IDAHO CITY, Idaho -- A Canadian mining company's plan to explore a massive molybdenum deposit in the Boise National Forest has raised hopes of an economic revival in southwest Idaho, but has drawn loud opposition from environmental groups who fear industrial-scale mining could threaten a critical watershed.

Over the next five years, Vancouver, British Columbia-based Mosquito Consolidated Gold Mines Ltd. plans to build several miles of new roads on 2,800 acres of the Grimes Pass backcountry north of Idaho City to drill for molybdenum, copper and other valuable minerals.

If the so-called CuMo Project is built, it would bring about 1,000 new jobs to a mountain basin that sparked a gold rush here more than a century ago, and it could become the biggest single private employer in Idaho, said John Moeller, a consultant for Mosquito at Forsgren Associates Inc. in Boise.

But while company officials emphasize that years of additional exploration is needed before a mine is proposed, conservation groups and public health advocates are already lining up to oppose the project, arguing it threatens a watershed that provides one-fifth of Boise's municipal water supply.

"Responsible mining means some places are simply too special to mine," said John Robison, public lands director for the Idaho Conservation League. "We are strongly encouraging Mosquito to pursue other resources."

Moreover, mining critics say antiquated federal mining laws have tied the hands of federal regulators, compelling the Forest Service to approve an exploration and potential mining plan regardless of whether the location is an appropriate site for a mine.

"At no point in the process can the Forest Service consider a "no action" alternative, and at no point can the public say, 'No thanks' to an open-pit operation," Robison said. "This is not a level playing field."

Earlier this month, the Forest Service wrapped up a 30-day comment period to gather public input on an environmental assessment for Mosquito's proposal to build up to 13 miles of temporary roads through the forest to access more than 100 drill sites.

Boise National Forest spokesman Dave Olson said the agency received more than 500 comments on the proposed drilling program, more than half of which were form letters generated by either conservation groups or Mosquito. Forest Service officials are scheduled to decide whether to finalize a finding of no significant impact for the project by the end of the year.

"We feel the Boise National Forest staff has done a commendable job reviewing the scope of the exploration work we have proposed and we look forward to a decision that will permit us to move ahead with additional exploration work," said Shaun Dykes, exploration manager for CuMo.

A world-class deposit

Molybdenum, a corrosion-resistant mineral with one of the highest melting points, is used principally as an alloying agent in steel, cast iron and super alloys in the manufacturing of products including nuclear reactors, jet engines, oil pipelines, furnace parts, dinnerware and steel tools.

About 56,000 metric tons of molybdenum was produced in the United States in 2008, making it one of the few mineral commodities the country exports, said Virginia Gillerman, an associate research geologist at the Idaho Geological Survey.

Much of that product came from Idaho's primary molybdenum mine at Thompson Creek near Challis, which recently announced plans to expand surface mining.

But the state's mineral production would increase sharply if CuMo is built. A June study by the state geological survey found the deposit could generate up to 125,000 tons of ore per day, making it one of the world's largest open-pit operations.

"We're not talking about a fly-by-night gold operation that will only be around for two years," said Gillerman. The mine would likely cost about $2.5 billion to $3 billion to build, but could yield approximately $70 billion in minerals, according to company estimates.

The CuMo deposit was discovered in 1963 near the headwaters of Grimes Creek in the mineral-rich Boise Basin of southwestern Idaho.

Prospectors found gold there in 1862, quickly drawing hordes of miners to the basin to pan in the rich alluvial riverbeds. By 1864, Idaho City had a population of more than 6,000 and was the largest city in the Pacific Northwest.

But the basin's boom went bust long ago.

Today, rusted ore carts, a miners' graveyard and a wooden penitentiary mark historical sites in Idaho City, whose population has dwindled to fewer than 500.

Gravel mounds and scum-lined ponds flank the scenic byway running through the town, evidence of a century of dredging for silver and gold.

"That whole valley has been turned upside-down," said Moeller, the consultant for Mosquito. "A mining operation that wants to develop a mine in the headwaters of the Boise River has a strong incentive to want to clean up some of the legacy of the past."

According to Moeller, funding for such a cleanup is unlikely to come from the state or federal government, but could potentially come from a well-financed mining firm in collaboration with conservation groups.

Such a partnership helped sustain an unlikely partnership between advocacy groups and the developers of a proposed cobalt mine in Idaho's Salmon-Challis National Forest west of Salmon (Land Letter, Aug. 26).

'Say anything but no'

While the CuMo mine would bring a major boost to Idaho's $1 billion-per-year mineral industry, its proximity to the Boise watershed has raised fears over how industrial-scale mining could affect the area's water quality.

Idaho's mining history is replete with examples of hastily built mines that over time released acid runoff and other heavy metals into the surrounding watershed. Taxpayers -- and wildlife -- continue to pay the costs associated with abandoned mining sites in north and north-central Idaho, including two Superfund sites.

While the exploration proposal would impact thousands of acres in the Grimes Creek headwaters, home to wild trout, wolverines, lynx and old-growth trees, the General Mining Law of 1872 bars the Forest Service from preventing mineral claim owners from exercising their mining rights.

"The Forest Service is going to say, 'How do you want the mine to occur?' -- not whether we want the mine to occur at all," Robison said.

The issue came to a fore at a recent Boise River conference hosted by the Idaho Environmental Forum that drew more than 100 people, including mining proponents, environmentalists, local officials, residents and Forest Service representatives to discuss the exploration proposal.

"Due to the statutory rights that mining has, there is no 'no action' alternative," Boise District Ranger Barbara Levesque said of the draft environmental assessment (EA) approving the project.

Her statement drew a puzzled response from Morty Prisament, a Boise resident and environmental planner who questioned whether a National Environmental Policy Act review was even necessary if Mosquito's right to mine was a foregone conclusion.

"Are you saying it's a non-discretionary action?" Prisament asked Levesque. "In other words, by right, the mining must be permitted?"

Levesque deferred to Moeller, who said that while the company retains the right to explore and develop its mineral claims, it is still subject to environmental laws that protect water and air quality and species.

To say the Forest Service has no authority to enforce subsequent laws such as the Clean Water Act, Endangered Species Act and other land management statutes would be overstating the rights of mineral claimants, said Joe Baird, an attorney at Baird Hanson Williams LLP who has represented mining firms in the state.

"They can say anything but no," Baird said of the Forest Service.

But federal agencies do reserve the right to require companies to include mitigation and bonding measures in mining plans to reduce threats to sensitive species and habitats, Baird said.

In theory, Baird said, the Forest Service could make such a project too expensive to pursue.

"Exploration will go forward," he said of the CuMo proposal. "But mitigation is something that is fully within the Forest Service's control and that's what is being taken a look at in the EA."

The more information, the better

To date, Mosquito has deployed a single drilling rig on a privately owned parcel near the proposed exploration site, said Moeller.

Bore holes drilled up to 3,000 feet into the earth have netted about 125,000 feet of core samples from the mining area, and by the time exploration is finished, the firm will likely have gathered more than 50 miles of core, Moeller said.

And while there are always environmental risks involved in mining, a robust exploration program can help engineers identify the types of rocks that could leach acid into groundwater and surrounding creeks, Moeller said.

Preliminary tests indicate mine tailings would be mostly acid-neutralizing, which will result in substantial cost savings and faster permitting, according to the firm.

"There's a whole new understanding of the need to know more before somebody starts mining," said Moeller, who characterized the CuMo project as part of a "new mining paradigm."

Concerns over drinking water remain paramount as the company continues the planning process, Moeller said. But existing statutes would require the company to meet quality standards exceeding drinking water in order to avoid harming aquatic species, he added.

"The macro-invertebrates and the fish and the diatoms (brown algae) and periphyton and all the other flora and fauna in a stream are much more sensitive to contaminants than people are because they are immersed in it daily," he said.

A coalition of conservation groups agreed with that assessment in comments to the Forest Service, but came to the opposite conclusion about whether the exploration proposal should move forward.

Among other things, the groups questioned the proposed project's impacts on federally threatened bull trout that may live in Grimes Creek near the project site; the rate at which new and existing roads in the project area would be reclaimed, and the number of stream crossings the project would require.

"Our organizations maintain that large-scale industrial mining in the Boise River watershed is unsuitable given the importance of this area to provide clean drinking water for downstream communities, irrigation water for agriculture, recreational opportunities, continued economic development and habitat for fish and wildlife," the Idaho Conservation League, Sierra Club, Idaho Rivers United and Golden Eagle Audubon said.