Abstract
The Jbel Saghro is interpreted as part of a long-lived silicic large igneous province. The area comprises two lithostructural complexes. The Lower Complex consists of folded metagreywackes and N070–090°E dextral shear zones, which roughly results from a NW–SE to NNW–SSE shortening direction related to a D1 transpressive tectonic stage. D1 is also combined with syntectonic plutons emplaced between ca. 615 and 575 Ma. The Upper Complex is defined by ash-flow caldera emplacements, thick and widespread ignimbrites, lavas and volcaniclastic sedimentary rocks with related intrusives that were emplaced in three main magmatic flare ups at ca. 575, 565 and 555 Ma. It lies unconformably on the Lower Complex units and was affected by a D2 trantensive tectonic stage. Between 550 and 540 Ma, the magmatic activity became slightly alkaline and of lower extent. Ore deposits show specific features, but remain controlled by the same structural setting: a NNW–SSE shortening direction related to both D1 and D2 stages. Porphyry Au(–Cu–Mo) and intrusion-related gold deposits were emplaced in an earlier stage between 580 and 565 Ma. Intermediate sulfidation epithermal deposits may have been emplaced during lull periods after the second and (or) the third flare-ups (560–550 Ma). Low sulfidation epithermal deposits were emplaced late during the felsic alkaline magmatic stage (550–520 Ma). The D2 stage, therefore, provided extensional structures that enabled fluid circulations and magmatic-hydrothermal ore forming processes.
Highlights
In northwest Africa, the Anti-Atlas, Ougarta and Hoggar domains consist of pericratonic terranes located at the margin of the West African Craton (WAC, Figure 1a) and that were mostly amalgamated from Palaeoproterozoic to Phanerozoic times [1,2,3,4,5]
Intense felsic magmatism may occur as silicic large igneous provinces (SLIPs) [12,14]
LIPs are commonly related to a wide variety of metal deposits [17] including world-class deposits such as magmatic sulfide ore deposits associated with mafic and ultramafic magmatism (Ni, Cu, PGE, Cr, Ti, Fe [18,19]), with carbonatite and peralkaline complexes (Nb, Ti, REE, Zr [20,21]), or with diamondiferous kimberlites [22]
Summary
In northwest Africa, the Anti-Atlas, Ougarta and Hoggar domains consist of pericratonic terranes located at the margin of the West African Craton (WAC, Figure 1a) and that were mostly amalgamated from Palaeoproterozoic to Phanerozoic times [1,2,3,4,5]. 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] 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. Its characterisation will be the subject of work currently in progress
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