Mining executive Tom Collier, who boasted in secretly taped conversations that he had leveraged his ties to Republican officials to advance a controversial project in Alaska, resigned Wednesday.

Collier, CEO of the Pebble Limited Partnership, offered his resignation a day after the group Environmental Investigation Agency (EIA) released recordings of Zoom calls in which he talked of currying favor with the White House and Alaska lawmakers to win federal approval for a massive gold and copper mine.

Collier and Ronald Thiessen, CEO of the Canadian parent company, Northern Dynasty Minerals, were recorded separately suggesting that GOP politicians would not block Pebble Mine even though some had raised concerns about its environmental impact.

Collier, who served as chief of staff to then-Interior Secretary Bruce Babbitt under President Bill Clinton, stood to receive $12.4 million in bonuses if the federal government approved a key permit for the mine and it could be upheld in court. Speaking to EIA investigators, who were posing as possible investors in the project, he touted his effort to funnel money to Republican politicians in Alaska and defeat those who sided with Democrats against the mine.

“I’ve supported all the Republican candidates in the state,” said Collier, who is registered as an independent. “I meet with the two senators, the congressman, the governor on a regular basis and they welcome me as someone they know supports the Republican Party.”

“Now, having said that, it’s entirely possible that we may have [former vice president Joe] Biden as a president, and if we do, I’m gonna brush off my Democratic credentials and start using them a little more actively than I do,” he added.

After the tapes became public Tuesday, several politicians mentioned by Collier and Thiessen in the recordings sought to distance themselves from the men. A spokesman for Alaska Gov. Mike Dunleavy (R) said, “The individuals in those videos embellished their relationships with state and federal officials at all levels.” Officials at the Army Corps of Engineers and the Environmental Protection Agency also said the comments in the tapes did not accurately reflect their agencies’ interactions with Collier and Thiessen.

In the statement, Northern Dynasty Minerals said Collier “has submitted his resignation in light of comments made about elected and regulatory officials in Alaska in private conversations covertly videotaped by an environmental activist group.”

A wide range of critics — including Alaska Natives, environmentalists and many anglers, such as the president’s eldest son, Donald Trump Jr.; the vice president’s former chief of staff, Nick Ayers; and Fox News host Tucker Carlson — have opposed the proposed mine out of concern that waste from the operation could pollute Bristol Bay. The waters, in southwest Alaska, are home to the world’s largest sockeye salmon fishery.

Within a matter of weeks, the U.S. Army Corps of Engineers could grant a permit for the mine. While the agency found in late July that the project would have “no measurable effect” on the area’s fish populations, it informed Pebble Limited Partnership last month that it had to do more to show how it would offset the more than 100 miles of streams and 2,300 acres of wetlands it would permanently destroy.

Thiessen, who was caught on tape disparaging GOP Sens. Lisa Murkowski and Dan Sullivan of Alaska, offered an apology Wednesday but did not step down from his post.

“The unethical manner in which these tapes were acquired does not excuse the comments that were made, or the crass way they were expressed,” Thiessen said. “On behalf of the company and our employees, I offer my unreserved apology to all those who were hurt or offended, and all Alaskans.”

Chris Wood, president of the conservation group Trout Unlimited, said in a phone interview that Collier’s resignation marked a blow for a project that does not deserve federal approval.

“Tom Collier is a fall guy for a project that is fundamentally flawed and has essentially been a flimflam operation from the very beginning,” Wood said. “From the beginning, it has been an exercise in obfuscation. They took more than a dozen years to get an application together, and then they lied about the scope and scale of the potential project — either to Congress or to investors. But no matter how you slice it, they lied.”

In the taped conversations, Thiessen and Collier suggested that while they were seeking a permit for a 20-year operation, it might expand and last for as long as 180 years. In Wednesday’s statement, Thiessen left open the possibility that they could apply for additional permits to extend the scope and duration of the mining operation.

“What we have said consistently, and is reinforced in the ‘Pebble tapes’ released this week, is the operator of the Pebble mine may decide at some point in the future to propose additional phases of development, but there exists no formal plan to do so today,” he said.

Pebble Limited Partnership has named former chief executive John Shively as interim CEO.