Mt Gibson Iron has temporarily suspended mining at Koolan Island's main pit due pit wall instability.
According to the miner it has halted the operation to "monitor and repair an area of instability in the upper part of the southern pit wall".
"A slump, which has potentially reduced the effectiveness of a small section of the seawall, occurred on 24 October.
"Based on evaluation over the weekend, Mount Gibson anticipates it will take approximately four weeks to complete remedial work necessary to repair the affected area and recommence production in Main Pit."
No employees have been put at risk, and all personnel working in the main put have been redeployed elsewhere on site.
In the mean time production in the Acacia East pit has been accelerated.
Mt Gibson expected four iron ore shipments from Koolan Island to be delayed in from the December quarter, however it still maintains its forecast full year guidance of 6.6 to 7 million tonnes.