Forming conditions and age of native silver deposits in Anti-Atlas (Morocco)

The Jbel Saghro Au(–Ag, Cu) and Ag–Hg Metallogenetic Province: Product of a Long-Lived Ediacaran Tectono-Magmatic Evolution in the Moroccan Anti-Atlas

“…The ore deposit might also be the result of basin inversion that expelled deep Ag-rich brines during, or at the end, of the Palaeozoic orogeny [41,175]. Recent 40 Ar/ 39 Ar age measured at 255 ± 3 Ma on adularia from stage 1 quartz vein supports the late Palaeozoic brine model [38].…”

“…Indeed geochronological methods (e.g., Re/Os, Ar/Ar) frequently give younger ages than expected though possible resetting of dating materials and (or) ore remobilisation are rarely discussed. For instance, the Imiter deposit would coincide with the Permo-Triassic boundary [38]. Similarly, a late Carboniferous age has been proposed for ore enrichment at BouAzzer with a possible earlier pre-mineralising stage [39].…”

“…This controversy mainly concerns the Bou Azzer (Co-Ni-), Imiter (Ag-Hg) and Zgounder (Ag-Hg) mines that represent the main three world-class ore deposits of the Moroccan Anti-Atlas after the Akka gold mine was closed few years ago. The Imiter concentration has been proposed to be associated with the 550 ± 3 Ma rhyolitic magmatism [51], a hypothesis recently controverted by Ar-Ar geochronology [38] and palaeo-fluid geochemistry investigations [41]. The Zgounder deposit is supposed to be emplaced around 564 ± 5 Ma at the same time as rhyolitic intrusions [46,52] although fluid geochemistry would suggest a Triassic fluid contribution [41,49] sedimentary.…”

Basinal Brines at the Origin of the Imiter Ag-Hg Deposit (Anti-Atlas, Morocco): Evidence from LA-ICP-MS Data on Fluid Inclusions, Halogen Signatures, and Stable Isotopes (H, C, O)

“…If the brines are linked to the Permian-Triassic formation, this process is younger than 260 to 200 Ma. Recently, an age of 254.7 ± 3.2 Ma was obtained by Borisenko et al (2014), using Ar/Ar dating on adularia from the Imiter Ag ores. Adularia can therefore be attributed to a diagenetic feldspatization at an age close to the Permian-Triassic boundary, and the Ag ores that were deposited slightly later than the adularia crystallization are thus younger than 254 Ma at least.…”

“…No detailed determination of the ore fluid chemistry in relationship to metal deposition exists and numerous studies question magmatic Neoproterozoic models of Ag deposition at Imiter (Essarraj et al, 2005;Borisenko et al, 2014). The present study focuses on the paragenetic sequence of Ag ores with the successive stages of fluid circulation in order to determine the physical and chemical properties and origin of the ore fluids as well as the mechanisms that control Ag ore formation.…”