Mineralogical and geochemical characteristics of the Amensif Cu, Pb, Zn, (Ag, Au) ore deposit, Western High Atlas, Morocco

Abstract

The Cu, Pb, Zn, Ag-Au deposit of Amensif is located on the northern flank of the western High Atlas. This deposit is hosted in Lower Cambrian carbonate bars and is structurally controlled by NE-SW to E-W trending fault structures and is spatially associated with the Permian 273 Ma Azegour granite. Ore reserves are around 0.5 Mt and grades are 3.21% Zn, 0.58% Pb, 0.86% Cu with 83.31 ppm Ag and 0.41 ppm Au. Sulphide mineralizations occur as a local replacement of carbonate bars rocks. Ore mineralization at Amensif is dominantly composed of chalcopyrite, sphalerite, galena, pyrite and arsenopyrite. Gold is hosted by arsenopyrite and silver was associated with galena and tetrahedrite-tennantite. Gangue minerals include predominantly chlorite, epidote, tremolite, calcite, dolomite, quartz, sericite, minor andradite and vesuvianite. We have recognized three major hydrothermal transformations that affected carbonate bars: intense silicification, hydrothermal dolomitization, locally skarnification and retrograde alteration. Silicification is the main hydrothermal alteration that was accompanied by important replacement textures between sulphide minerals. Lead isotope compositions of galena sampled from two regions in western High Atlas (Amensif and Tighardine) show a short range in 206Pb/204Pb (18.053–18.324), 207Pb/204Pb (15.534–15.577) and 208Pb/204Pb (37.780–37.986) and extend from relatively unradiogenic sulphides to radiogenic and internally inhomogeneous isotopic composition. The Pb isotope signature suggests that Pb-Cu-Zn minerals were generated during the remobilization of lead from the older reservoir in the Cambro-Ordovician volcano-sedimentary units. Combined field, lithological, structural, mineralogical and geochemical data of the Cambrian carbonate-hosted mineralization at Amensif deposit is compatible with polymetallic carbonate replacement deposit type mineralization.

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