Dongria Kondh tribespeople say their livelihood will be destroyed
India's Supreme Court has said two huge and controversial mining projects can proceed in the eastern state of Orissa.
The ruling follows fierce protests by farmers, campaign groups and tribes who have vowed to oppose the projects.
It means an arm of the British-listed mining giant Vedanta can now use bauxite from a mountain in Orissa which local hill tribes view as sacred.
In a separate ruling, South Korean steel firm Posco was given the go-ahead for a $12bn plant in the same state.
The BBC's Damian Grammaticus in Delhi says environmental and tribal campaigners are now calling on India's prime minister to halt the Vedanta project.
They say India's rush to development should not come at the expense of the traditional and sustainable way of life of tribal and marginalised people.
'Home to God'
Vedanta has an agreement with the Orissa state government to set up a bauxite refinery in the Niyamgiri mountains, as part of a vast project in Orissa, one of India's poorest states.
Niyamgiri is rich in bauxite, from which aluminium is derived.
Vedanta has already invested $1bn to build a giant alumina refinery close to the mountain.
The court has said Vedanta must invest at least $2.5m in the area to help local tribes.
But leaders of the 8,000-strong Dongria Kondh say no amount of money can compensate for the damage to their sacred mountain and the forests they depend on.
They have vowed to "fight to the death rather than leave their sacred home".
"Even if you kill us we will not give Niyamgiri," said one tribal member Jairam, in a press statement released on the tribe's behalf by British charity ActionAid.
Another member of the tribe, Jitu Jakeskia, said: "We are deeply connected with the mountain. It is home to our God Niyamraja.
"We will not allow the company to mine our land, our sacred place. Any compensation they offer is worthless to us."
The Indian and Orissan governments both back the Vedanta plan as part of efforts to industrialise and exploit mineral resources in the east of the country, which they say is under-developed.
The giant Posco project in Orissa is the country's biggest direct foreign investment.
It has faced stiff opposition for more than two years from local farmers who are angry over losing their land.
"Posco is permitted to continue the iron ore mining," the Supreme Court said.
Reuters reported that Posco had so far been able to acquire about a quarter of the 4,000 acres it says it needs for the plant.
The court gave it the green light to use another 3,000 acres of forest land, the agency reported.
Critics say the plant could displace 20,000 people. The company and the government argue that badly-needed jobs will be created in a poor part of the country.