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Mineralium Deposita

, Volume 51, Issue 1, pp 13–23 | Cite as

Detailed mineralogy and petrology of manganese oxyhydroxide deposits of the Imini district (Morocco)

  • A. Dekoninck
  • A. Bernard
  • J. Barbarand
  • B. Saint-Bezar
  • Y. Missenard
  • R. Lepretre
  • O. Saddiqi
  • J. Yans
Article

Abstract

Manganese ore in the Cenomanian-Turonian dolostone of the Imini district (south of the High Atlas, Morocco) displays a high Mn content due to the occurrence of pyrolusite, cryptomelane, hollandite sensu stricto, coronadite, romanechite, and lithiophorite. The orebodies occur mainly as three stratabound layers along the ~25-km-long ore belt following a WSW-ENE direction. Using scanning electron microscopy (SEM-EDS) coupled with X-ray diffraction (XRD), we here refine the mineralogy and petrology of Mn oxides and oxyhydroxides in order to constrain the paragenetic sequence and define the main processes of ore formation. Deposition and concentration of Mn oxyhydroxides follow a two-step sequence after dolomitization: (1) replacement of dolomite fabric (dolomite micrite and dolomite rhombs) by hollandite group minerals leading to a textural conservation and then (2) neoformation of collomorphous aggregates in an opened and brecciated system. These observations are consistent with a multistage evolution including multiple reworking and brecciation. Pyrolusite is the main Mn oxide observed in the Imini district during both early and late stages. The superficial environment provides supergene conditions suitable for the deposition of only Mn oxyhydroxides. This supergene environment and the occurrence of multiple bands of hollandite group minerals indicate an external migration (allochthonous supply) of Mn and associated elements, contemporaneous to an in situ chemical and mechanical dissolution of the host dolostone. The lithological heterogeneities of dolostone and its chemical environment compared to less permeable surrounding rocks may have provided the conditions to concentrate Mn oxides and oxyhydroxides.

Keywords

Imini Manganese deposits Weathering Cretaceous dolostone Hollandite group minerals 

Notes

Acknowledgments

We thank the IMINI mine and the Société Anonyme Chérifienne d’Études Minières (SACEM) for giving the field authorizations and advice on the location of sampling sites. Thanks are due to two anonymous reviewers who greatly improved this manuscript as well as A. Cheilletz and B. Lehmann for their careful editing.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.Département de GéologieNaGRIDD, Université de NamurNamurBelgique
  2. 2.Département des Sciences de la Terre et de l’Environnement, Laboratoire de Minéralogie et Géochimie AppliquéeUniversité Libre de BruxellesBruxellesBelgique
  3. 3.Département des Sciences de la Terre, Relief et BassinUniversité Paris Sud, UMR CNRS-UPS 8148 IDESOrsayFrance
  4. 4.Laboratoire GéosciencesUniversité Hassan IICasablancaMaroc

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