BY NORM TOLLINSKY
The Centre for Excellence in Mining Innovation’s (CEMI) Future of Deep Mining conference September 19th and 20th in Toronto presented delegates with a feast of new technologies and solutions to address the challenges facing the mining industry.
“We’ve been relying on methods that we’ve been using for the last 25 years as mines get deeper and deeper,” said CEMI president and CEO Doug Morrison. “We’re now at the point where it’s very difficult to see how using LHDs and trucks to move ore and sequential drill and blast to access development can continue in the future.”
The mining industry has to come up with new ideas to advance development faster, and manage the heat and geotechnical conditions at depth, said Morrison.
Muckahi Mining System
One of the highlights of the two-day conference was a presentation by Fred Stanford, president and CEO of Torex Gold Resources, about the Muckahi Mining System currently being introduced at the company’s Media Luna Project in Mexico. The Muckahi system, developed with the assistance of Medatech Engineering Services of Collingwood, Ontario, does away with LHDs and trucks by using twin monorails hanging from the back along a steeply inclined drift.
Stanford patented the Muckahi Mining System, but didn’t have to invent the core concept of hanging a monorail from the back. “It turned out they’ve been doing it in the coal mines in Europe for 40 years,” he noted.
A former president of Vale’s Ontario Operations in Sudbury from 2006 to 2009, Stanford said he realized many years ago while working at Creighton Mine in Sudbury that he was running a logistics business.
“We do a little bit of drilling and blasting at the front end and all the rest is moving stuff,” he said. “But we do a logistics business on single lane roads, which is not an efficient way to run a logistics business. After 25 years I finally figured it out. To get two-way traffic in a tunnel half the size, by definition, your vehicles have to be long and skinny.”
The system uses a back-mounted one-boom jumbo and service platform as well as a slusher to feed a tramming conveyor to move material away from the face.
Optimizing the primary blast is critical, said Stanford.
“It’s amazing how much the primary blast influences everything downstream. If you can get your fragmentation down, you can go to continuous as opposed to batch transportation. With an eight or 10-yard bucket on the front of an LHD, who cares about fragmentation? We can move it and throw it in an ore pass. It’s someone else’s problem, but if we blast it fine, we can eliminate ore passes and crushers. The drilling technology and explosives technology are there to do that. The trick is managing your workforce to get them to drill a hole where it’s supposed to be and put the explosives where they’re supposed to be. Incentive systems have a massive impact on that.”
The 30-degree ramps used to access the orebody are one-quarter the length of a ramp that’s excavated at a seven or 15-degree incline, drastically reducing the cost and the time it takes get to the ore, according to Stanford. The system also eliminates the need for remucks.
An all-electric solution, it also provides for a cleaner, healthier underground environment.
“The electrification problem in conventional underground mines is that you have a 50-tonne truck with a 50-tonne payload trying to grind up a 15-degree ramp. There’s no battery invented yet that can do that, but if you’re moving your ore on a conveyor, it’s plugged into the grid.”
The Muckahi Mining System, said Stanford, is ideal for new mines as well as down dip extensions.
Praising it as an “exciting solution for ore transportation,” Morrison warns there are some limitations to using fixed infrastructure in very deep, seismically active mines.
“What it does demonstrate, however, is that it is possible for us to design other systems to move ore much more cost effectively than we do at the present time,” he said. “There is no single magic bullet.”
Morrison also hailed presentations on the use of compressed gases for cooling and power as “some of the most significant developments made in the last 20 years.”
Hydraulic Air Compressor
Dean Millar, a professor at Laurentian University and president of Electrale Innovations, provided an overview of his hydraulic air compressor technology, which uses circulating water to compress air as it falls through a long pipe or borehole.
The technology was used more than 100 years ago in northeastern Ontario’s Cobalt camp to produce compressed air to power jackleg drills. A scaled down version of the Electrale hydraulic air compressor (HAC) was successfully demonstrated at Dynamic Earth in Sudbury and the first deployment of a commercial-scale system is planned for Kirkland Lake Gold’s Holloway Mine thanks to a $2.1 million grant from Canada’s federal government.
Millar told conference delegates the HAC can outperform conventional air compressors through energy savings as well as reduced maintenance.
“The HAC produces dry compressed air,” he explained. The damp air produced by screw compressors tend to rot pipes and cause ANFO misfires, “so energy savings are just part of the story in the cost/benefit analysis of the HAC. The other half is reduced maintenance.”
Daniel Cluff, an expert in cryogenics mining from Sudbury, told the conference that cryogenic chilling solution is further from commercial acceptance, but holds promise for selectively distributing cool air at depth and producing power for use underground.
Ambient air compressed using off-peak grid power or solar or wind power converts to a liquid at a temperature of minus 196 degrees Celsius. The cryogenic liquid is then pumped down the mine. When decompressed, it mixes with the airflow from the ventilation system to cool the underground workings. The energy that’s produced when the liquid air expands to a gaseous state can also be harnessed through a power recovery unit that includes a heat exchanger, a turbine and generator to produce electricity along with the chilling.
Unlike bulk air chilling, a cryogenic system lends itself to chilling on demand, per level, where and when needed simply by controlling the flow and release of the liquid air – just like ventilation on demand.
Highview Power has a 5-MW liquid air energy storage demonstration plant in operation in the U.K. and the Dearman Engine Company, also of the U.K., uses liquid air as an alternative to fossil fuel. The only exhaust is cool, clean air, said Cluff.
“We had an opportunity to compare our solution with what Hatch said they needed for a bulk air chiller at Glencore’s Onaping Depth Mine and were pleased with the results,” he told conference delegates.
Mechanical rock excavation
Several mining companies are also showing renewed interest in mechanical rock excavation.
In his presentation, Vale principal mining engineer Andy Charsley, said “we at Vale certainly see mechanical rock excavation having a future in deep mining, especially where we have broad horizontal extents where it takes time to get people out to them. We see mechanical rock excavation providing opportunities in the future for automation and continuous mining.”
Vale is planning to trial a mechanical rock excavation system, or tunnel borer, by the end of 2020 or early 2021 at one of its operations in Sudbury and is currently reviewing results from a request for proposals that closed September 10.
“The initial work that we’re going to embark on is to prove if they can cut rocks in the 250 to 300 mpa range and at a rate that’s commercially viable,” said Charsley.
Vale is banking on mechanical rock excavation delivering safety and quality improvements, while also speeding the rate of development. The technology promises to remove personnel from the face, produce higher-quality openings and allow for simultaneous drilling and ground control activities.
Currently, “six-metre advance rates per day are considered exceptional performance for drill and blast technology, but if we can get four metres per day, we’re doing pretty well,” said Charsley. “The OEMs claim that .4 metres per hour is an achievable rate for machine cutting. That works out to four metres in 10 hours and the potential for eight to 10 metres per day.”
Trevor Kelly, innovation manager at the Canada Mining Innovation Council (CMIC), followed Chrsley with an overview of plans by a consortium of mining companies comprising Agnico Eagle, Glencore, Newmont Glencore, Hatch and Vale to study the technology’s ability to cut hard rock through a pilot project.
A presentation by Martin Coté, a ground control engineer with Canmet Mining, brought delegates up to date on efforts to demonstrate the viability of lighter-weight synthetic rope as an alternative to steel cables currently used for mine hoists.
A synthetic rope using Kevlar fibres was installed and tested at Agnico Eagle’s Goldex Mine in northwestern Quebec in August 2016. The 3,000-foot rope was approximately 20 per cent of the weight of a steel cable, and compared favourably in terms of strength, said Coté.
“The current limit for a steel cable is about 7,000 feet, so most operations extracting below that are trucking ore up to shaft bottom,” explained Morrison. Should synthetic ropes prove viable, a single lift shaft could go considerably deeper.
According to Coté, more work on stretching, inspection and life expectancy will be required before synthetic rope is proven to be an acceptable alternative to steel cable.
Together with these and other technologies, including short interval control, battery-powered vehicles, and high tensile steel mesh, which were also featured in presentations, the CEMI conference demonstrated that there is no shortage of innovative mining technologies in the pipeline.
Another Future of Deep Mining conference is planned for September or October of 2020.
Norm Tollinsky is the former editor of Sudbury Mining Solutions Journal.