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

Usage license:: Get license information via the feedback formular.

Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

20 ECONOMIC GEOLOGY of porphyry. Where, as at Mt. Lyell, the rocks in contact are quartzite and slate, the fissuring and replacement were in the slate. This view has been adopted for the Spanish field by J. H. Finlayson (Econ. Geol., v, 1910, pp. 357-72, and 403-37), and Collins (77. I.M.M., xXxxi, 1922, p. 103); and the Skouriotissa Mine in Cyprus has been explained by C. G. Cullis and A. B. Edge as due to the replacement of pillow-lava (Ming. Mag., xxviii, 1923, p. 342). The replacement theory is supported by (1) the absence of contact metamorphism or of the baking of the slate; (2) the molecular replacement of porphyry or slate by pyrites, and not of its displacement by a molten intrusion’; (3) the frequent gradual passage from rock to ore, as described by Collins and Finlayson, and clearly shown at Rio Tinto; (4) the occurrence of the ore bodies in zones of shearing and faulting, the association with igneous rocks being due to the intrusions having made zones of weakness that were liable to subsequent fracture and impregnation by solutions from below; (5) the presence in the ore of about 3 per cent. of free silica, which would have been converted to iron silicate if the ore had been molten ; (6) the presence of such charac- teristic hydrothermal minerals as sulphides of iron, copper, lead, and zinc, also of gold and silver, quartz and sericite, and the absence of tourmaline, apatite, primary micas, pyroxenes, and iron-silicates, which are the characteristic igneous or pneumatolytic minerals. Lenticles of similar nature are well known at Rammels- berg in the Harz, at Ducktown in Virginia, and in the lower part of the Mt. Morgan gold mine in Queensland (cf. p. 52). B. SeconDarRY ORES SECONDARY ENRICHMENTS—(a) Burr, Montana ~The solubility of copper salts has led to the segregation of the disseminated primary copper minerals of contact and sedi- mentary ores. These secondary concentrations are the mainstay of some fields, as at Butte, Montana, which long gave the United States its predominance in copper output. Mining began at Butte in 1864 for alluvial gold; silver was worked from 1865 to 1893, and copper, unsuccessfully, from LR. H. Sales, 77, Amer. LM.E., xlvi, 1911, pp. 3-109.

Access restriction

Copyright

fullscreen: The Elements of economic geology

Monograph

Chapter

Table of contents

Download

Monograph

Chapter

This page

Image fragment

Citation links

Citation recommendation