OTTAWA — In one of her first tests as Environment Minister, Leona Aglukkaq will give thumbs up or down to a proposed mine in British Columbia that is a new version of a plan tossed out as ecologically disastrous by a former Conservative minister.

Chiefs from Tsilhqot’in First Nations say they have no doubt that a federal environmental assessment panel, which is weeks away from delivering a verdict on the New Prosperity mine at Fish Lake in the B.C. Interior, will reject it out of hand.

They say the plan for the billion-dollar gold-and-copper pit that Taseko Mines Ltd. wants to dig near the lake the Tsilhqot’in call Teztan Biny – a small body of water they consider culturally and spiritually sacred – is just as bad as the earlier version thrown out in 2010 by former environment minister Jim Prentice.

Representatives from environmental groups who sat in on the panel’s hearings this summer say they are cautiously optimistic it is preparing to say no to the mine. Scientists from Environment Canada, Natural Resources Canada and Fisheries and Oceans, as well officials from B.C.’s provincial ministries, expressed significant concerns about the project.

But Ms. Aglukkaq will make the final decision. And the chiefs say they are uncertain that she will have the confidence to oppose an environmentally unsound project should the panel rule against Taseko. The Conservative government is proud of its pro-development agenda.

“What we need and what we want is a government that is ready to stand up and tell industry that it is time we take a different approach and let’s involve First Nations people in every aspect of decision making,” said Joe Alphonse, the chair of the Tsilhqot’in National Government, who visited Ms. Aglukkaq in Ottawa this week with Chief Roger William of the Xeni Gwet’in.

It’s not the first time the Fish Lake mine has gone through the environmental assessment process. British Columbia conducted its own environmental assessment of Taseko’s earlier proposal in 2010 and approved it, citing the hundreds of jobs and millions of dollars worth of tax revenue it would generate.

The federal government followed up with its own assessment and concluded the project would be environmentally ruinous. Two days before he quit the Conservative cabinet, Mr. Prentice upheld that decision, saying the mine would result in “the destruction as well of a complex and highly productive ecosystem.”

Taseko went back to the drawing board and came up with its new proposal which, unlike the original plan, does not include draining Fish Lake. But the First Nations argue contamination from the tailings would still seep into the water, killing the fish and destroying the environment.

In 2012, the federal government changed laws to eliminate its own role in many environmental assessments. Then, in March of this year, British Columbia inked a deal that allows it to substitute its own assessment for the two-step process involving Ottawa.

But the new proposal from Taseko was already in the works so the federal assessment process continued. And the proposed mine is so large, it may have had been assessed federally in any case.

“We’re confident that the panel is going to arrive at the same conclusion as the last panel,” Mr. Alphonse said. But, once the panel makes its ruling, “it becomes a political decision and our fear begins.” .

During a meeting this week with Ms. Aglukkaq, Mr. Alphonse said, “I felt she was trying to spend a lot of time deflecting, not wanting to spend too much time talking about the issue.”

When The Globe and Mail asked Ms. Aglukkaq if she would be willing to reject the mining proposal should it be found environmentally unsound, the minister’s spokesman said there would be no comment while the “comprehensive, science-based evaluation” is under way.

A Taseko official said much the same. “We all need to let the process work, let the process carry on, await the report and see what the panel has to say about the project,” said Brian Battison, Taseko’s vice-president of corporate affairs. Taseko argues that independent experts say the company’s approach is sound.

Elizabeth May, the Green Party Leader, said Ms. Aglukkaq “is a stalwart partisan and she will do whatever [Prime Minister] Stephen Harper tells her to do.” But even Mr. Harper might have trouble insisting that project be allowed to proceed if the panel’s report is scathing, Ms. May said.

If the decision does not go their way, the Tsilhqot’in say they will physically block construction of the mine. “We have done everything we can,” Mr. William said, “but, if that’s not enough, our people are going to take action.”