June 15, 2022
While drill bits are diminutive in size, their role on an underground mining rig is anything but – in fact they are instrumental to the success of a drill shift, whether that’s in development or production drilling. They are also the most commonly replaced component on a drill system and as such can be a significant pain point for operators trying to achieve their metre targets. This is particularly relevant to drilling in hard ground, such as the abrasive, siliceous rock formations characteristic to Stawell Gold Mines (SGM) in Victoria’s central west.
Gold mining is inherent to the township of Stawell, which was founded in 1853 at the height of Victoria’s gold rush. This history is evident in the grand buildings that line the main street of town. Located 240 kilometers northwest of Melbourne within the Northern Grampians Shire, this rural town is one of the few to retain an active gold mining community. It’s current operator, Stawell Gold Mines (SGM) commenced in 1981, originally mining in both open pits and underground.
Unlike mines in remote Australian settings, SGM is considered a residential mine, with most of its staff living within the town itself. For this reason, SGM has a strong community relations focus, with active social media and a web-based community hub to provide clear communications about the mine’s activities and environmental impacts. SGM Mine superintendent, Mark Nellthorp, is one of the employees that lives in town.
“The mine is a part of the town’s fabric, and there’s always been respect for the community about what we do, whether that’s alerting people to blast times, or having forums on the environmental impacts,” says Mark, who oversees the mine’s operations. “Our owners are also very forward-thinking and are investing heavily into making the mine more sustainable, such as upgrading our processes and machinery.”
In 2017, Arete Capital Partners acquired SGM on behalf of private interests and this resulted in a change of mining strategy. After expanding underground exploration efforts of the site’s mineralised gold lodes, SGM shifted their focus to a previously unexploited flank of the ore body. They started production of this zone – known as Aurora B and situated on the east flank of the Magdala deposit – in 2019.
When production drilling started on the eastern flank, Mark and his team were faced with a new challenge: a magnetite-rich banded unit that the crew call the ‘BIF’ due to its visual similarity to banded iron formation.
“Unlike the basalt and quartz deposits we were familiar with drilling on the western flank, this ‘BIF’ is extremely hard to penetrate,” Mark explains. “We’ve had drilling experts who’ve worked around the world say they’ve never seen ground like it. On the production side, I had operators telling me they were getting just a few meters out of a drill bit before it was completely destroyed.”
Yet, as hard as the ground may be, the Aurora B is rich in gold and has effectively secured the mine’s future.
“Which is why we were keen to explore new drill bit options,” Mark elaborates. “When the opportunity arose to trial the Epiroc Powerbit X bits, we were more than happy to give them a go.”
What are Epiroc Powerbit X drill bits?
• These are specialized drill bits having each tungsten carbide button coated with a wear resistant diamond grit formula known as polycrystalline diamond (PCD).
• The PCD coating protects the buttons from losing their shape and is designed to drill into particularly hard ground.
• Epiroc invested into the R&D of this technology in direct response to customers’ pain points around frequent drill bit changes.
• The Epiroc Powerbit X product range includes face drilling bits – 35mm, 48 mm and 51 mm – and production drill bits in sizes of 76 mm, 89 mm and 102 mm
In full operation, SGM is capable of processing 850,000 tonnes of ore annually. According to Mark, development advance targets are 630m per month, for a drill meter equivalent of 56,000 drill meters per month, with production drilling targets set at 14,000 meters.
“But we are quite a competitive crew and always overachieve, hitting approximately 17,000m or 18,000m out of the two Epiroc Simbas we have in production,” he says. “Our production operators are highly experienced and very good at what they do, as are the drill rigs.”
Nonetheless, the ‘BIF’ proved problematic.
"We were getting maybe 7 meters or so out of a standard bit, so we’re very impressed with the Epiroc 76 mm Powerbit X we’ve been trialling – we’ve had five to start with – and the first one achieved 400 meters, which is exceptional in this ground,” enthuses Mark. “We’re a cost conscious mine, so if we can drill more meters, more effectively, and get our costs down, that’s the direction we want to take."
By eliminating most of the bit changes required on a shift, the production gains have been significant.
“Basically, there’s less downtime from pulling rods and changing bits and realigning these in the hole,” explains Mark. “If you can drill a hole on one pass and move on to the next one, that’s great. But if you have to change a bit halfway through on a 20 meter hole that would be costing – at a guess – something like 15 minutes in drill time per hole.”
There are other consequences too in terms of having to realign the drill, and Mark notes that the less movement on the drill rigs, the less wear and tear on the equipment.
“This is especially true in upholes – if the operator can’t get the string back exactly in the right spot, it starts putting pressure on the rods, which goes back into the drifter,” he elaborates. “With the Epiroc Powerbit X drill bits, as the buttons retain their shape, there’s less percussive energy that comes back into the rig itself. Whereas when the other bits start going blunt that percussion impacts the rest of the rig, causing problems to the motor and so on. So, the drill bit may seem like a small component, but when you consider its impact on how the overall rig performs, it’s the bit you want to invest in!”
While the economic and productivity advantages of using the Epiroc Powerbit X bits at SGM are definite motivators, Mark says safety is the more important driver.
“Safety is actually our biggest priority. SGM as a company is very clear that this is the number one priority,” he stresses. “I say to the crew regularly that at the end of the day targets are just that – targets. You don’t risk personnel injury to achieve targets. Safety first.”
The safety benefits of using the Epiroc Powerbit X have been evident in SGM’s trials.
“Not having to change the bits out so frequently means less time the operators have to get in and out of the cabin, which means less chances of slips and trips or coming across any other hazards on the wet, slippery ground,” says Mark. “Besides the physical hazards, there is also the concern around operators getting frustrated with having to pull rods and change bits all the time – workplace frustration can have impacts mentally.”
These safety benefits have been further confirmed by drill rig operator, Merv Hayward, who has been the key person trialling the Epiroc Powerbit X drill bits out at SGM.
"They make my job much safer – there’s less exposure to the drilling area during the shift which means less potential for slips, trips and falls,” he explains. “Basically, I screw the Powerbit X drill bit onto the guide rod at the start of the shift and then drill all shift."
Q&A with drill rig operator, Merv
What is the main benefit you’ve realised from using Epiroc Powerbit X drill bits in your daily routine?
Confidence that the Epiroc Powerbit X will achieve the desired meters for the shift.
Have you noticed an increase in production?
Yes. There are no unnecessary rod pulls to change the bits, which equals drill time that you never get back. Also, there are no stripped buttons left in downholes which can ruin a resharpened bit on contact.
While using the Epiroc Powerbit X did you have any interactions with your cross shift operator about the improved performance compared to normal bits?
Yes, the cross shift operator was extremely jealous of the meters achieved with the Epiroc Powerbit X during the trial period!
Have you thought about the effect on the environment by using Epiroc Powerbit X drill bits?
I’ve definitely thought about the wastage side of things, yes. Not throwing a brand new bit in the scrap bin after just 7 meters of drilling has got to be better for the environment!
Have the Epiroc Powerbit X bits reduced the amount of maintenance on the rig?
Yes. As the Epiroc Powerbit X breaks rock correctly for a very long period of time, the drifter internals and all related hoses and pumps are under far less stress.
As part of Epiroc’s service to the fleet at SGM, Epiroc contract supervisor Jarrod Wilde visits the site multiple times a week. A significant part of the maintenance service he provides to SGM is collecting drill bits and resharpening these for re-use.
“I go underground, collect the bits, and refurbish them back in the Epiroc workshop,” he says. “While SGM have only been trialling these Powerbit X bits for a short time, I can definitely see the benefit in carrying less bits out to site, not just me physically, but the amount of weight that’s on the ute. If we can reduce the weight on the ute that means less maintenance costs on the vehicle.”
Likewise, Jarrod recognises that the Epiroc Powerbit X will reduce a lot of waste.
“It will make a massive difference. Less actual bits manufactured has an effect across the whole supply chain in terms of reducing carbon emissions,” he points out. “There’s freight, packaging, and then transport to and from site – it all adds up.”
Kaelin McDougall, Key Customer Manager at Epiroc, weighs in on the benefits of reducing the amount of drill bits required.
"The potential impact of using Epiroc Powerbit X bits regularly is huge – for example reducing the number of bits required will translate to a decrease in manufacturing, and then there’s the physical implications,” he says. “Carrying these heavy bits from place to place, that takes an overall physical toll that may not seem much in one day but is a lot over time. Considering manual handling is one of the highest causes of injury in this industry, it’s an important point."
Moreover, Kaelin points out that from an environmental standpoint, it’s essential for mining operations such as SGM to reduce their waste and carbon emissions.
“This is more salient in a town such as Stawell where the mine is in the town itself – anything the mine can do to support its sustainability efforts is worthwhile,” he says. “In this sense the environmental benefits are just as valuable as the cost savings.”
Circling back to his earlier comment, Mark concurs that for SGM sustainability is a priority.
“Our owners have adopted a progressive approach to sustainability, and that means trialling components such as the Epiroc Powerbit X, as well as working with Epiroc to start converting our fleet to electric,” he says. “I believe with the success we’ve seen so far with the Epiroc Powerbit X drill bits in production, that this is an environmentally sound solution to the problem we’ve been facing with the hard ground conditions.”
Overall, Mark says the trial of the Epiroc Powerbit X have been successful and he’s confident they will be a cost effective and sustainable option for SGM production in the future.
“We are still in the trial stage, and have only had the five Epiroc Powerbit X, but we can see these as a huge bonus,” he concludes. “The way I’m looking at it is that we will use these selectively in the particularly hard ‘BIF’ conditions which is where we’ll see considerable benefit.”