Structural control, magmatic-hydrothermal evolution and formation of hornfels-hosted, intrusion-related gold deposits: Insight from the Thaghassa deposit in Eastern Anti-Atlas, Morocco

Abstract

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The Jbel Saghro Au(–Ag, Cu) and Ag–Hg Metallogenetic Province: Product of a Long-Lived Ediacaran Tectono-Magmatic Evolution in the Moroccan Anti-Atlas

“…615 and ca. 560 Ma [29,48,59,74,75,77,81,82]. (iii) Finally, late to post-orogenic granites with cogenetic volcanic and volcaniclastic cover are emplaced between ca.…”

“…560 and 550 Ma together with subsequent transtensional tectonics [5,29,47,74]. The transition from transpressive to transtensive tectonics remains the subject of debate but it likely occurred between 580 and 560 Ma [29,48,74]. There is still also an ongoing debate on the origin of the two late magmatic events, which are either described as arc-related [29] or as post-orogenic related to an asthenospheric rise beneath the West African Craton, without any active subduction [74,83].…”

“…Indeed, before the 1990s, the Anti-Atlas was mainly interpreted as a collisional belt and the formation of ore deposits was related to orogenic processes, e.g., [43,73,76]. Then, the geology and the ore forming processes were related to the complex evolution of active margin(s) in a subduction and accretion setting, e.g., [29,45,47,48,51,77,82]. This led to the discovery of new Au-Ag occurrences such as those of the Issarfane (0.5 Mt @ 1.8 g/t Au), Qal'at Mgouna and Thaghassa ( Figure 2).…”

“…This led to the discovery of new Au-Ag occurrences such as those of the Issarfane (0.5 Mt @ 1.8 g/t Au), Qal'at Mgouna and Thaghassa ( Figure 2). Simplified geologic map of the Jbel Saghro, after Hindermeyer et al [104], Tuduri [47] and Tuduri et al [48]. U-Pb radiometric ages obtained on zircon [29,48,51,78,[105][106][107][108].…”

“…The strong association of mineral deposits with fluids of moderate to high salinities, suggests interpretations favouring the influence of basinal brines in the ore-forming processes [40,41]. Indeed, processes involving basin-related and(or) surface-related brines resulting from evaporation of seawater in Triassic basins in the formation of ore deposits, up to now interpreted as, deposits related to the late Neoproterozoic felsic magmatic event [42][43][44][45][46][47][48] have been defended by several recent works [40,41,49] although the debate is still open [50]. This controversy mainly concerns the Bou Azzer (Co-Ni-), Imiter (Ag-Hg) and Zgounder (Ag-Hg) mines that represent the main three world-class ore deposits of the Moroccan Anti-Atlas after the Akka gold mine was closed few years ago.…”