Gov. Bill Walker and Lt. Gov. Byron Mallott on Friday asked the U.S. Army Corps of Engineers to suspend the environmental review process for the proposed Pebble mine project, citing the "unique" environment of the Bristol Bay region.
Pebble Limited Partnership has proposed the copper and gold prospect for a site that straddles the Bristol Bay salmon fishery headwaters.
Bristol Bay is the largest sockeye salmon fishery in the world. Without at least a preliminary economic assessment, Walker and Mallott said in the letter, the Army Corps would be "unable to take a hard look at all reasonable alternatives" in the draft environmental review.
"Given the unique characteristics of the region, the mine proposed by Pebble Limited Partnership (PLP) must be held to an extraordinarily high standard," the letter said.
There are "too many unanswered questions" for the review to advance further, a statement from the governor's office said Saturday afternoon.
The Army Corps had previously extended the comment period from 30 days to 90 days for the controversial project, after pressure from Sen. Lisa Murkowski and others. That extended the comment period to June 29.
But that extension wasn't enough to allay concerns, Walker and Mallott said in Friday's letter.
Pebble Limited Partnership "has yet to demonstrate to us or the Alaska public that they have proposed a feasible and realistic project," the letter said.
Groups opposed to the Pebble project have previously criticized what they said was a rushed environmental review by the federal government.
In a written statement on Saturday, Pebble CEO Tom Collier criticized the governor's request.
"We expect this type of stall tactic from [environmental non-governmental organizations] opposed to any kind of development but not from the Governor of Alaska and especially when the project is on Alaska land," his statement said. "Frankly, the governor does not make a compelling case to suspend the NEPA process."
Collier also said Pebble believes it can responsibly operate the mine.
"The governor has said we have a high bar to demonstrate how we can mine and protect the salmon in the area around Pebble," his statement said. "It is this Corps Environmental Impact Statement process that will give Alaskans answers and assurance to this very issue."
Pebble is owned by Canadian company Northern Dynasty Minerals.