Metal Information Center

Canadians can go to new depths for gold

February 23, 2008 – 7:56 am

The engineering skills of Sheffield-based Kvaerner Markham are playing a small but crucial role in increasing production at the Laronde mine, one of the largest and deepest gold deposits in Canada

The engineering skills of Sheffield-based Kvaerner Markham are playing a small but crucial role in substantially increasing production at the Laronde mine, one of the largest and deepest gold deposits in Canada. The UK company supplied upgraded winder equipment capable of hoisting 7kt of ore per day from a depth of over 2.2km, exploiting newly discovered gold and copper mineralisation at deeper levels.
Its international mining industry contacts also enabled Kvaerner Markham to pass vital market information onto the customer, regarding the revised South African code of practice for winders, which helped make the whole project viable.

The contract, for long established Canadian gold producer Agnico-Eagle Mines, involved upgrading an existing 4.88m diameter double drum hoist to a 5.79m diameter configuration with twin motor drive arrangement, at a total cost of GBP 1.2 million.

Kvaerner Markham had previously supplied the original hoist, mechanically refurbishing an ex-British Coal winder back in 1995, and has an ongoing relationship with Agnico-Eagle that was to prove beneficial to both parties.

Exploration drilling at the Laronde mine in Quebec having already revealed additional high grade gold reserves at depth, Agnico-Eagle took the decision in 1998 to increase production from the Penna Shaft, from the designed 2kt tonnes to 5kt per day, plus an allowance for 2kt tonnes of waste.

This was well beyond the capacity of the installed hoist, with its 50mm diameter rope, and investment in a new winding facility was clearly required to increase the hoisted tonnage from the lower loading station, at over 2km depth.
Having rejected alternative ideas, such as sinking a new hoisting shaft or adding a subshaft to lift rock from the mine bottom, on the grounds of cost (C$100 million plus), attention was directed toward reconfiguring the hoisting plant for higher tonnage production.

Bearing in mind current winder regulations in Quebec and the twin constraints of depth and tonnage to be overcome, the necessary diameter of a single rope would have been impracticable at 68mm plus, so a Blair Multi-Rope (BMR) hoist was considered instead.

Although feasible, this solution would have entailed incorporating a new hoist room, rebuilding the head frame and supplying the required ancillary services; moreover, safety factors in Quebec also meant paying a premium for the hoist and ropes, driving up the projected cost to around C$30 million.
During the course of the BMR study, Agnico-Eagle learned from Kvaerner Markham that in South Africa, where deeper shafts are the norm, regulations governing winders were being revised to allow a rope safety factor of 4.0, against 5.0 in Quebec.

The same safety factor would also apply in the United States, so Agnico-Eagle approached the Commission de la Sant‚ et de la Securite de Travail (CSST) to see whether 4.0 could be permitted in Quebec, on the grounds that it was technically viable and regulated in other countries.

After forming a special subcommittee and sending a technical delegation to South Africa, the CSST agreed the change, at the same time implementing improved standards for rope condition assessment (RCA) at factors below 5.0.

Meantime, an internal Laronde study revealed that a single 57mm diameter rope of six strand construction would meet the tonnage requirement under the revised regulations, making a conventional double drum winder again a viable solution and effectively ruling out the BMR option.

Having estimated that the cost of purchasing a brand new double drum hoist would be in the region of C$8-9 million, Agnico-Eagle elected to mirror what had been done when originally purchasing the Penna Shaft hoist.

Whereas before, Kvaerner Markham had downsized the reconditioned unit from 6.1m to 4.88m diameter, reutilising the majority of components, the company was now contracted to upgrade the equipment for high tonnage, deep shaft duties.

The company’s in-house design engineering team reconfigured the winder equipment in line with the revised code of practice, arriving at a drum diameter of 5.75m, a width of 2.29m and an uprated motor package totalling 8000hp; it would be rated for a 67,130kg pull and a rope speed of 15.24m/s.

The work was carried out at the giant Kvaerner Engineering and Construction manufacturing facility in Prince of Wales Road, Sheffield, one of the largest in Europe.

The drums themselves were replaced to meet the new size and rope pull, with the grooving designed in accordance with guidelines for rope coiling patterns.

The shaft was also replaced, as the new design called for twin motor drives, one at each end; this was machined in two parts, to limit the maximum lift to below 40t, and joined together using friction grip, hydraulically tensioned bolts.

The clutch was also replaced to meet the increased duty requirements.

Otherwise, the existing components were reconditioned and reutilised.

The original motor was a 4000hp direct drive DC unit and, fortunately, Kvaerner Markham had an identical model in store, which permitted a twin motor arrangement.

The existing white metal journal-type bearings had the capacity to support the new hoist, saving installation time and expense, and the lubrication system was readily adjusted for the new duty cycle.

Design brake torque was calculated to comply with the amended Quebec regulations and meant more braking capacity was needed.

The original winder had 18 disk brake units and a further six were incorporated, together with new brake frames to suit the large disc diameter.

Finally, the electrical control system was uprated to suit the revised configuration.

Relatively little modification was required to the existing hoist room, head frame and foundations at Laronde, although a new South African-sourced RCA machine was purchased to meet CSST rope inspection regulations.

The upgraded hoist running in 18h shifts has the maximum capacity of 7938t/d, which is sufficient to meet the objective of 7kt at 88% efficiency.

Thanks to the openness of the CSST to regulatory change, detailed technical studies by Agnico-Eagle and the active participation of Kvaerner Markham and other stakeholders, the Laronde deep shaft hoisting project has been an unqualified success, at considerably less cost than originally expected.