1298 Slot-Slash Panel

Introduction

In December 2003, production drilling began in the 1290 Ore body. This area of the mine has experienced considerable challenges due to the effect of high stress and subsequent increase in seismic activity during the mining cycle. To control violent rock behaviour and reduce seismic risk and blast hole damage, stakeholders put together a plan to alter this effect and be able to successfully mine this high-grade nickel ore body. Documentation of the steps in this process included geo-technical monitoring of this and the 1299 Stope scheduled in the autumn of 2004. Results will serve to compliment our knowledge of the rock mass and recognize potential benefits in mining similar geometries of our deeper mining areas.

Background

Different mining techniques with varying degrees of success have been used to extract ore from this area in the past. Mining has been primarily VRM, although blast-hole and as well as slot-slash (or even slot-slash/VRM) combinations have been used to struggle through this ground. The 1290 Ore body, commonly very narrow, dips at approximately 70 degrees along a sheared granite/gabbro hanging wall striking east of the main 400 Ore body. Mining is commonly sequenced in a linear direction from mined-out areas of the 400 Ore body, although a pillar was created with early year introduction of the 4770 Ore pass from 5600-6400 levels. Current mining of the 1298 Slot-Slash panel(6400-6600)is mined above 6400 as well as below 6600.

Design Considerations

Results from previous successes in the 1290 Ore body identified methods producing the most benefits and those that did not work. Historically, panels with a slot raise have been more successful. In addition to the slot, previous results also point to success with closely spaced holes drilled into the hanging wall, creation of a 'fracture zone'. It was agreed to reproduce a similar pattern in the current stope. As creation of a fracture mechanism from simply drilling closely spaced holes is questionable at best, it was agreed instrumentation of the stope take place. Creighton Mine engaged the services of INCO Mines Technology to determine if stresses can be effectively shed from the working area, allowing stress-free drilling of the remaining holes.

Mining Plan Implementation

As the drilling of the hanging wall destress holes progressed from the previously drilled panel to the eastern block limit, seismic activity became increasingly higher. As the drill pipe was being pulled out the hole they crushed and closed. As drilling progressed to the east, larger seismic events were observed further into the hanging wall. The largest of these was 2.3Mn. Seismic source parameters indicate a fundamental difference in the larger events. The shear component of the seismic waveform is larger, indicating a fault-slip source. The fact that the larger events did not trigger as many transducers as smaller events plotting at the panel indicates a redistribution of stress is taking place. Such an event occurred in the 2nd last hole to be drilled. After the large event occurred the last hole was not as seismically active as the previous. All the destress holes crushed and closed as the drill pipe was being pulled.

Later, two 215 foot long, 10" pilot holes were drilled to the bottom sill, one of which were reamed to 48" diameter. The raise bore hole and pilot did not close, but distorted to a cat's eye shape. Subsequently, holes drilled near the raise bore hole showed very little signs of squeezing.

Based on the theory that speed and accuracy were critical, the new "attack" plan incorporated the tight-knit team approach. Success was critical to precise scheduling of the resources.

In order to successfully drill accurate holes, the team was required to complete each hole quickly, not stopping. At times, drillers would be required to pull out and blasters load prior to the holes squeezing to the point they would become un-useable. This meant keeping the drill running 24-7 with shifts (ITH & Raisbore) relieving the previous shift right at the controls. In short "if drill pipe is in a hole it must be moving". In the event of a power failure, the Cubex 6200D was to pull out on diesel.

Comments

The history of this ore body had taught us that the traditional method of drilling off the panel and handing it over to the blasters completely drilled would not work. In 1298 Stope, personnel constantly monitored any deterioration of the drilled footage. As soon as holes were observed as becoming were critical but still loadable, the Cubex would pack up and the blasters promptly loaded everything drilled to that point. This reduced unnecessary cleaning of holes, and the increased void dimension further reduced stress related problems. Blasting triggered some seismicity, but because there was no further footage drilled off, no drill footage was wasted.

This process was repeated until the panel was taken to its planned tonnage. Though it may not seem that significant of a change, just re-thinking the approach allowed Creighton to mine a 1290 panel in three months losing only 60' of rods and one over-target (no value) hammer. The previous stope (1297), took fourteen months to complete with a loss of eight drill strings and hammers.

Another benefit generated from this process change was the decrease in seismicity caused during the mining cycle. Unlike previous panels we did not experience any damage or downtime from rockbursts.The most important benefit of all that came from these changes is that we are making the 1290 ore bodies a safer place for our people to work.

The following people formed the team that made this project a success.
Planning: Jon Treen, Glen Groom, Alan Crowther, and Allan Punkkinen
Raisebore Crew: George Demers, Rick Rouleau, and Mario Beauregard
Drillers: Arron Hutchings, Denis Parent Derek Drosdowsky
Blasters: Jimmy Macdonald, Guy Touchette