Anglo American Platinum said Friday that just 20 percent of its workers had been showing up at its shafts, forcing the closing of the company’s entire operation in the Rustenberg area, home to the world’s richest platinum deposit.

Leaders of the African National Congress, South Africa’s governing party, have struggled to contain the mining crisis despite their deep ties to trade unions. The wildcat strikes have been initiated by rival unions that criticize the A.N.C. and the traditional unions as being too complacent now that they are in power.

On Friday, a branch leader for the country’s largest mineworkers union, the National Union of Mineworkers, which is closely allied with the A.N.C., was shot to death near a mine run by Lonmin, the company at the heart of the deadly unrest in Marikana, Reuters reported. A union spokesman was quoted as saying that the leader had been killed “execution-style.”