Editing Mesabi Range (section)

==Geology==
There are four iron ranges in northern Minnesota: the [[Cuyuna_Range|Cuyuna]], the [[Vermilion_Range_(Minnesota)|Vermilion]], the Mesabi, and the [[Gunflint_Range|Gunflint]].  Most of the world's iron ore, including that contained in northern Minnesota, was formed during the middle [[Precambrian]]. During this period, erosion leveled mountains. This erosion released iron and [[silica]] into the waters of a new sea. [[Marine algae]] living in this new sea raised the level of atmospheric oxygen. This [[oxygen catastrophe]] caused the eroded iron to [[precipitate]] into the [[banded iron formation]]s found in northern Minnesota and other members of the [[Animikie Group]]. Over billions of years, geological forces left behind ore deposits of varied quality and concentrations – differences that would determine how the ore was mined from place to place. On the Mesabi Range, stretching {{convert|100|mi|km}} from Grand Rapids to Babbitt, soft ore lay close to the surface, where it could be scooped from open pit mines.<ref name="Iron Range Resources and Rehabilitation Board">{{cite web | url=http://mn.gov/irrrb/DataCenter/history/history-iron-range.jsp | title=History of the Iron Range | access-date=July 26, 2014 | url-status=dead | archive-url=https://web.archive.org/web/20140720115631/http://mn.gov/irrrb/DataCenter/history/history-iron-range.jsp | archive-date=July 20, 2014 | df=mdy-all }}</ref>

The overall structure of the range is that of a [[monocline]] dipping 5 to 15 degrees to the southeast.  Key [[fault (geology)|faults]] include the Calumet, La Rue, Morton, Biwabik, and the Siphon. The Duluth [[Gabbro]] complex to the east has caused [[metamorphic]] changes in the Biwabik [[formation (geology)|formation]]. The natural iron ores and the magnetite [[Taconite|taconites]] occur in this Precambrian Biwabik formation, which is a [[chert]]y layer {{convert|340-750|ft|m}} thick. The natural ores are located in elongated [[channels (geography)|channels]] or tabular deposits, while the magnetite taconites occur in [[stratigraphic]] zones. Natural ores have an iron content of 51 to 57 per cent while the taconites are 30 to 35 percent iron, and are [[Beneficiation|beneficiated]] to pellets contain 60 to 67 per cent. The natural ores are mainly mixtures of [[hematite]] and [[goethite]].<ref name=Ridge/>{{rp|519–520, 522, 527–528}}  The most common [[silicate]] is [[Minnesotaite]].  Also of note are the presence of [[algal]] structures in the Biwabik formation.<ref name=Gruner>{{Cite book |last=Gruner |first=John |author-link=John W. Gruner |title=The Mineralogy and Geology of the Taconites and Iron Ores of the Mesabi Range, Minnesota |publisher=Office of the Commissioner of the Iron Range Resources and Rehabilitation |year=1946 |page=8,38}}</ref>