Browsing by Subject "iron-formation"

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    Bulletin No. 45. Progressive Contact Metamorphism of the Biwabik Iron-fomation, Mesabi Range, Minnesota
    (Minnesota Geological Survey, 1968) French, Bevan M.
    The recent, spectacular growth of the taconite industry, and the expansion of taconite operations from the eastern to the central and western parts of the Mesabi range, emphasizes the importance of knowledge of the geology of the range. The earliest taconite plants were established in the Eastern Mesabi district, in areas in which the Biwabik Iron-formation was metamorphosed by the Duluth Gabbro Complex; most of the recent plants are in the Main and Western Mesabi districts, in areas of "unaltered" iron-formation. This report describes the changes in mineralogy and texture from "unaltered" taconite in the Main Mesabi district to highly metamorphosed taconite in the Eastern Mesabi district. It describes not only the silicate minerals, but also the opaque iron oxides, carbonate minerals, and carbonaceous material. Knowledge of the mineralogic changes is extremely important to the practical problems related to beneficiating characteristics of the magnetic taconites. The report is modified from a Ph.D. thesis submitted to the Graduate School at Johns Hopkins University by Bevan M. French. The Biwabik Iron-formation, on the Mesabi range in northern Minnesota, extends for about 120 miles in a generally east-northeast direction, from west of Grand Rapids on the Mississippi River to Birch Lake, east of Babbitt. The formation is the middle unit of the Animikie Group of Middle Precambrian age. On the eastern end of the Mesabi range, the Animikie Group has been metamorphosed by the intrusive Duluth Gabbro Complex; mineralogical changes in the sediments, particularly in the iron-formation, appear to have been caused by the gabbro. From the data of the present study, four metamorphic zones may be distinguished within the Biwabik Iron-formation by changes in mineralogy along the strike of the formation toward the gabbro contact:
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    Educational Series 3. Geologic Sketch of the Tower-Soudan State Park
    (Minnesota Geological Survey, 1966) Sims, P.K.; Morey, G.B.
    Of the many state parks in Minnesota none is more appropriate than the Tower-Soudan State Park. Situated in the wooded highlands of the Lake Vermilion area, the park is within one of the State's most scenic areas and at the same time is a symbol to Minnesota's heritage -a monument to the vast iron ore resources that have been the backbone of the strength and wealth of the nation. The central feature of the park is the Soudan Iron Mine. This, the first iron mine in the State of Minnesota, was operated nearly continuously from its discovery in 1882 until 1962, when it was closed. Through its active life, the mine yielded a high-grade iron ore that brought premium prices in the iron ore market and provided employment for thousands of miners. Although the Soudan Mine was shut down because of the high cost of its operation and the reduced demand for its ore, in a sense its demise can be attributed to technological progress. Concurrently with the building of the large modern taconite plants, such as those on the Mesabi Range 20 miles to the south, the iron and steel industry has undergone revolutionary changes. The high-grade natural ores such as those from the Soudan Mine have been largely replaced by the marble-sized pellets of the taconite plants as the preferred feed for the steel furnaces. Steel men have found that through the use of pellets, production of the furnaces is greatly increased. As operation of the furnaces is the most costly of all the operations in steel making, it is little wonder that the demand today is for pellets rather than for the natural ores used in the past.