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

Usage license:: Get license information via the feedback formular.

Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

[46 ECONOMIC GEOLOGY beds as rhombohedra of siderite), and of iron oxide and ferro- silicates. The precipitated iron would have been mixed with oolitic grains and shell fragments and have converted them into iron carbonate, which has been in some places altered into hematite, and in others further reduced to mag- netite. The origin of the iron as a direct precipitate has been adopted by many authors, including A. F. Hallimond for the British Jurassic ironstones (G.S. Gt. Brit, Spec. Rep. Min. Res., 29, 1925, pp. 11-14) and by G. Linck (N. Fahrb. Min., Beil. Bd., xvi, 1903, p. 497), and Eckel (Iron Ores, 1014, pp. 58-69). It was adopted by Cayeux (Etude Petrog. Roches Sed., Paris, 1916) for the Minette of Lorraine, but in his later monograph (Les Minerais de Fer Oolithique de France, Fasc. II, Paris, 1922) he attributes the precipitation to bacteria, and this view has been accepted by Dr. Rastall (Geol. Mag., 1925, p. 91). There is no direct evidence for the bacteria, and the main argument for their action is that the abundant fossils in the ore indicate that the sea-water cannot have contained sufficient iron for precipitation except by organic agency. The inorganic precipitation of the iron salt need have been no more rapid nor required a greater concen- tration of iron in the sea-water than in the formation of glauconite, which takes place on sea floors rich in organisms. The ore was formed apparently on shoals or in shallow basins whence most of the clay and silt were swept away ; accumu- lations of oolite grains and shell fragments were buried in the wave-concentrated iron precipitate. The calcareous constituents were altered into hematite by the material in which they were imbedded and not bv iron solutions that infiltered from outside. BrackBanp OrEs—Some sedimentary iron ores are of indirect organic origin, such as the blackband ironstones found in the coal-fields of the S.W. of Scotland, which con- tained so much carbonaceous matter that they were smelted without additional fuel. They usually consist of a breccia of ironstone fragments in clay; they were formed on the floor of a swamp or lagoon by the alternate deposition of carbonate of iron and coaly carbonaceous mud. As the beds shrank owing to the loss of water and compression, the ironstone crusts were broken and the fragments surrounded by the mud.

Access restriction

Copyright

fullscreen: The Elements of economic geology

Monograph

Chapter

Table of contents

Download

Monograph

Chapter

This page

Image fragment

Citation links

Citation recommendation