Workers at Goldfields's KDC mine have been on strike since Sunday.
Mfanayedwa Themba, who witnessed incident, said some of the thousands of protesters who gathered on Wednesday had wanted to stop a train "because the train is a part of the mine. It is a part of us." When they went onto the railway tracks, guards started firing teargas at them, he said.
The workers then ran to a stream where they washed their eyes, while security guards wearing gasmasks sat in vehicles.
Massive veld fires started after the gas was fired, and large clouds of smoke floated over the roads.
Workers from Gold Fields have been on strike since September 9, the latest in a series of wildcat strikes since the unrest at Marikana mine that left 44 people dead.
Earlier on Wednesday morning, National Union of Mineworkers (NUM) leaders spoke at the stadium, with some of them wearing T-shirts with "Hands off NUM. Hands off Cosatu" printed on the back.
'Hogwash'
On Tuesday, expelled ANC Youth League leader Julius Malema called for the resignation of the NUM's leadership, including its general secretary Frans Baleni.
Malema told about 15 000 striking workers at Goldfields the NUM's leaders did not listen to workers' needs.
NUM dismissed this, calling it "hogwash".
On Wednesday, some of the group wore balaclavas and carried sharpened sticks and planks.
NUM regional secretary Mbuyiseli Hibana said they were going to address members soon. "We want them to go back to work."
As Hibana told strikers their wage issue was something they needed to address with their employer, teargas was fired.
Armed guards from Gold Fields, both on foot and in armoured vehicles, were stationed around the mine. – Additional reporting by Sapa