File:Preliminary report on the geology of east central Minnesota including the Cuyuna iron-ore district (1918) (14761070471).jpg

Identifier: preliminaryrepor00hard (find matches)
Title: Preliminary report on the geology of east central Minnesota including the Cuyuna iron-ore district
Year: 1918 (1910s)
Authors: Harder, Edmund Cecil, 1882- Johnston, A. Walfred, author Geological Survey (U.S.)
Subjects: Geology Iron mines and mining
Publisher: Minneapolis, University of Minnesota
Contributing Library: Wellesley College Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

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of the Cuyuna district is associated with differentphases of the iron-bearing rock, varying in color, texture, and composi-tion according to the type of iron-bearing rock with which it is asso-ciated. Seven or eight main belts of the iron-bearing rocks run in anortheast-southwest direction through the district, and bodies ofiron ore or manganiferous iron ore occur at intervals along nearlyall of these belts. Both hard and soft ores are found, locally onebeing more abundant and elsewhere the other. They have suffered vary-ing degrees of hydration. Some consist of typical blue or reddish bluehematite, while others consist of yellow, ocherous limonite. All gradationsbetween these two extremes are found. Some of the rich hematite orelike that at the Armour No. 2 mine is finely crystalline, but most of theores and especially the more hydrated forms are amorphous. Locallyfibrous, botryoidal limonite or goethite occurs in veins and geodes, butdoes not constitute an important ore. PLATE XVIII
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B. MINOR PLICATIONS IN THE IRON-BEARING ROCKS AT THE WEST END OF THE ROWE OPEN PIT- THE CUYUNA IRON-ORE DISTRICT ii9 The manganiferous iron ore consists mainly of some form of ironoxide mixed with manganite, pyrolusite, or wad. In most of the man-ganiferous iron ore bodies, local masses of pure black manganese oreoccur but are usually present in minor quantity and are irregularly inter-mixed with manganiferous iron ore or manganiferous iron-bearing rock.The manganiferous iron ores vary in color from dark red or brown toblack, and are usually fine-grained to finely crystalline in texture. In afew places vugs of needle ore consisting either of pyrolusite or man-ganite have been encountered. The green and gray chloritic schist, commonly known as green schist,and the dark red hematitic schist do not belong to the iron-bearing rocksproper, but are closely associated with them. They generally occur as smalllenses within the iron-bearing layers, or they may bound such layers oneither side. T

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