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

I'HE FORMATION OF DEPOSITS 29 fadual; in lodes formed under such conditions the ore deposits may be similar through a vertical range of 6000 feet *S In the mines of Mysore, or of 4000 feet in the saddle- odes of Bendigo. The full succession in depth is determined 7 the correlation of lodes in different mining fields. The heavy metals are naturally often associated with deep-seated Plutonic rocks such as platinum with basic and gold with cid varieties, The great depth at which many gold lodes ere formed is indicated by their vertical uniformity, althougp there is usually a fall in the quantity of gold but ‘Mprovement in its quality as the lodes are followed down- ward, Primary tin ore is restricted to deep-seated high Joperature deposits. Some Cornish copper mines by ceper Working become tin mines, as ores of tin occur below those of copper. J Copper lodes often reach the surface, but in some cases, th 1 Cornwall and notably at Butte (cf. p. 91), the lodes at Th, Surface contained no copper but silver, lead, and zinc. i) three metals are usually intimately associated in ores ; zine © Often most abundant in the upper part of a lode, while "¢ increases below where the temperature was higher. Miva: and silver ores have a great vertical range, having near deposited in plutonic rocks at great depths, and also thro the surface, A general ascending sequence passing gan ugh tin, tungsten, copper, zinc, lead, iron, and man- i wo has been established,! but it is not universal, and is Dor Frees reversed. As the sequence depends upon the tem- for Tog of the rising solutions, variations are only natural 3 Pauses a of igneous rocks is probably slow, with many A fresh uring which the overlying temperature would fall. tem advance of the intrusive mass would cause the high at Lrature minerals to invade the zone where those formed rp temperatures had already been deposited. The to thoes: vould be expected to show variations comparable Theo In the successive layers of a crustified lode. formly Pista constituents of a lode are not as a rule uni- enosited along it, but are collected in rich bands or - : ii 12; RH. 8 E, H. Davidson, Geol. Mag. lviii, 1921, pp. 505-12; Rastall, Econ, Geol., xviii, 1923, p. a, H. Dewey, Proc. Geol. fn Hop 8925, PP. 107-35. The sequence of the veinstones is describe y H. B, Cronshaw, 77 LMM, xxx, 1921, p. 411.

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