Shavuka Mbidhi, from the Mineworkers Union of Namibia's Oranjemund branch, said the diamond miner had written to staff offering voluntary redundancies and at least 130 workers were expected to accept.

A spokeswoman for the miner said Namdeb was taking steps to ensure the sustainability of its mines.

"The business optimisation process includes options for all employees to apply for early retirement and voluntary separation," spokeswoman Pauline Thomas said. She declined to comment on the number of staff that could leave.

Diamond mining generates 20 percent of the southern African country's export earnings.

(Reporting by Nyasha Nyaugnwa; Writing by Alexander Winning; Editing by Andrew Heavens)