A state appeals court on Monday dealt a setback to environmentalists who challenged Minnesota's rules on hard-rock mining.

A state appeals court on Monday dealt a setback to environmentalists who challenged Minnesota's rules on hard-rock mining.

In a unanimous opinion, the Minnesota Court of Appeals said the rules developed by the Department of Natural Resources after public input in the early 1990s are valid. Environmentalists argued the rules are too vague to protect Minnesota's natural resources in a new age of mining on the Iron Range.

Two companies are preparing to build the first copper-nickel mines in Minnesota. Hard-rock mining carries greater environmental risk than northeastern Minnesota's iron ore and taconite mines.

In the first legal test of Minnesota's environmental rules for hard-rock mining, a three-judge appeals panel concluded that the DNR's rules do not exceed statutory authority or violate constitutional provisions.

DNR Deputy Commissioner Barb Naramore said the agency is pleased the judges affirmed the rules.

"We continue to believe that the current nonferrous rules fundamentally provide an effective framework for implementing our regulatory responsibilities and ensuring protection for public health and the environment," Naramore said in a statement.

Jon Cherry, president and chief executive of PolyMet Mining Corp., which is first in line to open a copper-nickel mine in Minnesota, said Minnesota's rules are among the strictest in the world, "and we demonstrated through the extensive environmental review and permitting process that we can meet or exceed these standards."

But conservation groups challenging the rules criticized the court's decision.

"Nonferrous mining presents new and unknown dangers, and DNR's rules are not sufficient to protect Minnesota's resources," said Kevin Reuther, legal director for the Minnesota Center for Environmental Advocacy.

The center represents five other conservation groups; all are considering an appeal to the Minnesota Supreme Court.

Friends of the Boundary Waters Wilderness, a co-petitioner, said it has already decided to ask the state Supreme Court to hear the case, the Star Tribune reported. The group's executive director, Chris Knopf, said Minnesota's metals mining rules allow new projects to move forward "under the guise of a rigorous environmental review."

PolyMet has received permits to build an open-pit copper-nickel mine near Babbitt and hopes to begin major construction next year. Twin Metals Minnesota plans to submit a formal plan next year for an underground copper-nickel mine just outside the Boundary Waters Canoe Area Wilderness.