Inco Limited operates nine mines in the Sudbury Basin, exploiting the nickel-copper orebodies of the Sudbury Igneous Complex. Mining depths vary from surface generally down to 4000 ft., and as deep as 7200 ft. at Creighton Mine. Figure 1 is a location map of the Basin, showing Copper Cliff North Mine and the other Inco mines currently operating. North Mine is located on an off-set from the main elliptical nickel irruptive and is currently the second most seismically active mine in the Basin after Creighton Mine.

The mine was originally a shrinkage and blasthole operation which closed in 1978 but in 1983 the mine re-opened as a vertical retreat mine (VRM) operation, mining several distinct orebodies. The principal ore zone is the 120 Orebody which is a steeply dipping, tabular orebody which varies in width from 25-80 ft. The direction of dip of the orebody changes with depth so that below the 2200 ft. level it dips at 70-80 degrees towards the shaft. For this reason all the major access drifts which would normally lie in the footwall are actually located in the hanging wall.

The primary VRM stopes were originally designed to be 40 ft. along strike and were separated by 80 ft. long pillars to be mined on a second pass. The stope/pillar design was based on an analysis using the generally accepted regional stress regime for the Sudbury Basin and the principal concern was the stability and mode of failure of the pillars. The stopes were to be filled with cemented rock fill and when the pillars were mined, they would be filled with un-cemented rock fill.

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