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

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

ORES OF TIN AND TUNGSTEN 73 Cornwall, Malaysia, including the islands of Billiton and Banka, and adjacent areas in southern Burma, Siam, and Yunnan; also in north-western Tasmania, Bolivia, and Nigeria ; small deposits have been found in Germany, New South Wales, and Alaska. No important supplies have been found in North America. Cornisa Mines—The tin-field of greatest historic interest is Cornwall, which was worked by the Pheenicians about 1000 or 600 B.c. They cast the tin into cross-shaped ingots weighing about 150 Ib. each, that were well adapted for transport on horseback and on the floor of a boat. The stream tin is derived from lodes which are generally associated with masses of Carboniferous or Lower Permian granite and quartz-porphyry dykes, both of which were injected when the Lower Paleozoic rocks of Cornwall and Devon were folded by mountain-forming movements. The pre- dominant rock is slate, locally known as killas, in which the lodes contain ores of copper ; but when the lodes pass down Into granite the copper is replaced by tin (Fig. 9, p. 21). Dol- oath Mine, which was 3 miles long and 3000 feet deep and 1 the deepest of British metal mines, was begun for copper ; the workings entered granite at the depth of between 120 and 1500 feet, and were continued for tin. The primary tin ore occurs mainly in the vein-quartz of the lode; but it In places impregnates the granite walls thus forming the Capel.” The significant minerals associated with tin ores contain boron and fluorine; they include tourmaline, a complex Variable borosilicate ((AlB),SiO, + %), topaz, the fluo- silicate of aluminium ((AlF),Si0,), and fluor-spar (CaFy). The felspar beside the tourmaline veins has been altered to kaolinite (p- 169). The Cornish tin lodes were formed under Pneumatolytic conditions by the attack of superheated steam with boric and fluoric acids upon the felspars and their conversion into tourmaline, topaz, and kaolinite, while the quartz was corroded, and cassiterite deposited. Where lime was present the fluoric acid formed fluorite. Primary tin ores throughout the world have this pneumatolytic Origin, with local variations. Mz. Biscuorr, Tasmania—The Mt. Bischoff tin mine in northern Tasmania was discovered in 1871; mining was

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