The Elements of economic geology

Bibliographic data

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 COPPER 91 1872 to 1874. In 1881 Marcus Daly of the Anaconda Silver Mining Co. found rich copper ores below those of silver ; the Anaconda Smelter, which began operations in 1884, led to Butte becoming the most prolific copper-field in the world. The mines occur in an Eocene granite rock, a quartz-mon- zonite, which in the Miocene was invaded by masses of aplite and dykes of quartz-porphyry, and covered by rhyolitic lavas. © The monzonite is traversed by three series of lodes. The. oldest are quartz-veins which trend E. to W., and contain silver in the northern and copper beneath silver in the southern parts of the field. These lodes were torn by N.W. to S.E. clefts and faults, which are charged with copper ores. The third series trends from N.E. to S.W., cuts across the two earlier series, and Contains ore broken from them and Some primary ore deposited by solution. The famous Anaconda Lode (Fig. 31) is one of the oldest Series, and has been worked for a mile and a half long, and to 2400 feet deep; its width is in places 100 feet, and large sections aver- aged 40 feet. The upper part of the lode consisted of iron-stained Quartz with silver ores; between 200 and 400 feet deep it held oxidized copper ores; and below } 400 feet occur large secondary bodies of chalcocite (Cu,S), Which are especially rich where the lode is crossed by faults. The Anaconda Lode is traversed by compound faults, such as the Rarus Fault, which has shattered a band of monzonite 'n places 130 feet wide; the broken rock is seamed with quartz-veins and impregnated with sulphides. . The Butte ore was at one time attributed to lateral secre- ton; but there seems no reason why some of the lodes should contain silver and others copper if both sets were filled from ey Same rock. The ores have probably been deposited by Solutions which came from the ore-zone beneath the mon- Zonite, and reached the surface through fractures consequent r «©

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