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

[O00 ECONOMIC GEOLOGY limestone. The ores in the field of Alston Moor are mainly in a zone about 600 feet thick; in Derbyshire they are worked to the depth of 1100 feet, and many of the upper veins are rich in fluorite. The primary lodes in Flintshire are along fault fissures in Carboniferous Limestone, and trend from N.W. to S.E.; they contain galena, blende, and about 15 oz. of silver to the ton. Some cross-courses contain secondary ore which contains no zinc, and is poor in silver. In the Isle of Man the Laxey Lode has been worked through the Carboniferous Limestone into slate and granite, to the depth of 1900 feet. The lead lodes in the Ordovician sandstones, grits, and graywackes are often more regular than those in limestone, as the fractures are simple and straight. The lodes of Lead- hills and Wanlockhead in Scotland (J. Mitchell, Ming. Mag., xxi, 1919, pp. 10-20) are confined to the Lowther Grits, as the fissures in the slates were closed by the collapse of the walls. The lodes are usually about 2 feet thick, but widen up to 18 feet. The ore is usually in shoots. The first-formed minerals in the primary ore are quartz, dolomite, and calcite ; next pyrites and chalcopyrite; subsequently galena and blende. A second mineralization produced much larger crystals. Finally surface waters formed the rare minerals for which the gossan and oxidized ore of these mines are famous. The age of the ore formation has been attributed to the Caledonian; but the parallelism of the lodes to the faults in the Hamilton and Sanquhar coalfields and the partial mineralization of some Lower Devonian felsite dykes indicate their Permian age. The Shropshire lead-field at Shelve and Snailbeach was worked by the Romans, and has been mined to the depth of 1650 feet; the lodes are in the sandstones of an anticline, and are unproductive in the shales. Barite is the chief veinstone in the upper part; the proportion of zinc to galena increases with depth. The lodes in Central Wales lie along faults in Ordovician slates and mudstones; they contain much brecciated rock and the walls are strongly slicken-sided. The lodes extend for miles trending E.N.E. with ore-shoots at intervals. Much of the ore is found along secondary fractures, some of which are horizontal flats. The lead ores in Cornwall and

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