July 16 (Reuters) - Canada's main stock index edged lower on Tuesday, as a steep fall in the shares of miner Turquoise Hill Resources and lower gold prices pressured the materials sector.

* At 9:49 a.m. ET (13:49 GMT), the Toronto Stock Exchange's S&P/TSX composite index .GSPTSE was down 17.71 points, or 0.11%, at 16,493.11.

* Shares in Turquoise Hill TRQ.TO slumped 38.9%, the most on the TSX, after the miner said development capital spending for the Oyu Tolgoi mine in Mongolia, that it partly owns, may exceed previous outlook.

** Earlier in the day, Rio Tinto RIO.AX, which owns a majority stake in Turquoise Hill, flagged a cost blowout of up to $1.9 billion and a delay of up to 30 months at the mine.

* The materials sector .GSPTTMT lost 0.2%, also weighed down by 0.2% drop in gold futures GCc1 to $1,409.2 an ounce. GOL/MET/L

* Six of the index's 11 major sectors were lower, with the heavyweight financials sector .SPTTFS up 0.1%.

* On the TSX, 93 issues were higher, while 134 issues declined for a 1.44-to-1 ratio to the downside, with 17.32 million shares traded.

* The second biggest decliner was NFI Group Inc NFI.TO, down 9.1%.

* The largest percentage gainers on the TSX were Seven Generation VII.TO, which rose 2.2%, and Pan American Silver Corp PAAS.TO, which gained 2.0%.

* The most heavily traded shares by volume were Turquoise Hill, Horizonte Minerals Plc HZM.TO and CannTrust Holdings Inc TRST.TO.

* The TSX posted one new 52-week high and three new lows.

* Across all Canadian issues there were 12 new 52-week highs and nine new lows, with total volume of 29.88 million shares.

(Reporting by Medha Singh in Bengaluru; Editing by Sriraj Kalluvila)

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