1. Environmental Geochemistry Group, LGIT - Maison des Géosciences, University of Grenoble - CNRS, 38041 Grenoble Cedex 9, France, European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex, France, and Geological Institute, Russian Academy of Sciences, 7 Pyzhevsky Street, 109017 Moscow, Russia