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The In Ouzzal Granulitic Unit (IOGU, southern Algeria) is an Archaean (3.2–2.5 Ga) and Paleoproterozoic (2.0 Ga) terrane of the Western Hoggar massif which has been affected by a very high temperature granulitic metamorphism. Its deep structure subject of controversy remains poorly known because of the lack of geophysical studies devoted to it. For this purpose, a magnetotelluric (MT) survey was conducted in October 2009 in the In Allarene area located south of IOGU, near Tirek and Amesmessa gold deposits. Thus, nine broadband soundings were collected along an East–West profile of 50 km long spreading on Kidal, Tassendjanet, In Ouzzal and Tirek terranes. MT data reveal three-dimensional In Allarene underlying structures. The crust of IOGU being reduced to its lower crust, is formed of two portions: an upper part of 7–8 km thick resting on a more conductive lower part. The Proterozoic crust of the adjacent terranes looks normal. The upper crust reaches about 15 km under Tirek and 15–20 km beneath Tassendjanet and Kidal. Unlike the Tekhamalt area, the two shear zones limiting IOGU do not have a clear electrical signature in the In Allarene area. On the other hand, the shear zone limiting Kidal from Tassendjanet, whose electrical signature is obvious, is rooted vertically in the crust and has a thickness of 4–5 km. According to the 3-D model, the most conductive feature is illustrated by In Allarene shear zone. The latter exhibit a high conductivity (~5 Ω m) at 5km depth and might be a key region to understand the extent of Neoproterozoic remobilization of this part of the In Ouzzal. This is all the more important as our results suggest that the In Allarene accident is a privileged place for the circulation of fluids responsible for gold mineralization known in the region, but exploited mainly a little further east (Tirek mine) and south (Amesmessa mine). These new data, which should be refined by one or more tighter profiles, already show that the In Allarene fault should be the subject of more extensive gold prospecting.

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Crustal Structure of the Southern in Ouzzal Granulitic Unit (IOGU, Hoggar) as Constrained by Magnetotelluric Data: Implications for Gold Mineralization

  • 章节

  • 发表日期：

    2025年

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  • Abderrezak Bouzid,
  • Aboubakr Deramchi,
  • Abderrahmane Bendaoud,
  • Abdelhamid Bendekken,
  • Nouredine Akacem,
  • Mohamed Hamoudi,
  • Khadidja Ouzegane,
  • Abdeslam Abtout,
  • Jean-Robert Kienast

摘要

The In Ouzzal Granulitic Unit (IOGU, southern Algeria) is an Archaean (3.2–2.5 Ga) and Paleoproterozoic (2.0 Ga) terrane of the Western Hoggar massif which has been affected by a very high temperature granulitic metamorphism. Its deep structure subject of controversy remains poorly known because of the lack of geophysical studies devoted to it. For this purpose, a magnetotelluric (MT) survey was conducted in October 2009 in the In Allarene area located south of IOGU, near Tirek and Amesmessa gold deposits. Thus, nine broadband soundings were collected along an East–West profile of 50 km long spreading on Kidal, Tassendjanet, In Ouzzal and Tirek terranes. MT data reveal three-dimensional In Allarene underlying structures. The crust of IOGU being reduced to its lower crust, is formed of two portions: an upper part of 7–8 km thick resting on a more conductive lower part. The Proterozoic crust of the adjacent terranes looks normal. The upper crust reaches about 15 km under Tirek and 15–20 km beneath Tassendjanet and Kidal. Unlike the Tekhamalt area, the two shear zones limiting IOGU do not have a clear electrical signature in the In Allarene area. On the other hand, the shear zone limiting Kidal from Tassendjanet, whose electrical signature is obvious, is rooted vertically in the crust and has a thickness of 4–5 km. According to the 3-D model, the most conductive feature is illustrated by In Allarene shear zone. The latter exhibit a high conductivity (~5 Ω m) at 5km depth and might be a key region to understand the extent of Neoproterozoic remobilization of this part of the In Ouzzal. This is all the more important as our results suggest that the In Allarene accident is a privileged place for the circulation of fluids responsible for gold mineralization known in the region, but exploited mainly a little further east (Tirek mine) and south (Amesmessa mine). These new data, which should be refined by one or more tighter profiles, already show that the In Allarene fault should be the subject of more extensive gold prospecting.