Polystage apatite recrystallization and svanbergite formation during weathering in an acid karstic environment
Authors: Mordberg, L.E.; Stanley, C.J.; Antonov, A.V.
Source: Mineralogical Magazine, Volume 72, Number 1, February 2008 , pp. 95-99(5)
Publisher: Mineralogical Society
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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: WEATHERING; SULPHATE-APATITE; ANATASE; SVANBERGITE; DEVONIAN
Document Type: Research article
DOI: 10.1180/minmag.2008.072.1.95
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