Multistage genesis of the late Cretaceous manganese karst-hosted Tasdremt deposit (High Atlas, Morocco)

Augustin Dekoninck, Gilles Ruffet, Yves Missenard, Oriane Parizot, Mohamed Magoua, Abdellah Mouttaqi, Gaetan Rochez, Johan Yans

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Résumé

The eastern part of the Souss Basin (Morocco) contains several Mn deposits in the Tasdremt district. ThreeMn orebodies occur within
the Cenomanian-Turonian dolostones and the Senonian (Coniacian to Maastrichtian) detrital series, the main orebody being located at
the boundary between them. The Mn ores consist of coronadite group minerals, mostly coronadite and hollandite, in a karstified
dolostone. New field observations, petrographic analyses, and geochemical data define the Tasdremt deposits as a karst-hosted
accumulation (11–60 wt.% Mn), particularly enriched in Ba (1.5–8.2 wt.%) and Pb (1.0–5.0 wt.%) with poor contaminations in Al,
Fe, and P. This study shows that the ore-forming process is similar to that occurring in the Imini C3 level, located ~ 100 kmto the northeast.
Such similarities with the high-grade pyrolusite-bearing ore suggest that the Tasdremt deposit is a lateral equivalent of the Imini
deposits. However, the scarcity of pyrolusite in Tasdremt results in lower Mn grades, the Tasdremt ores being considered an aborted/
incomplete system in comparison with the Imini deposits. 40Ar/39Ar geochronology of K-bearing Mn oxides yields late Cretaceous
ages, defining three phases at ~ 91.5 Ma, ~ 77.5–82 Ma, and ~ 65–67 Ma. Although the source of metals remains hypothetical,
mineralizing fluids were carried by O2-free groundwater that mixed with O2-rich shallow meteoric waters at the Tasdremt depositional
site. The dissolution of the host dolostones and the karst environment have provided suitable conditions for the precipitation of Mn
oxides, causing the coeval increase of pH and Eh, respectively. The Early Atlasic deformation during the Late Cretaceous is associated
with mineralization events and was responsible for creation of low stand reliefs from Tasdremt to Imini. This period enabled
karstification and mineralization. Connecting the Tasdremt deposits to other African Mn deposits is difficult since the latter consist
of laterite resting above PaleoproterozoicMn protores, and consequently formed under different conditions from karst-hosted deposits.
It is likely that other Mn occurrences formed along the Atlas belt in similar settings.
langue originaleAnglais
Pages (de - à)935-956
Nombre de pages22
journalMineralium Deposita
Volume56
Numéro de publication5
Les DOIs
Etat de la publicationPublié - 18 sept. 2020

Financement

We are grateful to the ?Office National des Mines et des Hydrocarbures? (ONHYM) for having shared documents, brought logistical and scientific support, and facilitated access to outcrops in the Tiranimine, Tasdremt and Aoufour deposits. We thank Dr. L. Dewaide for her help and advice to collect samples on the field. We appreciate the help of Prof. J. Wouters and Dr. N. Tumanov of the PC2 platform (UNamur) for collecting XRD patterns. We also thank J.-P. Cullus and Prof. F. Boulvain for preparing thin sections, as well as P. Kubben and Prof. A. Bernard for making polished sections. This research also used the resources of the Electron Microscopy Service located at the University of Namur (?Plateforme Technologique Morphologie ? Imagerie?). Y. Missenard and O. Parizot benefited from the French ?Institut des Sciences de l?Univers? (INSU) funding ? Tellus-Syster program. We warmly thank P. Vasconcelos and T. De Putter for their careful and constructive review of this paper. Finally, we express gratitude to A. Gilg (editor) for handling this manuscript to its final version, as well as G. Beaudoin (editor-in-chief).

Bailleurs de fonds
INSU
Institut des Sciences de l’Univers
ONHYM
Office National des Mines et des Hydrocarbures
Université de Namur

    mots-clés

    • manganese deposit
    • tasdremt
    • imini
    • 40Ar/39Ar
    • K-Mn oxides
    • karst
    • Morocco

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