The Elements of economic geology

Bibliographic data

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 I. Introduction

Collection:: Economics Books

THE FORMATION OF DEPOSITS 33 ‘posited ; and which of them are primary and which are iecondary, It also shows which of the minerals In an ore Vere deposited by the agent that introduced the metals, and whether the minerals are still as they were originally deposited or whether they have been redeposited by de- ending surface wagers, It also reveals in replacement ores, % the shadow of the original structure, what material the ore has replaced ; it may show, for example, that a phosphate of lime wag originally a trachyte (as at Clipperton Island) ; that a gold-bearing quartzite was originally a dolomite or a fossiliferoysg limestone ; that an ironstone has been formed by the alteration of a shelly limestone into a carbonate or oxide of iron, Many theories have proved untenable when microscopic study has shown that supposed sedimentary rocks were igneous, or that intrusive rocks were volcanic ash, and that a mineral that was thought to have been the frst constituent tq solidify in a molten magma was intro- duced long after the solidification of the rock. CHIEF Minera Deposits puz 10 SEGREGATION—Most of “he minerals of special use tq man consist of material that was widely scattered through the primeval matter of the ®arth. They have been concentrated by that beneficent Process of Segregation which draws like to like. The process ® sometimes dye to chemical affinity, and sometimes to the Toperties which Cause mechanical concentration by wind And water, The Primary mineral deposits are mainly due to ascending currents rising from the vast store of metals 'n the interior of the earth. Some rich secondary deposits re made upon or near the surface by the solution of scattered a descending rain-water, and its deposition in “oncentrated form. Some superficial deposits are due to the mechanical Separation of ore from dross by Nature's use of the methods adopted in ore-concentrating machinery. Other beds of mineral matter, such ag coal and limestone, are due to the gregarious habits of plants and animals ; they live in forests or jungles or in colonies, and leave their “Ssues, shells op skeletons in continuous sheets which are subsequently Compressed and cemented. Varied processes of concentration have formed all thoge mineral segregations >Y the use of which man has gained his control over nature, and developeq modern civilization,

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