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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Document type:: Monograph

Structure type:: Chapter

Title:: Part I. Introduction

Collection:: Economics Books

10 ECONOMIC GEOLOGY patches. The most characteristic concentrations are ‘ ore shoots,” which are often irregularly funnel-shaped or cylin- drical bodies of ore. Such shoots may be due to concentrated precipitation of the metallic constituents of a solution by reactions with the wall rock of the lode, or with a solution that enters the lode fissure from some side channel. A shoot may be formed where a metalliferous spring enters a sheet of water in a fissure. Some masses of iron ore have been formed as igneous segregations, such as that at Taberg in Sweden. Iron ore bodies of greater commercial value have been formed as concentrations by the descent of surface waters, which dissolve iron from some iron-bearing rock and carries it down until it js stopped by impermeable material and is precipitated in mass. Thus have been formed the rich masses of kidney iron ore of the north-west of England {cf. p. 135) and the colossal bodies of iron ore beside Lake Superior. Some funnel-shaped bodies of lead ores, which are often stalactitic, are due to the concentration of scattered particles of lead by descending solutions. EFFLORESCENT MinerALs—Exceptionally rich mineral concentrations are formed near the surface as ascending water there undergoes rapid chemical and physical changes, The water may evaporate and deposit its mineral matter as a bed of tufa or sinter around a spring, or as a widespread efflorescent layer or crust. In a dry climate very soluble salts may be thus deposited, such as the nitrate of soda of Chile and Peru; in a climate with alternate wet and dry seasons limestone and chert may be deposited by the water which has soaked into the ground during the rains, being sucked to the surface and evaporated during the dry weather. Efflorescent limestones may form a nodular sheet, such as that which mantles the undulating surface of the Mallee tountry in north-western Victoria, the Kankar of India, and the caliche of Mexico. The Mallee limestone is inter- bedded with chert and ironstone where the descending rain- water dissolved silica or iron. Amongst the important minerals formed by the alternate descent of rain-water during the wet season, and evaporation from the surface during the dry season are bauxite, the chief ore of aluminium (p. 153) and laterite. Superficial ores are formed on the floors of lakes and in

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