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

A492 ECONOMIC GEOLOGY 1000 oz. to the ton. The concentration of this gold is prob- ably due to each seam of Banket having been formed during a long pause in deposition, so that the layer was subjected to prolonged wave action, during which the gold was collected in the hollows between the pebbles, as in the riffle of an ore- concentrating plant.! The beds of ‘‘false banket,” or “ bastard reef,” in which the pebbles are angular, accumulated quickly, and gave no opportunity for such concentration of the gold ; and they may contain only a few grains or I or 2 dwt. per ton of gold, although in all respects, other than those due to long-continued beach action, they are identical with a rich underlying leader. The concentration of gold by water action is also shown by the so-called “shoots” inthe East Rand. They consist of gravelly stream beds across the beaches; and the flow of water down these pebbly channels concentrated gold in them. The minerals found in the Banket include diamonds, platinum, tourmaline, corundum, osmiridium, and zircon, and they are characteristic of alluvial deposits. The typical hydrothermal minerals are absent. If the ore had been formed by infiltration, it is improbable that the gold solutions would not have occasionally passed into the bastard reef, which in many places must have been at least as permeable as the Main Reef Leader. The Banket has been worked more extensively than any other gold ore, and the sections have been most carefully sampled and studied ; yet no case has been described of any infiltration channels, like the verticals of Dakota, by which the gold could have been introduced. That the gold was introduced during the deposition of the conglomerate, and not during the injection of the dykes at the long subsequent Ventersdorp period, has been shown where contemporaneous erosion has left a patch of the gold- bearing Banket surrounded by quartzite; the first case was recorded from the May Consolidated Mine (Gregory, Tr. I.M.M., xvii, 1908, p. 21; confirmed by E. T. Mellor, F. Chem. Met. Soc. S. Afr., 1916, xvi, p. 158). The placer theory of the Rand was adopted amongst *E. T. Mellor however regards the Banket as formed by sudden floods, a view rejected by R. B. Young, Journ, Chem. Met. Soc. S. Afr., 1916, xvi, p. 230; and by du Toit, Geol, S. Africa, 1926, p. 66.

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