TORONTO, Feb 15 (Reuters) - Canada's main stock index closed weaker on Friday, led by gold miners such as Goldcorp Inc and Barrick Gold Corp, after the price of the precious metal tumbled to a six-month low on weakening investor demand. The Toronto Stock Exchange's S&P/TSX composite index ended down 35.16 points, or 0.28 percent, at 12,686.63 after earlier dropping to 12,667.70, its lowest point since Jan. 17.