Abstract
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.
Highlights
Since the 2000s, the increasing request for metals and rare earth elements for new technologies initiated/restarted the interest in supergene deposits
Galena, was affected by weathering processes leading to the formation of a secondary, supergene mineralization, mainly represented by malachite, covellite, bornite II and chalcocite II
High Cu content can be observed in the greyish-red conglomerates and sandstones of the Basal Series, as well as in the Tamjout Dolomite Formation, to a lower extent
Summary
Since the 2000s, the increasing request for metals and rare earth elements for new technologies initiated/restarted the interest in supergene deposits. Minerals 2020, 10, 620 solvent extraction (SX) and electron-winning techniques [2,3] facilitate post-extraction treatments for non-sulfide ores (e.g., carbonates, such as malachite). In this context, exploration of new supergene targets has been carried out in many countries, including Morocco, during the last decade. The Tizert site (western Anti-Atlas, Morocco) is considered as the largest copper deposit in the western Anti-Atlas [4].
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