Dear Bernardo, et al
A few additions to Ian Coulson's list, and some comments.
The key data for this exercise is the experimental study of Munoz and
Swenson (1981, Econ Geol), with Munoz and Luddington (1974, Am J Sci and
1977 Am Mineral) for F-exchange. The comprehensive reworking of this data
is by Zhu & Sverjensky (1991, GCA). They give thermodynamic data that you
can input into EQ3/6 to model with if you are very careful about which data
bases you are already using. There are important issues of the effect of
solid phase chemistry on Cl/OH partitioning that have not been fully
resolved but are explored in some recent papers (e.g. below). Apart from
Micas, the only other system to have been investigated experimentally is
apatite-fluid, (the Korzhinskiy ref in Ian's list) but here there is now
considerable uncertainty over the validity of microprobe F analyses for
apatite (Stormer 1993, Am Min p.641), although Cl is probably OK. Where
people have tried to use amphibole halogen chemistry, they make the
assumption that the partitioning is identical to that of biotite.
A key point to appreciate in all this is that the actual exchange reaction
is between HCl and H2O, so that the Cl/OH ratio of the mineral reflects the
HCl/H2O fugacity ratio, NOT the salinity of the fluid - while Zhu &
Sverjensky's papers try to address this, the bottom line is that you are
getting into some very non-ideal fluid compositions in many common ore
systems, for which the thermodynamics does not work too well. Note that
many examples of Cl-rich minerals occur in settings where there is a low
water fugacity rather than/as well as a high salinity - e.g. volcanic
phenocrysts, high grade marbles.
Some important additions to Ian's list:
Yardley, 1985, Min Mag v.49, 77-79.
Kullerud, 1995, Contributions v.120, 42-59
Kullerud, 1996 Eur. Jl. Mineral, v.8, 355-370
Markl, Ferry & Bucher, 1998, Am J Sci, v.298, 707-757
Good Luck!
Bruce Yardley
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Professor Bruce Yardley
School of Earth Sciences
University of Leeds
Leeds LS2 9JT
UK
Tel. 0113 233 5200 Fax 0113 233 5259
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