Vertical crater retreat mining in the Sudbury Basin

Faced with rising costs and lower metal prices, several Ontario base metal sulphide mines have changed their method of mining to vertical crater retreat mining. This is a bulk mining method that utilizes large diameter holes and mines successive cuts remotely by blasting and cratering the bottom of the drill holes. The ore body is mined from the bottom up. The method in turn has required a change in materials handling to cope with the greatly increased productivity.

This paper presents an overview of vertical crater retreat mining in the Sudbury area using examples from several producing mines. The paper reviews the history of vertical crater retreat mining, various methods of applying vertical crater retreat layouts, the development of in-the-hole drills capable of drilling the large diameter holes required, methods of explosives loading and blasting to achieve the required cratering effect, methods of ground support including backfill placement, and the ore loading equipment presently being utilized including remote control load-haul-dump units and continuous loaders.

The safety aspect of vertical crater retreat mining has been of concern, and was the focus of a provincial inquiry. The benefits in improved safety are demonstrated through an analysis of various records kept by the mines and provincial agencies.

Future trends can now be envisaged, particularly in relation to deep mining. Some experimental work, which could have practical applications, is described.