U/Pb Ages of Magmatism in the Zgounder Epithermal Ag–Hg Deposit, Sirwa Window, Anti-Atlas, Morocco

The Zgounder epithermal Ag–Hg deposit (Jbel Sirwa inlier, Anti-Atlas, Morocco) is hosted in Neoproterozoic volcanosedimentary and magmatic rocks in a Pan-African belt. Strongly altered U-rich zircons were analyzed for in situ SIMS U–Pb ages of multiple rhyolitic intrusions spatially associated with the Ag–Hg mineralization. Morphological features, internal microstructures, and chemical characteristics allow the discrimination of two types of zircon, magmatic and hydrothermal. U/Pb data reveal four main geologic events: (1) ca. 815 Ma corresponding to inherited cores of zircons that reflect the reworking of Neoproterozoic crust during the Pan-African (~885–555 Ma) orogenic cycle; (2) 610 ± 7 Ma; (3) 578 ± 4 Ma corresponding to the emplacement-crystallization of multiple rhyolitic intrusions and the large magmatic input within the upper crust of the Pan-African chain during the late Neoproterozoic; and (4) 564 ± 15 Ma, a less-precise age obtained on hydrothermally altered domains that may be related to a dissolution-reprecipitation mechanism in U-rich magmatic zircons. Presently, this last age represents the best estimate for the timing of hydrothermal albitization/mineralization in the Zgounder epithermal Ag–Hg deposit.