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 I. Introduction

Collection:: Economics Books

THE FORMATION OF DEPOSITS 31 SWamps by the reduction of metallic salts by decomposing Tganic matter or bacteria; thus are formed fp oo and ores which are periodically dredged in Swedish a on that umerous beds of iron ore formed in swamps, suc as, Pa at the Mesa de los Pinos at Rio Tinto. The gossans or ficial hats” that cover most lodes are also due to the die formation of iron oxide. The iron pyrites in 2 ods 1s ox in by descending rain-water and is removed in soution a o “he quarts fy] of cavities or, as the miners descri ® wn MOuse-eater the insoluble veinstones are stained gona by the iron oxide formed from the pyrites. Some po! or Minera]g leached out of the gossan may be carrie Ss Along t}¢ lode (Fig. 10), and on reaching water-level may Fig, 10.—~Di1acran ILLUSTRATING SECONDARY . Exricuament, Diagram illustrating secondary enrichment ; 8, former surface of the country, which, with the top of the lode, ¢f, has been removed %Y denudation, Below the present surface, od, the rocks have been decomposed to the depth of thewater-table, WT. The upper part of the Jode has been altered to a gossan with Soncentrateq tich ore. Below the water- able is a fyrgh op secondary enrichment, below ¥hich the lode continues with primary low- Brade ore. ry & rd - ToPrecipitageq as iron sulphide with metallic gold, or oe “OPper Sulphide, such ag chalcocite, or pockets of silver- ca 2; thus haye been formed those secondary enrichments, Thich have yielded many of the richest prizes in mining 1story, . Bp, MINERAL Drposits—The complete evaporation of lakes and lagoong may give rise to thick widespread beds of salts, The largest of them are formed by the evaporation *f arms of the sea, in which the salts are precipitated in order of their insolubility— gypsum rock salt, and potassium and Magnesium chlorides, which remain in solution till the last of the bittern (P. 206) has evaporated. Beds of salt are also formeg by the evaporation of lakes; the kind of salt depends “Pon the Composition of the adjacent rocks; thus potash salts ine depositeq Where the rocks contain much potash felspar. Miner, sheets or seams may also be formed by plants and Ama] Which groy on the earth’s surface or in shallow waters

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