(Adds sector details; updates prices) Dec 18 (Reuters) - Canada’s main stock index shed initial gains on Friday to snap its three-day winning streak due to weakness in materials sector, while strength in energy stocks and upbeat domestic retail sales data helped limit losses. * The materials sector, which includes precious and base metals miners and fertilizer companies, lost 1.1% as Spot gold fell 0.1% to $1,884.71 per ounce, retreating from a one-month peak scaled in the last session. * At 09:41 a.m. ET (14:41 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 39.46 points, or 0.22%, at 17,613.48. * BlackBerry Ltd fell 6.6%, the most on the TSX, after the cybersecurity firm missed Wall Street estimates for third-quarter revenue. * The second biggest decliner was Enghouse Systems Ltd , down 3.5%. * The energy sector climbed 0.6% as U.S. crude prices were up 0.8% a barrel, while Brent crude added 0.6%. * Canadian retail sales grew 0.4% to $54.59 billion ($42.65 billion) in October, led by motor vehicle and parts dealers, Statistics Canada said. * The financials sector slipped 0.1%, while the industrials sector rose 0.2%. * On the TSX, 66 issues advanced, while 148 issues declined in a 2.24-to-1 ratio favoring losers, with 104.13 million shares traded. * The largest percentage gainers on the TSX were media company Corus Entertainment Inc that added 3.2%, and uranium producer Cameco Corp that rose 2.8%. * The most heavily traded shares by volume were Toronto-Dominion Bank, Royal Bank of Canada, and Enbridge Inc. * The TSX posted five new 52-week highs and no new low. * Across Canadian issues, there were 81 new 52-week highs and three new lows, with total volume of 120.84 million shares. (Reporting by Amal S in Bengaluru; Editing by Vinay Dwivedi)