The incident occurred last night and operations at the mine have been brought to a halt as a result.
The gold producer fell 8 percent as bullion sank nearly 1 percent.
The company says the current situation is clearly unsustainable.
Chief Executive Graham Briggs implied that any restructuring at the mine was likely to include job cuts.
Company spokesperson Marian Van der Walt says 105 illegal miners were arrested last month.
The group is believed to be responsible for at least three fires at the mine this month.