Rio Tinto may have had gone through some tough times in China, but the deals are back now – and there are champagne corks to prove it.

With great ceremony, Rio and Chalco, the listed arm of Aluminium Corp of China (Chinalco), signed an agreement on Thursday to invest jointly in an iron ore project in Guinea. The deal will see Chalco invest $1.35bn in the mine in return for a 44.65 per cent stake.

It's a big step for Chalco, marking the company's first iron ore asset, as well as its largest investment overseas. But just as important is what the pomp and circumstance says about Rio, which has striven to repair ties with China after last year rejecting an investment bid from Chinalco. The event was rich in symbolism – the Great Hall of the People is used for Beijing's most high-profile events – and the display of camaraderie was impossible to miss.

Rio chairman Jan du Plessis bounded from the stage after his remarks to greet Xiong Weiping, Chinalco president.

Chinalco is the largest shareholder of Rio, and China is Rio's largest customer for iron ore. But the relationship has often been strained. After Rio shareholders rejected Chinalco's $19.5bn investment bid last year, four Rio employees were arrested in Shanghai and later convicted of bribery and stealing commercial secrets.

The terms of the deal were outlined in March, when Chinalco and Rio signed a memorandum of understanding on the deal. The decision for Chalco to acquire the asset, instead of its parent, suggests optimism about the potential of the Guinea project. Chinese state-owned enterprises usually hand their best assets to their listed arms only after those assets become profitable.