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Item Bulletin No. 10. The Iron-Bearing Rocks of the Mesabi Range in Minnesota(Minnesota Geological Survey, 1894) Spurr, J.EdwardStudy of the rocks on the Mesabi Iron Range, Minnesota. In this bulletin the writer has endeavored to add to the knowledge of one of the most perplexing and fascinating fields in American geology. At the same time, some apology must be offered for the incompleteness of the work. Both time and opportunity have been too scanty for a thorough study and analysis of all of the problems which have presented themselves. New modifications of old principles. and new principles, will be found to bave been active in other areas, apart from that especially studied; and, not improbably, in this area itself. Economic geology in these departments is as yet rudimentary, but it is hoped that the main points bere presented will prove sound, and can safely be made the basis for more advanced work.Item Bulletin No. 15. Preliminary Report on the Geology of East Central Minnesota Including the Cuyuna Iron-ore District(Minnesota Geological Survey, 1918) Harder, E.C.; Johnston, A.W.The geologic work in the Cuyuna iron-ore district is being done jointly by the Minnesota Geological Survey and the United States Geological Survey. Since only a few outcrops of bed rock occur in the district or in the region adjacent to it, the study has been based largely on the results of exploration and mining work. Many drill cores and records of diamond drilling from various parts of the district have been examined, and in addition the occurrence and structure of the rocks as shown in the underground and open pit workings of various mines have been studied in detail, and detailed geologic and topographic maps have been made of several of the open pit mines. In order to gain a more comprehensive idea of the major structure of the rocks of east central Minnesota. and particularly to note if possible the relation of the rocks of the Cuyuna district to such major structure, a careful study of the rock outcrops of the region lying west, south, and east of the Cuyuna district was made. This included the detailed mapping of most of the rock exposures lying nearest to the Cuyuna district in Cass, Todd, Morrison, Mille Lacs, Kanabec, Pine, Carlton, and Aitkin counties, and a more general study of the outlying exposures in these counties and also in Stearns, Benton, and Sherburne counties. North of the Cuyuna district, in the region lying between it and the Mesabi district, no rock outcrops are known and the relation between the rock formations of these two districts will have to be determined by underground exploration.Item Bulletin No. 17. The Magnetite Deposits of the Eastern Mesabi Range Minnesota(Minnesota Geological Survey, 1919) Grout, Frank F.; Broderick, T.M.The Mesabi range is a belt of iron-bearing formation about 100 miles long, located about 80 miles north of Duluth, which is situated at the west end of Lake Superior. The trend of the belt is east-north- east. The iron-bearing formation, commonly called taconite, is largely drift covered throughout the main range and has few of the topographic features of a "range." It is called a range because iron-bearing formations in other districts form ranges; and at the east end of the Mesabi district there are some rocky hills rising 200 to 400 feet above the general level. This report is a discussion of the eastern end of the range-that part which lies between the town of Mesaba and Birch Lake, a distance of about 20 miles. This portion of the range is commonly called the "east Mesabi." It is distinguished from the rest of the range by several features, besides the topography above mentioned. In this area, outcrops are numerous; most of the iron is in magnetic form; recrystallization has increased the size of grain and reduced the porosity; there has been very little leaching or enrichment; and in places the beds are more highly tilted. These several peculiarities make the east Mesabi a logical unit for separate study. The field work was done in the summer of 1917, by Frank F. Grout and T. M. Broderick. The Mesabi Syndicate (D. C. Jackling, and Hayden-Stone and Company) were at that time actively exploring certain parts of the area and Mr. W. G. Swart, in charge at the Duluth office, made the work much more effective by rendering many drill records accessible to the Survey. A large number of samples have been assayed in their laboratories.Item Bulletin No. 19. Contributions to the Geology of the Mesabi Range with Special Reference to the Magnetites of the Iron-bearing Formation West of Mesaba(Minnesota Geological Survey, 1924) Gruner, John W.This paper treats the geology of that portion of the Mesabi Range that lies west of the town of Mesaba. The Mesabi Range east of Mesaba was recently surveyed by Grout and Broderick, and the Gunflint Range by Broderick. The subjects treated include (I) the stratigraphic subdivisions and structure of the iron formation, (2) the occurrence of large magnetite bodies, possibly ore reserves for the future, (3) the origin of the formation and of the ores. The geologic setting of the district as a whole is briefly reviewed.Item Bulletin No. 21. The Geology and Magnetite Deposits of Northern St. Louis County, Minnesota(Minnesota Geological Survey, 1926) Grout, Frank F.This bulletin treats the geology and mineral deposits of a large area in northern St. Louis County, extending northward to the Canadian boundary. It lies north of the Mesabi iron range and includes most of the Vermilion iron range. It lies south of the Rainy Lake area of Canada. Because it adjoins the world's greatest iron-producing area it has been the subject of much interest to explorers and prospectors seeking new deposits of iron ore and parts of the area have been surveyed by the United States Geological Survey and the earlier Minnesota state surveys. Much of the area, however, had not been surveyed in detail. The report includes a general map of the area (Plate I) several detailed maps of small areas of economic interest and 88 township plats. These township plats are essentially outcrop maps and cover the entire area. approximately 2800 square miles.Item Bulletin No. 36. The Geology of the Cuyuna District, Minnesota(Minnesota Geological Survey, 1955) Grout, Frank F.; Wolff, J.F., Sr.This report emphasizes initially the subdivision of the Cuyuna district into a North and a South Range, the former containing iron-bearing rocks comparable with those of the Mesabi district and its Michigan and Wisconsin equivalents and the latter being the equivalent of the younger Michigan iron-formations. The manganiferous iron ores produced on the Cuyuna Range, in east- central Minnesota, have been much desired for use in iron furnaces. The geology of the ore formations and their correlations with ore formations in other districts have been subjects of considerable disagreement, largely because the iron formations on the Cuyuna lie under 50 to 300 feet of glacial deposits. J. F. Wolff, Sr. has a lifelong familiarity with the rocks of the nearby Mesabi Range, and recognizes divisions of the iron formation into four members. He has also had years of work on the Cuyuna area and recog-nizes the same four members, with analogous subdivisions inside the members, and similar sequences of other formations above and below the iron formation. Other men have not wholly agreed on the sequence because of the scarcity of exposures, and the lack of drill cores and records over much of the area. There are also geologists who question the correlation of Mesabi and Cuyuna series, because the "South Range" iron ores on the Cuyuna lie some thousands of feet up in the slates above the main iron-bearing beds of the North Range; and no such high beds of ore have been found in the slates thousands of feet above the Mesabi ore horizons. Only a few hundred to a thousand or more feet of the thickness of the slates overlying the Mesabi iron formation have been penetrated by drills in the Mesabi district, and these were not high enough to encounter the possible South Cuyuna member. This report presents the maps and sections prepared by Wolff, and his interpretation of the sequence, and a comparison with other districts. Some drilling planned by Grout to check the underground sequence of beds was generously supported by funds allotted by the Legislature to the University for research. These two studies of detail are here reported, with scattered data from outlying areas, and suggestions of correlations with the more remote iron ore districts south of Lake Superior. The possible use of the lean manganiferous iron formation of the Cuyuna Range as an emergency resource of manganese, should foreign supplies on which we normally depend be cut off during wartime, is here recommended for further research.Item Bulletin No. 38. The Stratigraphy and Structure of the Mesabi Range, Minnesota(Minnesota Geological Survey, 1954) White, David A.The later Precambrian Animikie group in northeastern Minnesota consists of three sedimentary units: the Pokegama (quartzite), Biwabik (iron-rich rock), and Virginia (argillite) formations. "Mesabi range" designates the preglacial outcrop belt, 1/4 to 3 miles wide and 120 miles long, of the Biwabik formation. Varieties of iron-rich rock ("taconite") are either granular or slaty and consist dominantly of chert, iron silicates, magnetite, and siderite. The Lower Cherty, Lower Slaty, Upper Cherty, and Upper Slaty members of the Biwabik formation, which averages 600 feet in thickness, can be further subdivided as shown on a detailed longitudinal stratigraphic section. These members are fairly uniform along most of the range, but only one cherty and one slaty member exist on the Westernmost Mesabi, where the lithic units are intertongued. The areal distribution of rock units on the Westernmost Mesabi is shown on a geologic map. The Biwabik, Pokegama, and Virginia formations are considered conformable. Mesabi rocks probably correlate with those of the Emily district 30 miles away. Chert, greenalite, minnesotaite, stilpnomelane, magnetite, some hematite, and siderite probably formed either during deposition or diagenesis. The rocks are essentially unmetamorphosed. The Pokegama and Biwabik formations were probably produced by the migration of a series of coexisting environments of deposition during an advance, a retreat, and a second advance of the Animikie sea. The deposits formed, during the retreat, in successive environments seaward from shore, were clastic material, carbonaceous-pyritic mud, chert-siderite, chert-magnetite, and iron silicate. Fine clastics of the Virginia formation, perhaps furnished by an outburst of volcanic activity, spread across the former environments of chemical sedimentation. Possible conditions of iron sedimentation were as follows: derivation of iron and silica by weathering of a low-lying land mass, perhaps under an atmosphere rich in carbon dioxide, and a seasonal climate; tectonic stability; and deposition in a shallow, quiescent epicontinental sea. The Animikie beds strike about N. 75 degrees E. and commonly dip 6-12 degrees SE. A structure contour map on the base. of the Biwabik formation shows numerous small anticlines, synclines, monoclines, and faults. Three major joint sets are present. The few rocks intrusive into the Biwabik formation include diabase sills, the Duluth gabbro, and the Aurora syenite sill. Contact metamorphism by the soda-rich Aurora sill has produced crocidolite in adjacent taconite. Minor internal folding of Animikie beds seems to be more prevalent where the underlying rocks are volcanic or sedimentary rather than granitic. The Mesabi range is covered by glacial drift which thickens southward, commonly from 20 to 200 feet, away from a ridge known as the Giants Range. Drift is as much as 500 feet thick over the Westernmost Mesabi. A map of the thickness of drift shows many drift-buried preglacial bedrock valleys that extend from notches in the Giants Range southward across the Mesabi range. Cretaceous iron-ore conglomerates, which at places overlie the Biwabik formation, occur as erosional remnants on bedrock ridges. The scattered soft iron-ore bodies in the Biwabik formation are residual concentrates of oxidized iron minerals formed by the leaching of silica from the chert and iron silicates in taconite. Conditions favoring ore concentration are thought to be as follows: accentuated fracturing at folds and faults allowing ready circulation of leaching solutions; a high iron content in taconite; reducing rather than oxidizing conditions of deposition of the original taconite; the fine size of the grains in taconite and the intimate intermixing of different minerals; a lack of metamorphism, which coarsens the grain; and the availability of large amounts of solutions. The soft ores may have been concentrated by downward-circulating ground waters.Item Bulletin No. 43. The Geology of the Metamorphosed Biwabik Iron-Formation, Eastern Mesabi District, Minnesota(Minnesota Geological Survey, 1962) Gundersen, James Novotny; Schwartz, George M.The construction of large concentrating plants and opening of pits for large-scale mining and milling of taconite during the past decade has emphasized the importance of all aspects of the geology of the Eastern Mesabi district. It had been known from the earliest explorations in the Mesabi district that the eastern twenty-mile portion was characterized by a hard, siliceous, magnetite rock which Winchell called "taconyte." It was soon learned that this rock had not yielded to natural enrichment as had many areas in the main part of the range. Later, as the large complex concentrating plants went into operation, it became evident that intensive study of certain aspects of the geology, including detailed lateral as well as vertical stratigraphic variations, together with mineralogical and petrographic characteristics, would be extremely important to the successful operation of the huge pits and concentrating plants. The only detailed publication on the Eastern Mesabi was by Grout and Broderick in 1919, a study that necessarily depended mainly on outcrops, whereas large amounts of diamond drill core and extensive vertical exposures in the pits are now available. The earlier mineralogical work was done before x-ray methods were well developed and before the complex amphibole and pyroxene groups were well understood. It was therefore obvious to the Director of the Minnesota Geological Survey that a modern detailed study was needed to supplement the excellent earlier work of Grout and Broderick. Fortunately, Dr. E. W. Davis, who had spent much of a lifetime on developing a process to concentrate taconite, was a consultant for the Reserve Mining Company. He fully understood the significance of a detailed knowledge of taconite, and as a result of his suggestions the company established an excellent postgraduate fellowship at the University of Minnesota to aid in fundamental research on the characteristics of taconite. Dr. James N. Gundersen, currently of the Department of Geology, Los Angeles State College, was appointed to the fellowship. The Minnesota Geological Survey agreed to assume field and other expenses and to direct the work. The results published in this bulletin speak for the character of the work accomplished. The bulletin is adapted from Dr. Gundersen's thesis submitted for the degree of Doctor of Philosophy. He deserves the highest praise for the energy and devotion he has given to the problem. The economically important Eastern Mesabi district of Minnesota is the type locality for the iron-formation rock type taconite, a stratified quartzose rock containing significant amounts of iron-bearing oxides, hydroxides, silicates, and, locally west of the district, carbonates. Five basic types of taconite massive, layered, laminated, shaly bedded, and shaly are delineated for detailed classification of the stratified structure and mineralogy of the Biwabik iron-formation in this district.Item Bulletin No. 6. Iron Ores of Minnesota(Minnesota Geological Survey, 1891) Winchell, N.H.; Winchell, H.V.We have attempted to give, in this bulletin, such information concerning the iron ores of Minnesota as might be wanted by the explorer, the miner, the geologist and the citizen of the state. There has been a great demand recently for such a discussion of the iron ores of the Northwest. As the discovery of new mining grounds has, year after year, extended the interest in iron mining among a greater number of individuals and corporations who naturally look to the official survey for information and guidance, so have the number and complexity of the problems involved increased. We have not essayed the settlement of all the scientific questions that have arisen through this extension of the field of observation. We have simply collected the new facts as we have learned them and have made an initial effort to group all of them, both old and new, under a classification intended to make them indicate some general principles. Our results are not wholly in accord with those of some of our predecessors-as theirs were not with theirs. We would have been glad to have taken more time for further field and laboratory work. It is evident, however, that we should never reach perfection. It was equally evident that justice to a large and expectant constituency required the preparation of a report on the iron ores, however far it might fall short of rendering justice to the subject. It is only through successive partial studies, and the publication of the incompleted results that some additions are made to our knowledge of the geology of the ores of iron. Our contribution to that fund of knowledge will go with others, both earlier and later, to enable some fortunate future geologist to prepare an exposition that will be both thorough and complete. We shall be satisfied if we may be able to add a small quantum to that end.