Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev st., 1113 Sofia, Bulgaria; Institute of Isotope Geology and Mineral Resources, ETH Zurich, Clausiusstrasse 25, CH-8092 Zurich, Switzerland
GIGC-IPE, Université Libre de Bruxelles (CP 160/02), 50 av. Roosevelt, B-1050 Brussels, Belgium (Aspirant du F.R.S.-FNRS); UMR-CNRS 6112, LPGN, Université de Nantes, 2 rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France