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

I = ECONOMIC GEOLOGY [cNEOUS ORES—TITANIFEROUS MAGNETITES Veins of hematite, either amorphous or in brilliant crystals of specular iron, are formed around volcanic vents where iron chloride vapour is decomposed in contact with steam. Igneous ore on a larger scale may be illustrated by the hill of Taberg in Sweden, which consists of a boss of basic and ultrabasic rock. The outer zone consists of olivine-hyperite {composed of olivine, the basic felspar anorthite, and rhombic pyroxene) rich in titaniferous magnetite. The hyperite passes into the rock which Wadsworth (1882) named Cum- berlandite: it contains 31 per cent. of iron and is composed of olivine and titaniferous magnetite, which are intergrown as in ordinary igneous rocks. The iron mass at Taberg was formed as a segregation of iron oxides in basic igneous rock. It was worked, until 1870, as iron ore, and a picture of it was published in 1755 by the Royal Society (Phil. Trans., xlix, p. 34, pl. ii) as a mountain of iron. Though this mass, estimated at 100 million tons, stands beside a railway 8 miles S. of Take Wetter, it is no longer worked. as it contains too much titanium. Enormous masses of gabbro with bands of titaniferous magnetite mixed with spinel exist in Northern Sweden and Lapland, as at Routivaara. These bands have been repre- sented as formed by direct segregation as at Taberg; but according to Peterson they include angular fragments of gabbro, and there is no transition between ore and rock. The bands were formed after the gabbro and not as the first stage in its consolidation; they contain 68 per cent. of iron oxide, but are valueless at present owing to their 14} per ~ent. of titanium oxide. ConTacT ORES Ironstones formed at igneous contacts are well developed in the Pacific coastlands of America from Alaska to Chile. They usually consist of masses of magnetite at the contact of limestone with rocks identified as diorite. The ores are actually replacements; they often contain from 45 to 65 per cent. of iron and are low in phosphorus, but may contain so much sulphur as to require roasting. The ore may in-

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