Investec has maintained its 'buy' rating and 3,303p target price for diversified mining group Rio Tinto after the firm's upbeat second-quarter operational update on Tuesday.Analyst Hunter Hillcoat said that the most important division, iron ore, delivered production ahead of Investec's forecasts: 66m tonnes were mined in the second quarter, up 7.0% on the first quarter and ahead of the 62.2m forecast.Meanwhile, copper output also beat expectations in the second quarter, with 146,200 tonnes coming in well ahead of the 112,000 estimate. The company now expects mined copper to total 565,000 tonnes this year, higher than its previous guidance (540,000), Hillcoat pointed out."All other key divisions were in line with or better than our expectations," he said.The stock was up 2.32% at 2,871.5p by 10:53.BC