Lo delta 18-O

Alison and Helen:

in addition to the advice you already got, you may want to know that Paul Aharon
[GCA 52 (1988) 2321-2331] has also reported very depleted aragonite (not
aharonite) from the Antarctic, with minus 15.7 permil delta 18-O. His was almost
concurrent with the paper by Faure, Hoefs, and others, mentioned by Yong-fei
(which I had overlooked in my summary of depleted silicate and carbonate values,
GCA 61, 1997, page 569-576 and Figure 3) . --  Your Mexican calcite with minus
15.9 permil is at any rate very interesting. For associated water under
conditions of a mineral deposit you want, at the highest, about minus 20 permil,
if equilibrium is to hold, and since we were not in the Antarctic or at the
North Pole, there should have been a Tibetan-like high plateau. Are there fluid
inclusions for a T-estimate? How homogeneous is the calcite?

Apologies to Paul about the swipe - and to Faure and Hoefs about the omission.

Peter Blattner
C/ GNS, Box 30-368, Lower Hutt, New Zealand