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

ORES OF MANGANESE AND CHROMIUM 149 Eocene sandstones of the Southern Caucasus. Manganese ores, probably also of sedimentary origin, occur in pre- Cambrian metamorphic rocks, such as spessartite beds in the Gondite Series in India, and the extensive -deposit at Wigg, in Minas Geraes in Brazil. Manganese deposits are still being formed in the sea; nodules of pyrolusite due to the decomposition of volcanic fragments litter the ocean floor and grains and nodules are formed in shallow seas, as in Loch Fyne, by precipitation from river water. The residual ores are economically the most important. They occur where manganese disseminated through a rock has been concentrated by removal of the rest. Thus the Silurian Batesville Limestone of Arkansas contains manganese which has been left as nodules where the rock has been dis- solved (R. A. F. Penrose, Ann. Rep. G.S., Arkansas, for 1890, i, 1801, p. 177). The botryoidal manganese ore of the La- fayette district of Brazil is regarded by Miller and Singewald (Min. Dep. S. Amer., 1919, pp. 182-3) as residual from a siliceous pre-Cambrian limestone. The manganese ores of Bahia are attributed by the same authors (tbid., p. 189) to the superficial decomposition of rocks containing manganese. This process has also formed the manganese ores with the laterites of tropical countries, such as India, East Africa, and the Gold Coast. The high-grade Gold Coast ore is residual and due to the weathering of phyllites, schists, and a quartzite containing spessartite (Kitson, Gold Coast G.S,, Bull. i, 1925, pp. 12-16). Lateritic ore often contains so much iron that it is sold as manganiferous iron ore. Iron and manganese ores present a gradual passage from iron ore containing less than 5 per cent. of manganese, through manganiferous iron ores containing between 5 and 30 per cent. of manganese and over 30 per cent. of iron, and ferru- 8!10Us manganese ores containing from 25 to 50 per cent. of manganese and from 10 to 30 per cent. of iron, to manganese ore which contains over 40 per cent. of manganese and less that 10 per cent of iron. The price of manganese ore is fixed by the unit or per- centage of manganese. Usually the ore must contain 50 per cent. of manganese, but 45 per cent. ore is used ; before the War the price varied from od. to Is. for each unit in the

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