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Stable Isotope Geochemistry

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Thu, 10 Oct 96 10:43:09 +0100
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[log in to unmask] (Torsten Vennemann)
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Dear Forum

More details to Jim's comment: 
>In the "good old days" when uranium was used almost exclusively to reduce
>water (and some, like Simon Sheppard, happily still use uranium), we could
>take a sample of H2 of known isotopic composition, oxidize it to H2O, and
>then reduce this water back to H2 while retaining its original dD value to
>about +/- 1 per mil or so.  Torsten Vennemann tried this at Michigan a few
>times with zinc reduction but I don't recall his results.

Here are the results:

Sample 1: (a low dD water, not SLAP): three normal conversions with zinc 
with no stretching factor applied: -414, -416, -417 permil. Three other 
samples that were converted to H2 with zinc, then passed over CuO to oxidize 
H2 to H2O, then reduced with zinc again: -417, -414, -414 permil.

Sample 2: (VSMOW): Normal: -0.4, -1.5; Re-oxidized and then reduced again: 
-12, -11 permil.

Why the difference between samples 1 and 2? Who knows? Some contaminants in 
VSMOW?

Torsten.


*********************************
Dr. Torsten W. Vennemann
Institut fuer Geochemie
Wilhelmstr. 56
D-72074 Tuebingen
Germany
phone ++49-(0)7071-2974992
Fax ++49-(0)7071-296870
e-mail: [log in to unmask]
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