On the heels of bringing on a new general manager for the project this week, the Phoenix, Arizona-based producer confirmed acid injection work has begun at a limited number of wells at the site, after which it is recovering solution from adjacent wells. Its current acid supply in on-site storage is expected to last for several months.

"The purpose of these activities is to test the modified (retro-fit) wells under small-scale operating conditions and to gain knowledge on the new ‘push-pull' operating procedures," the company said.

It first built three storage tanks with a 7,500-tonne combined sulphuric acid capacity last year.

As for the mine's other forthcoming work, Excelsior said it will be taking on small-scale activities during this time when health risks to its workforce is still a concern.

"Any significant interruption in the workforce could negatively impact larger operations," it noted.

Excelsior is targeting a sustained production rate of 25 million pounds of copper per year from Gunnison. It is currently calling the restart "eventual" and did not offer an updated timeline for it to come online.

Gunnison, located in Cochise County, went on a temporary work idle earlier this year to mitigate the spread of the coronavirus.

The operation is permitted for 125 million pounds per year of copper cathode production.