The Toronto Stock Exchange's S&P/TSX fell 99.12 points, or 0.60 percent, to 16,327.35.
Leading the index were Cronos Group Inc, up 3.4 percent, Premium Brands Holdings Corp, up 3 percent, and Enghouse Systems Ltd, higher by 2.6 percent.
Lagging shares were First Quantum Minerals Ltd, down 10.6 percent, Peyto Exploration & Development Corp, down 7.9 percent, and New Gold Inc, lower by 6.7 percent.
On the TSX 93 issues rose and 145 fell as a 0.6-to-1 ratio favored decliners. There were 13 new highs and 17 new lows, with total volume of 193.7 million shares.
The most heavily traded shares by volume were First Quantum Minerals Ltd, Bombardier Inc and Encana Corp.
The TSX's energy group fell 4.09 points, or 2.7 percent, while the financials sector slipped 1.99 points, or 0.6 percent.
West Texas Intermediate crude futures fell 2.93 percent, or $1.85, to $61.28 a barrel. Brent crude fell 1.95 percent, or $1.41, to $70.77 [O/R]
The TSX is up 14 percent for the year.