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

74 ECONOMIC GEOLOGY begun in 1873, but was delayed by the heavy rainfall, which ultimately helped by providing cheap water-power. The country (Fig. 26) consists of slates and quartzite of Cambrian or Ordovician age; in Devonian times they were folded and intruded by masses of granite and ring-dykes of quartz-por- phyry. The mine is situated among a group of altered and faulted dykes, a funnel-shaped mass of horizontally bedded brown sand containing in places from 10 to 15 per cent. of cassiterite. As this bedded material occurs in a hollow sur- rounded by quartz-porphyry Mt. Bischoff was regarded as a volcano, with the crater filled by the sands of the ‘ Brown Face.” Some concretions of carbonate of iron were regarded as water-worn pebbles. An adjacent white sand and clay known as the * White Face,” was rich in tin derived from aki of B.F. An w Fro, 26.—SECTION ACROSS THE Mount BiscHOFF MINE, TASMANIA. S, slate; P, quartz-porphyry ; Q, quartz-vein; W.F., the White Face; B.F.. the Brown Face. broken veins of cassiterite. Examination of the mine in 1904 led me to the conclusion (Science Progress, 1906, pp. 126, 127) that these materials were not alluvial, but were due to the settling of quartz grains left as the country was decomposed by pneumatolytic solutions. The Brown Face is a gossan due to the weathering of a mass of tin-bearing pyrites in porphyry and slate. The slate was injected by quartz-porphyry dykes and both rocks were charged with pyrites and cassiterite introduced by boric and fluoric acids, 1 The geology of the mountain was described by Kayser, dust. Assoc. Adv. Sei. iv, 1892, pp. 352-8. The topaz was recognized by von Groddeck (Z. d. g. G., xxxvi, 1884, p. 643). A later account of the mine has been given by J. G. Weston-Dunn (Econ. Geol, xvii, 1922, pp. 154-93). Pseudo-bedded tin deposits in the Malay Peninsular have also been de- scribed bv Scrivenor and Jones.

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