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Polystage apatite recrystallization and svanbergite formation during weathering in an acid karstic environment

Published online by Cambridge University Press:  05 July 2018

L. E. Mordberg ,
C. J. Stanley  and
A. V. Antonov
L. E. Mordberg*
Affiliation:
Centre of Isotopic Research, Russian Research Geological Institute (VSEGEI), Sredny pr. 74, St Petersburg 199106, Russia
C. J. Stanley
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
A. V. Antonov
Affiliation:
Centre of Isotopic Research, Russian Research Geological Institute (VSEGEI), Sredny pr. 74, St Petersburg 199106, Russia
*
*E-mail: leonid_mordberg@vsegei.ru
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Abstract

A Devonian weathering profile was developed near the contact of Riphean dolostone containing disseminated carbonate-fluorapatite and intensively pyritized black shales. Samples from the profile were investigated by XRF, SEM, electron microprobe and ion microprobe. Rock-forming minerals are apatite, diaspore, chlorite and kaolinite, while accessory minerals are svanbergite, anatase, pyrite and zircon.

Primary marine carbonate-fluorapatite is represented by extremely weathered crystals concentrated near the footwall. Dissolution of apatite and pyrite provided an acidic environment that is expressed in the formation of S-rich apatite and svanbergite. The environment allowed Ti migration which formed anatase in weathered apatite grains. Coupled substitution Na+ + S6+ = Ca2+ + P5+ is suggested in S-rich apatite. A large volume of dissolved carbonate rocks was a source of Sr necessary for svanbergite formation. Apatite of the third generation formed at the final stage of weathering is represented by small (10—30 μm) very well shaped crystals.

Keywords

weatheringsulphate-apatiteanatasesvanbergiteDevonian
Type
Research Article
Information
Mineralogical Magazine , Volume 72 , Issue 1 , February 2008 , pp. 95 - 99
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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