UPDATE 2.35pm: Shares in Aditya Birla slumped after the company admitted it could not say when its ageing Nifty copper mine might come back online.

Aditya Birla was forced to halt operations at Nifty in the East Pilbara on March 21 because of a mine cave-in.

The Department of Mines and Petroleum issued a notice prohibiting all mining operations at Nifty but has since granted the company permission to carry out a two-phase investigation process.

"All further activities will largely depend upon completion of these two phases," Aditya Birla said in a statement.

About 400 workers who have been stood down because of the shutdown will be represented at a conference at the Fair Work Commission today following an application by the Australian Workers' Union.

Earlier this month, the workers, most of whom are on indefinite unpaid leave, threatened legal action against Aditya Birla.

The company said it was attempting to mitigate costs and was liaising with its insurers.

However it said it could not provide production guidance because it could not estimate when mining operations at Nifty could resume.

Aditya Birla said it was also unable to estimate the total financial impact of the shutdown.

The ASX refused a request by Aditya Birla to keep its shares in suspension until it could provide more accurate information.

The company also this morning posted a full-year loss of $224,000 on revenue of $317.4 million, which was down 37 per cent on the previous year.

Aditya Birla also owns the Mt Gordon copper mine in near Mt Isa in Queensland, which is on care and maintenance.

The company said it held cash reserves of $136.78 million at the end of March.

Aditya Birla shares closed down six cents, or 20.34 per cent, at 23.5 cents after emerging from a trading halt.

The West Australian

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