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<p>Southeastern Tunisia hosts numerous coastal and endorheic salt flats, with the Om El Khialete sabkha representing a significant sodium sulfate deposit. These minerals have many diverse industrial, pharmaceutical, and military uses. Among them, mirabilite is the most abundant evaporite mineral in this sabkha, constituting Tunisia’s only known sodium sulfate reservoir. However, its origin, formation processes, and spatial-vertical distribution within the basin remain subjects of debate. The current study emphasizes the evolutionary processes that led to the deposition of mirabilite layers, a mineralized form of sodium sulfate, which represented a significant indicator of the paleoclimate and hydrological conditions in this region. Brine and sediment samples were subjected to chemical analysis to determine alkaline content and major elemental composition. These analyses were complemented by X-ray diffraction (XRD), thin section petrography, and scanning electron microscopy (SEM).Geochemical investigations revealed two primary types of brines within the sabkha. The dominant type, composed of sodium and magnesium sulfate, is concentrated in the center-east and southeast of the basin. The second type, sodium chloride-rich brine, is found in the northwestern and northern sections. The mineralogical composition of the basin deposits and adjacent wadis sediments primarily consists of mirabilite, thenardite, eugsterite, quartz, and gypsum, with quartz and gypsum being predominant in wadis samples. Lithological analysis of boreholes sediments allowed the identification of three distincts stratigraphic sets: A, B, and C. Set B, characterized by substantial solid mirabilite deposits, serves as the primary brine reservoir within the Bni Mhira clay formation. As a future extraction strategy, it is recommended to focus operations towards the sabkha center, where the mirabilite layers are thickest, while avoiding the currently used “fish stop” hierarchical exploitation method, which is inefficient. By integrating these findings with earlier research, particularly on the distribution and extent of the Bni Mhira clay formation, this study supports the hypothesis that the sabkha evolved from an ancient shallow depression into its current arid, closed- sabkha environment.</p>

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Characterization and spatial distribution of the mirabilite layers in sabkha Om El khialete, southeastern Tunisia

  • 期刊论文

  • 发表日期：

    2025年11月15日

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  • Aicha Ghrab,
  • Lara Maritan,
  • Maria Chiara Dalconi,
  • Andrea Fasson,
  • Xiangli He,
  • Mohamed Ali Tagorti

摘要

Southeastern Tunisia hosts numerous coastal and endorheic salt flats, with the Om El Khialete sabkha representing a significant sodium sulfate deposit. These minerals have many diverse industrial, pharmaceutical, and military uses. Among them, mirabilite is the most abundant evaporite mineral in this sabkha, constituting Tunisia’s only known sodium sulfate reservoir. However, its origin, formation processes, and spatial-vertical distribution within the basin remain subjects of debate. The current study emphasizes the evolutionary processes that led to the deposition of mirabilite layers, a mineralized form of sodium sulfate, which represented a significant indicator of the paleoclimate and hydrological conditions in this region. Brine and sediment samples were subjected to chemical analysis to determine alkaline content and major elemental composition. These analyses were complemented by X-ray diffraction (XRD), thin section petrography, and scanning electron microscopy (SEM).Geochemical investigations revealed two primary types of brines within the sabkha. The dominant type, composed of sodium and magnesium sulfate, is concentrated in the center-east and southeast of the basin. The second type, sodium chloride-rich brine, is found in the northwestern and northern sections. The mineralogical composition of the basin deposits and adjacent wadis sediments primarily consists of mirabilite, thenardite, eugsterite, quartz, and gypsum, with quartz and gypsum being predominant in wadis samples. Lithological analysis of boreholes sediments allowed the identification of three distincts stratigraphic sets: A, B, and C. Set B, characterized by substantial solid mirabilite deposits, serves as the primary brine reservoir within the Bni Mhira clay formation. As a future extraction strategy, it is recommended to focus operations towards the sabkha center, where the mirabilite layers are thickest, while avoiding the currently used “fish stop” hierarchical exploitation method, which is inefficient. By integrating these findings with earlier research, particularly on the distribution and extent of the Bni Mhira clay formation, this study supports the hypothesis that the sabkha evolved from an ancient shallow depression into its current arid, closed- sabkha environment.