DULUTH, Minn. (AP) — Minnesota regulators will review the proposed expansion of a taconite mine after environmentalists warned of potential water pollution.

Northshore Mining wants to expand its mine near Babbitt. But the Duluth-based environmental group Save Our Sky Blue Waters says expansion could mean digging taconite out of a new area with rock that has a higher-than-usual sulfide content, which the group says could lead to acid mine drainage off the site.

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The group petitioned the Department of Natural Resources for an environmental assessment worksheet, but the DNR declared the request moot because Cliffs Natural Resources, which owns Northshore Mining, filed its own request for a review.

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The potential for acid runoff has fueled the debate over whether the state should allow copper-nickel mining in northeastern Minnesota.

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