Just heard this announced on my local TV news channel:
Orbital Identification of Carbonate-Bearing Rocks on Mars.
Bethany L. Ehlmann, John F. Mustard, Scott L. Murchie, Francois Poulet, Janice L. Bishop, Adrian J. Brown, Wendy M. Calvin, Roger N. Clark, David J. Des Marais, Ralph E. Milliken, Leah H. Roach, Ted L. Roush, Gregg A. Swayze, James J. Wray
Science 19 December 2008: Vol. 322. no. 5909, pp. 1828 - 1832.
Here's the NASA news release:
December 18, 2008
Scientists Find 'Missing' Mineral and Clues to Mars Mysteries.
This is the journal published report of some results announced at some recent conferences. I discussed before though that there were some discrepancies from a pure carbonate signature in the spectra:
I don't have access to the full paper in Science so I don't know if further analysis allowed them to pin down more strongly the carbonate signature.