Dear Listmembers

No, this is not about the removal (hot, cold, wet or dry) of organic matter
from calcite.

I recently analysed the isotopic composition of calcite from
cc-qtz-prehnite veins that occur in the prehnite-pumpellyite metamorphic
zone in the South Island of New Zealand.  What I thought was going to be
just another night on the MS turned out to be quite exciting.  The 13C
values (PDB) I measured for the calcite ranged between -29.2 and -38.0 per
mil.  In case your wondering, I recently prepared a new batch of phosphoric
acid in the old "traditional", true green colour style.    I suspect that
the low 13C values of the calcite are probably as a result of oxidation of
CH4 which was produced during metamorphism of organic matter in the host
sediments.   Is anyone aware of other studies that have measured such low
13C values of vein calcite? Any comments are appreciated.

Thanks
Kevin


**********************************************************
Dr Kevin Faure
Department of Geochemistry
Geological Survey of Japan
1-1-3 Higashi
Tsukuba
Ibaraki 305
Japan

Tel. and Fax: +81-298-54-3726