The deal also foresees building a 560 km (350 mile) railway to carry the ore to the Atlantic coast, a bulk commodities and container port and two hydroelectric power stations. Local ecology groups say they fear the contract, whose detailed terms have not been made public, may not contain sufficient safeguards to protect against environmental damage, for example through parallel logging activities by the Chinese.

"We demand immediate publication of the contract made between the government and the consortium led by China National Machinery & Equipment Import & Export Corp.. This way, Gabonese will know if their interests are being protected," Marc Ona Essangui, who heads a coalition of environmental groups, said.

Essangui told a news conference the groups believed the Chinese consortium was being granted exemption from all taxes for 25 years. They called for a full environmental impact study.

Gabon has part of the Congo Basin forest, the second largest forest in the world which conservationists fear is being damaged by uncontrolled, illegal logging as well as by a proliferation of mining projects.

In the last few years, China has snapped up multi-billion-dollar energy, mining and infrastructure deals in Africa, like Belinga, as it seeks to secure oil and raw materials for its expanding, resource-gobbling economy.

While many African governments praise Beijing for its "no strings attached" approach to aid and trade, Western critics say China cuts corners by ditching safeguards against corruption and labour and environmental abuses.

Following public concern expressed by the environmental groups, Gabonese President Omar Bongo last month invited two of their members to be part of an inter-ministry commission tasked with supervising the Belinga project.

Bongo, Africa's longest serving ruler, has maintained more than three decades of cordial ties with Beijing. He said last month he agreed with the idea of preserving nature but also had to consider Gabon's development.