The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

138 ECONOMIC GEOLOGY is a common primary vein mineral and often replaces sand- stone, as shown by the * whinny boles * or nodules of siderite in Glasgow quarries. Where however siderite occurs as a hydrothermal product it is usually associated with copper, lead, and zinc. Thus in the hydrothermal siderite lodes of Czecho-Slovakia and the Siegerland (cf. p. 134) quartz is the chief veinstone, pyrite and chalcopyrite are frequent, while blende, galena, tetrahedrite, bornite, various nickel and cobalt minerals, and stibnite also occur. A little copper has been found at Bilbao, but the amount is small and the ordinary hydrothermal minerals are absent. The nearest igneous rocks are too remote to have taken part in the ore for- mation, especially as there is no ore beside them. The Bilbao ores are therefore probably due to the perco- lation of descending waters along the fractures beside the down-faulted crown of the Bilbao anticline. Solutions passed through the shattered rocks, leached out their iron, and en- tering the limestone altered it to carbonate of iron and pro- duced siliceous ores where the solutions entered sandstones and sandy shales. Subsequently the upper part of the ore was altered into hzmatite. Lake Superior—The iron fields that have proved of the highest industrial importance are beside Lake Superior, and have supplied most of the ore to the iron works of Penn- sylvania.! They still hold 2500 million tons of ore. The chief fields on the southern side of Lake Superior are those of Marquette, Menominee, and Gogebic; on the north- western side are the Mesabi and Vermilion fields whence lower-grade iron ores, on the same geological horizon, extend eastward into Canada. The ore is mostly hematite associated with jaspers and chert; some of the ore was a ferruginous carbonate with oolitic grains and greenalite, which from its analogy with glauconite, was doubtless of marine origin (Fig. 42). The Iron Formation belongs to the Keewatin Series, of which the typical rock is a basic pillow-lava. This series rests on gneisses and coarse schists with intrusive granites, and is covered unconformably by sedimentary rocks and conglomerates. The whole area of the iron fields was probably buried under the red sandstones and associated L U.8.G.S., Monographs Nos, 19, 28, 36, 43, 45, 46, 52, 1802-1911.

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