At 12:09 PM 2000/03/09 +0000, Bruce Yardley wrote:
>...
>... Where people have tried to use amphibole halogen chemistry, they
>make the assumption that the partitioning is identical to that of biotite.
A dubious practice! According to my data in 1970 J Petrol 11 147-181, X(Cl)
in hydroxyl sites in hornblende is roughly double that in coexisting 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...
Also true for fluorine. For every hydrous mineral there is an exchange
reaction showing that its F/OH reflects fHF^2/fH2O in the fluid. This
reaction can be linearly combined with the corresponding Cl/OH mineral-fluid
reaction so that H2O cancels out and Cl/F in the mineral is seen to reflect
fHCl/fHF in the fluid.
Dugald M Carmichael Phone/V-mail: 613-533-6182
Dept of Geological Sciences and Geological Engineering
Queen's University FAX: 613-533-6592
Kingston ON K7L3N6 E-mail: [log in to unmask]
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