There has been no communication with the workers since soon after an evacuation order was given on April 16, the company said.

The workers were below level 520—which is 520 metres from surface. There are two refuge areas below that level that are designed to provide safety in a hazardous environment.

"We do not know if some or all of the eight missing workers were able to access these refuge chambers," the Canada-based firm said.

The water level at the mine has settled at approximately level 520 and communications and electrical power have been re-established to that level, Trevali said.

The miner said it has completed about 3,643 metres of an estimated 5,000 metres of decline ramp rehabilitation which it thinks will be needed to access lower mine levels.

"The company has a three-stage dewatering plan, of which the first two stages—the repurposing of existing piping to commence initial dewatering efforts, followed by the installation of underground pumping infrastructure to facilitate an increase in pumping capacity—are now complete and actively pumping," Trevali said.

"The third stage, which is currently in progress, involves the installation of 5,000 metres of new piping and higher-capacity pumps to increase pumping capacity. Multiple welding crews are mobilised for this assembly effort.

"The objective of the plan is to dewater the mine to continue the search and rescue efforts for the missing colleagues while working towards completely dewatering to the lowest level of the mine," it said.

Trevali's share price shed another 5% day on day on April 25, closing the session at C$1.05 (US$1.05)—the lowest level since July 2020. The stock has fallen from C$1.89 on April 15.

Perkoa had previously been guided to produce 128 million-145 million payable pounds of zinc in 2022, which compared to Trevali's consolidated zinc guidance of 247 million-280 million lbs.

Trevali suspended Perkoa guidance on April 21.