Rio Tinto says a tie-up with Chinalco, China's largest alumina producer, will give it unprecedented access to explore resource-hungry China for copper and other minerals. The resource giant signed a joint-venture agreement with Chinalco to form Chinalco Rio Tinto Exploration Co Ltd, to explore for copper, coal and potash in mainland China. ''The formalisation of our exploration JV is an important milestone in the expanding relationship between Rio Tinto and China,'' Rio Tinto chief executive Tom Albanese said in a statement. ''Given that mainland China is highly prospective, the JV has the potential to create valuable opportunities for both partners.'' The deal comes as relations between Rio and China, its biggest customer, slowly improve after four of its staff were jailed in Shanghai for bribery and stealing commercial secrets last year during tense iron ore pricing talks.