The canoe country of northern Minnesota is a resilient place. However, the newest threat in the north woods-a perpetual flow of acidic, toxic, metal-laden drainage from sulfide mining-is forever. In recent years, concern has increased as mining companies propose to extract copper, nickel, platinum and other precious metals from low-grade, sulfur-laden ores in the wetlands of northeastern Minnesota.

Obtaining the ore is still done the old-fashioned way-by blasting and ripping up rock in the style of strip mining. Crushed rock goes back into the holes, then gets a compacted soil covering on top and a plastic liner underneath. These barriers reduce the rain getting into the rock and the drainage coming out, but they can’t eliminate it.

If this were a taconite mine of the type so familiar to Minnesotans, the interaction of rain and tailings wouldn’t be a big concern. Iron is mined in oxide ores, which react with air and water to make rust. Sulfide ores, on the other hand, react with air and water to make sulfuric acid, which leaches toxic metals as it flows over crushed rock and drains into the surrounding environment.

A viable solution has already been demonstrated by neighboring Wisconsin. Its legislature, moved by problems with the Flambeau mine near Ladysmith, temporarily suspended permits for sulfide mining until applicants prove by example that their kind of mine can be operated and closed down without substantial environmental harm.

Minnesotans should insist that the legislature write these three principles into law:

No permits for mines that will produce drainage requiring perpetual treatment.

No permits for mines that can’t put up an adequate “damage deposit” to ensure that taxpayers won’t get stuck with the costs of problems they might leave behind.

No mining in locations that would threaten places already protected for such special qualities as wilderness, scientific, cultural, historical or recreational interest.