Dec 7 (Reuters) - Canada’s main stock index fell on Monday, dragged down by weakness in energy stocks, while rising tensions between the United States and China sapped appetite for risky assets. * The energy sector dropped 2.4% as U.S. crude prices were down 0.9% a barrel, while Brent crude lost 0.9%. * Reuters exclusively reported that the United States was preparing to impose sanctions on at least a dozen Chinese officials over their alleged role in Beijing’s disqualification of elected opposition legislators in Hong Kong. * At 09:42 a.m. ET (14:42 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 58.33 points, or 0.33%, at 17,462.64. * Pot producer Aurora Cannabis fell 4.8%, the most on the TSX. The second biggest decliner was oil producer Gibson Energy Inc, down 4.4%. * The financials sector slipped 0.7%. The industrials sector fell 0.3%. * The materials sector, which includes precious and base metals miners and fertilizer companies, added 1.2% as gold futures rose 0.1% to $1,838.2 an ounce. * On the TSX, 69 issues were higher, while 149 issues declined for a 2.16-to-1 ratio to the downside, with 28.67 million shares traded. * The largest percentage gainers on the TSX were miner OceanaGold Corp, which jumped 25.8%, and uranium producer Cameco Corp, which rose 4.2%. * The most heavily traded shares by volume were Suncor Energy Inc, Hexo Corp and Zenabis Global Inc . * The TSX posted four new 52-week highs and no new lows. * Across all Canadian issues, there were 39 new 52-week highs and five new lows, with total volume of 56.94 million shares. (Reporting by Amal S in Bengaluru; Editing by Krishna Chandra Eluri)