AT 12.28pm (AEST), BHP Billiton rose 43 cents, or 1.11 per cent, to $39.25 and Rio Tinto was $1.26 higher at $71.33.
Mr Mueller said investors were still very uncertain given the impact of the Federal Government's planned resources super profits tax and ongoing turmoil in Europe.
"There is a huge amount of uncertainty because of political disruption, which causes investor confidence to go and hide," he said.
"Retail spending and confidence is low and the Reserve Bank has been aggressive increasing rates."
"We are not sure if the European thing is going to cause a major disruption again."
Gold stocks were also strong with Newcrest Mining adding 63 cents, or 1.82 per cent, to $35.27.
Eldorado Gold Corp was up 76 cents, or 3.8 per cent, at $20.73 while Lihir Gold rose 9 cents, or 2 per cent, to $4.35.
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Early movers included MAP Group, which rose four cents to $2.98 after announcing an increase in airport traffic in May.
Among the banks, NAB was up 41 cents at $25.21, ANZ was 10 cents higher at $23.05, CBA was eight cents higher at $52.58 and Westpac was 19 cents higher at $23.45.
At 12.40pm (AEST), the spot price of gold in Sydney was $US1242.70 ($1430.33) per fine ounce, up $12 from Thursday's closing price of $US1234.60.
The most traded share by volume was Environment Clean Technology Ltd, with 97.7 million shares traded for $4.5 million.
Environment Clean Technology shares were down half a cent, or 10 per cent, to four cents.
Market turnover was 996 million securities changing hands for $1.9 billion, with 516 stocks up, 389 down and 348 unchanged.
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