Bell Financial Group senior adviser Chris Kimber said BHP Billiton and Tio Tinto had led the market down, on a day of low volumes, after the recent good run.
"BHP and Rio have had a big run and there's nothing wrong with a bit of a rest," Mr Kimber said.
"Oil and copper came off, and we have had low volumes today."
BHP was down 78 cents, or 1.97 per cent, at $38.77, and Rio Tinto had lost 96 cents, or 1.37 per cent, to $68.88.
Both stocks had risen over the last five sessions.
Market turnover during the morning was $1.93 billion on 936 million shares.
Oil and gas producers declined after the price of crude dropped below $US77 a barrel overnight as US crude oil inventories data showed petroleum supplies continue to grow.
Woodside was down 47 cents at $48.59, Santos fell 21 cents, or 1.37 per cent, to $15.09 and Oil Search dropped six cents to $5.84.
Gold miners slumped after the precious metal dropped.
The spot price of gold in Sydney was $US1,102.50 per fine ounce, down $US18.15 from Thursday's closing price of $US1,120.65.
Lihir was down nine cents, or 2.62 per cent, at $3.35, and Newcrest, which also produces copper, dropped 92 cents, or 2.59 per cent, to $34.66.
Gas prices will continue to rise before leveling offShare market lower at noon
