Darren
NBS - 30 is a biotite, with 3 to 4 wt.% water in
the OH site of the mineral. On heating to 1450 C
in the TCEA, the water comes off and is converted
to H2 and CO by the glassy carbon reaction. (At
1450 C, experiments indicate biotite breaks down
incongruently to olivine/pyroxene and a small
percentage of water - rich melt.) The rest of the
oxygen (about 45% by weight) in the mineral is
structurally bound to Si and Al tetrahedral
groups without H. I believe this O does not
readily react with C to make CO. It is
well-known for some minerals that the isotopic
composition of O is different for different O
sites in the mineral structure, for example the
OH and SO4 groups of alunite (work of Stoffregen,
etc). The OH group readily exchanges O and H at
relatively low T's with water, for example,
whereas the O in bound to Si and Al does not
exchange so readily in biotite (our work at
Butte, MT ore deposit suggests D/H exchange at
150 ± C with water, but little O exchange). At
any rate, in our lab our tests suggest that CO
derived from heating mica in the TCEA does not
give delta 18O/16O results similar to that
reported by NBS---I'd interpret this to mean we
don't get all the O off, and that O we get off is
not equivalent to bulk O of mineral due different
isotopic composition of the OH site from bulk
mineral and partial degassing fractionation
effects.....
I wish this worked on the TCEA... might be a
clever way to get all the O out somehow
(melt/react the mineral mixed with a reductant or
flux).
JOHN DILLES
>Dear Colleagues
>
>Looking through the Isogeochem archives there
>was a discussion back in 2001 on the dD of NBS
>30 (see one such message below). We have been
>analyzing NBS 30 here using our TCEA and the
>results compared to our other internal and
>international standards are not very good. Have
>I missed some vital information around the
>community about analyzing NBS 30 for dD and d18O
>using a TCEA? We are getting good results for dD
>but not for d18O.
>
>Thanks
>
>Darren
>
>>Subject:
>>Re: delta D of NBS-30
>>From:
>>Willi A. Brand
>>Reply-To:
>>Stable Isotope Geochemistry <[log in to unmask]>
>>Date:
>>Mon, 10 Sep 2001 08:13:51 +0200
>>Content-Type:
>>text/plain
>>
>>Hi,
>>a number of years ago, during the early stages of high temperature
>>pyrolysis developments at Finnigan I ran NBS30 at the 1-5-milligram
>>level and got astonishing results. I do not recall the exact numbers but
>>I had two distinct cluster values. My conclusion at the time was that
>>the material was not homogeneous at the single grain level and I
>>discontinued using it for the purpose. Has anyone experienced something
>>similar?
>>Willi
>>--
>>””””””””””””””””””””””””””””””””””
>>Willi A. Brand, Stable Isotope Laboratory [log in to unmask]
>>Max-Planck-Institute for Biogeochemistry
>>Carl-Zeiss-Promenade 10, 07745 Jena, Germany Tel +49-3641-643718
>>P.O.Box 100164, 07701 Jena, Germany Fax: +49-3641-643710
>>http://www.bgc-jena.mpg.de/pages/public/Iso+Gas-Lab/BGC_Gaslab.html
>>http://www.bgc-jena.mpg.de/pages/public/Iso+Gas-Lab/BGC_Isolab.html
>>””””””””””””””””””””””””””””””””””
>
>
>Dr Darren Grocke
>Associate Professor & Director of SIBL
>
>Stable-Isotope Biogeochemistry Laboratory (SIBL)
>McMaster University
>School of Geography & Earth Sciences
>1280 Main Street West
>Hamilton, Ontario, L8S 4K1
>Canada
>
>http://www.science.mcmaster.ca/geo/research/sibl/index.html
>Phone: 905 525 9140 ext. 26334
>Fax: 905 546 0463
--
John Dilles, Professor of Geology of Mineral Resources
Department of Geosciences, Wilkinson Hall 104
Oregon State University
Corvallis OR 97331-5506
fax: 541-737-1200; phone 541-737-1245; e-mail [log in to unmask]
Dilles/Mineral Deposit Website
http://www.geo.oregonstate.edu/people/faculty/dillesj.htm
MERIT WEBSITE
http://www.geo.arizona.edu/~mdbarton/MDB_MERIT.html
OSU Summer Geology Field Program
http://www.geo.oregonstate.edu/classes/fcamp/
Volcan-Ig-Petrol-Econ-Res (VIPER)
http://www.geo.oregonstate.edu/research/viper.htm
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