THE SUDBURY BASIN: On track at Lindsey

Falconbridge Ltd.’s Thayer Lindsley (or T.L.) project, an exploration play on a deep-seated nickel/copper orebody a few kilometres outside of Sudbury, Ont., now has a shaft sunk to the 1,310-metre level. At the time of our visit, two N. Morissette Canada diamond drills were coring horizontally toward Zone 4B, some 300 metres from the shaft station on 1310 level. During earlier surface drilling in 1987, one thick intersection through Zone 4B cut 255.5 ft (77.9 metres) grading 0.235% nickel, 4.4% copper, 0.12% cobalt, as well as precious metal values.

Technically, the interesting part of this shaft sinking is that hydraulic jumbos and full-face rounds are being used. J.S. Redpath Ltd. is sinking the 1,660-metre shaft; Redpath is only about 300 metres away from reaching that target. And so far, the project has been a success.

* At 12.5 ft. (3.8 metres) per day, the advance rate is better than the average 11.0 ft. (3.4 metres) using conventional benching sinking methods.

* Simultaneous shaft-sinking and equipping of the shaft.

* An outstanding safety record — in 560 days of shaft-sinking, Redpath has not had a single lost-time accident.

* A sinking stage that can stay in place even during blasts.

Adding to these accomplishments a unique burn-hole cut; single, full-face blasts; and a remodelled shaft clam mucker called a “Brutus” shaft mucker. It is little wonder, then, the project constituted a featured paper at the annual convention of the Canadian Institute of Mining and Metallurgy in Ottawa in May of this year.

On a recent visit to the project by The Northern Miner Magazine, Redpath project engineer Graham Speirs, who was co-author of the paper (along with Morris J. Medd, Redpath vice-president of contracting), took us on a tour. As Speirs explained it, he groundwork for the T.L. project was laid at the Underground Research Laboratory of Atomic Energy of Canada at Pinawa, Man. There, Redpath sunk a 4.6-metre-diameter extension of the existing shaft another 176 metres using a 2-boom jumbo and full-face blasting.

At the T.L. project, a 2-boom, shaft-sinking jumbo for full-face rounds is being used. The electric/hydraulic rig was designed by Maclean Engineering of Collingwood, Ont., and incorporates two SIG HBM100 rock drills. When not in use, the entire rig hangs at the shaft collar, not in the shaft-sinking stage, known as the Galloway. That way the drill rig stays out of harms way during other shaft work. It also prevents congestion in the Galloway itself. The drill descends under the bucket. Once set up, it drills an 86-hole, full-face round. Should one boom go down for repairs the second can cover the whole face.

Speirs has experimented to perfect the burn cut. Initially, a pilot hole was cut with a raise-bore machine. He then switched to a 6-hole configuration with three of the holes reamed to 4 inches, then an 8-hole cut and, finally, a 9-hole cut with five of them enlarged to provide that initial breakout space.

“We’ve had our problems,” he said. For example, because the SIG 100’s hammer and rotation do not have separate controls, Speirs tried SIG 150s. These machines over-taxed the jumbo’s hydraulic systems and were replaced with the original drills. As well, few shaft sinkers are accustomed to shaft jumbos and full-face rounds. “This is all new to the miners. We have had to re-program them.” In blasting, Speirs opted for ICI Powermex 500, a water gel explosive in 4-ft.-long cartridges that make for rapid loading. Said Speirs: “Boyes Explosives has helped us a lot.”

All in all, Speirs is sold on the full-face, jumbo method of sinking shafts. “We set up the jumbo once a day and drill 13.0 ft. With the old method, you would take three rounds, load three times and blow smoke three times.” And, he could have added, on average advance only 11 ft. (3.3 metres). In addition, this method allows for the simultaneous sinking and equipping of the shaft. While the sinking continues below the 4-deck Galloway, the shaft is lined with concrete and outfitted with bunton, guides, cable, piping and so on. No longer is the Galloway hoisted 210 or 240 metres above the blast, because fly rock is minimal with the parallel-hole, full-face sinking.

The shaft clam mucker is specially designed by O.J. Industries of Salt Lake City, Utah. This shaft mucker was fitted with a custom-made 0.57-cu.-metre ( 3/4 cu.-yd.) bucket. The Brutus, as it is called, has a 4-metre-long (13-ft.) boom reach, 300 mm (or 12 inches) longer than any formerly available. The higher capacity bucket achieves higher production rates and the longer boom allows for a longer shaft bucket and reduces reset time.

The Thayer Lindsley deposit occurs along the base of the Sudbury Igneous complex. Scot Halladay, Falconbridge project geologist, pointed out four zones of interest to Falconbridge. Zones 1, 2 and 3, which occur between roughly 400 and 1,500 metres below surface, are within the sublayer between the hangingwall Norite and the footwall Metabasalt and Granite. Current interpretation positions Zone 4B entirely in the granite away from the contact. Halladay said that, generally, Zone 4B in the granite is richer in precious metals and copper than the contact-hosted mineralization.

In 1971, Falconbridge began sinking a shaft toward Zones 1 and 2. Because of a slump in nickel prices and following an economic re-evaluation, the shaft was stopped at 95 metres.

The big intersection in 1987 prompted the latest shaft-sinking. The target is 1,660 metres. Once that is reached, an exploration drive toward Zone 4B, which is south of the shaft at 1310 level, will be excavated. An east-west drift nearly 700 metres long will be driven in granite to allow diamond drilling on 25-metres centres. A similar project is planned for the 1585 level. The shaft bottoming should be completed by early March, 1991.

Falconbridge project engineer Dawson Proudfoot pointed out that ground conditions have been relatively good so far. The shaft has been excavated through norite. “The nice thing about norite is that it might be blocky but it doesn’t burst violently under stress the way granite does,” he said. Stations are secured, both walls and back, with rebar and shotcrete.