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 II. Ore deposits

Collection:: Economics Books

ORES OF GOLD 44 which ig telluride, can always be distinguished from the pre- Cambrian, and that as the local Kainozoic earth-movements Were tensional, the shearing and crushing of the Homestake Ore show that it must be pre-Cambrian. The Alaska Treadwell Mine at Jumeau, an island off the [28st of Alaska, is famous, like the Homestake Mine, for its long success in working low-grade material. The country is Carboniferous slate interbedded with altered lavas known a5 greenstones. Both rocks are intruded by albite-diorite dykes, Which have been shattered by earth-movements and enriched with gold-bearing quartz and sulphides, including Pyrite, stibnite, galena, blende, and molybdenite. Innumer- able sma veins ramify through the shattered diorite and form large bodies of ore, of the value of about 8s. a ton. Thanks to abundant water-power, the mines were worked on a great Scale at the cost of about 55. 6d. a ton. The difficulty in Mining was the maintenance of such large excavations. Though the veins were usually a few inches thick, they were So Crowded that the rock had to be removed for a width of 200 feet, ang after the mine had been worked to the depth of over 1000 feet the timber pillars collapsed, the walls fell ‘0 and the mine was flooded by the sea. The Porcupine Goldfield is of interest as the youngest ¥ the great goldfields, having been discovered only in 1909. It is in northern Ontario (483° N., 81°W.), on the slope towards Hudson Bay. The field consists of Keewatin Pillow lavas, with well-preserved variolitic surfaces, and tuffs. This series was followed by the Timiskaming sediments in- cluding sandstones, in which the false-bedding is often well- Preserved slates ang conglomerates. Both these series have been ntruded by quartz-porphyry, which is also pre-Palzo- 20IC. The relations of the rocks are well seen N. of the Dome Mine (Fig. 13) where the Timiskaming beds are gently foldeq into two anticlines and two synclines, and have at the base 4 thick conglomerate which rests on the lavas. The rocks at the mine are folded into an anticline with a Bentle dip to the N., but a very steep dip to a compressed SYacline on the southern side. Further S. is an extensive ‘A. G. Burrows, ¢ : » Ontars, Dept, Mines, pe 15, Porouging Gold Area,” 337d Ann. Rep

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