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The Oued Belif magmatic rocks dated Serravalian-Tortonian include intrusive (12.9 ± 0.5 Ma) and extrusive (8.3 ± 0.8 Ma) bodies. These consist of granodiorite intrusions and associated tuffs, breccias and rhyodacitic laccolite domes, and lava flows. The emplacement of these magmatic bodies induced a thermal effect on their host rocks as well as the activation of weathering processes where metasomatic and hydrothermal fluids played an essential role. Previous authors have long considered that pedogenic processes mainly accounted for outcrop mineral parageneses. The present study of mineral assemblages in host fractures, fluid inclusions, and the alteration stages of magmatic rocks help define a pervasive prograde alteration of lateral polarity, intensifying under the effect of increasing temperature in the field of faults serving as conduits for mineralizing hydrothermal fluids. The prograde alteration evolves according to the sequence: prophyllitic (chlorite-albite-anorthite), phyllitic (sericite-quartz; (sericitization)), argillic (secondary silica-smectite-illite-kaolinite), and advanced argillic (kaolinite, quartz ± talc and/or pyrophyllite). The observed mineral sequences and assemblages conform to those currently described in hydrothermal alteration environments of felsic rocks accompanying VMS (volcanogenic massive sulfide)-type deposits. Talc and pyrophyllite presumably due to the destabilization of kaolinite, coupled with sericite, albite and adularia, support the contention that those weathering products in the Oued Belif area are rather of the adularia-sericite type and are thus hydrothermal in origin. Moreover, phlogopite bearing skarns and garnet skarns in contact with the granodiorites and rhyodacites testify to a dominant calci-magnesian metasomatic phase, with F-rich phlogopites deposited from fluorinated halogen-rich fluids. Veins and breccia fills also display an early porphyry mineralization consisting of pyrite, chalcopyrite, cuprite, and native gold, in a gangue of adularia, sericite, albite, quartz, and alunite. This gangue can neoform from percolating hydrothermal fluids in the rock vugs and micro-cracks. The fluid inclusion measurements help assess the temperature range of mineralizing fluids, from the porphyritic (T ≈ 570 °C) to the epithermal (T ≈ 195 °C) conditions.

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The Porphyritic, Epithermal, and Metasomatic Mineral Assemblages Associated with Post-magmatic Alteration Processes at Oued Belif, NW Tunisia

  • 会议论文

  • 发表日期：

    2025年

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  • Wiem Ben Aissa,
  • Rania Ben Aissa,
  • Abdessalem Ben Haj Amara

摘要

The Oued Belif magmatic rocks dated Serravalian-Tortonian include intrusive (12.9 ± 0.5 Ma) and extrusive (8.3 ± 0.8 Ma) bodies. These consist of granodiorite intrusions and associated tuffs, breccias and rhyodacitic laccolite domes, and lava flows. The emplacement of these magmatic bodies induced a thermal effect on their host rocks as well as the activation of weathering processes where metasomatic and hydrothermal fluids played an essential role. Previous authors have long considered that pedogenic processes mainly accounted for outcrop mineral parageneses. The present study of mineral assemblages in host fractures, fluid inclusions, and the alteration stages of magmatic rocks help define a pervasive prograde alteration of lateral polarity, intensifying under the effect of increasing temperature in the field of faults serving as conduits for mineralizing hydrothermal fluids. The prograde alteration evolves according to the sequence: prophyllitic (chlorite-albite-anorthite), phyllitic (sericite-quartz; (sericitization)), argillic (secondary silica-smectite-illite-kaolinite), and advanced argillic (kaolinite, quartz ± talc and/or pyrophyllite). The observed mineral sequences and assemblages conform to those currently described in hydrothermal alteration environments of felsic rocks accompanying VMS (volcanogenic massive sulfide)-type deposits. Talc and pyrophyllite presumably due to the destabilization of kaolinite, coupled with sericite, albite and adularia, support the contention that those weathering products in the Oued Belif area are rather of the adularia-sericite type and are thus hydrothermal in origin. Moreover, phlogopite bearing skarns and garnet skarns in contact with the granodiorites and rhyodacites testify to a dominant calci-magnesian metasomatic phase, with F-rich phlogopites deposited from fluorinated halogen-rich fluids. Veins and breccia fills also display an early porphyry mineralization consisting of pyrite, chalcopyrite, cuprite, and native gold, in a gangue of adularia, sericite, albite, quartz, and alunite. This gangue can neoform from percolating hydrothermal fluids in the rock vugs and micro-cracks. The fluid inclusion measurements help assess the temperature range of mineralizing fluids, from the porphyritic (T ≈ 570 °C) to the epithermal (T ≈ 195 °C) conditions.