Block cave economics

Tonnage is tantamount to profitability at New Gold’s New Afton mine in south-central British Columbia. The mine has moved and milled as many as 22,000 tonnes of ore in a single day and routinely extracts 18,500 from Canada’s only block cave.

Like other prolific block caves, New Afton enjoys enviable efficiency at extremely low operating costs. But the mine has also had to conquer one of the biggest block cave challenges: mud rush.

Mitigating mud rush hazards was the major motivation for implementing automated loading at New Afton. As the block cave grew, more and more drawpoints became finely fragmented and wet. By 2016, one in five drawpoints were assessed as high-risk. To ensure operator safety, New Afton stopped manual mucking in those drawpoints and implemented line-of-sight tele-remote loading.

“When 20 percent of your ore source needs to be remotely mucked, you run the risk that you can’t supply your mill with adequate tonnages,” says mine manager Peter Prochotsky, who joined New Afton in 2009 as a mining engineer and has seen the operation grow from a development project into Canada’s highest-tonnage underground mine. “The line-of-sight systems just weren’t keeping up with the growing production demand over the years and we needed a new way of doing things.”

shift for a smaller Sandvik LH410 based on the trial performance of Sandvik LH514. The mine calculated that an automated Sandvik LH410 had the potential to muck 75 more buckets each shift than the existing remote solution, a productivity increase of more than 55 percent.

“To transition from a line-of-sight solution to an automated solution, we calculated a 54-day payback period,” Prochotsky says. “If we continued using line-of-sight tele-remotes, that production loss was, essentially over 54 days, the value of a brand new Sandvik LH410. And we obviously made the choice pretty quickly that it was the right way to go.”

New Afton’s existing block cave extraction level layout wasn’t optimized for automation. Two dedicated colleagues worked hand in hand to champion the project, implementing the system and building operator buy-in.

Bob Garner, a technical expert with decades of block cave experience, led the operational side and trained operators on the AutoMine system. Electrical instrumentation technician TJ Williams complemented Garner’s skills with technical expertise, handling installation of all electrical systems.

“We needed to figure out the infrastructure, figure out the Wi-Fi, where we were going to put antennae points, how far apart they had to be, and then teach the loader its path and dial everything in to get it running efficiently,” says Garner, who previously gained experience with tele-remote loaders in Indonesia. “TJ brought computer skills and did all the groundwork in the operator’s room while I was out there in the drive running the loader, showing it what we wanted it to do.”

An average 100-metre tram from a drawpoint to an ore pass was 60 percent faster with the automated system than line-of-sight.

Williams says most of the mine’s line-of-sight operators were comfortable running AutoMine within five days.

“The Sandvik automated loaders are much more technologically advanced than the competitor loaders featuring aftermarket line-of-sight, but the learning curve wasn’t steep,” he says. “Everybody picked it up really easy.”

New Afton initially used its Sandvik LH410s for production mucking on the mine’s extraction level, one of the block cave’s five main underground levels. The mine’s shortest trams are within three or four metres of the ore pass and the longest current tram is around 150 metres. The average tram distance between drawpoint and ore pass is only 75 metres, limiting automation’s benefits.

“The longer the distance from drawpoint to ore pass, the faster the loader can tram and complete a cycle and the greater the value of automation,” Prochotsky says.

Despite the limitations created by the level’s short trams, the automated Sandvik LH410’s cycle time is almost twice as fast as the mine’s line-of-sight loaders. Manual mucking is still faster in the areas New Afton can use it, but the automated Sandvik LH410’s lower downtime and higher utilization compensate for its modestly higher cycle time.

“At the end of the day the tonnes moved by a manual loader and an automated loader are very similar,” Prochotsky says.

On top of recouping the investment cost of the automated loader in less than two months of operation, New Afton has experienced equipment health benefits on its bottom line. AutoMine steers the loader with pinpoint precision and its collision avoidance features help eliminate damage while enabling high speeds that accelerate overall cycle time.

“We used to do about $10,000 of collision damage per loader per month, directly related to operating our line-of-sight loaders in a tight environment,” Prochotsky says. “This cost has dropped to zero thanks to AutoMine.”

The mine has also realized a 30 percent increase in tire life on the automated Sandvik LH410s compared to the mine’s other 10-tonne loaders.

After successfully managing the step change from line-of-sight, where operators stood in the drive and ran loaders in first gear, to automated loading, and improving mucking efficiency while mitigating mud rush hazards, New Afton started thinking bigger.

For the first 18 months, operators oversaw the automated Sandvik loaders from two underground control rooms. In early 2019 New Afton finalized a permit amendment process with British Columbia’s Ministry of Energy, Mines and Petroleum Resources to allow the mine’s operators to run AutoMine from a third chair on surface, eliminating travel time and enabling automated mucking through shift change.

“We think that’s really going to enable us to unlock the productivity benefits of automation,” Prochotsky says. “The gains we expect to see from this change should more than close the narrow gap between manual and automated mucking productivity. This will also be a huge improvement in workplace quality for our operators and will enable 24-hour production, even when we’re blasting.”

Prochotsky says. “If we can save 90 minutes in each shift, that’s a huge efficiency gain that also de-risks the project.”

Prochotsky contends New Afton couldn’t have implemented automated loading at a more ideal time. The mine is entering a new phase in its life and building a new extraction level, with drawbells expected to come online in 2021.

“The opportunity to take your learnings and put them into action happens infrequently in block cave mines, as a new level is only developed every five to 10 years,” he says. “We’re fortunate that we brought the AutoMine system in at really the perfect time for us, to learn how to use it for maximum benefit and position ourselves to take full advantage of it in future mine design.

“By implementing automation before we designed our next block cave, we’re able to incorporate the learnings from our current production level and design our next block cave for automation, and that will drive up productivity,” Prochotsky adds.

For New Afton, AutoMine has proven to be the complete automation solution management assessed it to be.

“If another mine manager came to me and asked me who they should automate with, I think that Sandvik has the best system on the market, and it’s really because they have the total package,” Prochotsky says. “They’ve got field service representatives available to come to your site to help train your people, they’ve got great safety documentation that allows you to make sure there won’t be any incidents or accidents underground, and they’ve got a product that works. It’s a pretty simple solution in my mind.”