Turkka Kulmala explains how a raise borer is defying traditional raise drilling methods and helping a goldmine in Finland surpass the demands of a challenging market
As he drives down a foggy access tunnel, Jani Ollikainen comments, “It’s toughest in the winter – sometimes you can hardly see anything,” The production planner at Agnico Eagle’s Kittilä goldmine is en route to see the Rhino 100HM raise borer work on a previously mined and back-filled stope, opening up a new slot hole into the next stope above. The Rhino is a highly productive raise boring system, and the team at Kittilä is taking advantage of its benefits to meet ever-increasing production targets.
The Agnico Eagle Kittilä goldmine, a two-hour ride north of the Arctic circle in Finnish Lapland, is a 4,000-tonne-per-day operation that expects to produce around 200,000 ounces of gold in 2016. It uses the Rhino 100HM raise borer for slot hole drilling in production and also for drilling shafts for the mine infrastructure. At the underground mine, the largest primary gold producer in Europe, raise boring of slot holes replaced drop raises built by drilling and blasting using regular long-hole top-hammer drill rigs, which had become a bottleneck.
“When we realised that the traditional raise drilling method did not meet our production needs, we had a joint vision of the way we should move forward,” says Matias Suomela, general supervisor, underground, at Kittilä.
Using long-hole drilling for the drop raises not only doubled the number of holes, due to the smaller diameter, but also made it necessary to blast the drop raise in five-metre breaks, which requires a lot of space and involves considerably more work stages. Now, with a raise borer, all of this could be replaced with a single machine and a single operator.
A safety consideration was also involved in the initial process design stage. The old method required redrilling after each blast to open closed holes thanks to the challenging rock conditions in the sulphide-rich mineralisation. Redrilling holes after blasting is inherently risky because of any undetonated explosives possibly left in the holes that could explode during redrilling. The new method eliminates this risk entirely because the slot holes require no blasting at all.
TRB-Raise Borers, a nimble mine technology company based in Tampere, Finland, nearly 900km south, had a solution for the demanding specification. Together with Sandvik – the Rhino is equipped with Sandvik tools and distributed by Sandvik – the company has supplied raise boring solutions for diameters of up to 4.5m since 1972. The applications have mostly involved conventional raise boring and box boring jobs to build ventilation shafts, ladderways and even nuclear waste depositories.
In addition to the actual drilling unit, the rubber wheeled unit powered with a turbo-charged 186kW diesel engine carries all the required auxiliary equipment, including drill rods and non-rotating stabilisers, a hydraulic crane for handling them, hydraulic power pack and pressure washer as well as the necessary power and water supply connections. The operator sits in an air-conditioned and soundproofed safety cabin. In other words, the Rhino 100HM is a self-sufficient unit and can transport all the equipment required in the Kittilä mine’s conditions.
A turbo-charged 186 kW diesel engine carries all the required auxiliary equipment, including drill rods and non-rotating stabilisers, a hydraulic crane for handling them, hydraulic power pack and pressure washer as well as the necessary power and water supply connections.
TRB-Raise Borers CEO Jarko Salo says that operator commitment is of particular importance in slot hole boring, where drill tailings are flushed down on the rig and need to be properly managed to prevent the muck from damaging vulnerable components.
Rhino raise borers’ forte had always been good productivity, while the mobility may sometimes have left some room for improvement. However, mobility was precisely what the Kittilä engineers expected for their new application: the capability to rapidly set up the machine at any given location within the mine, to drill the slot holes required for mine development effectively and productively, and to relocate and set up again quickly, perhaps on the opposite side of the mine.
It was of utmost importance to Agnico Eagle Kittilä that this rig would also be ‘plug and play’ as opposed to conventional raise borer systems that require extensive set-up times. “Otherwise we wouldn’t have been able to accelerate the process, and opening up a stope would actually take almost the same time as with the long-hole method,” Suomela says. “We kind of specified a mining jumbo that simply drills larger holes.”
Elen Toodu, Agnico Eagle underground planning engineer, says, “For us it was amazing how fast we were able to start up and commission this rig.” During the first 11 months of operation the rig clocked roughly 1,400 hours of drilling. The output over the period from July 2014 to July 2015 totalled 64 stopes, 11 mine infrastructure shafts and 2,993 drilled metres, averaging 5.3 stopes and almost 250 drilled metres a month.
Miners can also use the Rhino 100HM for developing the mine infrastructure, a major benefit for a mine undergoing fast expansion, such as Kittilä. This is closely linked with the availability of drilling capacity in excess of the rig’s main task, production drilling.
Quick and smooth
“What convinced me was the quick and smooth set-up,” Suomela says. “We have learned the specifications required of a drilling site, with proper support, heights and other clearances. After driving the rig to the site, it takes less than one hour to set up and you’re good to go. In that sense it was a very successful choice. We can now open up the stopes much quicker, which is a major asset for us since the throughput time per stope is such a crucial parameter in our operation,” he says.
‘Much quicker’ in practice means a total stope cycle of five to six days instead of up to three weeks with the previous long-hole method.
“We now need only two blasts even for those 40-metre stopes, and we have eliminated the need to open up the drop raise in five-metre breaks,” says Toodu, who is in charge of planning the mining process from one month through to a year and a half ahead. “Before Rhino, we couldn’t imagine blasting 145 stopes a year. Without it, we surely wouldn’t be that happy about the idea of mining more than 15 stopes a month at times.”
The raise boring tools consist of a standard 11-inch pilot bit and two standard raise boring cutters installed on a reaming head made out of forged and accurately machined high-alloy tool steel. The tools’ dimensions and accurate gripping surfaces are specifically designed for compatibility with the grippers of the manipulators used for handling the reaming head and drill rods.
“They have a very good service life of tools,” says Göran Strand, product line manager for raise boring at Sandvik, confirming the high standard of maintenance achieved by Agnico Eagle Kittilä.
The Rhino’s drilling capacity amounts to seven to 20 metres per shift depending on the type of rock. Drilling accuracy is ensured by replaceable welded support plates on the bit body and wear pads on the stem. The cutters, including cemented carbide buttons, are designed to have a high rate of penetration and long service life.
For rig operator Jorma Kinnunen, the Rhino is like a hard-working colleague. Once he hooked the rig up with the power and water supply and started the drilling operation, the bulk of the work is carried out by Rhino 100HM’s automation system. Outside of loading new drill rods, he doesn’t need to intervene much in the regular operation of the machine. “It’s a good machine and runs well,” Kinnunen says.
He says the planned changeover time of one to two hours leaves a fairly generous leeway for transfers and routine maintenance, since the actual set-up normally takes no more than half an hour.
Using long-hole drilling for the drop raises made it necessary to blast the drop raise in five-metre breaks, which requires a lot of space and involves significantly more work stages. Now, with a raise borer, all of this could be replaced with a single machine and a single operator.
As Jarko Salo points out, operator commitment is of particular importance in slot hole boring, where drill tailings are flushed down on the rig and need to be properly managed to prevent the muck from damaging vulnerable components. Salo stresses the close partnership and common vision in tailoring Rhino 100HM to Agnico Eagle Kittilä’s unique needs. “Any improvements have quickly been engineered, implemented and put straight into action,” he says. “This has very much been a partner relationship, and we have also received excellent ideas from the Kittilä mine staff.”
Future steps in the development of Rhino 100HM concept have already been introduced. The next generation includes more capabilities, smaller dimensions and easier maintenance. The upgraded version will provide even higher productivity, with actual results available later in 2016.
Eagle flies high
Agnico Eagle is an international gold producer, with exploration and mining operations in Finland, Mexico and Canada, where it is headquartered. Its Kittilä goldmine is the largest operational gold mine in Europe, having started in 2008 with two open pits, Suurikuusikko and Rouravaara. In 2010, underground operations began at Kittilä, and its known reserves are expected to last until 2037. Around 177,374 oz of gold were produced in 2015, and its 4000-tonne-per-day operation is expected to produce around 200,000 oz of gold in 2016.
Turkka Kulmala is with Sandvik. Find the original version of his article at HERE.