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 I. Introduction

Collection:: Economics Books

THE FORMATION OF DEPOSITS 25 sinter, and chert are magmatic ; the term covers both gps and aqueous products, and is too comprehensive to be © practical value. A third use of the term magmatic is that of J. E. Spurr who in his * Ore Magmas’ (1923, restated in 77. Amer. LM.E. Ixxiv, 1927, pp. 99-115) adopts an intermediate post- tion; he excludes ores due to magmatic waters, and regards a large variety of lodes as due to the intrusion of highly concentrated and dense magmatic residues” allied to peg- matites., He states that ‘‘ a magma is a solution ’ (1923, P- 73). His ore-magmas include magmatic waters in which the material dissolved is highly concentrated. The material tuptures the rocks and as ‘* veindikes' fills the fissures it has made. These magmas behave like cement which, when stay into a foundation, forces its way into rocks in thin sheets like a dyke. This view i gold-quartz veins was adopted by T. Belt (Mineral Veins, 1861) for those of Victoria; and being interested in his memoir 1 examined many Victorian quartz: lodes in reference to their origin as igneous intrusions ; but the lodes seemed due to solutions, which, though hot, were cooler than even pegmatites, and which rose through fissures and in places replaced the walls; this replacement is shown by the passage from pure quartz to the country through a silicified zone, and by the included masses of rock being in their original place and having been enclosed by the growth of quartz around them. The walls have been altered by impregnation by solution and not baked by 2 molten intrusion; and the tongues in the adjacent rocks present the aspect of filled cracks and aqueous replacements. Spurr compares his “ veindikes” to pegmatites, which occur galore in countries such as Scotland and Kenya Colony, where ore deposits are deplorably scanty; pegmatites are associated with such useful mineral as mica, apatite, kaolinite, and the gems and sparse metallic minerals as of Hn occur in them; but pegmatite seldom contains workable metallic ore, The distinction between molten rock material, magmatic waters, and Spurr’s Ore Magmas is not easy to define, because there is no absolute division between molten and dissolved materials. For practical purposes, however, a solution 1s

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