The province granted a five-year extension to a certificate that had been given to an earlier version of the New Prosperity mine near Williams Lake.
The Tulsequah Chief mine, in the province's northwest, has been determined to have "substantially started," meaning the certificate will remain in effect for the life of the project.
Tsilhqot'in Nation members live in the area where the New Prosperity gold and copper mine would be built. Chief Joe Alphonse says it should be illegal for the province to grant an extension without his band's consent.
The nation became the first aboriginal band in Canada to win title to its territory last June in a historic Supreme Court of Canada decision.
"This decision has given hope to First Nations and indigenous people all around the world," said Alphonse. "It's a way for the province and Canada to hit the reset button and re-establish what type of relationship they want to have with First Nations people.
"They want to continue to move forward the way they always have, and we're here to say, 'No, that's not the case.'"
The nation won title for land just outside the New Prosperity mine region, but the project is in an area where the Tsilhqot'in has other established aboriginal rights.
The province's environment minister said in a phone interview Thursday that extension decisions are based on fairly narrow criteria, including whether circumstances have prevented a company from starting a project.
Mary Polak said she is legally barred from re-reviewing projects or considering whether certificates should have been granted in the first place.
Polak said the ministry consulted with the Tsilhqot'in and considered their feedback. But she said the province does not need the agreement of local First Nations to extend such certificates.
"Their position has to be relevant to the criteria. If some of those views are with respect to the project itself, to saying we don't think the project itself should have ever gone forward, well, that decision was already made."
Taseko, the company behind the $1.5-billion mine is fighting the federal environment minister's rejection of the proposal. It applied last fall to convert two judicial reviews of the federal decision into a lawsuit and is awaiting a court decision.
Polak said she had extended a certificate for an earlier version of the project, not the version that had been rejected by the federal government. If the court ruled in its favour, Taseko could apply to amend the certificate with the new elements of its plan.
Another Tsilhqot'in chief, Roger William, said the band opposes the mine because it is concerned about effects on Fish Lake and surrounding rivers.
"An open-pit mine is going to possibly destroy the rivers and then the lake. Fish Lake itself is a sacred site, we have a lot of history."
A spokesman for Taseko said the revised version of the project won't affect the waters. Brian Battison said despite opposition from Tsilhqot'in leaders, many other community members have been supportive.
He said the region holds the tenth-largest undeveloped gold and copper deposit in the world. He said the mine would generate about $10 billion total in new tax revenue for the provincial and federal governments, as well as nearly 2,000 direct and indirect jobs.
"It's worth fighting for," he said. "People want to see it go ahead. They want to see the jobs and the economic development and the new taxes it'll generate for governments."
In a different part of the province, the Taku River Tlingit First Nation of Atlin has been opposing the Tulsequah Chief Mine for more than a decade. Chieftain Metals, which owns that project, did not immediately respond to requests for comment.
A B.C. Supreme Court judge ruled last July that the government breached its duty to consult the band when it first declared the mine "substantially started" in 2012. The ruling forced the province to make the decision again, but after more consultation.
Polak said she is confident the province adequately consulted with the Taku River Tlingit before she made her announcement this week. But John Ward, a spokesman for the First Nation, said the band disagrees with the decision and will review it carefully.
"I don't know what it's going to take to change things," he said. "We're not opposing mines, we just want better processes, more responsible processes. We want assurance the land isn't going to be ruined for future generations."
— By Laura Kane in Vancouver