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 LEAD, ZINC, AND SILVER 99 N.N.E. and the other to W.N.W.; they contain quartz and carbonates, galena, and silver ore; (2) the Noble- Quartz veins are rich in silver, especially argentite (Ag,S), and trend some to N.N.E. and others to E.N.E.; (3) the Pyritic-Lead veins contain quartz, galena and blende, and some copper ores; they generally trend to N.N.E. or N.E. The younger lodes include the Barytic-Lead veins, and were formed in fissures at a lower temperature than the others; they trend W.N.W. ; their constituents, galena, blende, Pyrite, quartz, fluorite, and barite, show extreme crustifi- ‘ation, as in the often-quoted Three Princes Lode. The deep-seated origin of the Freiberg lodes is indicated by the ores of uranium and radium. The lodes were formed during the earth-movements near the end of the Paleozoic. The Occurrence of these four different groups of lodes in the same tountry rock is an argument against the formation of ores by fateral secretion, The lead and zinc mines of Clausthal in the Harz Mountains of Centra] Germany were worked even earlier than those of Freiberg. The field is in a fractured belt of Devonian and Lower Carboniferous rocks broken by Hercynian faults. Most of the lodes trend to W.N.W., and are connected by cross-lodes at regular angles, so that the field is cut by inter- secting fissures into rhomboids. The richest ore-bodies are Where fissures intersect. The lodes have often a sharp foot- wall, but may pass gradually into the country on the hanging wall, They have been worked to the depth of 3000 feet. The British lead mines 2 include various types of primary lodes. They are mostly in the Ordovician and Carboni- ferous rocks. The lodes in the Carboniferous Limestone of the Pennine Range, at intervals from Derbyshire to Northumberland, occur along steeply inclined faults, whence horizonta] « flats” pass off along the more permeable beds. The flats are replacement bodies, and if connected with the fissures their ores are rich in zinc, which in the lodes increases ‘Ndepth, A lode is often rich in limestone, and becomes thin Ad poor in shale or igneous rock, and remakes if it re-enter ! They are regarded as Miocene by von Koenen, Jahrb. preuss, geol. Landesanst,, xiv, 1804, pp. 79, 81. The Hercynian age is supported by EB, Hornung, Z.d.g.G., vii, 1903, p. 303. G.S. Gr, Bris. Spec. Rep. Min. Res., Nos. 1%, 19-23, 26-6.

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