South African miners began striking at a mine owned by AngloGold Ashanti Ltd. (NYSE: AU), the third-largest gold producer, continuing an outbreak of labor unrest in the region that threatens the global supply of precious metals, which could send prices up.

Workers began striking late Thursday at Johannesburg-based AngloGold's Kopanang mine, which employees 5,000 people and accounts for 4 percent of the company's production. An AngloGold spokesman told Bloomberg that no demands had been made.

The AngloGold strike follows unrest at KDC West of Gold Fields Ltd. (NYSE: GFI), which ended two weeks ago. Protests in the region have intensified after workers from Lonmin Plc (London: LMI), the third-largest platinum producer, were killed by police in an August clash. Earlier this week, Lonmin conceded to give workers a raise in basic wages to 12,500 rand ($1,500) per month, up from 5,400 rand. Workers had complained of what they call unbearable living conditions and low wages.

Anglo American Plc (London: AAL), the largest platinum produce and Impala Platinum Holdings Ltd. (PINK: IMPUY), the second-largest platinum produce, the second-largest producer, have also dealt with strikes. Further tension has arisen from turf wars between the established National Union of Mineworkers and more radical Association of Mineworkers and Construction Union.

South Africa accounts for around 75 percent of the world's platinum production and around 8 percent of global gold prodcution.

Shares of AngloGold were up 34 cents, or 0.94 percent, to $36.64 in mid-Friday trading.