* TSX down 28.87 points, or 0.18 percent, at 16,153.76
* Eight of the TSX's 10 main groups move lower
TORONTO, Dec 22 (Reuters) - Canada's main stock index slipped on Friday but was on track for its sharpest weekly gain in almost three months.
* At 10:15 a.m. EST (1515 GMT), the Toronto Stock Exchange's S&P/TSX composite index .GSPTSE was down 28.87 points, or 0.18 percent, at 16,153.76. It remains on track for a 0.7 percent rise for the week, its sharpest weekly gain since late September.
* Eight of the index's 10 main sectors moved lower, with the energy group climbing 0.2 percent, while decliners outnumbered advancers by a 1.3-to-1 ratio.
* Among the most influential decliners on the index was First Majestic Silver Corp FR.TO , which fell 8.9 percent to C$8.86 after Bank of Montreal analysts cut the stock to "underperform" and lowered its price target.
* First Quantum Minerals Ltd FM.TO declined 2 percent to C$17.27, while the overall materials group, which includes precious and base metal miners and fertilizer companies, added 0.3 percent.
* Teck Resources TECKb.TO rose 1.1 percent to C$32.50 after the miner reached a wage deal with one union at its Quebrada Blanca copper mine in Chile, ending an eight-day strike. The Canadian economy paused in October, reinforcing expectations that growth cooled in the second half of the year and taking some steam out of bets that the central bank could raise interest rates as soon as January. U.S. crude oil CLc1 prices were down 0.6 percent at $58.03 a barrel, while Brent LCOc1 lost 0.4 percent to $64.67. O/R