* S&P/TSX composite down 0.9 percent at 11,573.82
* Mining, energy, financials lead slide
* Barrick falls more than 3 percent (Adds details, quotes)
By Claire Sibonney
TORONTO, Jan 21 (Reuters) - Toronto's main stock index was lower on Thursday, as miners and energy producers were hit by softer commodity prices and financials retreated on uncertainty ahead of a White House proposal to crack down on risk-taking by U.S. banks.
President Barack Obama will make the announcement at 11:40 a.m. (1640 GMT). The tighter guidelines, which are expected to be broad and would require congressional support, are among a series of measures designed to revamp the country's financial regulatory system. [ID:nN21203704]
"It puts a little bit of uncertainty in the market, but obviously his statements are going to take a long time to sort out as it usually does in the political system," said Bruce Latimer, a trader at Dundee Securities.
All of Toronto's six big banks were lower, with Toronto-Dominion Bank (TD.TO), down 1.53 percent at C$62.88 and Bank of Nova Scotia (BNS.TO), off 1.61 percent at C$45.21, among the index's top decliners.
At 10:49 a.m. (1549 GMT) the Toronto Stock Exchange's S&P/TSX composite index .GSPTSE was down 105.5 points or 0.9 percent at 11,573.82 after falling 1 percent minutes earlier.
Barrick Gold Corp (ABX.TO), the world's No. 1 gold producer, was the biggest single drag on the index, as its shares fell 3.03 percent to C$38.49.
Gold fell 1 percent to a 2-1/2 week low below $1,100 an ounce as the U.S. dollar extended gains against the euro, which curbed buying of the precious metal as an alternative asset. [GOL/] [ID:nLDE60K11K]
Fluctuating oil prices hit the TSX energy sector, with the subindex .SPTTEN retreating 0.74 percent [O/R].
$1=$1.05 Canadian Reporting by Claire Sibonney; editing by Rob Wilson