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 FIVE MINOR METALS 115 cementing broken pieces of the silicates and country rock, or replacing those materials and especially the biotite. According to C. W. Knight, the one fact that may be stated "with certainty is that the sulphides were introduced after the norite-micropegmatite had solidified. This is proved beyond doubt ** (C. W. Knight, Rep. Ontario Nickel Comm., 1017, p. 113). The ore bodies form lenticles, pipes, or veins; they are arranged in two groups, one near the margin of the gabbro, and the other in “off-set ”’ bodies away from It. Most interest was at first paid to the marginal ore bodies, and they were explained as due to the heavier magma hav- Ing sunk to the base forming the gabbro, while the lighter floated up to form the micro-pegmatite, and to the metallic sulphides having collected at the base of the molten gabbro. The off-set bodies were regarded as dykes from the lower Part of the gabbro. This origin for the ore was suggested by D. C. Davies in 1883 and by F. D. Adams (G.S. Canada, V1, 1893, p. 13), and for the basic rock as well by T. L. Walker (0.57.G.S, liii, 1897, pp. 52, 56). This theory was authorita- tively advocated by Barlow and Coleman. The igneous origin of the ores has been adopted in recent years in a modified form by Tolman and Rogers (Stanford Univ. Publ., 1916), who regard the ores as having been formed later than the gabbro by magmatic solutions, and by Spurr who describes the ores as ““veindikes "’ (Ore Magmas, 1923, p. 567); E. Howe (Econ. Geol., ix, 1914, p. 514) and A. M. Bateman (ibid., XIX, 1024, pp. 504-20) accepted part of the sulphides as intro- duced in solution, but consider that part was injected in a molten state, The igneous theory was early rejected by Posepny (1891), Beck (1901), and by C. W. Dickson in 1903 (Tr. Amer. LM.E., xxxiv, 1903, pp. 3-67), who published evidence that the sulphides were the last constituents to solidify and Not the first. This view was expressed by the author (Presid. Address Geol. Sect. British Assoc., 1907, p. 499, and 1 1909 at the discussion on the question at the British Association in Winnipeg ; also Geol. Mag., 1908, p. 40, and in Physical Chem. Rock Formation,” Tr. Faraday Soc., xx, 1924, pp. 454-6). The igneous theory has been emphatically rejected as opposed to both the field and microscopic evi- dence by C. W. Knight (1917, Rep. Ontario Nickel Commission,

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