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.
Nine miners died after an underground fire the Doornkop mine on Gauteng’s West Rand.
The bodies of eight men were found on Thursday after a fire broke out underground.
Another two Harmony workers have died after blasts at the Joel and Kusasalethu mines.