China Railway Group, the nation's largest construction firm, said Wednesday it had signed an agreement to invest in a $2.9 billion copper and cobalt mining project in Congo.

It planned to set up an investment joint venture for the project with registered capital of $100 million with several other Chinese firms and Congolese companies, according to a statement to the Shanghai bourse.

China Railway will hold a 43 percent stake in the investment firm in the central African country, it said.

The company, which will contribute $1.83 billion to the project from loans and other forms of financing, said the investment is still subject to approval from Chinese and Congo authorities.

The project has proven copper reserves of about 6.8 million tonnes and cobalt reserves of 420,000 tonnes, it said.