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Néoprotérozoïque terminal REGIONAL GEOLOGY The massif of Ougnat is constituted of a basement schiste-sqndstone of the upper Neoproterozoic surmounted by a set of volcano-sedimentary formations of the terminal Neoproterozoic and limited by a Paleozoic cover. The basement is represented by a succession of sandstone, pelites and grauwackes. It shows locally intrusions of granite, granodiorite and diorite. The terminal Neoproterozoic consists of acidic and basic facies separated by volcano-detrital and sedimentary episodes. II is subdivided in three formations which are from the oldest to the most recent : - Volcanic formation of Tamerzaga, which includes ignimbrites, rhyodacites and andesites. This formation contains the mineralization of Boumadine. - Formation of transition which is volcano-sedimentary, it starts by a level of tuffs, and continues by deposits of breccias, sandstone, limestones, pelites and conglomerates. - Volcanic formation of Aoujane Aissa which is essentially formed of ignimbrites and dacite. These formations are crossed by basic dykes (dolerite, microdiorite and andesite) which are reduced at the mine to andesite dykes NS to N 170°. The massif of Ougnat was subjected to a Neoproterozoic shearing, causing regional faults N30° and associated secondary fractures. It has also been affected by a last stage of extensional fractures NS before finally being assigned by the hercynian essentially compressive Several indices and mineralized occurrences have been recognized in the massif of Ougnat. They can be classified into two types : � Lead-copper mineralization in quartz-carbonate gangue and barium filling fractures EW (Hercynian or probably Liassic). This type of mineralization doesn't have a big economic importance; � A polymetallic sulphide mineralization PBGC, type Boumadine with concentration of Zn, Pb, Ag and Au filling fractures NS to N 160° (Neoproterozoic). The massif also contains other substances such as barite and pyrophyllite. LEGENDE Quaternaire Couverture paléozoïque Ensemble basique terminal Formation d'Aoujane Aissa Formation de transition Formation de Tamerzaga Socle (Néoprotérozoïque supérieur) Granite de Mellab Rhyolites Sill basique de Bou Isseghi Dykes Piste Faille CARTE GEOLOGIQUE SIMPLIFIEE DE L'OUEST DE L'OUGNAT Ü 0 Vers Isilf 2 Km NS N30 NNW Ç Mine Vers Mellab
LOCAL GEOLOGY The Boumadine deposit is hosted in ignimbrite of the volcanic formation of Tamerzaga (terminal Neoproterozoic) based, through a level of detrital brechia, on the folded and metamorphosed basement (upper Neoproterozoic). At the outcrop, the ignimbrite is very heterogeneous and greenish with feldspath phenocrysts in varying proportions. It has an average depth of 400 m around the mine and it decreases until it disappears to the north. It should be noted that some intrusions are contemporaneous to deposit of ignimbrite. This includes trachyandesite sills, chonolites of ryholite, dykes and andesite. Three episodes of alteration were distinguished in the sector of Boumadine, a propylitization affecting formation of Tamerzaga, quartz-sericite alteration around mineralized veins accompanied by development of chlorite and carbonates and related to sulphide deposition with an abundance of pyrite and finally an alteration affecting the post-mineralized formations and marked particularly by a dominant chloritization and reddening. The tectonic pattern affecting Boumadine deposit is characterized by a large accident N160 °, which contains the main mineralization, accompanied by crushing zones (oriented NS and NNW-SSE) in which the veins are hosted. The entire veins are intersected by a hercynian fault system that causes their fragmentation. Boumadine mineralization consists of veins extending over 4 km on the surface. It is marked by discoloration areas (limonite) structures along the subvertical NS and NNW-SSE direction and the thickness of veins varies from 1 to 4 m. This mineralization is hosted in the ignimbrite as veins with 250 to 350 m of deep. It consists of massive pyrite, sphalerite, galena, arsenopyrite and of many other minerals in lesser quantity (chalcopyrite, cassiterite, stannite, enargite, gray copper, etc....). Pyrite is the matrix and forms the central part of the body vein, other sulphides, particularly galena and sphalerite, are more concentrated in the margins of veins. The Boumadine mineralization is epithermal whose equivalents are vein deposits of the Andean chain.
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