Iron Ore

Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in colour from dark grey, bright yellow, deep purple, to rusty red. The iron itself is usually found in the form of magnetite (Fe3O4), hematite (Fe2O3), goethite, limonite or siderite. Hematite is also known as “natural ore”. The name refers to the early years of mining, when certain hematite ores contained 66% iron and could be fed directly into blast furnaces. Iron ore is the raw material used to make pig iron, which is one of the main raw materials to make steel. 98% of the mined iron ore is used to make steel.
Minnesota’s iron ore was actually discovered while prospectors were searching for gold. Since the object of their search was gold, the iron was ignored. It turned out the iron would become much more valuable to northern Minnesota than the small amount of gold found.

Iron ore was discovered on the three iron ranges at different times. The first ore shipped from the Vermilion Range was in 1884, the Mesabi Range in 1892, and the Cuyuna Range in 1911.

Coal

Coal is mined using giant machines to remove the coal from the ground. There are two basic methods to remove coal: surface mining and underground mining. Surface mining is used when the coal is typically less than 200 feet below the surface. Giant machines are used to remove the top layers of soil and rock to expose the coal. The coal is excavated, and after the mining is complete, the soil and rock are returned to fill the mine. The area is then revegetated (glossary term) and can be used for other purposes, such as cropland, wildlife habitat, recreation, commercial, or industrial use. This method is used most frequently in the United States because much of the coal resource base is near the surface and it is less expensive than underground mining.

Underground mining is used when the coal is buried several hundred feet below the surface or more. Some mines can extend to depths of more than 1,000 feet. Miners use heavy machinery to cut out the coal and rely on conveyor systems to transport the coal to the surface. Some underground mines require elevator shafts to move miners and coal to and from the surface.

Strip mining is accomplished by two techniques, area stripping and contour stripping. Where coalbeds are relatively flat and near the surface, as in much of the Western United States, area stripping is the dominant technique. In area strip mining, overlying material is removed from a seam of coal in long, narrow bands, or strips, followed by removal of the exposed coal. With the exception of the first cut, overburden from each cut is discarded in the previous cut from which the coal has been removed. These parallel cuts continue across the coal seam until the thickness of the overburden becomes too great to be removed economically or until the end of the coal seam or property is reached. Both single and multiple seams, near the surface, can be mined in this manner.

Overburden removal is usually accomplished in the United States with draglines and shovels. Much of the overburden contains layers of shale, limestone, or sandstone and must be blasted before it can be removed. After the overburden is removed, coal is usually drilled and blasted, then loaded into coal haulers with either a shovel or front-end loader.