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 LEAD, ZINC, AND SILVER ror Devon generally occur in the Devonian slate or killas, aS cross-courses through the copper lodes; they have been worked to the depth of 1800 feet; the ores were deposited after the tin and copper. The Spanish lead mines were opened by the Pheenicians and were worked by the Romans to the depth of 600 feet. The Linares field, 160 miles S. of Madrid, was from 1870 to 1910 the most prolific lead-field in the world. Its mines are of great variety; they are mainly vertical lodes trending W.SW parallel to the great Guadalquivir fault—a con- SPicuous feature in the geology of Southern Spain. The Arroyanes Lode consists of several parallel veins along faults In granite; it is 5 miles long, usually 3 feet thick, and has been worked to the depth of 1300 feet. Further N. is the Guindos line along fractures in Silurian and Ordovician rocks; the lodes are productive in quartzite, but are closed When the lode track crosses slate. The lodes were formed slowly, for one generation of veins was fractured and dis- Placed, before a second set was deposited. Further N. in the Sierra Morena is the Centenillo Mine, Which was also worked by the Romans; one of its lodes, the Mirador, is a sheet of pug, which has to be valued by Sampling as the galena is invisible; it is a Hercynian lode that was ground to powder by Alpine faulting. The leaching of the ore is indicated by the absence of zinc. ‘The age of the Linares system is probably Hercynian, as the local Triassic conglomerates contain fragments of the ore and lode-quartz. A little ore extends into the Trias by Secondary migration. The Comstock Lode in Nevada is one of the most famous And richest in mining history (Becker, U.S.G.S., Mon. 3, 1882). Alluvial gold was worked in the field for years before the discovery in 1859 of its silver-lead ores. The German Physiographer, von Richthofen, described the lode as a con- tact formation in a long series of igneous rocks, which he regarded as lavas, each characteristic of a separate age. They ar NOW regarded as variously altered andesites (U.S.G.S., ull. 17, 1885), and the lode as formed along a fault up which thse Superheated water that altered the andesite into propylite. At one time the lode was attributed to lateral secretion by Water percolating through theadjacent rocks, dissolving metals

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