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 IRON 14] pre-Palzozoic. The mines occur to the N.E. of Lake Wener and W.N.W. of Stockholm, near the towns of Norberg, Persberg, Granjesberg, Striberg, and Dannemorra. The field consists of gneiss and schists, with halleflinta, much of which was an acid lava, a variety of gneiss known as leptite, crystalline limestones and dolomites, and ‘ Skarn,” which is a schist containing hornblende, augite, chlorite, garnet, epidote, calcite, and quartz. The ore is mainly magnetite with about 60 per cent. of iron and I per cent. of phosphorus, and it is practically free from titanium. The ores occur in sheets or thin lenticles, some of which are more than a 1000 yards long and 100 yards thick. The ores are often banded, and extend parallel to the country. Similar ores occur in Norway and owing to their association with igneous rocks, F16. 45.—THE MAGNETITE OF THE ADIRON- DACKS. The magnetite of the Adirondacks showing the magnetite (black) replacing the fel. spar, P, and quartz, Q, in granite at Cook Hill (after Alling, 1925). were claimed by Kjerulf and Dahl (1861) as eruptive in origin; but as the ore sometimes occurs as a cement between the rock fragments it is younger than the enclosing rocks, and the simple igneous theory is invalid. Origin by magmatic differentiation (Johansson) is equally impossible for ores in dolomite, . The usual explanation of these ores, based on their apparent conformity to the country and banded structure, is that they were sedimentary like those of the Mesozoic. H. Sjogren attributed the ores to metasomatic action by descending solutions ; but as he referred the process to too late a stage this view was generally rejected. In recent years the ores have been often regarded as contact products owing to the associated minerals, which are however equally characteristic of regional metamorphism ; and the ores are not always associated with igneous rocks and some of them are isolated in limestone.

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