TORONTO (Reuters) - Toronto's main stock index fell broadly yesterday, driven lower by commodity weakness in general and a steep drop in gold prices in particular.

Gold retreated one percent on a technical sell-off and a decline in safe-haven buying after an initial rally that might have lifted gold to a record high fizzled.

"I think the biggest movement today was a strong reversal in the precious metal sector," said Francis Campeau, broker at MF Global Canada in Montreal.

Gold-mining stocks were down 1.3 percent with shares of Barrick Gold falling 0.5 percent to C$47.86, and Goldcorp Inc. losing 0.8 percent to C$46.74.

US crude oil futures also ended lower as tropical storm Alex in the Gulf of Mexico took a path that offered little serious danger to oil and natural gas production.

The TSX index's energy sector slipped 1.6 percent. Suncor Energy Inc. was off 0.8 percent at C$33.00, and EnCana Corp slumped 2.7 percent to C$33.12.

The Toronto Stock Exchange's S&P/TSX composite index closed 100.85 points, or 0.86 percent, lower at 11,607. Seven of its 10 main groups were down.

"We're seeing a decline in the index because of all three heavyweight groups are down," said Elvis Picardo, analyst and strategist at Global Securities in Vancouver.

In addition to the weaker energy and materials sectors, banks also fell even though leaders at the Group of 20 summit in a Toronto on the weekend agreed to give banks more time to adopt tougher rules. Decliners included Royal Bank of Canada, down 0.8 at C$52.81, and Toronto-Dominion Bank, 0.9 percent lower at C$70.69.

The G20 meeting failed to provide many new incentives for the market to trade on, agreeing to let countries take different paths towards assuring lasting growth and making their banking systems safer, a reflection of the uneven and fragile economic recovery in many countries.

While targets for debt and deficit ratios in the G20 communique were mildly positive for the market, analysts said they were skeptical about implementation and warned that markets are focused on broader issues right now. "Following the summit, we kind of opened flat across the world," Mr. Campeau said.