The U.S. Bureau of Land Management on Wednesday said it has formally renewed mineral exploration leases for Twin Metals, the Chilean-owned mining company hoping to build a large underground copper-nickel mine near Ely.

The 10-year lease renewal gives Twin Metals renewed access to national forest land on which to search for minerals and prepare to develop a mining project.

The Obama administration had put those leases on hold pending an environmental review. But the Trump administration for months now has been moving to clear the path for Twin Metals, in what could be the state's second major copper mine after Polymet, the open pit mine proposed about 30 miles away near Hoyt Lakes.

A company statement said the renewed leases are the next step before Twin Metals submits a detailed project plan for its $3 billion mine and processing operations just outside the Boundary Waters Canoe Area Wilderness expected to employ some 850 people.

That formal mining proposal could be submitted to state and federal agencies in a matter of months, the company said Wednesday.

"This lease renewal is a critical step to allow us to present a proposal for our underground mine project," said Kelly Osborne, Twin Metals chief executive officer. "It's very good news for us and for the communities in Northeastern Minnesota who look forward to the hundreds of jobs and major economic development this mine will bring."

The BLM said it received more than 39,000 comments during a public input period on Twin Metals over the winter and that those comments spurred changes in the "terms and conditions of the leases, as well as to add environmentally protective stipulations'' before they were renewed.

According to a statement from the agency, if and when Twin Metals Minnesota submits a formal proposal to develop a mine, the agency would undertake a detailed environmental impact statement that would "thoroughly analyze the potential environmental impacts from the proposed mine."

To prevent the Superior National Forest land in question, generally near the Kawishiwi River along Minnesota Highway 1, from being indefinitely tied up by the leases with no action, the terms placed on the renewed leases include new diligent development requirements, whereby the lessee is obligated to submit a complete, proposed mine plan of operations, obtain all necessary permits, and meet certain project milestones for mine construction within this ten-year term, or the leases will be terminated."

The BLM said the new terms also disallow the use of strip mining, rim cutting or open pit mining methods, among other environmentally protective measures. The company has always said it would use mostly underground mining to harvest the minerals.

"Mining on public lands balances conservation strategies and policies with the need to produce minerals that add value to the lives of all Americans by providing raw materials used in the manufacture of medical aids, automobiles, smart phones and computers, and household appliances," said Joe Balasg, assistant Interior Secretary who oversees the BLM, in a statement Wednesday. "Under President Trump's leadership... this action may reduce the vulnerability to disruption of critical mineral supplies if it leads to the development and production of critical minerals in an environmentally responsible, regulatory-consistent, and economically feasible manner. Mining strategic metals in the United States is beneficial to national security, national and local economies, and job creation."

Critics, however, said the administration is rushing headlong toward a potential disaster for the region's water-rich environment and the adjacent BWCAW. There's concern over various pollution and disruption to the BWCAW, especially acidic runoff that could spoil the pristine lakes and rivers in the area.

"Today's announcement by the Bureau of Land Management is a continuation of the Trump administration's assault on the Boundary Waters Wilderness,'' said Tom Landwehr, executive director of the Campaign to Save the Boundary Waters. "The 'review' completed by the administration was wholly insufficient to determine the impact of sulfide-ore copper mining on land immediately adjacent to the Boundary Waters."

Under the Obama administration in 2016, the Forest Service concluded that copper mining posed "an inherent risk of irreparable harm to an irreplaceable Wilderness." Critics of copper mining in the area noted the Trump administration cancelled a more complete study that would have fully determined the extent of that harm.

"It is now more clear than ever that the Trump administration is steamrolling the American people and allowing a foreign mining company to write the rules when it comes to America's most popular wilderness,'' Landwehr said in a statement.

Supporters say the project can advance without environmental harm and will expand the region's economy.

"In northern Minnesota, mining is our past, our present, and our future," said U.S. Rep. Pete Stauber, who represents Northeastern Minnesota. "With 21st century technology, we can responsibly develop the resources needed for the modern world and unleash the economic engine of Northeastern Minnesota."