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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Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

ORES OF LEAD, ZINC, AND SILVER 107 ore particles (A. Winslow, Missouri G.S., vii, pt. 2, 1804, PP. 477-87). The process was most active in the Carboni. terous, but is still going on (Winslow, 4bid., p. 487); and C. E. Siebenthal has shown (U.S.G.S., Bull. 606, 1915, pp. 124, 125, 128-9, 131-3) that the well waters of Missouri tontain lead, zinc, and copper. The distribution of the ore was determined by the descending solutions. Where the Potosi Dolomite has been exposed by removal of the Davis Shale the ore is in compact shallow deposits; where the dolomite was covered by shale the galena is dispersed in fissures and over the surface of beds of shale. Buckley holds that instead of the lead having originally come up fault planes, it was scattered sparsely through the Pre-Palzozoic rocks of the St. Francois Mountains, which formed islands in the Cambrian Sea. Analyses record ‘002 per cent. of lead and +002 per cent. of zinc in the granite ; ‘005 per cent. of lead and -017 per cent. of zinc in the Archean rhyolite ; and -006 per cent. of lead and 015 per cent. of Znc in the diabase. Buckley calculated that ‘002 per cent. of lead in the Archean rocks would amount to 68,000 short tons per square mile for every 1400 feet in thickness. The lead would have been carried to the sea and deposited in the Paleozoic rocks; during their denudation the scattered Particles would have been dissolved and carried into the lime- Stones, and there concentrated and precipitated as the ore. The low Proportion of zinc in the ores is probably due to the greater solubility of its salts. (0) “Frars ” anp Ore-Bopies Due to DESCENDING SOLUTIONS— Some bodies of lead ores are due to replace- ent by descending solutions, as in the deeper parts of Jnclinal troughs in the Muschelkalk (Middle Trias) of Silesia, and the lead ores in the Devonian and Carboniferous Limestone of Aachen, which were apparently formed during the Hercynian movements and enlarged during the Alpine Movements. The shallow ore-bodies in the Mendip Hills are doubtless also of secondary origin; they occur as ir- regular lenticles of galena in the upper part of the Carboni- ferous Limestone, and similar zinc ores occur in the adjacent Permian Dolomitic Conglomerate. The two metals have apparently been separated as they were carried down from former lead-zinc deposits above the present surface.

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