Resumen de Le skarn Mo-W-Cu à grenat, wollastonite, pyroxène et vésuvianite d'Azegour (Haut-Atlas, Maroc)

Samia Berrada Hmima, Eric Marcoux, Ahmid Hafid

• The Mo-W-Cu skarn of Azegour is generated at the expense of a sequence dominated by calcareous sedimentary rocks Cambrian in age, within the metamorphic aureole of a Permian granite. Metasomatized layers constituting the skarn are several meters thick, and mainly composed of massive garnetite and/or wollastonitite and seldomly of pyroxenite. Garnets belong to three different types easy to recognize due to their different colors: green-black, brown-black and orange, this later one being present only in the northern part (Toulkine zone) of the skarn. The green-black garnet is very common, forming crystals up to 8 cm, and composed of andradite with locally a core of Al-rich andradite (up to 5% Al2O3). The very common brown-black garnet form thick layers associated with quartz. It often reveals a core of pure andradite surrounded by a Al-rich andradite (up to 10% Al2O3), close to the grossular domain. Orange garnet is only grossular. Pourcentage of spessartine is always weak (4% maximum). Wollastonite is slighly manganiferous, while vesuvianite is F- and Cl-rich (up to 3.3% and 1.2% respectively). Mineralogical association allow to establish the formation of the skarn around 620--650°C, under a pressure of 1.7--2 kbar, and a fCO2 of 31 mole %, in a reducing environment (fO2 of 10-18 to 10-17 atm.). The skarn of Azegour marks the end of Hercynian orogeny and whitnesses of the perennity of a reducing environment highly favorable to sulphide crystallization. Mo-skarn of Azegour seems to have formed at higher temperatures than other Hercynian W-skarn such as Salau (France).