UPDATE 2.20pm: One-hundred-and-nine workers at Aditya Birla's ageing Nifty copper mine in the Pilbara have accepted voluntary redundancies with the company still unsure when the mine can be re-opened following a cave-in.

Aditya Birla said the 109 workers represented about 26 per cent of its 400 staff at Nifty and the redundancies would cost it about $2.5 million in entitlement payouts.

It said accepting the redundancies would not "seriously undermine" the resumption of operations.

Nifty staff have been on indefinite leave following a sinkhole incident on March 21 which forced operations to a halt.

Aditya Birla is still working to get a Department of Mines and Petroleum (DMP) prohibition notice lifted so it can resume mining activities.

"Whilst the company is proceeding with all necessary work to ensure that the Nifty operations are reinstated in the earliest possible timeframe subject to the DMP's approval, and the results of the testing and analysis to date report positive signs for such resumption, the exact timing is still unknown," the company said in a statement.

"Further ongoing testing and observation work is being undertaken."

Aditya Birla shares closed steady at 19 cents.

The West Australian

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