The Reno

Mine D (‘D’ is for ‘deep’) is the latest phase of the Kidd Creek zinc-copper mine in Timmins, Ont. Mining production began in 1966 and had progressed from an open pit to underground as No.1, No.2 and No.3 mines. However, by the early 1990s, the productive life was expected to be only another 10 years.

An underground drill program in 1993 from the bottom of No.3 mine (60 level, which is nominally 6,000 feet or 1,800 m below surface) changed the understanding of the orebody, so No.3 mine was extended to 68 level (6,800 feet or 2,070 m deep). Diamond drilling continued from 68 level, and was able to comfortably reach 88 level (2,680 m depth). A few holes reached all the way down to 2,740 m and they were still hitting mineralization.

With the help of Boart Longyear’s powerful LM150 diamond drill, the discovery was investigated with a pre-feasibility study followed by a feasibility study from late 1994 to mid-2000. On July 19, 2000, the board of directors of then-100%-owner, Falconbridge Ltd., approved Stage 1 of the Mine D project: to extend the mine from 68 level to 88 level by sinking a winze, extending the ramp, and doing development and additional drilling.

CMJ interviewed Glen Davidge in early January about the 6.33-year-long Mine D construction project, which is just ending. Davidge is superintendent of mine engineering and technical services for the project and has been involved with it from the start, more than a decade ago.

He began with an analogy: “You live in a ranch-style house and you want to install three floors of basement. So you brace and raise the house, excavate and pour the basement walls, and then lower the house back onto the basement. The builders have to go through your house to get to the basement, while you continue living in the house. Meanwhile, you’re remodeling the main house. This process goes on for six years and the mortgage is renegotiated twice.” (Annual ore production from Kidd Creek increased from 2.27 million to 2.63 million tonnes per year while Mine D was being built, and there were two changes of ownership during that period: Noranda in 2002, and Xstrata in 2006.)

Shaft-sinking

Stage 1 of Mine D is divided into three blocks of about 200 m–68-75 level, 75-82 level, and 82-88 level–with loading pockets built on levels 77, 83 and 90.

The project actually consisted of completing two shafts totaling about 2.2 km.

The smaller job was a 452-m, concrete-lined, 7.0-m-diameter ventilation shaft sunk from surface to 16 level by J.S. Redpath as part of a complete restructuring of the mine’s ventilation system.

The main shaft-sinking work–the No.4 shaft–was engineered and built by Cementation. This is a winze from the collar on 47 level (1,432 m depth) down 1,580 m to a depth of 3,012 m below surface. The circular shaft with steel framing was excavated to 8.5 m diameter, with a 7.6-m-diameter concrete lining. Services in the shaft include: a 250-mm compressed air line; two 102-mm process water lines (for drilling); two 150-mm pump discharge lines; two 150-mm concrete slick lines; two 15-kV power cables; and fibre optic and leaky feeder cables for communications. Two ventilation ducts used during shaft-sinking have since been removed.

There were two stages in excavating the shaft. A 1.8-m-diameter pilot raise had already been driven through No.3 mine as part of the ventilation system, so the first part of the job was a slashing exercise. To improve the schedule, a bulkhead constructed on 47 level allowed for shaft-slashing beneath, at the same time the headframe and underground hoistrooms were excavated and constructed above. The bulkhead was removed when the main cage hoist was ready for sinking duty.

The production and main cage hoists are twin 5.5-m-diameter double-drum Siemag hoists with 4,500-kW ABB synchronous motors powered by a cyclo-converter drive. (The drums were designed to be skidded from surface down the ramp in two pieces.) The production hoist controls two 19-t-capacity skips, traveling at 16 m/sec in balance. The sinking gear on the other hoist has been replaced by a two-deck, 120-person main cage and counterweight that travel at 10 m/sec. As well, there is a 2.47-m-diameter, single-drum Siemag hoist that runs the 12-man auxiliary cage at 5 m/sec.

There are really two underground hoistrooms on opposite sides of the shaft with horizontal ropeways about 100 m above 47 level. The larger service hoistroom houses both the auxiliary and main cage hoists, while the production hoistroom has only the production hoist. The hoists are run remotely from surface.

Where the extended pilot raise ran out at 80 level, the shaft-sinking was done using 5-m half-benching, with one side blasted and then the other, offset by 2.5 m. This created a sump for the water and reduced the risk for rockbursts.

To permit skipping to commence from Block 1 in July 2004, a bulkhead was placed just below the loading pocket on 77 level, blocking off the two skip compartments so shaft-sinking could continue below. When shaft-sinking had reached below 90 level, this process was repeated allowing production to begin from Block 2 using the 83 level loading pocket in November 2005. The shaft-sinking was completed to 3,012 m below surface in March 2006 with completion of the shaft sump.

Development work

Vertical development work by J.S. Redpath consisted of driving 6.9 km of Alimak raises, mostly 3 m in diameter. Larger raises were excavated using a two-pass system: an Alimak pilot raise followed by slashing to 6.1-m diameter. One was from 88 to 44 level, and a second was driven from 77 to 44 level to tie into the mine’s ventilation system. Four 3-m circular orepasses were also driven in each block.

Ramps and lateral development work totaled 25.3 km, mostly done by J.S. Redpath. The 5.1-m x 5.1-m arched service ramp at 17% grade was extended from 68 to 90 level, with mining levels spaced every 40 m vertically, and a connection from the shaft stations to the ramp on 75, 82 and 88 levels. Equipment included two Atlas Copco M2C drill jumbos, Tamrock 1400 LHDs (about 7-m3) for mucking, and Toro 50D and 40D trucks for ramp waste haulage. Almost all the waste was used as backfill aggregate in No.3 mine.

Initially ground support consisted of bolt and screen using scissor lifts or MacLean bolters. This has migrated to shotcrete support, nominally 50 mm thick, sprayed on using Driftech equipment. It is allowed to cure for four hours, quality checked, and then the heading is supported with 2.1-m resin-grouted bolts. The shotcrete is carried from the shaft to the heading in ‘transmixers’–Marcotte carriers fitted with a 6-m3 cement mixer.

Mine D has consumed a prodigious amount of concrete, so the concrete delivery was important. A concrete batch plant was built on surface, owned and operated by Lafarge Canada. The plant was connected to underground with two steel-lined, oil well-type lines: one used for the shaft lining and the other for shotcrete and other construction needs. The transmixers picked up the concrete from the line on 68, 75 and 82 levels. The Mine D project typically consumed 25,000 m3 of shotcrete and concrete per year, peaking at about 32,000 m3 in 2004. The largest single pour was 6,000 m3 in about one week when the plant worked around the clock. Despite the length of the concrete lines, there were very few quality-control problems, according to Davidge.

A number of additional jobs were accomplished while the mine continued to operate. Ventilation was completely changed from a suction system with many underground fans to just five main fans, three on the surface and two on 60 level. An intranet backbone was put in place for monitoring activities such as the loading pockets, the vent fans and Mine D phones. A pastefill plant built for Mine D worked so well that it is now displacing the cemented rockfill system in the rest of the mine.

Up to six diamond drills worked underground during the project, mainly operated by Forages Garant & Fr
res, putting out 100 to 130 km of drilling a year.

Safety challenges

As a large brownfield project at depth, Mine D was an ambitious venture. It was run by a project management team of Falconbridge staff with consultants seconded from AMEC, Hatch and other companies. Over the six years of the project, there was a large turnover of personnel, including on the management team.

There were an average of 420 people on two shifts building Mine D (which more than doubled the personnel at the site), peaking at 645 in 2004. Work on the project totaled 5.63 million person-hours. Only 15 people were still working on the construction by the end of 2006.

An early weak safety record led management to vigorously adopt the internal responsibility system (IRS), which meant spending lots of time training employees of the three dozen different contractors on safety and teamwork. Through a safety focus and work meetings at the start and end of each shift, everyone learned what everyone else was doing, so there was very little interference. “There were complications, but we worked through them,” says Davidge.

As the teamwork and co-operation improved, so did safety performance. During late 2003 and 2004, the project worked 1,000,000 person-hours without a lost time accident (LTA). Since the last lost time accident in December 2005, the project has recorded more than 550,000 person-hours of work without a LTA, with much of the work being non-standard tasks as the various jobs are finished off. The construction group worked 3.8 years, the Redpath ramp and lateral development group worked 3.5 years, and the Redpath Alimak group went 5.25 years with no LTA. Cementation worked the whole of 2006 without a LTA, and the last six months without even a medical aid accident. Forages Garant twice worked a full year without a LTA, and is currently extending this period.

In summary

Block 1 of Mine D has been in production since 2004, and Block 2 since 2005. The last big milestone of Stage 1–the completion of the ore-handling system on the 90 level–was completed in December 2006. Mine D is expected to supply about half of Kidd Creek’s ore in 2007.

The production date matches the feasibility study, and the project is essentially on budget, remarkable for a six-year timeframe, given the escalation of costs for supplies and labour. Xstrata will publish the final costs and the new mineral inventory of Mine D soon.

Now that there is deep access, Stage 2 of the Mine D project will examine the potential for mining lower blocks. The drills are already turning.

Is Mine D the deepest?

The No.4 shaft at Kidd Creek Mine D, which is really a winze collared at 1,432 m depth, ends in a sump 3,012 m below surface. This puts the shaft bottom at 2,733 m below sea level, which may make the Timmins, Ont., mine a record-holder.

“We believe this is currently deeper below sea level than any other mine,” says Glen Davidge, superintendent of mine engineering & technical services for Xstrata Copper at Mine D. “Our lowest stope in Block 3 is 2,700 m below surface (2,423 m below sea level). We believe that’s the deepest base metal mine in the world, but we’re not sure. As far as we can find out, this is the deepest mine (below surface) in North America.”

If you have information that confirms or refutes these statements, please drop us a line, or contact Davidge directly at GDavidge@xstratacopper.ca.

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