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

ORES OF IRON 139 igneous rocks of the Keweenawan. All the rocks are pre- Paleozoic, as the Keweenawan is correlated with the Scottish Torridon Sandstone. The ore is generally hematite, and contains usually between -02 and -05 per cent. of phos- phorus ; it occurs in very varied positions, which have one feature in common. The ore-bodies rest on an impermeable Fig, 42.—LakE Superior IRoN Ores. - The Mesabi type (after H. Garde, Bik. ¥ern-Kontorets Ann., 1918). The ore occurs as a widespread sheet beneath an old land surface, and overlies and is partly interbedded with iron-bearing chert, lL Quartzsite, Old land surface. Iron ore. Iron-bearing chert (taconite). bed which may be a synclinal in slate or serpentine, or it may, as at Mesabi, fade off in irregular tongues into ferrugin- ous or greenalite chert. The iron ore has been formed by replacement and deposited where solutions, which had dissolved iron from the overlying red sandstones of the Keweenawan or from basic igneous rocks, or from ferru- ginous or greenalite cherts, were stopped in their descent (Fig. 43). The bulk of the iron probably came from an oolitic Fra. 43.—Lake Superior ORES. The Lake Superior ores formed by replace- ment bounded below by an impermeable surface. From Cuyuna, Minnesota, (after Van Barneveld). The rocks con- sist of cherty iron carbonates, amphi- bolite, slate, diabase dyke, DD. The ore is in solid black. ) chert series in which the ore was a chemical precipitate as in the Mesozoic and Clinton bedded ores. The Gellivaara and Adirondacks—The famous ore-field of Gellivaara in Swedish Lapland contains massive bodies of magnetite in biotite-gneiss. - The Ifoot-wall of the chief body at Gellivaara that was being worked at my visit was

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