More than 100,000 gold miners are on strike in South Africa for higher wages.
The National Union of Mineworkers says its members want a 14% pay rise.
Economists say the strike could cost the gold mining sector $US25 million per day in lost output.
The strike began at 6pm on Thursday. Coal and diamond miners are already on strike.
The BBC reports that this time of the year is known as "strike season" in South Africa.
Most unions are demanding salary increases twice that of inflation - which is currently at 5%.
The average mine worker earns 3800 South African rand ($US570) each month, according to NUM.
