Canada's main stock index fell on Tuesday, weighed by a 2.4% drop in energy stocks, while investors remained on the sidelines ahead of a two-day US Federal Reserve meeting.

At 9:38 a.m. ET (13:38 GMT), the Toronto Stock Exchange's S&P/TSX composite index was down 63.43 points, or 0.31%, at 20,101.53.

The energy sector dropped 2.4%, while the materials sector, which includes precious and base metals miners and fertilizer companies, lost 0.8%.

Teck Resources Ltd fell 3.7%, the most on the TSX, after the miner posted second-quarter revenue and profits below analyst's expectations, followed by oil producer Suncor Energy Inc, down 3.4%.

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BHP Group has made a C$325 million ($258.45 million) approach for the Canadian nickel-copper miner Noront Resources, rivaling an offer from Australian mining billionaire Andrew Forrest's Wyloo Metals.

The financials sector slipped 0.3%. The industrials sector rose 0.1%.

On the TSX, 76 issues were higher, while 147 issues declined for a 1.93-to-1 ratio to the downside, with 12.99 million shares traded.

The largest percentage gainers on the TSX were the electronics company Celestica Inc, which jumped 10% after an upbeat second-quarter earnings and TFI International Inc, which rose 9.1% after multiples brokerages raised price targets on its stock following second-quarter results.

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The most heavily traded shares by volume were Bank of Montreal, Royal Bank of Canada, and Suncor Energy Inc.

The TSX posted no new 52-week highs and no new lows.

Across all Canadian issues there were 29 new 52-week highs and seven new lows, with total volume of 21.96 million shares.