The Lake Vermilion-Soudan Underground Mine State Park is a

Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...

state park at the site of the Soudan Underground Mine, on the south shore of Lake Vermilion, in the Vermilion Range (Minnesota). The mine is known as Minnesota's oldest, deepest, and richest iron mine, and now hosts the Soudan Underground Laboratory. As the Soudan Iron Mine, it has been designated a U.S.

National Historic Landmark A National Historic Landmark (NHL) is a building, district, object, site, or structure that is officially recognized by the United States government for its outstanding historical significance. Only some 2,500 (~3%) of over 90,000 places listed ...

History

In the late 19th century, prospectors searching for gold in northern Minnesota discovered extremely rich veins of hematite at this site, often containing more than 65% iron. An open pit mine began operation in 1882, and moved to underground mining by 1900 for safety reasons. From 1901 until the end of active mining in 1962, the Soudan Mine was owned by the

United States Steel Corporation United States Steel Corporation, more commonly known as U.S. Steel, is an American integrated steel producer headquartered in Pittsburgh, Pennsylvania, with production operations primarily in the United States of America and in several countries ...

's Oliver Iron Mining division. By 1912 the mine was at a depth of 1,250 feet (381 m). When the mine closed, level 27 was being developed at 2,341 feet (713.5 m) below the surface and the entire underground workings consisted of more than fifty miles of drifts,

adit An adit (from Latin ''aditus'', entrance) is an entrance to an underground mine which is horizontal or nearly horizontal, by which the mine can be entered, drained of water, ventilated, and minerals extracted at the lowest convenient level. Adit ...

s, and raises. In 1965, US Steel donated the Soudan Mine to the State of Minnesota to use for educational purposes. The primary underground mining method used was known as cut and fill. This involved mining the ceiling and using Ely Greenstone and other waste rock to artificially raise the floor at the same rate as the ceiling was being mined out. As a result, the floor and ceiling were always 10–20 feet (3–6 m) apart. There was no need to move waste rock to the surface, because it was moved short distances and left in place. This technique was particularly suited to the Soudan Mine due to the strength of the hematite formations and the weakness of the encasing Greenstone. This method was not possible in the nearby mines in

Ely, Minnesota Ely ( ) is a city in Saint Louis County, Minnesota, United States. The population was 3,268 at the 2020 census. Located on the Vermilion iron range, Ely once had several iron ore mines. It is an entry point for campers and canoers into the Bo ...

, because the iron formations there were fractured and thus were not as structurally stable as those at Soudan.

State park

The park is in Breitung Township, on the shore of Lake Vermilion in northern Minnesota's Vermilion Range. It has become a popular tourist site, often visited on the way to and from Ely and the

Boundary Waters Canoe Area Wilderness The Boundary Waters Canoe Area Wilderness (BWCAW or BWCA) is a wilderness area within the Superior National Forest in the northeastern part of the US state of Minnesota under the administration of the U.S. Forest Service. A mixture of forests ...

. The state park is operated under the

Department of Natural Resources This article lists subnational environmental agencies in the United States, by state. Agencies with a variety of titles and responsibilities are included, e.g. Department of Environment, Department of Environmental Conservation, Department of E ...

. It is a

, meaning that it is also listed on the

National Register of Historic Places The National Register of Historic Places (NRHP) is the United States federal government's official list of districts, sites, buildings, structures and objects deemed worthy of preservation for their historical significance or "great artistic ...

. As of 2021, the surface buildings are open to the public, and during the summer months there are daily tours of the mine. Visitors are lowered in the antique 1924 electric mine hoist to level 27, the mine's lowest level at 2,341 feet (713.5 m) below ground. As of 2021, tours of the previously active underground physics laboratory were no longer offered. Lake Vermilion State Park, originally separate from Soudan Underground Mine State Park, began with the purchase of about 3,000 acres from U.S. Steel in 2010.Park Info
,

Minnesota Department of Natural Resources The Minnesota Department of Natural Resources, or Minnesota DNR, is the agency of the U.S. state of Minnesota charged with conserving and managing the state's natural resources. The agency maintains areas such as state parks, state forests, recr ...

. The park includes the Stuntz Bay Boathouse Historic District. In 2014, the two adjacent parks were combined into one.

Underground laboratory

Jaspilite banded iron formation, Soudan Underground State Park

In the 1980s, scientists from the

University of Minnesota The University of Minnesota, formally the University of Minnesota, Twin Cities, (UMN Twin Cities, the U of M, or Minnesota) is a public land-grant research university in the Twin Cities of Minneapolis and Saint Paul, Minnesota, United States. ...

began to develop the Soudan Mine as a site for sensitive physics experiments because of the very low rate of

cosmic rays Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our ow ...

in the deep underground site, and also because they could inexpensively use the still-operating mine hoist. The mine laboratory was originally home to the Soudan 1

proton decay In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron. The proton decay hypothesis was first formulated by Andrei Sakharov ...

experiment and its successor, Soudan 2 which operated from 1989-2001. The University and the Minnesota Department of Natural Resources later expanded the laboratory to accommodate other physics projects, such as the MINOS

neutrino A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...

detector,

dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not a ...

search experiments CDMS-II, SuperCDMS, and CoGeNT, and also a work on

electroforming Electroforming is a metal forming process in which parts are fabricated through electrodeposition on a model, known in the industry as a mandrel. Conductive (metallic) mandrels are treated to create a mechanical parting layer, or are chemically p ...

copper to create pure radiation free copper. Low-background materials screening facilities were in use and in continuing development. The mine was proposed as one possible site for a U.S. Deep Underground Science and Engineering Laboratory, but that project was instead awarded to the

Homestake Mine (South Dakota) The Homestake Mine was a deep underground gold mine (8,000 feet or 2,438 m) located in Lead, South Dakota. Until it closed in 2002 it was the largest and deepest gold mine in North America. The mine produced more than of gold during its lifetime ...

. Parts of the laboratory had been open for daily tours, and there was an annual open house with more access to the facilities and representatives of the experiments to help with the tours and answer questions. The laboratory, along with public tours, were closed circa 2016.

2011 fire

A fire broke out late on March 17, 2011, in the main shaft at the 25th level. The fire was smothered using 70,000 gallons of fire-fighting foam, filling the 27th and lowest level of the shaft (27th level) from floor to ceiling. The Underground Laboratory lost power but remained safe. The mine tours were closed for the summer of 2011, but the above ground tours and interpretive center reopened. After a major cleanup effort, underground tours resumed on May 26, 2012.

References

External links

Soudan Mine Geology
*Soudan Iron formation geology, photo galleries:
Lake Vermilion-Soudan Underground Mine State ParkNational Register of Historic Places: Mines: Soudan MineSoudan Underground LaboratoryDeep Underground Science and Engineering Laboratory
(proposed)
Tower Soudan Historical SocietyNHL summaryCleanup underway at Soudan Mine Fire
* {{authority control 1963 establishments in Minnesota Historic American Engineering Record in Minnesota Industrial buildings and structures on the National Register of Historic Places in Minnesota Iron mines in the United States Laboratories in the United States Mining museums in Minnesota Museums in St. Louis County, Minnesota National Historic Landmarks in Minnesota Protected areas established in 1963 Protected areas of St. Louis County, Minnesota State parks of Minnesota Underground laboratories Underground mines in the United States University of Minnesota Mines in Minnesota National Register of Historic Places in St. Louis County, Minnesota