Genesis of the Jurassic carbonate-hosted Pb–Zn deposits of Jebel Ressas (North-Eastern Tunisia): evidence from mineralogy, petrography and trace metal contents and isotope (O, C, S, Pb) geochemistry

Jemmali, Nejib, Souissi, Fouad, Vennemann, Torsten W., and Carranza, Emmanuel John M. (2011) Genesis of the Jurassic carbonate-hosted Pb–Zn deposits of Jebel Ressas (North-Eastern Tunisia): evidence from mineralogy, petrography and trace metal contents and isotope (O, C, S, Pb) geochemistry. Resource Geology, 61 (4). pp. 367-383.

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Abstract

The Jebel Ressas Pb–Zn deposits in North-Eastern Tunisia occur mainly as open-space fillings (lodes, tectonic breccia cements) in bioclastic limestones of the Upper Jurassic Ressas Formation and along the contact of this formation with Triassic rocks. The galena–sphalerite association and their alteration products (cerussite, hemimorphite, hydrozincite) are set within a calcite gangue. The Triassic rocks exhibit enrichments in trace metals, namely Pb, Co and Cd enrichment in clays and Pb, Zn, Cd, Co and Cr enrichment in carbonates, suggesting that the Triassic rocks have interacted with the ore-bearing fluids associated with the Jebel Ressas Pb–Zn deposits. The δ¹⁸O content of calcite associated with the Pb–Zn mineralization suggests that it is likely to have precipitated from a fluid that was in equilibrium with the Triassic dolostones. The δ³⁴S values in galenas from the Pb–Zn deposits range from -1.5 to +11.4‰, with an average of 5.9‰ and standard deviation of 3.9‰. These data imply mixing of thermochemically-reduced heavy sulfur carried in geothermal- and fault-stress driven deep-seated source fluid with bacterially-reduced light sulfur carried in topography-driven meteoric fluid. Lead isotope ratios in galenas from the Pb–Zn deposits are homogenous and indicate a single upper crustal source of base-metals for these deposits. Synthesis of the geochemical data with geological data suggests that the base-metal mineralization at Jebel Ressas was formed during the Serravallian–Tortonian (or Middle–Late Miocene) Alpine compressional tectonics.

Item ID: 27341
Item Type: Article (Research - C1)
ISSN: 1751-3928
Keywords: alpine orogeny; basinal brines; isotopes; Jebel Ressas; NE-Tunisia; Pb–Zn deposit
Date Deposited: 31 May 2013 05:19
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040203 Isotope Geochemistry @ 30%
04 EARTH SCIENCES > 0403 Geology > 040306 Mineralogy and Crystallography @ 30%
04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 40%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8499 Other Mineral Resources (excl. Energy Resources) > 849999 Mineral Resources (excl. Energy Resources) not elsewhere classified @ 100%
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