TORONTO (Reuters) - The Toronto Stock Exchange's benchmark index finished a losing week by closing slightly lower as worries over the subprime mortgage market in the United States spooked equity investors.

The S&P/TSX composite index finished down 11.73 points, or 0.1 percent, to close at 13,466.28.

The drop extended a plunge of 280 points booked during Thursday's session.

Yesterday's drop began much more steeply with the index down almost 250 points in the morning, but it recovered significant ground in the afternoon, especially in the final minutes. The index lost 0.73 percent on the week.

"It's one of those things where investor patience is being tested," said Adrian Mastracci, portfolio manager and president at KCM Wealth Management Inc. in Vancouver, British Columbia. "When it looked pretty ugly this morning, everybody ran for cover. There's not a lot of fondness for uncertainty."

The Bank of Canada injected a total of C$1.685 billion into the financial markets yesterday in a bid to calm investors, ease liquidity concerns and bring the overnight rate down toward the bank's target.

It joined a number of other central banks around the globe that sprang into action to head off a mortgage-induced crunch.

"I do think those mortgage-loan worries have still yet to be totally recognized and we still don't know the exact damage that they will do in the final analysis," Mastracci said.

He added the upcoming earnings reports from Canada's big banks should shed more light on their exposure to the subprime mortgage market in the US.

Six of the TSX benchmark's 10 main groups declined, including the key financial services sector, which lost 0.33 percent.

Canadian Imperial Bank of Commerce fell C$1.79, or two percent, to C$87.51. Toronto-Dominion Bank dropped 62 Canadian cents, or 0.9 percent, to C$67.36. Bank of Nova Scotia gave up 58 Canadian cents, or 1.2 percent, to C$48.31.

Energy, industrials, health care and the resources-laden materials groups all finished in positive territory.