10-12 Geochemical Constraints on Diapir-Related MVT Zn–Pb–Ba–Sr Mineralization at Sakiet-Koucha (Tunisia): Insights from Microthermometry, REE+Y, Halogens, and Isotopes.

Session: Geochemistry and Mineralogy (Posters)

Poster Booth No.: 49

Presenting Author:

Larbi Rddad

Authors:

Rddad, Larbi¹, Jemmali, Nejib ², Walter, Benjamin Florian³, Raza, Mohsin⁴, Benaouda, Rachid⁵, Jinari, Abdessamad⁶, Mouguina, El Mostafa⁷

(1) Earth and Planetary Division, Physical Sciences, Kingsborough Community College, New York city, , (2) Géologie, Université de Gafsa Faculté des Sciences de Gafsa, Gafsa, , (3) Department of Petrology and Mineral Resources, 3Eberhard Karls University Tübingen (EKUT), Tübingen, , (4) Applied Geosciences, Laboratory for Environmental and Raw Materials Analysis (LERA), Adenauerring, , (5) CritMET - Critical Metals for Enabling Technologies,, Constructor University, Bremen, , (6) Department of Geology, Cadi Ayyad University, Marrakesh, , (7) Department of Geology, Cadi Ayyad University, Marrakesh, ,

Abstract:

The Sakiet-Koucha Zn–Pb–Sr–(Ba) deposit in northern Tunisia formed through a structurally focused, multi-stage hydrothermal system associated with Triassic salt diapirism. Mineralization is divided into three stages: (I) early galena and celestite in caprock dolostones, (II) breccia-hosted sulfides, and (III) stratiform to vein-type sphalerite–galena mineralization in the organic-rich Bahloul Formation. Fluid inclusion analyses reveal that ore-forming fluids evolved from warm, moderately saline brines in Stage I (161–185 °C; 17–24 wt.% NaCl equiv.) to cooler, mixed fluids in Stage II (114–179 °C; 19–24 wt.% NaCl equiv.), and finally to hotter, chemically reactive fluids in Stage III (191–212 °C; 20–23 wt.% NaCl equiv.). This thermal and chemical evolution reflects progressive fluid–rock interaction, fluid mixing, and changes in redox conditions.

Crush-leach molar ratios (Cl/Br = 546–942; Na/Br = 475–1124) indicate halite dissolution as the dominant salinity source. Sulfur isotope data show a transition from early inheritance of bacterially reduced sulfur (δ³⁴S ≈ –0.5‰ to –0.19‰) in Stage I, to mixed sulfur sources and the onset of thermochemical sulfate reduction (TSR) in Stage II (–2.77‰ to +28.5‰), and dominant TSR in Stage III (+10.79‰ to +21.14‰). S–O isotopes from barite and celestine suggest that sulfate was ultimately sourced from Triassic evaporites. Carbon and oxygen isotope compositions of host carbonates and calcite cements indicate interaction between hydrothermal fluids, marine carbonates, and organic-derived CO₂ under evolving temperature and redox conditions. Lead isotopes in galena are narrowly distributed across all stages, reflecting a homogenized Paleozoic basement source with minor contributions from Cretaceous sedimentary units. Principal component analysis (PCA) supports this interpretation, linking Sr and SO₄²⁻ to evaporites and Zn, Pb, and Ba to basement-derived fluids and carbonate–organic-rich lithologies.

Mineralization is interpreted as Miocene in age and coincident with Alpine orogenesis, which reactivated basement-rooted faults and focused fluid flow along peridiapiric structures. Ore deposition was controlled by episodic fluid pulses, fluid–rock interaction, fluid mixing, and redox-driven destabilization of metal complexes. The Sakiet-Koucha system shares key features with other diapir-related deposits worldwide, highlighting peridiapiric flanks and fault zones as prime exploration targets in salt-influenced southern Tethyan basins.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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