South32 says the viability of the Worsley alumina refinery is in doubt because of the West Australian government’s stricter approach to environmental approvals, prompting the miner to record a $US389 million ($581 million) impairment.

Shares in South32 slumped by more than 11 per cent to a 16-week low on Monday as the miner downgraded production forecasts for Worsley and two other assets.