The cause of Saturday's collapse was not clear but it occurred during "dismantling" of the mine, which officially stopped producing in 2021 after nearly 50 years because of depleted reserves, the company said.

"All site activities have been suspended until further notice and an investigation is underway to determine the circumstances of the accident," COMINAK said.

Orano owns a 59% stake in COMINAK. Spain's ENUSA and Niger's state-run miner SOPAMIN hold 10% and 31% respectively.

(Reporting By Boureima Balima; Writing by Edward McAllister; Editing by Andrew Cawthorne)