Iron and Iron Compounds

Iron from ores of the Upper Midwest built the cities of America in the 20^th century. Still today over 95% of the iron ore mined in the US comes from either Minnesota or Upper Michigan. The main iron bearing ore found in the Upper Midwest is magnetite (Fe₃O₄). Magnetite contains different iron ions. Two of three iron ions have a 3+ charge and the other has a 2+ charge. As the name suggests, this iron ore has magnetic properties. Early explorers found magnetite in the bedrock because the magnetite would interfere with their compass readings.

Major iron ore beds are found in several locations in the Upper Midwest. In Wisconsin, the Penokee Range near Hurley and Mellen there are deposits of magnetite. In fact, Hurley is located in Iron County, a name that reflects the presence of the mineral in the area. Up until in the 1960's iron mines operated in the area. The mines closed because it became unprofitable to extract the iron from the ore. In 2011, mining companies started lobbying state politicians to modify environment regulations regarding mining for a proposed open pit mine in the Penokee Range.

Figure 1 - Iron Deposits in the Upper Midwest

Source: Unknown

Other areas that contain iron rich deposits in the upper Midwest include Northern Minnesota’s Mesabi or Iron Range. This region has produced iron ore for over 100 years and still today produces 70% of the United States iron ore. In Upper Michigan there are several regions which currently yield magnetite ore near Marquette and Iron Mountain. These deposits formed form about 1 to 2 billion years ago when the land around what is now Lake Superior started to rift (or pull apart). This rifting occurred from the Lake Superior regions southwestward through Minnesota, Iowa, and into Kansas. Large lava flows resulted from intense volcanic activity. This rifting and volcanic activity produced the iron deposits in the region.

Although the northern part of the state is associated with iron mining, iron ores were discovered first in the southern part of the state. Deposits near Mayfield (Iron Ridge), Baraboo (Baraboo Hills), and Jackson County, east of Black River Falls were discovered some as early the mid-1800's and were subsequently mined after that. After the Jackson Couny Mine shut down and the pumps stopped draining the mine, water started to fill the site. Today, the form mine is known as Lake Wazee. It is the deepest inland lake (355 feet) in Wisconsin and is hot spot for scuba divers because of its clear and deep waters.