BULGARIAN GEOLOGICAL SOCIETY, Annual Scientific Conference “Geology 2004”, 16 – 17.12.2004 STABLE ISOTOPE STUDY AND ORIGIN OF ALUNITE FROM ADVANCED ARGILLIC ALTERATION SYSTEMS IN BULGARIA Catherine Lerouge1, Christine Flehos1, Angel Kunov2, Atanas Hikov2, Sylvina Georgieva2, Jean-Luc Lescuyer1, Rumen Petrunov2, Nadezhda Velinova2 1 BRGM, BP 6009, 45060 Orléans cédex 2, France, e-mail address:
[email protected] 2 Bulgarian Academy of Sciences, Geological Institute, Sofia, Bulgaria, e-mail address:
[email protected] Introduction isotope systematic of alunite from nine occurrences of vari- The zones of advanced argillic alteration (AAA) are ma- ous type chosen among each district of both metallogenic prov- jor exploration targets for shallow high-sulphidation Cu-Au inces, for their different types: high-sulphidation epithermal epithermal and deeper porphyry-type deposits. The formation deposit of Chelopech, porphyry copper/epithermal deposits of alunite results from the alteration of host volcanic and vol- of Assarel and Petelovo, subeconomic deposits spatially as- cano-sedimentary rocks by acidic, sulphate-bearing hydrother- sociated with low-sulphidation mineralization (Breznik, mal fluids (Hemley et al., 1969). These fluids may be gener- Madjarovo) and uneconomic occurrences of Ropotamo, ated in different ways: magmatic-hydrothermal, steam-heated, Stomanovo, Boukovo and Sarnitsa. The aim was to test the magmatic steam and supergene environments, each one potential use of combined mineralogy and stable isotopes of characterised by specific mineral assemblages and stable iso- alunite to discriminate “fertile” from “barren” alunite. tope signature of alunite (Rye et al., 1992). AAA alunites from Mineralogical and chemical data major high-sulphidation Cu-Au ore deposits are dominantly Twelve samples of advanced argillic quartz + alunite al- magmatic-hydrothermal or magmatic-steam.