Geology groupies: Take note.

For a limited time, the Lake Vermilion-Soudan Underground Mine State Park is offering a new, more scientific walking tour geared toward explaining details about how geologists figured out where and how to extract iron ore from the area.

Guides at the park in northeastern Minnesota bring visitors a half-mile underground in an elevator-like cage. While typical tours then transfer visitors to a train for a ¾-mile ride to a large underground "room" where ore has been extracted, the new tours involve walking there.

"It gives us an opportunity to stop at locations that people on the train are never going to see," said Park Manager Jim Essig.

The new tours emphasize how mines were mapped, he said.

Visitors will be given head lamps with their hard hats, as well as hand-held flashlights, so they can see and hear about the various types of rock formations that can be found in the area.

On the new tours, which will be held weekdays at 2 p.m. throughout September for $20, guides will explain how geologists used core drilling to figure out where mining might pay off and how to reach and excavate materials safely.

"You drill a hole ... with a drill that has an empty center," Essig explained. A core of rock is then pulled out so geologists can see the layers of geological formations underground.

The Soudan area is unusual, he said, because the deposits sit vertically.

"Often, when you think of deposits, they're horizontal to the Earth" because they were formed on old seabeds, Essig said. "Ours are vertical. We have essentially columns of ore that run vertical to the Earth."

Scientists believe that's due to shifting tectonic plates, Essig said.

The Soudan mine's rocks — 2.5 to 2.7 billion years old — are among the oldest on the continent, said Harvey Thorleifson, director of the Minnesota Geological Survey.

"They've been deformed through multiple cycles of mountain building and continental collision by which the North American continent grew," he said. "In contrast, the iron ore on the Iron Range is a layer on top of those older more complex rocks."

Tour guides will also point out one of many faults in the area, which are no longer active, officials said. Visitors will walk underneath a fault line in the mine.

"We can see the fault where rocks moved relative to each other, but that motion is no longer taking place," Thorleifson said.

The new walking tours are the type typically reserved for geology classes or science groups, Essig said, but officials decided they wanted to offer something different to the general public.

The mine, which opened in the late 1800s, was once known as the Cadillac of underground mines. It closed in 1962 because of high operating costs and changing technology, according to the state Department of Natural Resources. A year later, the mine and 1,200 acres around it were donated for a state park.

While the new tour may give insight into how companies are exploring the region for the controversial possibility of copper-nickel mining, the tour is not being timed to coincide with that, Essig said, and guides won't address the issue specifically.

"I really try to keep my staff steered away from getting too deep into the controversy of copper-nickel mining," Essig said.

The new tours will involve walking on uneven surfaces in 51-degree darkness with some wet spots, so visitors are advised to dress accordingly and wear sturdy shoes.

Call the park at 218-300-7000 for more information.