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Mineralium Deposita

, Volume 47, Issue 5, pp 545–562 | Cite as

Phosphorite-hosted zinc and lead mineralization in the Sekarna deposit (Central Tunisia)

  • Hechmi Garnit
  • Salah Bouhlel
  • Donatella Barca
  • Craig A. Johnson
  • Chaker Chtara
Article

Abstract

The Sekarna Zn–Pb deposit is located in Central Tunisia at the northeastern edge of the Cenozoic Rohia graben. Mineralization comprises two major ore types: (1) disseminated Zn–Pb sulfides that occur as lenses in sedimentary phosphorite layers and (2) cavity-filling zinc oxides (calamine-type ores) that crosscut Late Cretaceous and Early Eocene limestone. We studied Zn sulfide mineralization in the Saint Pierre ore body, which is hosted in a 5-m-thick sedimentary phosphorite unit of Early Eocene age. The sulfide mineralization occurs as replacements of carbonate cement in phosphorite. The ores comprise stratiform lenses rich in sphalerite with minor galena, Fe sulfides, and earlier diagenetic barite. Laser ablation–inductively coupled plasma mass spectrometry analyses of sphalerite and galena show a wide range of minor element contents with significant enrichment of cadmium in both sphalerite (6,000–20,000 ppm) and galena (12–189 ppm). The minor element enrichments likely reflect the influence of the immediate organic-rich host rocks. Fluid inclusions in sphalerite give homogenization temperatures of 80–130°C. The final ice melting temperatures range from −22°C to −11°C, which correspond to salinities of 15–24 wt.% NaCl eq. and suggest a basinal brine origin for the fluids. Sulfur isotope analyses show uniformly negative values for sphalerite (−11.2‰ to −9.3‰) and galena (−16‰ to −12.3‰). The δ34S of barite, which averages 25.1‰, is 4‰ higher than the value for Eocene seawater sulfate. The sulfur isotopic compositions are inferred to reflect sulfur derivation through bacterial reduction of contemporaneous seawater sulfate, possibly in restricted basins where organic matter was abundant. The Pb isotopes suggest an upper crustal lead source.

Keywords

Zn–Pb deposits Sedimentary phosphorites Sekarna Central Tunisia 

Notes

Acknowledgments

This paper is part of a Doctorate thesis of the first author. We would like to express our thanks to Sheldon A. Skaggs (Department of Geology, Building University of Georgia Athens) for lead isotope analyses. We wish to thank Karen Duttweiler Kelley (USGS, Denver USA) for constructive comments and for English edits. We are grateful to Christian Marignac for the editorial handling and his effort to improve this article. Yves Fuchs and Etienne Delloul, two reviewers of this article, are gratefully acknowledged for their critical and constructive comments that helped significantly improve the manuscript. Bernd Lehmann, editor-in-chief of the journal, is thanked for his constructive comments on the article. S. Bouhlel gratefully acknowledges support by Fulbright Scholar Grant that made possible the carbon, oxygen, and sulfur analysis at the USGS Denver, USA.

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Hechmi Garnit
    • 1
  • Salah Bouhlel
    • 1
  • Donatella Barca
    • 2
  • Craig A. Johnson
    • 3
  • Chaker Chtara
    • 4
  1. 1.Department of Geology, Faculty of Sciences of TunisEl Manar UniversityTunisTunisia
  2. 2.Department of Earth SciencesUniversity of CalabriaArcavacata di Rende (CS)Italy
  3. 3.U.S. Geological SurveyDenverUSA
  4. 4.Groupe Chimique Tunisien (G.C.T.)GabesTunisia

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