A mining company with big plans for mineral deposits near Patagonia has finished a clean-up project that sealed off waste from an old mine in the area.
Australia-based South32 said in a Jan. 17 news release that more than $30 million had been spent on remediation work at the former Trench Camp Mine since 2017. It’s a major step for the site, which received six violation notices from state environmental regulators in 2014 after monsoon season rains caused heavy metals to leach into nearby waterways.
Prior to the remediation, old mine tailings sat directly on the ground, which allowed stormwater to soak through the waste material and into the earth. During periods of heavy rainfall, the contaminated water would then enter local waterways, South32 wrote in the release.
That system of tailings storage, while once common, has now been redesigned as a “dry stack system,” the company said, “which means the tailings are highly compressed with low moisture levels – minimizing the risk of run-off.”
“South32 works to high standards because that matters deeply to our stakeholders, whether they own wells downstream from our site, own livestock close to the waterways, or own shares in our company,” South32 Hermosa Project President Pat Risner said in the release.
During a tour of the clean-up site in June 2018, South32 representatives said the tailings storage facility would hold waste from the old mine as well as from new mining operations planned for the same area. It also includes a water treatment plant that will filter rainwater that drains off the tailings.
The 261-acre Trench Camp site is part of South32’s Hermosa Project in the Patagonia Mountains, southeast of the town of Patagonia, where it has plans to mine silver, lead, zinc and manganese. The Hermosa property includes 454 acres of private land, according to South32 communications director Jenny Fiore, and is surrounded by another 100 acres of private land and approximately 26,000 acres of unpatented mining claims.
But the old Trench Mine – once owned by bankrupt mining giant ASARCO – was not subject to current environmental regulations, which hadn’t been implemented at the time of its operation, according to Laura Malone, waste programs division director at the Arizona Department of Environmental Quality. She said a bankruptcy trust was going to be on the hook for cleaning up issues like the orange sludge that flowed out in 2014.
Instead, when the Trench Camp property was sold for just $10 in 2015, buyer Arizona Mining committed to carry out the clean-up as part of the sale terms.
“Part of that purchase agreement was all this work that they’re doing to address those type of issues on the site,” Malone said. “It was all embedded into the overall purchase of this property.”
Even though the company was obligated to do the work, the remediation project was processed through ADEQ’s Voluntary Remediation Program.
Arizona Mining purchased the Trench Camp site from a trust that sold off ASARCO properties and South32, which already owned a partial stake in Arizona Mining, bought out the company for $1.3 billion 2018.
According to the 2015 purchase agreement, the Trench Camp site was discovered in 1875 and used as an underground mine for zinc, lead, silver, gold and manganese.
Change of plans
The clean-up comes as South32 seeks permits to begin mining operations at Hermosa, which contains two major mineral deposits.
Brad Ross, professor at the University of Arizona Lowell Institute for Mineral Resources, said voluntary remediation projects are seen as a tool for mining companies to generate goodwill with regulators as they apply for new permits.
“There’s a belief by these companies that demonstrating that they’re serious about reclamation and such is part of demonstrating that they will do the things that they’ve promised they’re going to do for the overall project,” he said. “It’s more of, ‘Let me show you what I’m going to do,’ instead of just saying that ‘I’m going to reclaim these things.’”
But, Ross added: “Once they make that commitment, they’re obligated then. And then (ADEQ) actually monitors progress and does their inspections and if they aren’t keeping up with things they can get fined. So they definitely take on some obligation once they start that process.”
The final clean-up project at the Trench Mine site, which includes an active water treatment plant, differs significantly from the initial plan by South32 predecessor Arizona Mining, which would have used a cheaper passive water treatment system.
In 2015, Arizona Mining said it was planning to construct a passive water treatment system estimated to cost $2.6 million. It’s not clear what the total cost of the initial plan was.
Carolyn Shafer, board member with the mining watchdog group Patagonia Area Resource Alliance (PARA), asserted that ADEQ required the company to build an active treatment plant after an expert hired by PARA submitted a report to the department.
ADEQ spokeswoman Erin Jordan confirmed that the initial plan was for a passive treatment system and that PARA had submitted comments during a public comment period, but denied that the department had required the company to build an active treatment plant.
She said that ADEQ had approved a proposal including the passive treatment system and Arizona Mining later changed its plans for the clean-up, which was ultimately completed by South32.