July 22 (Reuters) - Canada’s main stock index fell on Thursday, as Iamgold Corp plunged 15% on lowering its outlook, while rising worries about the Delta coronavirus variant also weighed. * After two straight days of gains, the Toronto Stock Exchange’s S&P/TSX composite index was down 27.61 points, or 0.14%, at 20,082.44, at 09:42 a.m. ET (13:42 GMT) * The United States on Wednesday extended the closure of land borders with Canada and Mexico to non-essential travel through Aug. 21 amid increasing concerns over the Delta variant. * The materials sector, which includes precious and base metals miners and fertilizer companies, lost 1.3% as gold futures fell 0.5% to $1,793.6 an ounce. ** Iamgold hit a 16-month low and slid to the bottom of the TSX, after the company lowered its full-year production outlook, citing lower output at its Westwood and Rosebel mines. * The energy sector dropped 0.4%, even as U.S. crude prices were up 0.5% a barrel, while Brent crude added 0.4%. * The Canadian province of Quebec on Wednesday rejected a liquefied natural gas export project for the Port of Saguenay, citing environmental concerns, in the latest blow to North American LNG development. * The financials sector slipped 0.2%, while the industrials sector rose 0.5%. * The largest percentage gainers on the TSX were Cae Inc , which jumped 5.7% on being added to the S&P TSX 60 index, and Mullen Group which rose 4.5% after its second-quarter earnings topped estimates. * Lithium Americas fell 3.8%, ahead of a court ruling next week that will determine whether to block the company from excavating its Thacker Pass site in Nevada. * The most heavily traded shares by volume were Orea Mining , up 22.2%; Bombardier, down 1.4% and Iamgold Corp, down 15.3 percent. * On the TSX, 67 issues were higher, while 160 issues declined for a 2.39-to-1 ratio to the downside, with 12.74 million shares traded. * The TSX posted no new 52-week highs and no new lows. * Across all Canadian issues there were 14 new 52-week highs and 3 new lows, with a total volume of 27.50 million shares. (Reporting by Susan Mathew in Bengaluru; Editing by Ramakrishnan M.) Our Standards: The Thomson Reuters Trust Principles.