Diagenetic minerals from saline diapirs as thermodynamic, chemical and isotopic tracers of evolution in the North Tunisian sedimentary basin and their impacts on ore deposits genesis

• Mohja Dermech ^[1] ; Abdelkrim Charef ; Mariem Trifi ^[2]
  1. [1] Université de Tunis El Manar

     Université de Tunis El Manar

     Túnez

     
  2. [2] Sciences Faculty of Bizerte, Carthage University
• Localización: Carbonates and Evaporites, ISSN 0891-2556, Vol. 35, Nº. 4, 2020
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • To suggest the impacts of diapir evolutions on the ore deposits genesis, combined mineralogical, Raman spectrometry and C-, O- and H- isotopes studies of fluid inclusions trapped by their minerals were studied. In diapir zone, the evolution of hydrothermal fluids has been distinguished:

    type I hot fluids (365 °C) had formation water origin (δD ≈ − 21‰) and moderate salinity (12–23% wt% eq. NaCl) which were trapped by minerals where Mg/Ca ≥ 1, in particular, magnesite and secondary by dolomite 1.

    later, type II fluids less hot which were divided into two members. The first was the N2-dominant fluids (≈ 250 °C) and more saline (23–43 wt% eq. NaCl and/or KCl) which were trapped in particular by some dolomite 1, dolomite 2 and quartz. The end member was CO2-rich fluids; their trapping temperatures varying from 150 to 270 °C and salinities > 35 wt% eq. NaCl and/or KCl were trapped by minerals where Mg/Ca < 1, in particular in dolomite 2. These type II fluids were of formation water origin (− 52 < δD < − 16‰) which came probably from the dehydration of Triassic materials (mainly gypsum). All CO2 could be previously provided by thermal decomposition of Triassic carbonate. But N2 was of deep origin. The major halokinetic stages that happened at lower Cretaceous period and during the end of Tethysian rifting (associated to basic magmatism) had generated type I and II fluids.

    the last hydrothermal fluids (type III) derived from organic matter (− 80 < δD < − 65‰). Their temperature and salinity ranges were from 50 to 160 °C and 18.4–23 wt% eq. NaCl, respectively.

    The last halokinetic stage occurred during the dominant compressive and transpressive pyrenean and Alpine collision period. The similarities observed between geochemistry characteristics of type III and ore-bearing fluids of some peridiapiric mineralizations implying that only the last hydrothermal events had contributed to the genesis of ore deposits in the diapir zone.