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A militant South African labour union has wrested majority control at the world's richest platinum mines, shaking up the industry and potentially boding ill for the ruling ANC, analysts say.

The dominance by the upstart Association of Mineworkers and Construction Union (AMCU) comes after it gained worldwide notoriety last year in a violent strike that saw police shoot dead 34 miners.

Nearly a year later, workers en masse have abandoned the seemingly once-untouchable, ANC-allied National Union of Mineworkers (NUM), which shed 41,000 members countrywide in 2012.

The stakes are high, said mining analyst Peter Major from financial services group Cadiz.

"This two-union duke-out means power, money, political and economic clout and prestige for the winner," he told AFP.

With wage bargaining rights, cars and on-site offices among the victor's perks, the bitter, sometimes deadly rivalry has raised fears of further unrest after paralysing stoppages and bloodshed last year.

AMCU now holds sway at the three largest platinum miners who employ a combined 84,000 workers northwest of Johannesburg.

The union represents 40 percent at world number one producer Anglo American Platinum, 58 percent at Impala Platinum's Rustenburg operations, and 70 percent of workers at Lonmin.

AMCU's meteoric rise flipped the situation from just a year ago, when NUM had 65 percent at Implats and 50 percent at Lonmin.

NUM's fall from favour cuts to the heart of its parent federation, the Congress of South African Trade Unions (Cosatu), which is a key ally of the African National Congress.

The last time such radical changes were seen was during the rise of black unionism under apartheid in the early 1980s.

"This is the biggest upheaval since NUM was allowed in 1981," said Major, pointing to the year that union organisers were granted access to the country's mines.

AMCU has shrewdly used its newfound influence to strengthen its base, while capitalising on accusations that the NUM has abandoned workers by cosying up to the political elite.

The upstart's gain in the Rustenburg platinum belt is a loss for the ANC, which has relied on its union allies to drum up support for elections.

Paul Stewart, mine sociology expert at the University of the Witwatersrand, said election time usually saw NUM shaft stewards transform into "election foot soldiers going door-to-door campaigning for the ANC".

"Arguably one of the most significant social and political bases of the alliance has been eroded and has possible implications for elections," he said.

The ANC, which is facing increasing frustration from South Africans ahead of polls next year, has rallied to win back the union's lost ground.

"Rise and defend the NUM. Go into the informal settlements to recruit for NUM and the ANC," a regional leader told a campaign in Marikana a week ago.

But the lost membership's effect on votes is still unclear, according to political analyst Aubrey Matshiqi.

"It is too early to tell whether the politics of inter-union rivalry between AMCU and NUM will deliver a shift in the political landscape," he said.

--- 'Violence and instability' could harm miners and mine companies --

Also unknown is the long-term impact on the platinum industry which is facing job cuts on the back of heavy 2012 profit falls.

Several assassinations have taken place on both sides, and a hit on a prominent AMCU leader led to a wildcat strike at Lonmin in May.

After forcing hefty pay hikes by sidestepping historic wage negotiation channels, AMCU is demanding increased concessions from mining companies and the government.

At the same time, it is avoiding formal commitments itself.

It was the only union to abstain from a pact to stabilise the mining industry which companies signed with labour unions and the government begin July.

Union leadership has long been a stepping stone to political power -- a key reason for the bitter rivalry.

What started as joint opposition to the white-minority regime has become a mutually beneficial relationship, blurring the lines between labour, business and government.

ANC deputy president Cyril Ramaphosa is a NUM founder, one of the country's richest people and until January this year Lonmin chairman.

Now he is President Jacob Zuma's heir apparent, destined eventually to head Africa's largest economy.

But there is a caveat to AMCU's power.

It doesn't extend yet far beyond the platinum industry, and holds only 17 percent against NUM's 64 percent in the gold sector.

Rustenburg has long been the NUM's weakest region, which helped AMCU to usurp it, but the older union still retains majority status at two smaller miners.

With workers living in dire conditions next to some of the world's richest mineral wealth, the tug-of-war may meanwhile force unions to put worker interests first, said Matshiqi.

However "in the context of violence and instability, that competition may be to the detriment of the sector and the workers themselves," he added.