ST. PAUL (AP) — A state appeals court has dealt a setback to environmentalists who challenged Minnesota's rules on hard-rock mining.

In a unanimous opinion, the court said on Monday the rules developed by the Department of Natural Resources are valid. Environmentalists argued the rules are too vague to protect Minnesota's natural resources.

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.

Friends of the Boundary Waters Wilderness plans to ask the Minnesota Supreme Court to hear the case.

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