Aug 27 (Reuters) - China’s state reserves administration said on Friday it would sell off 30,000 tonnes of copper, 50,000 tonnes of zinc and 70,000 tonnes of aluminium via public auction on Sept. 1. The auctions will mark the third round of metal sales by the National Food and Strategic Reserves Administration since early July in a rare release of state stockpiles aimed at cooling high prices. The administration auctioned a total 270,000 tonnes of the three metals last month. (Reporting by Tom Daly; Editing by Jacqueline Wong) Our Standards: The Thomson Reuters Trust Principles.