Last week, 34 people were gunned down by police in a hail of bullets from automatic weapons when authorities moved in against 3,000 striking workers armed with machetes, spears and handguns who were camped on a hill at Lonmin's Marikana mine, about 100 km northwest of Johannesburg..
"The final ultimatum has been extended to Monday, the 20th following Thursday's events," spokeswoman Gillian Findlay said on Sunday.
"Employees may be dismissed if they fail to heed the final ultimatum," she said.
London-based Lonmin accounts for 12 percent of global platinum output. It is already struggling with low prices, weak demand and may miss its annual production target of 750,000 ounces as the quarter to the end of September is typically its best.
The strike was sparked by a turf war between the powerful National Union of Mineworkers and the upstart Association of Mineworkers and Construction Union, which has accused NUM of caring more about politics than workers in mine shafts.
NUM has been a breeding ground of leaders for the ruling African National Congress party and one of the union's former top officials now sits on Lonmin's board as a non-executive director.
Ten people were killed prior to the police shooting, including a NUM shop steward who was hacked to death.
NUM General Secretary Frans Baleni, on a nationally televised talk show, said on Sunday he was not sure if the miners would return to work.
The deadly protest could also hurt the ANC and its long-standing labour allies by laying bare workers' anger over enduring inequalities in Africa's biggest economy.
Ousted ANC youth leader Julius Malema turned up the heat on his rival President Jacob Zuma at the weekend by telling a group of cheering miners at Marikana that Zuma was more interested in protecting mine owners than workers.
Platinum sells for about $1,440 an ounce but a worker drilling underground at tonnes of rock face to extract it makes less than $500 a month.
Zuma has called the killings "shocking" and called for a commission of inquiry to look into the matter.
Zuma has declared a week-long period of mourning from Monday to commemorate the lives of South Africans who have died violently, including those killed at the Lonmin mine.
