Éditeur(s) : HAL CCSD
Résumé : International audience
The Imiter silver mine is a world-class deposit located in the Easternpart of the Anti-Atlas (Morocco). The deposit is hosted by Cryogenianblack shales and Ediacaran volcanics, and unconformablyoverlain byPaleozoic sedimentary rocks. The paragenetic sequence for the ganguemineral is composedby amacroscopically white quartz (Qz1) associatedwith the deposition of galena and scarce silver mineralsas matrixof hydraulic breccias, followed by a grey quartz (Qz2) associated withthe main silver deposition event and a first generation of scarcedolomite(Dol1). A third episode is characterized by massive pink dolomite precipitation(Dol2) with minor quartz (Qz3) and base metals. Finally, asurficial event affects the mineralisation and is responsible for a secondaryore enrichment.Microthermometry study coupled with Raman analyses reveals thatfluid inclusions are CaCl2-dominated. The general trend is a decreaseof temperature from Qz1 (250°C) to Dol1 (80°C) then Dol 2 (probablybelow 70°C) depositions. Fluid salinity increases from Qz1 (6.3 to 19.0wt % NaCleq) to Dol1 (27.2 % wt NaCleq), and decreases with the precipitationof Dol2 associated with quartz 3 (15 %wt NaCleq). The 18Oisotopic composition of fluids in equilibrium with quartz and dolomitesuggestsamagmatic,metamorphic and/or basinal origin for the fluid atthe origin of Qz1, and that meteoric / surficial basinal brinesmay be atthe origin of Dol2.The proposed model to explain the ore forming processes in Imiter is amixing of Ca-brines, probably providing chloride complexes, with a hotNaCl fluid of lower salinity, leading to the precipitation of silver.Theresults favour the important role of calcic brines, whose origin remainsmatter to debate in such a giant depositand for whom age of emplacementis strongly discussed.
24 ème Réunion des sciences de la Terre 2014
Pau, France

insu-01080858
https://hal-insu.archives-ouvertes.fr/insu-01080858

Éditeur(s) : HAL CCSD
Résumé : International audience
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.
Let's talk ore deposits, proceeding of the eleventh biennial sga meeting
Antofagasta, Chile

hal-00601984
https://hal-brgm.archives-ouvertes.fr/hal-00601984
https://hal-brgm.archives-ouvertes.fr/hal-00601984/document
https://hal-brgm.archives-ouvertes.fr/hal-00601984/file/SGA2011_0234.pdf