Mapeo de redes de fracturas mediante imágenes Landsat-8 OLI en la zona minera de Jbel Tijekht en el Anti-Atlas oriental de Marruecos

Jbel Tijekht is one of the most important geological structures of the Ougnat-Ouzina ridge in the Eastern Anti-Atlas. This crescent-shaped massif was affected by a network fractures that is visible at different scales. It is particularly rich in numerous mineralized veins of barite, and is associated with other minerals (e.g. pyrite, chalcopyrite, sphalerite and galena). In order to study fracture systems in the mining zone of Jbel Tijekht, we opted for a combination of remote sensing and field investigation that became an important tool for fracture mapping and mineral exploration. This work presents a methodological approach to detect structural lineaments. For this purpose, various techniques were applied to the Landsat 8 image to improve the visibility of linear structures. After the radiometric and atmospheric corrections, the colors composites and directional filters applied to the Principal component (PC1) allow for the establishment of a lineaments map of Jbel Tijekht. The validation and the correction of lineaments are based on preexisting documents combined with field observations. Statistical analysis of the lineament map allows for identification of at least three directional fracture systems with average NS, NE-SW, and ENE-WSW orientations. NS and NE-SW systems show a high density in the largest part of the study area. These results clearly overlap different tectonic structures and existing veins. It allowed for the establishment of a geological link between lithology, fractures systems and mineralization. The fracture density can be attributed to the last variscan brittle phases, reflecting the rheology of rock units; the high fracture density is observed in competent rocks such as the Tabanit sandstones. These zones constitute a favorable area for mineralization deposits.El Jbel Tijekht es una de las estructuras geológicas más importantes de la cordillera de Ougnat-Ouzina en el Anti-Atlas Oriental. Este macizo en forma de media luna fue afectado por una red de fracturas que es visible a diferentes escalas. Es particularmente rico en vetas mineralizadas de barita y está asociado con otros minerales (por ejemplo, pirita, calcopirita, esfalerita y galena). Para estudiar los sistemas de fracturas en la zona minera de Jbel Tijekht, optamos por una combinación de teledetección e investigación de campo que se convirtió en una importante herramienta para la cartografía de las fracturas y la exploración de minerales. Este trabajo presenta un enfoque metodológico para detectar los lineamientos estructurales. Para ello, se aplicaron diversas técnicas a la imagen del Landsat 8 para mejorar la visibilidad de las estructuras lineales. Tras correcciones radiométricas y atmosféricas, los colores compuestos y los filtros direccionales aplicados al componente principal (PC1) se pudo establecer un mapa de lineamientos para Jbel Tijekht. La validación y corrección de estos lineamientos se basan en documentos preexistentes combinados con observaciones de campo. El análisis estadístico del mapa de lineamientos permite la identificación de al menos tres sistemas de fractura direccional con orientaciones promedio NS, NE-SW y ENE-WSW. Los sistemas NS y NE-SW muestran una alta densidad en la mayor parte del área de estudio. Estos resultados claramente se superponen a diferentes estructuras tectónicas y a las vetas existentes. Esto permitió establecer un vínculo geológico entre la litología, los sistemas de fracturas y la mineralización. La densidad de fracturas puede atribuirse a las últimas fases de fragilidad del orógeno varisco, lo que refleja la reología de las unidades de roca; la alta densidad de fractura se observa en las rocas competentes como las areniscas de Tabanit. Estas zonas constituyen un área favorable para los depósitos de mineralización

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

Field, geochemistry and Sr-Nd isotopes of the Pan-African granitoids from the Tifnoute Valley (Sirwa, Anti-Atlas, Morocco): a post-collisional event in a metacratonic setting

International audienceIn the Tifnoute Valley, three plutonic units have been defined: the Askaoun intrusion, the Imourkhssen intrusion and the Ougougane group of small intrusions. They are made of quartz diorite, granodiorite and granite and all contain abundant mafic microgranular enclaves (MME). The Askaoun granodiorite and the Imourkhssen granite have been dated by LA-ICP-MS on zircon at 558 ± 2 Ma and 561 ± 3 Ma, respectively. These granitic intrusions are subcontemporaneous to the widespread volcanic and volcano-detrital rocks from the Ouarzazate Group (580-545 Ma), marking the post-collisional transtensional period in the Anti-Atlas and which evolved towards alkaline and tholeiitic lavas in minor volume at the beginning of the Cambrian anorogenic intraplate extensional period. Geochemically, the Tifnoute Valley granitoids belong to an alkali-calcic series (high-K calc-alkaline) with typical Nb-Ta negative anomalies and no alkaline affinities. Granitoids and enclaves display positive εNd-560Ma (+0.8 to +3.5) with young Nd-TDM between 800 and 1200 Ma and relatively low 87Sr/86Sr initial ratios (Sri: 0.7034 and 0.7065). These values indicate a mainly juvenile source corresponding to a Pan-African metasomatized lithospheric mantle partly mixed with an old crustal component from the underlying West African Craton (WAC). Preservation in the Anti-Atlas of pre-Pan-African lithologies (c. 2.03 Ga basement, c. 800 Ma passive margin greenschist-facies sediments, allochthonous 750-700 Ma ophiolitic sequences) indicates that the Anti-Atlas lithosphere has not been thickened and was never an active margin during the Neoproterozoic. After a transpressive period, the late Ediacaran period (580-545 Ma) is marked by movement on near vertical transtensional faults, synchronous with the emplacement of the huge Ouarzazate Group and the Tifnoute Valley granitoids. We propose here a geodynamical model where the Tifnoute Valley granitoids as well as the Ouarzazate Group were generated during the post-collisional metacratonic evolution of the northern boundary of the West African craton. The convergence with the peri-Gondwanan active margin produced brittle fracturing of the cratonic boundary without thickening, allowing rising of magmas. The Tifnoute Valley granitoids display a metasomatized lithospheric mantle source mixed with a minor ancient (2 Ga) continental crust component from the underlying WAC