Sector heavyweights Rio Tinto RIO.AX and BHP BHP.AX slid 1.1% and 0.4%, respectively. By Poonam Behura April 26 (Reuters) - Australian shares closed marginally lower on Wednesday, with losses in mining stocks outweighing gains in gold and energy explorers as the country's soft March quarter inflation data failed to improve risk appetite. The shares pared some losses immediately after the data showed smaller price increases but made their way into negative territory by closing time.