The Polymetallic (W–Au and Pb–Zn–Ag) Tighza District (Central Morocco): Ages of Magmatic and Hydrothermal Events

International audienceThe W–Au, Pb–Zn–Ag, and Sb–Ba deposits of the polymetallic Tighza-Jbel Aouam district (central Meseta, Morocco), hosted in Paleozoic rocks surrounding late Variscan granite stocks, have been considered of magmatic-hydrothermal origin. The spatial distribution of the mineralization was attributed in early studies to zoning around a supposed hidden batholith. New geophysical data (El Dursi 2009) and U/Pb geochronology on zircon and monazite grains (this study) allow revision of this model, giving insights of a more complex setting and history for the Tighza-Jbel Aouam district. The W–Au mineralization formed at 295–280 Ma and is related to a magmatic event visible only in a large hydrothermal biotitic alteration halo, thus suggesting the presence of a hidden batholith. This mineralization cuts the granitic stocks that are dated at 320–300 Ma. From the occurrence of large veins, stockworks, sheeted veins, and disseminations in skarns, the W–Au deposit is considered similar to a porphyry-type deposit. The currently mined Pb–Zn–Ag deposit, which is spatially separated from the W–Au deposit, developed during an epithermal magmatic-hydrothermal episode dated at 254 ± 16 Ma. The polymetallic district of Tighza-Jbel Aouam thus appears to contain Cordilleran-style, porphyry-type mineralization (W–Au) followed by epithermal mineralization (Pb–Zn–Ag), both being related to pulses of calc-alkaline magmatism. Late Variscan and Permo-Triassic transpressive tectonics in the region localized magma emplacement and the generation of genetically associated hydrothermal fluids, with the magmas originating in the mantle and the continental crust