『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
(10-30μm) very well shaped crystals.
Keywords: weathering; sulphate-apatite; anatase; svanbergite;
Devonian』
Introduction
Geological setting and mineralogy
Material and methods
Results and discussion
Conclusions
Acknowledgements
References