The South32 Hermosa Mine Project received authorization from the Arizona Department of Environmental Quality (ADEQ), to expand its dry-stack, lined tailings storage facility by amending its current Aquifer Protection Permit (APP).
The existing storage facility is already in use and was part of the company’s voluntary effort in 2020 to clean up mine waste left behind by the site’s previous owner.
Dry-stack tailings storage is a method that stores processed mine waste known as tailings through dewatering until the waste becomes a dry, sand-like material.
This approach uses less water than traditional mine waste ponds– South32 says the Hermosa Project will use 90% less water than other mines in the region.
This announcement follows an Arizona appeals court ruling that upheld a lower court’s decision confirming the project’s effluent complies with state standards.
South32 was first issued an APP for the Hermosa Project in 2018.
The project is designed to source two federally designated critical minerals: zinc and manganese.
Production is expected to begin in 2027.
