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 30 and as the deeper ore is poorer, in 1923 only 7 lode mines were at work, The Ballarat Goldfield is another historic field. The discovery of its rich alluvial deposits in 1851 established the mining fortune of Australia and led to the great influx of Population. The field consists of Lower Palzozoic slates and quartzites, with felsite dykes derived from granite that outcrops 2 miles to the east. At Ballarat West the lodes are continuous quartz-veins, that vary in width from 2-10 feet, and expand into replacement bodies 100 feet thick. The gold occurs in irregular shoots which have been worked to the depth of 1300 feet; the gold yield decreased downwards though in places the copper, galena, and blende increased. In the goldfield of Ballarat East the quartz-veins form an irregular branching and intersecting network. Most of the quartz is barren, but along the veins are rich irregularly branching patches of gold. These “ nuggety patches” have given rise to the nuggets (a term probably based on ingot) which were found in the local gravels. Nuggets are usually rounded masses of gold, some of which are free of quartz and have g concentric structure. The Welcome Stranger Nugget, found at Moliagul in N.W. Victoria, contained £10,000 worth of gold. The belief is persistent among TURers that the nuggets grow in the gravels, as none have been found in lodes, and as the gold in nuggets is ** finer’ (Le. purer) than that in the adjacent lodes. Support to this view was given by an experiment that suggested that gold dissolved in water circulating through the deposits would be precipitated on free gold, which would grow into nuggets, as flints grow in chalk. The existence of gold in the water of alluvial deposits in British Guiana hasbeen proved by Sir J. B, Harrison. It has also been found in the rotting vegetation of many placers; but this gold has probably been carried there mechanically, just asin the * moss-mining of California the gold in the ash of moss collected from the rivers was probably filtered from the water and not precipi- tated from it. Aliuvial gold is finer than it was when in a lode, as silver, being more soluble, is removed by prolonged Lo. . ory, A Baragwanath, Mem. G.S. Victoria, xiv, 1923; J. W. Gregory ibid, iv, 1907.

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