"It is now clear that none of the eight missing workers reached the refuge chamber," Trevali Mining said.
The zinc mine was impacted by a serious flood on April 16 and has been shut since while a recovery operation for the missing miners was underway.
"This is devastating news, and we would like to offer our deepest sympathies to our colleagues' families and friends during this difficult time," said Trevali chief executive Ricus Grimbeek. "We will continue our search efforts unabated and reaffirm our commitment to work at full speed to find our colleagues."
The company said it would provide further details as more information became available.
Trevali will need to refinance its main debt facility by mid-year, complicated by the shutdown of its Perkoa mine in Burkina Faso after a serious flooding incident that triggered a major fall in its share price.
Shares in the firm on the Toronto Stock Exchange have fallen to C$0.65 from C$1.96 in the last trading session before serious rains caused the flood event.
The firm has withdrawn production guidance for Perkoa.
The Perkoa mine - located in the Sanguie province, about 120 west of Ouagadougou - has a 2,000 tonne per day millinig operation. The mine has been in commercial operation since 2013, currently producing a zinc concentrate
In 2021, Trevali saw zinc production of 316.2 million pounds.