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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Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

12 ECONOMIC GEOLOGY gold, but tellurides and blende. The average gold contains about I per cent. of silver, and becomes finer with increasing depth owing to the greater solubility of silver, The Champion Lode is in places 40 feet thick but it narrows to a mere lode- track. It was worked in prehistoric times and has been mined to the depth of 6000 feet. The lode-quartz, when released from pressure in the mine workings, is apt to fly to pieces in fata] explosions or * rock-blasts.” Vorcanic FiELDs—Rocky Mountains anD New ZEALAND —In many volcanic areas gold-quartz veins occur along intersecting fractures due to earth-movements or to the shrinkage of the rocks. Typical examples occur in the Rocky Mountains of Colorado and the adjacent States, These mountains consist of Palzozoic, Jurassic, and Cretaceous rocks, in places covered by Eocene conglomerates. After deposition of the conglomerate volcanic eruptions discharged a volcanic breccia and vast lava flows of andesite and rhyolite, The volcanic areas were afterwards faulted and gold lodes deposited along the faults. Thus the Smuggler Vein of the Telluride Goldfield is a fissure vein which runs for many miles N. and S. and has been worked to the depth of 3500 feet; it consists mainly of quartz, with rhodocrojsite (MnCO0,), calcite, siderite, and barite. It is cut across by the Revenue Vein, a lead-silver lode, and both of them are cut by the Pandora Vein of gold-quartz along a fault that throws the southern part of the Smuggler Vein to the E. In the Camp Bird Field in Ouray County, Colorado, the volcanic breccia ig traversed by a five-mile-long fissure vein,1 which intersects numerous earlier lead-zinc lodes and contains shoots of pyritic gold-quartz ore that extend along the lode for over 1000 feet, and are about 500 feet high ; they appear to have been fed by pipes of ore that go 800 feet deeper. The gold ore encloses fragments of the older lead-zinc ores; it shows no crustification, and appears to have formed by a single filling of the fissure, The lodes in the volcanic areas are not themselves vol- canic, and are more recent than the eruptions. The ores were deposited by solutions rising along fractures due to the For latest account of the lode, cf, Spurr, who calls it a compound veindike, Zeon, Geol, xx, 1925, pp. 114-52.

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