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

20 ECONOMIC GEOLOGY Magmatic water from the ore-zone rises through the overlying plutonic rocks and carries metals upward along fractures and fissures. Ore formation is naturally often associated with igneous intrusions, because they rise most readily in fractured areas, and as the intrusion of an igneous mass would rupture the adjacent crust. The predominance of lodes in the older rocks is natural, because these rocks are nearest the ore-zone and have had the longest time for impregnation from it. Ores occur in later igneous rocks where the ascent of materials has been rendered possible by increased gas pressure Depth in Miles ) 2 0) 0) Bm ~ 687° Critical Temperature 2600° Dissociation Temperature = 50 F16. 8.—DIAGRAMMATIC SECTION OF ThE EARTH'S Crusr. Diagrammatic section of the earth’s crust showing a rise of the barysphere (dotted) above its normal level of about 40 miles to less than 30 miles, whereby it carries the ore-zone (xxx) above the 20ne of the dissocia. tion of water at the depth of 30 to 40 miles. The rising water-vapour converges into the main ascending currents and condenses to water on reaching the critical temperature of water at the depth of from 6-12 miles. due to heat and the existence of channels due to fractures and fissures. From the ore-zone there is an ascending sequence, successive metals being deposited as they come under suitable con- ditions of pressure and temperature. Gold ores are most abundant in the pre-Palzozoic rocks. Tin and tungsten generally occur in and near the plutonic rocks which are exposed in the roots of the upper Pal@ozoic or Altaid moun- tain system; they are not found in any quantity in con- nection with the Alpine-Himalayan movements. Copper

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