Tsilhqot'in First Nations won a major victory yesterday in a two-decades long struggle after a federal decision blocked Taseko Mines Ltd. from developing its controversial New Prosperity gold and copper mine.

"It's a huge, huge burden that's just been lifted off of our shoulders," says Chief Joe Alphonse, Tribal Chair for the Tsilhqot'in National Government. "We've been fighting to preserve this area for 20 years so we're feeling ecstatic."

The decision came after Environment Minister Leona Aglukkaq concluded that the mine was "likely to cause significant adverse environmental effects that cannot be mitigated."

This is the second time in three years that Taseko's mining plans have been halted by the federal government -- a move Alphonse calls unprecedented.

"I think Ottawa supported us in this," he says, adding that the support was much needed. "First Nations across Canada feel under attack by industry and this decision gives hope to all First Nations that if you follow the process things will fall in your favour."

Taseko still has the option of submitting a new development proposal to open its mine, which was expected to create close to 2,000 jobs and $1 billion in government revenue.

"The Government will continue to make responsible resource development a priority and invites the submission of another proposal that addresses the Government's concerns," the environment minister said.

In a statement, a spokesperson for Taseko wrote that "the company fundamentally disagrees with the decision the federal government has made and believes they based their decision on a panel report which contains serious flaws."

When Taseko's initial bid was rejected in 2010 the company spent $300 million to develop a second proposal to address the federal government's concerns.

Taseko is dissatisfied with the treatment its new proposal has been given by the Canadian Environmental Assessment Agency, and in December 2013 it filed a federal judicial review to challenge the agency's findings and what Taseko describes as the agency's "failure to comply with principles of procedural fairness."

Alphonse says the Tsilhqot'in are ready to take the fight to court.

"The court system is based on facts and their bid was based on political posturing," he says.

Companies must realize that First Nations cannot be overlooked and must be included in the discussion from the beginning, says Alphonse.

"There will be challenges as there will always be when you try to move a project forward, but the only way we're going to get there is if we work together," he says.

If companies don't want to adhere to that, it's time for them to move on, says Alphonse.

The Tyee reached out to Taseko Mines Ltd. The company was unable to respond by deadline.

Kristian Secher is completing a practicum at The Tyee.