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

[02 ECONOMIC GEOLOGY from them, and depositing them in the fault fissure in itregu- larly distributed rich bodies known as Bonanzas. The deep- seated origin of the ore is however probable from the abnor- mally high temperature, which rises in the mine 1° F. for every 33 feet of descent. The lode has been worked to a depth of 3000 feet despite the difficulties due to the heat and disastrous irruptions of boiling alkaline waters. The lead lodes at Aspen in Colorado were formed along fractures in shale, and that at Ceeur d’Alene in Idaho in a band of quartzite crushed between faults. II. ReprLAcEMENT ORrEe-BODIES (a) Massive Primary OrE-BODIES—BURMA—Primary fis- sure lodes and replacement bodies of lead ore often occur together. The Bawdwin Mines in Burma work extensive lead, zinc, and silver deposits (Coggin Brown, Rec. G.S. India, xlvii, 1917), of which the outcrops were mined by the Chinese. The ores are in a dome-shaped sheet of pre-Palzozoic rhyo- litic tuffs underlain by granite. This dome of tuffs has been broken through by compound faults, which form shear- zones up to 500 feet in width. Some thin persistent lodes have been formed on the faults ; the Burman Lode is usually 2 feet in thickness, and its ores, according to Coggin Brown, yield from 15 to 37 per cent. of lead, 13 to 27 per cent. of zinc, and from 9 to 4I oz. to the ton of silver. The Shan Lode is a similar parallel lode in which the appearance of chalcopyrite on the 300 feet level indicates the probability of more copper at a greater depth. In the 500 feet shear- zone the rocks have been faulted and so altered that their volcanic origin is only recognizable in microscopic sections ; in this zone an enormous replacement deposit, the Chinaman ore-body, reaches 100 feet in width. It was formed, like the pyritic masses (p. 86), by the replacement of a com- pletely shattered block of country rock. (6) Ores write IeNEOUS Rocks—CoNTacT ORrEs—Lead ores formed by direct contact are uncommon as they are driven from positions of high temperature; but some deep-seated contact ores beside granite masses are known as at South Hill, Idaho. Ores WITH QUARTZ-PORPHYRY SHEETS—LEADVILLE— Important deposits of lead ores occur with sheets of quartz-

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