UPDATE 1-S.Africa wildcat mining strikes spread to iron sector

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JOHANNESBURG, Oct 3 (Reuters) - South African miners went on a wildcat strike at Kumba Iron Ore's Sishen mine on Wednesday, a fresh sign of escalating labour unrest in Africa's largest economy.

As many as 75,000 miners, or 15 percent of the South African mining sector's total workforce, are already out on strikes that have hit platinum and gold mining firms and further threatened the country's shaky growth prospects.

The recent weeks of labour strife, in which more than 45 people have been killed, have stirred up criticism of the ruling African National Congress and President Jacob Zuma, who faces a challenge from ANC rivals ahead of a party leadership conference in December.

"Our members at Sishen say the guys went on strike from 2 a.m. this morning and our understanding is that senior executives flew down there early this morning," said Gideon du Plessis, deputy general secretary of the trade union Solidarity.

Solidarity was not participating in the strike. A Kumba spokesman declined to comment but said the company would issue a statement shortly.

Kumba, a unit of global miner Anglo American , is one of the world's top 10 producers of iron ore, which is used in the production of steel. The company produced 41.3 million tonnes of ore in 2011.

The industrial action in the iron ore mining sector comes amid a worsening security situation in South Africa's strike-hit platinum belt and a national truckers' strike that has started to squeeze fuel suppliers in the country.

(Reporting by Ed Stoddard and Agnieszka Flak; Writing by Jon Herskovitz; Editing by Pascal Fletcher)

((Edward.Stoddard@thomsonreuters.com)(+27 11 775 3160)(Reuters Messaging: edward.stoddard.thomsonreuters.com@reuters.net))