Graham,

you may wish to have a look at some of the fundamental papers of Nick
Pingitore Jr.

I analyzed stable isotopes and trace
element contents of mixed aragonite-calcite samples from
a sulfur deposit. At least in HCl leachates, trace
baryte was likely dissolved in a few samples. Weaker acids are
necessary to look for lattice bond barium in carbonates.

Good luck
Michael

******************************************************************
Dr. Michael E. Boettcher
Biogeochemistry
Max-Planck-Institute for Marine Microbiology
Celsiusstr.1
D-28359 Bremen
FRG