Processes of Formation of Iron—Manganese Oxyhydroxides in the Atlantis-II and Thetis Deeps of the Red Sea

  1. John Parnell,
  2. Ye Lianjun and
  3. Chen Changming
  1. G. Yu. Butuzova1,
  2. V. A. Drits1,
  3. A. A. Morozov2 and
  4. A. I. Gorschkov3

Published Online: 3 APR 2009

DOI: 10.1002/9781444303872.ch6

Sediment-Hosted Mineral Deposits: Proceedings of a Symposium Held in Beijing, People's Republic of China, 30 July-4 August 1988

Sediment-Hosted Mineral Deposits: Proceedings of a Symposium Held in Beijing, People's Republic of China, 30 July-4 August 1988

How to Cite

Butuzova, G. Yu., Drits, V. A., Morozov, A. A. and Gorschkov, A. I. (1990) Processes of Formation of Iron—Manganese Oxyhydroxides in the Atlantis-II and Thetis Deeps of the Red Sea, in Sediment-Hosted Mineral Deposits: Proceedings of a Symposium Held in Beijing, People's Republic of China, 30 July-4 August 1988 (eds J. Parnell, Y. Lianjun and C. Changming), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303872.ch6

Editor Information

  1. Department of Geology, The Queen's University of Belfast, Belfast BT7 INN, UK

Author Information

  1. 1

    Geological Institute of the USSR Academy of Science, 7 Pyzhevsky per., 109017 Moscow, USSR, Russia

  2. 2

    Institute of Oceanography of the USSR Academy of Science, 23 Krasikova Street, 117218 Moscow, USSR, Russia

  3. 3

    Institute of Ore Geology and Mineralogy of the USSR Academy of Science, 35 Staromonetny per., 109017 Moscow, USSR, Russia

Publication History

  1. Published Online: 3 APR 2009
  2. Published Print: 27 SEP 1990

ISBN Information

Print ISBN: 9780632028818

Online ISBN: 9781444303872

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Keywords:

  • goethite, forming platey microcrystals;
  • manganite microconcretions;
  • goethite - hematite association;
  • complex of iron - manganese oxyhydroxide mineral phases, occurring in Atlantis-II and Thetis Deeps;
  • kinetics of crystallization of amorphous phase

Summary

A complex of iron–manganese oxyhydroxide mineral phases is recognized in ore deposits of the Atlantis-II and Thetis Deeps in the Red Sea. In the ore material of the Atlantis-II Deep goethite and hematite predominate among the ferruginous phases; the manganese phases are mainly represented by todorokite and manganite. In the Thetis Deep the iron ore material contains a predominant magnetite–lepidocrocite association, and the manganese component is mainly represented by asbolanes. The bulk of the iron–manganese oxyhydroxides in the ore material of the Red Sea is formed by oxidation of Fe2+ and Mn2+ supplied to near bottom water by hot brines. The processes of transformation of amorphous hydrated particles into individual crystalline phases depend on physico-chemical conditions in the mineral-forming medium, i.e. on the relative concentrations of manganese, iron and oxygen, and pH value, as well as on the catalytic and adsorption activity of the amorphous hydrated particles. Stratified brines in the Atlantis-II Deep determine different physico-chemical conditions. The process of formation of todorokite mainly takes place in the upper part of the brines, where in an alkaline environment with high oxygen content hydrated thixotropic macrostructures of nMnO2·mH2O are formed. These particles can adsorb cations, leading to the formation of minerals with losse tunnel structures. Favourable conditions for manganite formation are found in the lower part of the brines with oxygen deficiency, large amounts of manganese and low pH. Under these conditions the amorphous manganese hydroxides are less hydrated and contain no adsorbed cations besides manganese. The bulk of goethite and hematite is also formed in the lower part of the brines or in the sediments during diagenesis. Ferrihydrite, present in the upper parts of the sediment section, is formed through microbiological processes in the layer of the brines transitional to seawater. In the Thetis Deep there is no bottom water stratification. In the bottom water there, the manganese content is considerably lower than that in the brines in the Atlantis-II Deep. Under such conditions, the MnO2 gel coagulates slowly and this leads to the formation of asbolanes with layer structures. The main factor affecting the magnetite and lepidocrocite formation is the kinetics of crystallization of the amorphous phase which in turn depends on the iron: oxygen ratio. Due to an active supply of hydrothermal iron magnetite is formed, while lepidocrocite crystallizes when the hydrothermal activity diminishes.