Minnesota regulators must reconsider old and largely untested rules for hard rock mining to see if they are adequate to protect the Boundary Waters Canoe Area Wilderness, a judge says.

Specifically, the state Department of Natural Resources (DNR) must determine whether sulfide-ore copper mining is so polluting that it should be banned in the Rainy River headwaters, an area in northern Minnesota that drains into the Boundary Waters.

Ramsey County District Court Judge Laura Nelson on Wednesday remanded the mining rules matter to the DNR over the objections of Twin Metals. Twin Metals is owned by Chilean mining giant Antofogasta, which is trying to develop a copper-nickel mine just outside the Boundary Waters.

"The fact that they [the DNR] agreed to this shows some willingness to reconsider," said Katie Crosby Lehmann, a lawyer for Northeastern Minnesotans for Wilderness. "Science has changed since the rules were written almost 30 years ago."

The Ely-based nonprofit sued the DNR over the nonferrous mining rules last year under Section 10 of the Minnesota Environmental Rights Act. That section gives anyone a right to challenge a state law they think fails to protect a natural resource from pollution. This is the first time anyone has exercised that right, Lehmann said.

The remand follows a settlement Monday in which the U.S. Bureau of Land Management agreed to revisit its decision to extend 13 prospecting permits for Twin Metals, permits that would expand the copper-mine plan. As part of that, the bureau will conduct the environmental assessment required by federal law.

The settlement, approved Monday by a federal judge in Washington, D.C., came after a coalition of environmental groups, including the Center for Biological Diversity and the Campaign to Save the Boundary Waters, sued the BLM for violating federal law when it extended the prospecting permits without assessing environmental impacts.

Jennifer Bjorhus • 612-673-4683