The Cu-Mo±Au Mineralizations Associated to the High-K Calc-Alkaline Granitoids from Tifnoute Valley (Siroua massif, Anti-Atlas, Morocco): an Arc-Type Porphyry in the Late Neoproterozoic Series

The Tifnoute valley Cu-Mo±Au mineral occurrences are located NW of Siroua massif in the central Moroccan Anti-Atlas. This mineralization appears to be associated to the Imourkhssan granite and the Asskaoun granodiorite dated respectively 561 ± 3 and 558 ± 2 Ma. These highly potassic granitoids show an arc signature and are in-placed in an extensional tectonic setting typical of the post-collision Late Pan-African period. In places, these rocks are strongly to slightly affected by hydrothermal alterations of phyllic, propylitic and argillic types with development of a pyritic facies around the Imourkhssan granite. The mineralization can be divided into two types: A molybdenite mineralization and some sulphides spatially linked to the Imourkhssan granite. It is disseminated in the granite or appears in lamellar or pluri-millimetric fragments. It also occurs as spots and nets along chloritized fractures planes oriented NNE-SSW and dipping 40 to 60 SE. The paragenesis consists of molybdenite, pyrite, chalcopyrite and sphalerite. Talat N’Lbnour Cu-Au mineralization linked to NS fractures affecting Askaoun granodiorite. The vein is about 0.5 to 2 m thick that extends about 400 m. The mineralized fractures are filled essentially with quartz, siderite and chlorite. Metallographic study reveals a diverse paragenesis that consists of pyrite, chalcopyrite, gold, bornite and chalcocite. The secondary paragenesis consists of chalcopyrite, covellite, bornite, malachite, azurite and hematite. These features of these mineralizations are discussed in the context of an arc-type Cu-Mo±Au porphyry mineralization. Keywords: Anti-Atlas, Siroua, Molybdenum, Copper, Gold, Porphyry

The Ediacaran volcanic rocks and associated mafic dykes of the Ouarzazate Group (Anti-Atlas, Morocco): Clinopyroxene composition, whole-rock geochemistry and Sr-Nd isotopes constraints from the Ouzellarh-Siroua salient (Tifnoute valley)

International audienceBelonging to the huge Ouarzazate volcanic Group that covered the whole Anti-Atlas during the late Ediacaran (580-545 Ma), the Tifnoute valley volcanic formations are mainly pyroclastic and show a large composition, from trachybasalt to rhyolite and are crosscut by dolerite dykes. The Tifnoute valley volcanic rocks are located within a rigid salient of the Anti-Atlas that gives them special extreme characteristics. Due to the heavy greenschist alteration that affects this volcanic group, we focused the more immobile elements, but as REE can also be affected, we used the composition of unaltered clinopyroxene crystals to determine the nature of these volcanic rocks. The clinopyroxene is an augite diopside in the basalt, an augite in the andesite and an augite-salite in the dolerite. Petrography of the Tifnoute mafic volcanic rocks and clinopyroxene compositions indicate the presence of two magmatic series: (i) older high-K calc-alkaline (alkali-calcic) andesite and basalt characterized by the early crystallization of Fe-Ti oxides and of the late fractionation of plagioclase, the modal proportion of the latter increasing from the basalt to the andesite and (ii) younger alkalic dolerite dykes. With clinopyroxene trace element compositions obtained using laser ablation ICP-MS, we calculated the composition of the melts in equilibrium with the pyroxenes.The volcanic rocks of the Tifnoute Valley have positive εNd570 (+1.7 to +5.0), low Sri (<0.7063), and NdTDM model ages ranging from 0.80 to 1.14 Ga, indicating a mostly depleted Neoproterozoic source with limited involvement of the Eburnian lithosphere for the Tifnoute magmas. This depleted source is the young lithospheric mantle for the alkali-calcic series and the asthenosphere for the younger alkalic series. The Tifnoute Valley volcanic rocks emplaced in a Pan-African transtensive post-collisional environment that evolved towards the major rifting event that will give rise to the Rheic ocean, in a similar way to what occurred just after the Variscan orogeny during the Triassic period that evolved to the Tethys ocean opening