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The Koudia El Hamra Ag–Pb–Zn deposit, Jebilet, Morocco: Mineralogy and ore fluid characterization

Abstract : The Koudia El Hamra silver - base metal (Pb-Zn) deposit is located in the Upper Visean - Namurian Sarhlef schist, Jebilet Hercynian Massif (Morocco). Ore bodies consist of N-S to NE-SW quartz-chlorite veins hosted by Hercynian black shale. Mineralogical and paleo-fluid investigations (microthermometry, Raman spectroscopy) and stable isotope data (O, C, S) have shown that high salinity brines (30 to 35 wt% NaCl+CaCl2 equiv.), likely from sedimentary origin deposited base metal (Zn) - carbonate assemblage at minimal temperature around 220°C. Then brines deposited silver ore - galena assemblage at lower salinity (9 to 15 wt% NaCl equiv.) and similar average minimal temperature (around 220°C). The main driving mechanism for silver ore deposition is the dilution of ore-bearing brines by low-salinity fluids probably combined with reduction of brines in the host black shale. Ore brines likely have come from the Permian-Triassic Atlasic basins related to the extension coeval with the Central Atlantic opening. Those brines probably have percolated into the basement through Hercynian faults (N-S to NE-SW) reworked during the Permian-Triassic to Lower Jurassic extensional events. The source of silver seems to be in black shale and/or in abundant mafic to intermediate magmatic rocks (i.e. microdiorite dykes) consistently observed close to the ore bodies. Silver ores are superimposed on the same lineament to preexisting Fe-As-(Sn) assemblages related to Hercynian events in the central Jebilet and mainly due to the circulation of magmatic and/or metamorphic fluids. However, silver ores have no genetic relationship with magmatic-metamorphic events as suggested by former models. The metallogenic model proposed for the Koudia El Hamra deposit is similar to those proposed for several other silver - base metal (Pb-Zn) deposits from Morocco like the Roc Blanc silver deposit (Jebilet massif) and major silver deposits from the Anti-Atlas belt (Imiter, Zgounder and Bou Azzer) and from Western Europe.
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https://hal-insu.archives-ouvertes.fr/insu-01803965
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Submitted on : Thursday, May 31, 2018 - 10:58:49 AM
Last modification on : Wednesday, June 24, 2020 - 4:19:32 PM

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Félix Nshimiyimana, Samira Essarraj, Mohamed Hibti, Philippe Boulvais, Adrian Joseph Boyce, et al.. The Koudia El Hamra Ag–Pb–Zn deposit, Jebilet, Morocco: Mineralogy and ore fluid characterization. Journal of African Earth Sciences, Elsevier, 2018, 145, pp.1-17. ⟨10.1016/j.jafrearsci.2018.04.019⟩. ⟨insu-01803965⟩

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