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 27 xlvi, 1890, p. 366), from study of the rocks in Mull, as due to solfataric action, and it is known as propylitization. The Superheated water may not be pure; it may contain iron sulphate ang gold which is deposited in the altered portion of the igneous rock, as for example, in the propylitized Porphyrites around Wood's Point and at Walhalla in Victoria. A second process pneumatolysis, is due to the action of super- heateq Water or steam associated with boric and fluoric acids, Of Sometimes phosphoric acid. In this case the change is More intense; the felspars are altered to kaolinite (china- clay), topaz; and tourmaline; and tin, brought up as vapour of stannic chloride or stannic fluoride is deposited as tin Oxide, cassiterite. This process produces tin ore and others, 3nd also micy, phosphate, and pegmatite. } A third type of deposition is by alkaline solutions which dissolve silica and metallic sulphides, and re-deposit them, "ith quartz 46 the common veinstone, as the solutions cool 2thigher levels, This process has formed most of the primary odes, ang in them the metals are usually present as sulphides. A fourth kind of deposition is by chloride solutions, which at the Nevada Hot Springs carry iron, arsenic, antimony, 30d mercury, These metals may be deposited as sulphides or oxides. “Small veins of hematite are formed around volcanic steam vents by the decomposition of iron chloride by Steam, Lobe Srrycryrg AND DeprH oF ORE FormarioN-——The Structure of Joes depends upon the spaces in which they are formed. Aq solutions rising through fissures are cooled on *PProaching the surface they deposit material as successive layers or crusts on each wall of the fissure (cf. p. 11). The Rature of the layers varies during the formation of the vein. The temperature and composition of the water probably varies Spasmodically, with renewed earth-movements or in- ‘rusions, ang these changes affect the layers of these crusti- fled lodes (Posepny. Tv. Amer. 1.M.E., xxiii, 1804, p. 207). In most lodes the metallic ores are derived from below ; the Yeinstones may be largely contributed from the rocks on ‘he sides, as water percolating through them brings with it silica, carbonate of lime, and barium oxide derived from felspar, and they are deposited as quartz, calcite, and barite (BaSQ,).

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