At 0811 GMT, shares in Eramet slumped 19% to EUR61.65.
The company said all operations have stopped and rail traffic has been suspended in the West African country, and that it has begun procedures to ensure the safety of staff and facilities of its two subsidiaries there, Comilog and Setrag.
The former operates the Moanda manganese mine–the world‘s largest–and Setrag is a rail transport company.