Vale Inco is studying the feasibility of using a vertical conveyor system as an alternative to skipping or ramping ore and waste rock as part of several new mine developments at depth in its Sudbury mines.
Vertical conveyor technology has been used in one form or another since 3,000 B.C., but there have been only a handful of applications in underground mining and tunneling operations.
A pocket lift system proposed for the company’s Garson Deep project would be the highest vertical conveyor system in the world with a vertical height of 1,250 feet (384 metres), approximately the same height as Vale Inco’s Superstack.
Garson’s Number 2 shaft currently descends to the 4,242-foot level. A ramp from there winds down to the 5,100-foot level, but plans are under way to mine an indicated and inferred resource of seven million tons all the way to the 7,000-foot level.
Vale Inco has several choices, explained Gary Poxleitner, senior mine evaluation engineer with the company’s mine project development group. It can haul the material from an extended ramp system, deepen the existing shaft, construct a winz or install one or more vertical conveyor systems.
Trucks
Trucking material from 7,000 feet underground all the way to the 4,242-foot level is problematic.
“It would be a challenge getting the production rate we want using trucks,” said Poxleitner. “You can keep adding more trucks, but only to a point.” A simulation to determine the maximum number of trucks and daily tonnage handling capacity on a ramp system extending 3,800 feet from the 4,200-foot level suggested it would be difficult achieving the production rates the company is looking at.
Vertical conveyor systems could also be considered for other mine-deepening projects Vale Inco is planning for the Sudbury Basin.
Poxleitner and several colleagues visited three vertical conveyor system installations in the U.S. to evaluate the technology. The first was a 580-foot Flexowell belt system used to haul waste at the Manhattan Water Tunnel Project in New York City. They looked at a system at a second water tunneling project in Atlanta and visited White County Coal’s Pattiki Mine in Carmi, Illinois, that uses a 905-foot vertical lift system with a capacity of 2,000 tonnes per hour.
“We were hesitant and skeptical at first,” said Poxleitner. “It wasn’t until after we toured the facilities in the States that we got comfortable with it.”
A vertical conveyor system, like a hoist/shaft system, offers the advantage of the shortest distance from Point A to Point B, along with the continuous handling and low cost of conveyor belt technology. It’s also quick to install, energy efficient and easy to maintain.
Savings
Preliminary estimates indicate that a vertical conveyor system would offer a six per cent saving in capital costs and a 24 per cent saving in operating costs.
Material would have to be crushed to a maximum size of six inches prior to being introduced to the system and a magnetic separation system would be needed to remove scrap steel from the material being conveyed.
Metso Minerals offers three types of vertical conveyor systems, explained Poxleitner. The Flexowell belt has a maximum 250-metre vertical lift capacity, the Pocketlift accommodates a 500-metre height and the Pocketrope system, still on the drawing board, promises 1,000 feet of lift.
It’s the Pocketlift system that Vale Inco is considering, but it’s also evaluating Metso Minerals’ new Pocketrope system for the Deep Mining Research Consortium, a CAMIRO-managed, Sudbury-based research group funded by Vale Inco, Xstrata, Agnico-Eagle, Barrick Gold, Rio Tinto, Goldcorp, CANMET, the City of Greater Sudbury and the Ontario government.
The Pocketlift system would use Kevlar ropes, which are light and strong, to double the vertical lift, but Metso has yet to build one, and Vale Inco has decided to consider only proven technologies.
“Metso would like to set up a test plant somewhere to try it out,” said Poxleitner. “With a 3,000-foot vertical lift capacity, it competes very well with the traditional shaft option.”
There are some 60,000 vertical conveyor systems installed around the world, but very few of them in Canada, and very few in hard rock mines.
“It never seemed to catch on in Canada,” said Poxleitner. “We tend to hang on to the idea of shaft sinking rather than look at alternative ways of conveying material.”
In order to install a vertical conveyor system beginning at the 4,200-foot level at Garson Mine, it would be necessary to transport all of the components down the shaft, create a large enough excavation for the drive units and discharge system, and reconstruct everything underground. It would also be necessary to excavate a 10-foot wide raise to accommodate the system.
