Open-pit mining
After mining finishes, the mine area may undergo land rehabilitation. Waste dumps are contoured to flatten them out, to further stabilise them. If the ore contains sulfides it is usually covered with a layer of clay to prevent access of rain and oxygen from the air, which can oxidise the sulfides to produce sulfuric acid, a phenomenon known as acid mine drainage. This is then generally covered with soil, and vegetation is planted to help consolidate the material. Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals. There are no long term studies on the success of these covers due to the relatively short time in which large scale open pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become "acid neutral" and stop leaching to the environment. The dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with a fence, to prevent access, and it generally eventually fills up with ground water. In arid areas it may not fill due to deep groundwater levels. Instead of returning the land to its former natural state, it may also be reused, converting it into recreational parks or even residential/mixed communities.
Cleveland-Cliffs Inc.
Demand for American iron ore hit peaks during World War I, World War II, and the post-WWII consumer boom. In 1933, Edward Greene (the son-in-law of Jeptha Homer Wade II) replaced William G. Mather as the head of the company. The Mather A Mine opened in the early 1940s and the Mather B shaft in the 1950s. As the Cold War continued, reserves of mineable hematite dwindled in northern Minnesota and Cleveland-Cliffs returned some of its focus to its traditional areas of interest around Marquette, Michigan, where new deposits of magnetite were opened. The first pellet plant was built at Eagle Mills in 1954, followed by the first grate/kiln plant at the Humboldt Mine in 1960. The Republic Mine was converted from a shaft mine to an open pit and concentrator in 1956 and a two-kiln pellet plant was added in 1962. The Empire Mine opened in 1963 and was expanded in the mid- and late-1970s; the Pioneer Pellet Plant was opened in 1965 to pelletize the underground ore from the Mather B Mine in Negaunee. In 1974 the Tilden Mine opened in Ishpeming. This mine was and is the only mine in the world with the ability to produce both hematite and magnetite pellets.