Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8913360 | Journal of African Earth Sciences | 2018 | 54 Pages |
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.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geology
Authors
Félix Nshimiyimana, Samira Essarraj, Mohamed Hibti, Philippe Boulvais, Adrian Joseph Boyce, Christian Marignac, Lhou Maacha,