Around 2,000 workers affiliated with the National Union of Mineworkers (NUM) downed tools at the mine on Friday, demanding higher wages.
"The work stoppage is still continuing today," Implats spokesman Johan Theron said.
Implats, the world's second largest producer of platinum, and rivals Anglo American Platinum and Lonmin are still reeling from a five-month strike in South Africa that ended in late June. That stoppage was led by NUM's arch rival the Association of Mineworkers and Construction Union (AMCU).
The Marula operation of Implats was not hit by that strike as its NUM-affiliated workforce signed a wage deal last year.
But Theron said on Friday that it seemed the Marula miners now wanted the same wage deal that AMCU obtained for its members at other Implats' mines.
In the engineering and steel sectors, over 200,000 workers associated with the NUMSA metal workers' union downed tools in a separate dispute last week, forcing General Motors to suspend production at its main South African plant.