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

130 ECONOMIC GEOLOGY cent. of iron, and ferrous, FeO, with 77:7 per cent.), each forming a series of compounds. Iron is readily soluble; it is present in most spring waters, and gives many their medicinal qualities. Itispresent in them as bicarbonate, as sulphate, and as double salts of ammonia and humic acid, formed, in the absence of air, by organic acids. Iron is readily precipitated from these solutions; from the bicarbonates on exposure to air, and from the sul- phates by organic matter, when the iron is deposited as pyrite in a dust too minute for recognition under the micro- scope ; it causes the dark blue colour of clay, which is altered to brown or yellow on conversion of the pyrite into iron oxide. The humates may be decomposed by oxidation, iron-secreting bacteria, or decomposing organic matter. Ore Suppries—Iron near the earth's surface is subject to alternate solution and redeposition in a concentrated form as iron ore. Ninety per cent. of the available iron ores have been thus formed. According to the estimates by Eckel {Iron Ores, 1914, p. 41) of the world’s iron ores 63 per cent. are sedimentary; 5 per cent. are normal replacements; 10-7 per cent. are contact ores or of doubtful origin; 133 per cent. are residual; and 7-9 per cent. are secondary con- centrations. Of the sedimentary ores, 40 per cent. are Jurassic in age, 15 per cent. Carboniferous, and 16 per cent. Ordovician. Of the total iron ores of Europe (Roesler, U.5.G.S., Bull. 706, 1921, p. 18) 35°2 per cent. occur in France owing to the enormous quantity of Lower Jurassic ore in Lorraine ; the British Isles have 18-2 per cent., Sweden 12-5 per cent., Germany III per cent., and Spain § per cent. The quantity of known iron ore is colossal. According to Roesler’s estimate the sedimentary ores known in 1921 amounted to over 8,400,000,000 metric tons, of which France holds nearly half. The supplies already known will last for 1000 years at the output of 1913. There are still larger quantities of material which contain iron but is not re- garded as ore. Whether an iron-bearing material can be ased profitably depends upon its composition, the cost of fuel, and accessibility to markets. An igneous rock with 35 per cent. of iron may be of no commercial value, while material with half as much may be worth mining as an iron-bearing flux. Some iron ores are now useless owing

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