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 GOLD 57 height at different lines of bores indicates the river gradient, from which can be inferred the amount of meander between the two lines, and where the current would have been suffi- ciently powerful to concentrate the gold. - The samples from the drill holes indicate the relative amount of gold, but not the actual yield, for they are a concentrate, much of the lighter material having been washed away during the drilling. } A deep lead cannot be worked until it has been drained. A shaft is sunk to a suitable depth below that of the lead. A drive known as the ** reef drive,” as it is in the bedrock, 1s made under the lead, which is drained by bores put into it from this drive. Some mines had to pump several million gallons of water a day for years before it was possible to enter the lead. Lead mining under favourable conditions has been very profitable; the Madame Berry Mine, e.g. paid £1,300,000 in dividends on a capital of £15,000. When part of the lead is drained it is entered by the upper or wash drive,” from which the gravel or * wash ” is dropped through shoots to the reef drive, whence it is raised to the surface. The gold is washed out of the sand; none is found in the pebbles, The costs of working are estimated per square fathom, as most of the gold is in the lower part of the gravel, and the yield depends more on area than on thickness. The probable value of a lead depends on constant re- enrichment, as the gold usually travels but a short distance. A lead which crosses rocks intruded by granodiorite and likely to contain numerous gold-quartz veins, may be ex- pected to be richer than areas without igneous rocks. The distribution of the leads depended on the nature of the plateay basalts, and the mining has shown that they were formed by the confluence of lavas from many vents and not by eruption from fissures. _The Kanowa Lead in Western Australia, as its gold has been dissolved and redeposited, raised the question whether the mines had to comply with the regulations for alluvial or lode mining. Though the evidence proves that the gold as it now occurs, was deposited from solution, it has been wisely treated as alluvial. The problem bears on the nature of the gold of the Rand (cf. p. 61). RAND BaANkET Marine placer deposits occur on the coasts

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