Shrinkage Stoping

Shrinkage stoping is a method of mining which is flexible for narrow orebodies that do not need any backfill during stoping. Successive horizontal slices of ore, which are most of the time of about 10 feet (3 metres) high, are taken along the length of a stope, in a form which is very similar to the cut-and-fill method. The ore is removed from the .stope through drawpoints at the bottom horizon which is spaced about every 25 feet (7.5 metres) along the strike. A sufficient amount of ore is left in the place to provide a floor in which to work from when taking the next cut. This process demands considerable co-ordination and plan making.

When the blasting of the ore is done, it fills a space that is about 1.5 times the size of the space it filled as a solid mass. We call this action a swell and is a very important factor in determining the amount of ore which is to be drawn from the bottom of the stope in order to keep an apropriate working space. The ore which is broken is drawn down from chutes below, this way it is "shrinking" the quantity of broken ore in the stope.

The process is continued in an upward direction until the stope either reaches the next level or is stopped at some predetermined elevation. Horizontal crown pillars are left behind at the top of the stope.

Shrinkage stoping is dependant on gravity to keep the broken ore moving to the draw points, so due to this, it works only in steeply-dipping orebodies. There is no provision for support, so the wall rocks must be competent and strong. The orebody must also have sufficient width to permit a working width all the way up the stope, in most cases no fewer than two metres.

Sublevel CavingOre is developed from a series of sublevels which are spaced at regular intervals throughout the orebody in sublevel caving. Mining begins at the top of the orebody. A series of ring patterns is drilled and blasted from each and every sublevel. The broken ore is mucked out after every blast and the overlying waste rock caves on top of the ore which is broken.