Characterization of Weathering Processes of the Giant Copper Deposit of Tizert (Igherm Inlier, Anti-Atlas, Morocco)

The giant Tizert copper deposit is considered as the largest copper resource in the western Anti-Atlas (Morocco). The site is characterized by Cu mineralization carried by malachite, chalcocite, covellite, bornite and chalcopyrite; azurite is not observed. The host rocks are mainly limestones (Formation of Tamjout Dolomite) and sandstones/siltstones (Basal Series) of the Ediacaran/Cambrian transition. The supergene enrichment is most likely related to episodes of uplift/doming (last event since 30 Ma), which triggered the exhumation of primary/hypogene mineralization (chalcopyrite, pyrite, galena, chalcocite I and bornite I), generating their oxidation and the precipitation of secondary/supergene sulfides, carbonates and Fe-oxyhydroxides. The Tizert supergene deposit mainly consists of (i) a residual patchwork of laterite rich in Fe-oxyhydroxides; (ii) a saprolite rich in malachite, or “green oxide zone” where primary structures such as stratification are preserved; (iii) a cementation zone containing secondary sulfides (covellite, chalcocite II and bornite II). The abundance of Cu carbonates results from the rapid neutralization of acidic meteoric fluids, due to oxidation of primary sulfides, by carbonate host rocks. Chlorite is also involved in the neutralization processes in the sandstones/siltstones of the Basal Series, in which supergene clays, such as kaolinite and smectites, subsequently precipitated. At Tizert, as can be highlighted in other supergene Cu-deposits around the world, azurite is absent due to low pCO2 and relatively high pH conditions. In addition to copper, Ag enrichment is also observed in weathered rocks; Fe-oxyhydroxides contain high Zn, As, and Pb contents. However, these secondary enrichments are quite low compared to Cu in the whole Tizert site, which is therefore, considered as relatively homogeneous

(U-Th)/He dating of supergene iron (oxyhydr-)oxides of the Nefza-Sejnane district (Tunisia):new insights into mineralization and mammalian biostratigraphy

The mining district of Nefza-Sejnane (Tunisia) encloses numerous ores and raw material deposits, all formed in relation with successive Fe-rich fluids of meteoric and/or hydrothermal origins. Here, for the first time in Tunisia, (U-Th)/He ages were obtained on supergene goethite from various localities/deposits of the district highlight direct dating of significant weathering episodes during late Tortonian and late Pleistocene. These weathering events are most likely associated with favorable conditions that combine (i) wet climate displaying sufficient meteoric water/fluid; and (ii) regional exhumation, due to large-scale vertical lithospheric movements enhancing the percolation of fluids. Matched with previous works, these results refine the stratigraphic frame for the polymetallic mineralization and clay deposits in the district, confirming the influence of meteoric fluids circulation during the late Cenozoic. As a consequence of the new (U-Th)/He data, we moreover propose a taxonomic and stratigraphic revision of the well-known mammalian fauna from the Fe-rich Douahria locality, suggesting an early Tortonian age for the fossils, i.e., prior to the first episode of meteoric event in the area