Atanassova, Rossitza

Kouzmanov, Kalin

Vassileva, R. D.

English

Vassileva Rossitsa D.

Atanassova Rossitza

Kouzmanov Kalin

University of Szeged

Acta Mineralogica-Petrographica, Abstract Series, Szeged, Vol. 7, 2012 147 Joint 5th Mineral Sciences in the Carpathians Conference and 3rd Central-European Mineralogical Conference 20–21 April, 2012, University of Miskolc, Miskolc, Hungary COMPOSITIONAL VARIATIONS OF THE TENNANTITE-TETRAHEDRITE SERIES FROM THE MADAN Pb-Zn DEPOSITS, BULGARIA: OSCILLATORY ZONING AND CONDITIONS OF FORMATION  VASSILEVA, R.D.1 Geological Institute, Bulgarian Academy of Sciences, BG-1113 Sofia, Bulgaria; 2 University of Geneva, Switzerland 1*, ATANASSOVA, R.1 & KOUZMANOV, K.2 * E-mail: rosivas@geology.bas.bg  The tennantite-tetrahedrite solid solution series is the most common among the sulphosalt minerals in the Madan base metal deposits, Central Rhodopes, Bul-garia. Found in veins and metasomatic orebodies of the Petrovitsa and Gradishte deposits, these minerals closely associated with the main sulphides – galena, sphalerite, chalcopyrite and pyrite. Textural characteris-tics, mineral relationships and fluid inclusion studies suggest that tennantite-tetrahedritess at Madan precipi-tated in the late stages of mineralization at temperatures close to 200°C. Large compositional variations are responsible for the observed fine oscillatory zoning of the crystals, according to EPMA and LA-ICP-MS inves-tigations. A generalized formula for the tennantite-tetrahedritess was proposed by JOHNSON et al. (1986): (Cu,Ag)6 Cu4 (Fe,Zn,Cu,Hg,Cd)2 (Sb,As,Bi,Te)4(S,Se)13. Although in the Madan samples Cu content is always higher than 10 apfu, Cu can be considerably substituted by Zn, and less commonly by Fe and Ag. Such compo-sitions correspond to zincian varieties (1.7–1.95 apfu Zn) with low Fe-content (0.08–0.45 apfu). Silver is characteristic of the Petrovitsa samples, reaching 0.30 apfu. The Gradishte samples reveal highly variable As/Sb ratios, mostly belonging in composition to the tennantite and intermediate members of the solid solu-tion (Fig. 1). Tennantite-tetrahedritess from Petrovitsa have As/Sb ratio < 0.78, generally in the range of 0.10–0.55, corresponding to tetrahedrite. Bismuth and tellu-rium were below the limit of detection of the EPMA, however detected by LA-ICP-MS analyses at a ppm level. Selenium commonly substitutes for S. Based on microprobe analyses the following average crystal-chemical formulae can be assigned: Gradishte: (Cu+5.99–6.00Ag0–0.01)Σ6Cu2+4(Fe0.08–0.45Zn1.61–1.93Cu2+0.06–0.2 Cd0.01)Σ2(Sb0.03–2.85As1.12–3.98)Σ4(S12.73–12.93Se0–0.05)Σ13. Pet-rovitsa: (Cu+5.70–5.86Ag0.11–0.30)Σ6Cu2+4(Fe0.06–0.21Zn1.81–1.95 Cu2+0.10–0.25)Σ2(Sb2.23–3.66As0.33–1.74)Σ4(S12.71–12.90Se0-0.03)Σ13. The presence of tennantite-tetrahedritess in the hydrothermal mineralization suggests increased activity of Sb and As in the fluids, as well as increased fS2. Im-portant Zn-incorporation in the studied samples is in-dicative for high fO2 (SPIRIDONOV et al. 2005), result-ing in enhanced Cu2+/Me2+ ratios. A vertical zonation in the Madan hydrothermal system is observed, consisting of As-rich members (mostly zincian tennantite), typi-cally found at depth (Gradishte ~400 m.a.s.l.), while in the upper levels (Petrovitsa mine ~970 m.a.s.l.) tetra-hedrite compositions tend to prevail. Silver incorpora-tion is often related to the late stage of formation of tetrahedrite, compared to the main sulphide paragenesis.  Acknowledgements. This study is part of the SCOPES IZ73Z0-128089 and SNF 20021-127123/1 projects of the Swiss National Science Foundation. The authors are grateful for the financial support of the BG051PO001-3.3.05-0001 Project of the Bulgarian Ministry of Science and Education.  References JOHNSON, N.E., CRAIG, J.R. & RIMSTIDT, J.D. (1986): Canadian Mineralogist, 24: 385–397. SPIRIDONOV, E., MALEEV, M., KOVACHEV, V., KULIKOVA, I., NAUMOVA, G. & FILIMONOV, S. (2005): Proceedings of the Bulgarian Geological Society, 80th Anniversary, 79–82.   Fig. 1. BSE image of Gradishte tennantite-tetrahedritess reveals typical oscillatory zoning (A), controlled by As and Sb fluctuation (B). Location of the profile is indicated on the BSE image. 

Compositional variations of the tennanite-tetrahedrite series from the Madan Pb-Zn deposits, Bulgaria : oscillatory zoning and conditions of formation

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Compositional variations of the tennanite-tetrahedrite series from the Madan Pb-Zn deposits, Bulgaria : oscillatory zoning and conditions of formation

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