Structural Analysis and Paleostress Evolution in the Imiter Silver Mining Region, Eastern Anti Atlas, Morocco: Implications for Mineral Exploration

Abstract

Development and concentration of many ore deposits at the regional and district scales closely depend on structural geology, especially in polydeformed basements. The superposition of many deformation periods highlights the complexity of the structural context and expected potential location of mineralization zones. The formation and concentration of hydrothermal ore deposits is highly dependent on structural controls. On the NE flank of the Saghro massif (Eastern Anti-Atlas, Morocco), the Imiter silver mining region has been affected by multiple tectonic events since the Precambrian and throughout the Phanerozoic. In this investigation, a structural analysis of the different geological units revealed multi-stage deformation, beginning with the late Pan-African-Cadomian event, and ending with the last Cenozoic exhumation of the area. At least eight tectonic regimes have been identified. The Imiter basement, formed by the Cryogenian-early Ediacaran “flysch-like” Saghro Group, has been folded in low-grade metamorphic conditions, followed by an ENE-WSW brittle compressive event. These deformations occurred before to the early Ediacaran during the compressional and/or transpressional late Pan-African-Cadomian events (600–580 Ma). The unconformably overlaying deposition of the late Ediacaran Ouarzazate Group takes place in a WNW-ESE extensional setting and then involved in a NNW-SSE compressional event that occurred concurrently with a regional exhumation and erosion stages. A similar extensional event appears to have controlled the middle Cambrian sedimentation, the oldest Paleozoic deposits in this area. During the late Carboniferous, Variscan shortening was recorded by NW-SE transpressional deformation responsible for combined dextral strike-slip and southward thrusts. The Imiter silver mining region is part of the Moroccan Sub-Meseta Zone along with Paleozoic inliers of the Skoura and Tamlelt on the southern side of the High Atlas. The Mesozoic evolution began with the Late Triassic NNW-SSW transtensional tectonic regime with a northeast trending CAMP (Central Atlantic Magmatic Province) dyke during the Pangea breakup. Ultimately, the Imiter silver mining region experienced NNW-SSE Atlasic shortening during the uplift of the adjacent High Atlas. Over time, the direction of implemented tectonic stress and its effect on various geological units can elucidate the relationship between tectonism and hydrothermal silver mineralization in the Imiter region. In conclusion, structural analysis and investigation of paleostress development can be one of the most important factors for successful exploration plan and resource recovery in the Imiter region. An analysis of geological structures in determining feasible mineralization zones is crucial for future safe mining operation in the study area and can be extrapolated to other ore mining regions.

Analyse structurale et reconstitution des paléochamps de contraintes tardi-hercyniens dans la boutonnière d’Aouli (massif de la Haute Moulouya, Maroc)

“…Dans le massif de Jebilet, Zouicha et al (2022) ont révélé deux épisodes déformation au cours de la période tardi-hercynienne: (i) le premier compressif NNE-SSW et daté entre 310 et 280 Ma et (ii) le deuxième extensif E-W, daté de 280-260 Ma et permettant la formation de grabens et d'hémi-grabens N-S remplis en sédiments permiens. Les effets de la phase de déformation tard-hercynienne avec les mêmes directions des axes de contraintes ont été également observés dans le Maroc central (Allary et al, 1976), dans les Rehamna (El Kamel, 1987), dans le district minier d'Imiter (Anti-Atlas oriental) (Atif et al, 2022) et dans le Haut Atlas central (De Koning, 1957;Laville, 1980;Ferrandini et al, 1987). En ef- (Emberger, 1965a), de la carte géologique de Mibladen au 1/50.000 (Raddi et al, 2013), en plus des failles cartographiées au cours du présent travail.…”