* ANC general council due to shape rand, mining policy
* Finance minister says billions lost to corruption
* Zuma tries to mend strained alliance
(Adds comments from finance minister)
By Jon Herskovitz
DURBAN, Sept 20 (Reuters) - South African President Jacob Zuma faces a major battle to shore up his authority this week when the ruling ANC meets to shape policies, notably on the strong rand and on left-wing calls for mine nationalisation.
The meeting of the African National Congress, which opened in the coastal city of Durban on Monday, marks one of the most important political events in years for the party, which has ruled since the end of apartheid in 1994.
The National General Council could leave Zuma weakened if he fails to hold on to old allies, who want left-leaning economic policies, or to win over some new ones.
With his term due to run until 2014, he is already widely seen as an ineffective leader. Former backers have indicated they may not support him for a second term, while economic growth looks set to slow in Africa's biggest economy, and a dispute that led to 1.3 million state workers going on strike has yet to be resolved.
"The difficulty for someone such as Zuma is that he has to appease so many different challenges and demands. And, being someone who is a consensus-seeking leader, you will always look weak in the process," said Roland Henwood at the University of Pretoria's Institute for Strategic and Political Affairs.
One of Zuma's main tasks is to repair an alliance with the powerful labour federation COSATU, strained by a three-week state workers' that was suspended earlier this month, and union accusations of cronyism and corruption in his government.
BILLIONS LOST TO CORRUPTION
Finance Minister Pravin Gordhan told delegates to the conference that the country has lost billions of rand through corruption.
"It's a cancer. If you don't catch it early enough and if you don't tackle it early enough, it will become the end," Gordhan said in a speech at the meeting.
Zuma will also need to fend off various rivals in the splintered ANC who are lining up to challenge Zuma at the next ANC leadership election in 2012. Due to the ANC's electoral dominance, that person is likely to be South Africa's next president.
Analysts expect Zuma, who was due to address the meeting at about 0800 GMT on Monday, to pay lip service to economic proposals made by COSATU, such as letting the rand fall from current 2-1/2 year highs. But they also believe he is not forceful or decisive enough to push through any major change.
The calls for mine nationalisation by COSATU and the ANC's Youth League are not likely to lead to any major change for a sector that accounts for about 6-7 percent of GDP, analysts said..
Mine nationalisation would place an enormous financial burden on the country. The Mail and Guardian newspaper cited cost estimates of at least 2 trillion rand ($280 billion), more than double the annual state budget.
Finance Minister Pravin Gordhan told Reuters in an interview on Monday that nationalisation was "not government policy", and that South Africa wanted "stable and competitive currencies".
The Durban meeting lasts until Friday. The next major event on the ANC calendar is the National Policy Council, including the leadership election, in 2012. (Editing by Marius Bosch and Kevin Liffey)