Police said at a news conference that it was in self-defense, noting that strikers even possessed a pistol taken from a police officer they had beaten to death on Monday. But video footage indicates the miners may have simply been trying to flee tear gas that police had fired at them moments earlier.
As the miners rushed away from a hill they had occupied and that was being teargassed, police opened fire, including with automatic rifles. Police were perhaps jumpy, knowing that the strikers were armed and that two officers had already died earlier in the week.
"Police stop shooting our husbands and sons," read a banner carried by the women on Friday. They knelt before shotgun-toting police and sang a protest song, saying "What have we done?" in the Xhosa language.
National Police Chief Mangwashi Victoria Phiyega told a packed news conference that Thursday was a dark day for South Africa and that it was no time for pointing fingers, even as people compared the shootings to apartheid-era state violence and political parties and labor unions demanded an investigation.
Zuma returned home from a summit in Mozambique and announced an official inquiry into the killings, which he called shocking and tragic. The president headed directly to the mine, 40 miles northwest of Johannesburg, where his office said he would visit injured miners in the hospital.
At least 10 other people were killed during the week-old strike, including the two police officers battered to death by strikers and two mine security guards burned alive when strikers set their vehicle ablaze.
Makhosi Mbongane, a 32-year-old winch operator, said mine managers should have come to the striking workers rather than send police. Strikers were demanding monthly salary raises from $625 to $1,563. Mbongane vowed that he was not going back to work and would not allow anyone else to do so either.
"They can beat us, kill us and kick and trample on us with their feet, do whatever they want to do, we aren't going to go back to work," he said. "If they employ other people, they won't be able to work either. We will stay here and kill them."
Research released by the Bench Marks Foundation, a nongovernmental organization monitoring the practices of multinational mining corporations, found that Lonmin had a bad track record with high levels of fatalities and keeping workers in "very poor living conditions."
The mining company said earlier that it would withhold comment on the report until the situation cooled down.