TORONTO -- Canada's main stock index closed lower Monday, weighed down by losses in the energy and gold sectors as commodity prices retreated.

U.S. financial markets were closed for Memorial Day, but international trading put more pressure on crude prices as speculation continued about a potential ramp-up in production from OPEC countries and Russia.

The reports on the potentially increased supplies, which could offset disruptions from Venezuela and Iran, have put pressure on the energy sector as the move suggests there aren't fundamental supply constraints, said Allan Small, a senior investment adviser at HollisWealth.

"I think everybody knows there's a lot of oil sloshing around, it's just a matter of whether people want to throw it out there."

Trading outside the U.S. for the July crude contract closed down US$1.41 a barrel at US$66.47.

The drop helped push the S&P/TSX composite index down 59.53 points to close at 16,016.14, with gold stocks also pulling down the index.

International trading of gold sent the August contract down US$6.30 at US$1,302.70 as tensions eased on the North Korea summit, said Small.

"I think the price of gold is reflecting the easing of tensions, which seems to happen every other day."

The Canadian dollar averaged 76.92 cents US, down 0.16 of a US cent, as the currency may have also felt the effect of easing oil prices, said Small.

"It didn't get a boost when oil went higher, but it may be pulling back because oil is going lower," he said.

"I think we're range bound. I think that 75-76 to 80 cent range is where we're going to be, with a few exceptions."

Canadian Pacific Railway closed down $4.38, or 1.81 per cent, to $237.06 as the unions representing train operators and signalling workers have given CP Rail notice that they plan to strike as of 10 p.m. ET on May 29.

Pan American Silver Corp. closed down 93 cents or 3.98 per cent at $22.44 after the Vancouver-based miner said it had cut back operations at its northern Mexico silver mine because of security fears along the access roads.

Corus Entertainment Inc. closed down 21 cents, or 3.17 per cent, to $6.41 after it said the Commissioner of Competition had blocked the $200-million sale of its French-language specialty channels Historia and Series+ to Bell Media Inc.