Rare earth elements as proxies of supergene alteration processes from the giant Imiter silver deposit (Morocco)

Johann Tuduri (1) , Olivier Pourret (2) , Alain Chauvet (3) , Luc Barbanson (4) , Abdelaziz Gaouzi (5) , Aomar Ennaciri (5)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 Institut Polytechnique LaSalle Beauvais
3 Géosciences Montpellier
4 ISTO - Institut des Sciences de la Terre d'Orléans
5 SMI - Société métallurgique d'Imiter

The giant Imiter silver mine located at the northern edge of the West African craton in Morocco is assumed to be a late Neoproterozoic epithermal deposit mainly characterized by a hypogene paragenesis of Agrich sulphides and sulfosalts, and Ag-Hg alloys occuring preferentially in quartz-rich veins. The secondary enrichment zone at Imiter reaches a thickness of 50 to 150 m below ground surface. The upper levels, famous because of giant native silver crystals, grade up to 300 kg/t. Metallographic observations, SEM-EDS and XRD analyses reveal the presence of a quite complex secondary paragenesis made of acanthite, cinnabar, imiterite, perroudite, cerussite, mimetite, iron oxyhydroxides, synchisite and coronadite. Supergene alteration processes of the giant Imiter silver mine deposit consist of the remobilisation of the primary hypogene paragenesis by (i) deep and old basinal brines and (ii) downward infiltrations of surficial waters becoming progressively more reduced and F-enriched in response to fluid-rock interactions. Development of such a supergene mineralization strongly suggests prevalence of arid to semiarid conditions.

Keywords: Ag; secondary ore; sulfohalide; lanthanides

Domains: Earth Sciences

Johann Tuduri, Olivier Pourret, Alain Chauvet, Luc Barbanson, Abdelaziz Gaouzi, et al.. Rare earth elements as proxies of supergene alteration processes from the giant Imiter silver deposit (Morocco). 11th Biennal meeting SGA 2011, Sep 2011, Antofagasta, Chile. pp.982. ⟨hal-00601984⟩