(Adds commentary, details, market reaction)
* TSX down 312.79 points, or 2.27 percent, to 13,466.65
* All 10 of the TSX's main groups are down
By Solarina Ho
TORONTO, Sept 22 (Reuters) - Canada's main stock index tumbled more than 2 percent on Tuesday as a sell-off in commodities walloped resource stocks, leading to across-the-board declines.
Gold, copper and crude oil prices all fell amid a stronger U.S. dollar and persistent demand worries, particularly out of top resource consumer China. The declines sent the index's materials group, home to resource stocks, sinking 4.3 percent.
First Quantum Minerals Ltd sank 10.5 percent at C$5.64, while Goldcorp Inc fell 3.2 percent to C$17.02.
The decline also dragged the remaining nine key sectors into the red, with energy sliding 1.6 percent and financials, which have considerable exposure to resource companies, retreating 2.1 percent.
Toronto-Dominion Bank, fell 2.5 percent to C$51.28, while Royal Bank of Canada declined 2.1 percent to C$71.61.
At 11:31 a.m. EDT (1531 GMT), the Toronto Stock Exchange's S&P/TSX composite index had fallen 312.79 points, or 2.27 percent, to 13,466.65.
All 10 of the index's key groups were mired in negative territory. Declining issues outnumbered advancing ones on the TSX by 229 to 16, for a 14.31-to-1 ratio on the downside. The index had posted two new 52-week highs and 11 new lows.
"This market has done this before. You really don't have to have a major reason - once the selling starts, it accelerates. And the buying is the same," said David Cockfield, managing director and portfolio manager at Northland Wealth Management.
"It's volatility and a tendency for people trying to follow the market rather than just invest ... they jumped all over the mining stocks."
U.S. crude prices were down 2.9 percent to $45.35 a barrel, while Brent crude lost 2.0 percent to $47.95.
Gold futures fell 0.9 percent to $1,123 an ounce.
Cockfield said if the downward volatility continues, buying opportunities could present themselves but cautioned "Our view is if you get caught up in volatility, you're going to lose." (Reporting by Solarina Ho; Editing by James Dalgleish)