The attack returned the spotlight on simmering tensions between workers and companies in South Africa's mining industry and their potential to disrupt operations in the home of around 80 percent of the world's known platinum reserves.

The violent confrontations are likely to increase as several platinum miners are reviewing operations and are mulling, or have announced, possible closures and suspensions of their shafts in the face of a difficult market.

Aquarius said on Wednesday about 200 people, some of them armed, forced their way on to mine property and clashed with security guards. They are believed to be former employees of a mining contractor, who were dismissed following an illegal strike in June.

"The night shift and the day shift have proceeded as planned and the situation is calm," the spokeswoman told Reuters.

The world's fourth-largest platinum miner said it had lost some 2,800 metric tons (3,086.5 tons) of production as a result of the incident. This follows the company's plans to limit mining activities to conserve cash and guard its reserves until economic circumstances change.

Police said petrol bombs were confiscated. Ballistic testing and autopsies will be conducted.

"A case of murder and attempted murder is being investigated," it said in a statement.

The miner's Johannesburg-listed shares tumbled at the start of trade on Thursday to their lowest since listing on the bourse in 2004, hitting 4.50 rand.

They were down 6.67 percent at 4.62 rand by 0919 GMT, compared with a 0.18 percent drop in the All-Share index .JALSH.

The incident follows violent confrontations between rival unions at Impala Platinum (IMPJ.J), the world's second-largest producer, which hit production at its flagship mine.

The platinum sector in South Africa is battling the impact of falling prices, weak demand, soaring costs and a government safety drive that has cut production as operations are suspended for safety violations.

(Reporting by Agnieszka Flak; Editing by Jon Herskovitz and David Cowell)

• A Permanent Economic Emergency