Case Study

The creeping cone method was used at the Selebi North Mine in August 1995. Sloughing from the hanging wall and footwall was noticed once the stope spans exceeded 30 m. The implementation and use of this method lead to better accuracy of longhole drilling, fragmentation, and reduced secondary blasting. As a result, haulage drives were not required, which saved approximately half a million in associated costs.

The pillars in the figures are numbered for ease of identification. An example of the modified creeping cone sequence is shown below. Production begins by blasting blocks 1 and 2 (Figure 2) and ends with block 12 (Figure 6). Load haul dump(LHD) machines working in the sublevels are used to draw some of the broken ore and to maintain the cone in its desired shape and position of creep.

Figure 1 (left): Development and drilling pattern of modified creeping cone method, Figure 2 (right): Production blasting in blocks 1 and 2

Figure 3 (left): Cone is formed inside stope, Figure 4 (right): Cone moves from unsupported to supported transition zone

Figure 5 (left): Ore is drawn from a slot raise, Figure 6 (right): Final stage of the mining sequence

With the modified creeping cone method at the Selebi North Mine:

• Dilution is decreased from 55.7% to 19.23%.
• Revenues are increased by 41.44%.
• Grade of run-of-mine ore is increased by 10.5%.

There are both advantages and disadvantages to the modified creeping cone method:

Advantages

• Offers access to the broken ore at all times throughout the life of the stope.
• Allows the stope to be mined as quickly as needed without sloughing from walls.
• A minimum amount of ore is left in the stope.

Disadvantages

• Broken ore is tied up in the stope for a long time to help support walls.
• Loss of ore in the stopes due to trapping by sloughing sidewalls.

References

This article was designed and created by John Forster, Stephen Soock, Nyree Grimes, Jihoon Ryan Hong, and Jordan Cooper as part of the MINE 448 Underground Mine Design Course taught by Professor Stephen McKinnon at Queen's University.