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

Nshimiyimana, F., Essarraj, S., Hibti, M., Boulvais, P., Boyce, A. J. , Marignac, C. and Maacha, L. (2018) The Koudia El Hamra Ag–Pb–Zn deposit, Jebilet, Morocco: mineralogy and ore fluid characterization. Journal of African Earth Sciences, 145, pp. 1-17. (doi: 10.1016/j.jafrearsci.2018.04.019)

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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.

Item Type:Articles
Additional Information:This study has been financed by Georessources Laboratory (Cadi Ayyad University - Morocco), CREGU – University of Lorraine, (Nancy, France) and MANAGEM Group – Morocco.
Glasgow Author(s) Enlighten ID:Boyce, Professor Adrian
Authors: Nshimiyimana, F., Essarraj, S., Hibti, M., Boulvais, P., Boyce, A. J., Marignac, C., and Maacha, L.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Journal of African Earth Sciences
ISSN (Online):1879-1956
Published Online:08 May 2018

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