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 II. Ore deposits

Collection:: Economics Books

ORES OF COPPER 89 latterly for the manufacture of sulphuric acid. The pyritic mass contained occasional intergrowths of primary bornite and chalcocite. Most of the pyrites was massive; but in some surfaces in the open-cut the structure of the replaced Schist could be seen by a sheen like a watermark. The North Mt. Lyell Mine has a richer quartz-ore containing AN average of 6 per cent. of copper in pyrites, bornite, and chalcocite ; it is also along the Mt. Lyell Fault (Fig. 30); the upper part is a pipe-lode and in places lies between schist And conglomerate : this pipe rises from a replacement de- POsit, 100 feet thick and 1500 feet long, which has replaced both rocks. In September, 1925, the ore reserves of the North Mt, Lyell Mine were a little over a million tons con- “aining 6 per cent. copper, 1-33 oz. of silver, and ‘015 oz. of cold per ton. There are four chief theories as to the origin of these pyritic masses. The first regarded them as sediments deposited at the same time as the adjacent rocks (von Roemer, 1873- 76; von Groddeck, 1879; Klockmann, 1894, 1902 ; Ber- g€at, 1906). Dr. E. D. Peters (1893) adopted this view for Mt. Lyell, regarding the ore as a lake deposit, and it is fetained by B. E. Crump in his recent work Copper (1925, P. 154). According to the second theory they are fissure- odes, due to lateral secretion (Collins, 1885), or to ascending solutiong (Gonzalo y Tarin, 1888, De Launay, 1889, and Vogt, Z. prakt, G., 1899, pp. 241-54, who regarded them as Peumatolytic after-effects of the porphyry intrusions). A third view explained the ores as contact deposits and was adopted for Mt, Lyell by Daly (Tr. I.M.M., ix, 1901, p. 86) and T. A. Allan, once manager of the Tharsis Mine, but is Inconsistent with the occurrence of some of the ore bodies apart from any igneous rock. The alternative theories "OW held are either that the ores are igneous intrusions (Broughton Edge) or, as suggested by the author in 1904, are due to hydrothermal replacement of rock which had been completely shattered by earth-movements, and saturated °y sulphate solutions. Faulting near the contact of quartz- Porphyry and shale produced fissures in the quartz-porphyry, while the shale was rendered impermeable by compression. Hence at Rio Tinto the ore occurs mainly as a replacement

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