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

54 ECONOMIC GEOLOGY Bauxite is therefore chiefly developed on tropical plains and low plateaus, and it is often associated with laterite ; for the ground-water dissolves iron and deposits it at the surface when it evaporates during the dry season. This process forms a bed of laterite overlying bauxite, which passes through the stage of lithomarge into the bedrock. A second mode of bauxite formation is, as at les Baux (Fig. 47), by the action on clay of sulphuric acid set free from decomposed pyrites; the acid acts on the silicate of alumina and forms alum (a double sulphate of aluminium and potassium) and aluminium sulphate ; they are carried up into the limestone, and deposited as veins and pockets of bauxite. A third mode is by the action of alkaline solutions raterite , Bauxite ihre Redeposite auxite Shale Slate Latenite Bauxite Limestone with pockets of Bauxite Pyritic Shale Fi16. 47.~D1AGRAM OF THE VARIOUS PROCESSES OF BAUXITE FormaTiON, Vein due to ascending solution. Pockets of bauxite in limestone due to sulphuric acid rising from pyritic shale. Surface action forming sheets of bauxite beneath laterite and overlying lithomarge. In the left part of the section is a bed of redeposited sedimentary bauxite. which, rising up fault planes, act on the wall rocks, remove the silica, and leave a vein of alumina. Secondary or detrital bauxite is formed by the washing of primary bauxite into lakes, where it is deposited in beds associated with ordinary clay, and by residual nodules of bauxite being left on the removal bv solution of a bed of limestone. [n the British Isles the best-known .bauxites occur in sedimentary beds between two series of basalts in north- sastern Ireland; the bauxite is of low grade, mostly contain- ing under 52 per cent. of alumina, and both silica and titanium are often high. In Scotland, near Saltcoats, pisolitic bauxitic clay containing from 35 to 52 per cent. of alumina has been formed by the alteration of Carboniferous volcanic ash.

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