fronts;
- A concrete sill pillar is constructed on the first (lowest) sill cut of a mining front if there is an expectation ore will be mined up to this sill from below.
The backfill cycle is an integral part of the production cycle of the mining method. Over the remaining life-of- mine, approximately 2,200 tonnes per day will be required.
Backfill will be primarily run-of-mine waste, either directly from underground development or from open pit waste (acid generating material).
Stopes are backfilled to provide a working floor and to store potentially acid generating (PAG) waste encountered over ........