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

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.

The Missing Link in the Genesis of the Lower Paleozoic Copper Deposits of the Anti-Atlas (Morocco): The Late Triassic Central Atlantic Magmatic Province Event

“…The occurrence of copper mineralization in the Anti-Atlas Lower Paleozoic cover was governed by the CAMP tectonomagmatic event, associated with the Upper Triassic fragmentation of Pangea. At that time, the Anti-Atlas is considered to be the southern shoulder of the northern Atlas-Triassic rift and can be viewed as a large area undergoing a left-lateral transtensional tectonic regime, bordered northward by the South Atlas Fault [111][112][113][114] and by the Bas Drâa Fault at the foot of Jbel Ouarkziz to the south [25]. Between these two regional lineaments is a stretched area that develops en échelon fault corridors filled with CAMP doleritic magma (Figure 13).…”

Origin of the Moroccan Touissit-Bou Beker and Jbel Bou Dahar Supergene Non-Sulfide Biomineralization and Its Relevance to Microbiological Activity, Late Miocene Uplift and Climate Changes

“…Similarly, a climate with alternating wet and dry seasons could promote the formation of weathering and oxidizing solutions, which ultimately would lead to the development of karst networks and replacement of the sulfides [3]. Equally important, uplift and longwavelength vertical movements [15,32,[75][76][77][78] may lead to enhanced fracturing of the host rock, creating preferential pathways for the downward and lateral flow of metal-bearing groundwaters and consequently migration of the supergene alteration front.…”

Neoformation of exotic copper minerals from gel-like precursors at the Exótica deposit, Chuquicamata, Chile

“…If the partial pressure of CO 2 is high enough, azurite is thermodynamically favored (Vink 1986;Kiseleva et al 1992). Additionally, azurite requires more acidic conditions than malachite and can transform into it (Vink 1986;Crane et al 2001;Melchiorre and Enders 2003;De Putter et al 2010;Poot et al 2020). Due to their different stability, azurite cannot be transformed into chrysocolla, while malachite can be replaced by chrysocolla (Vink 1986;Crane et al 2001).…”