Platinum producer Lonmin has said there are new reports of violence at its eastern operations in South Africa.
Only 13% of workers reported for duty in the morning.
Lonmin is racing to resume ore extraction at its Marikana site.
However, there is no guarantee striking workers will return this week after the end of a mourning period for colleagues killed in a wave of labour unrest.
In total, 44 people were killed in union violence around Marikana, 34 of whom were shot dead by police.
