Gold Fields said workers at the KDC East mine had ignored a final deadline set for 16:00 (14:00 GMT).
Last week, some 11,000 miners at Gold Fields' KDC West mine heeded a company ultimatum and returned to work.
South Africa's mining sector has been hit by a wave of recent unrest which has left almost 50 people dead.
Most strikes have been over pay, although the stoppage at KDC East - at Carletonville west of Johannesburg - relates to a local trade union dispute not wages.
"All 8,500 people who were on strike did not come back," spokesman Sven Lunsche told AFP news agency.
"They did not return to work, so we have issued dismissal letters to all of them."
He said the miners had 24 hours to appeal against their dismissal.
"We have now reached a stage where we can't hold off any more. Our hands were forced and we have now done it," Mr Lunsche said.
"We are monitoring the situation very closely and have police on standby but it has been very quiet.