The red and gold hills and plains surrounding the town of Tennant Creek in the Northern Territory are a scenic reminder of just how beautiful the Australian outback can be. The landscape also obscures the scars left behind by early resource extraction.
When Dion Farrell’s engineering consultancy DAC Enterprises was engaged by the NT Government to remediate Tennant Creek’s legacy of open shafts, degraded infrastructure, tailings dams and waste rock dumps, his team was delivered a list of hundreds of work locations that would need attention.
These mostly hand-dug mine sites were between 60 and 100 years old, and they presented a significant hazard to public safety.
“You’d get to some of them, and they’d be maybe three metres wide by three metres long, and then 60 m deep – straight-down shafts,” Farrell said.
“In very peculiar spots too: there’d be untouched land, and then up on top of a hill somewhere, we’d have a GPS marker showing where these were. We’d have to try and make our own track through to a spot up on a hill … and there would be a random hole where someone’s dug trying to find gold.”
A mine shaft like that would be too dangerous for even specially prepared members of Farrell’s team to enter, so it was particularly important to secure them from members of the public – both suspecting and unsuspecting.
“There are a lot of prospectors – single-man prospectors – who head out and try to find these spots and sift around the areas that were left,” Farrell said. “So there definitely were safety issues with them being the way they are, because it’s just a straight drop. If you’re going down, you wouldn’t be able to get back out.”
Bush walkers were also a concern, he suggested, especially ones who like to head off the beaten track.
Custom work
From May 2024, the DAC Enterprises team worked over the next five months to backfill 182 mine voids, fence and signpost 16 mine voids, and install 27 shaft covers and 35 covers for adits, the horizontal passages that provide access to an underground mine.
The $5.5 million program was undertaken as part of the NT Department of Mining and Energy’s Legacy Mines Small Mines Safety Program.
“We had over 300 work activities to do, but they varied from backfilling the open shafts and stopes, to manufacturing and installing adit covers as well as shaft covers – that was fabrication and welding,” Farrell said. “Then there were the old drill holes, where they’d gone down for drill explorations. We had to go and cap those: dig down, cut them off, cap and back fill them.”
He estimated that even accessing these sites required 120 km of access road upgrades. And because the shafts and adits were all different sizes, the team had to manufacture a bespoke cover for each one.
“They gave us a design based on a standard size, and the original thought was, ‘let’s make one size and put it over everything’,” Farrell said.
“But when we got down there, we couldn’t do that, because some of them were on the side of a hill. You had the cover, and half of it would be hanging out in the middle of the air.”
Instead, the team used the provided design as a template and scaled it to the site’s needs.
“We had to go through and measure every single one up individually and figure out how big does this need to be,” Farrell said. “We fabricated them in Darwin, then we made splicing joints on the fabrication; that way they could be transported in sections.”
The largest of these covers measured eight metres by six metres and had to be split into two-metre sections to be transported to the site, where it was reassembled.
Rough terrain
Among the challenges the team faced, Farrell estimates the pure logistics of the project to be the most daunting. Working over 100 km2, the team divided itself into five work crews to get the job done, planning from day one the most efficient approach to the task.
“We did a lot of internal risk assessments – working out what the risks would be and how we could mitigate them,” he said. “We had a bit of an understanding of what was involved, but then we got down there and had a good drive around to work out the terrain and how far away the material was.”
That terrain wasn’t always forgiving either. There were hills that the team struggled to walk up, which presented a challenge when they needed to drive an excavator to the summit.
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When it came time to actually do the work, the team set up an online platform on which they shared information about the sites so that they would know what to expect when they arrived. That also helped with reporting to the client after the job was done.
“Our guys could go and take pre-works photos and [create] a checklist of everything that needed to be done,” Farrell said. “They could take photos afterwards, and then it was submitted. We had close to 400 reports for the whole job, because, for some, we had to go back and do extra works.”
Apart from the appreciation of the local community and satisfaction in a job well done, Farrell hopes to bring his team’s new expertise to a similar project in Alice Springs and beyond.
“There are another five or six regions, from my understanding, where they’re going to do exactly the same work that they’ve done here.”
Remediating old mine complexes forms part of the circular economy imperative. Learn more at this on-demand webinar.
A job well overdue. A Brave soul must have spearheaded this one even in getting capital approval.
But why is it a local imitative and not a national project mister prime minister?