Résumé: The El Aouana igneous rocks are part of the Miocene magmatic suite that extends from Northern Tunisia to Morocco through the Algerian coast in the Maghrebin chain. These rocks are composed of volcanic (andesites and dacites) and subvolcanic (micodiorites and microgranodiorites) lithologies that intruded both the Cretaceous and Oligo-Miocene nappes, and the Miocene post-nappe sediments. The andesites are composed of plagioclase, amphibole and pyroxene phenocrysts that are set in a microlithic groundmass. The dacites are plagioclase-rich and rare, highly altered ferromagnesian minerals. The microdiorites and microgranodiorites are hornblende-bea­ring rocks with plagioclase, pyroxene and rare biotite phenocrysts that are set in a microcrystalline groundmass. Geochemical observations show that the rocks are calc-alkaline with I-type affinity. They are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) compared to high field strength elements (HFSE) and heavy rare earth elements (HREE). The negative Nb, P and Ti anomalies observed on the multi-element patterns are imprints of magmas originated from subduction zones. Field, petrological and geochemical investi­gations show that the El Aouana Miocene igneous rocks are emplaced in a post-collisionnal setting. These rocks show similarities with the metaluminous, post-collisionnel granitoids of north-eastern Algeria which are thought to have been derived from a metasomatized mantle source as a consequence of ‘slab break-off’ underneath the North African margin.

Résumé: Abstract The Hameimat North and South massifs, located in the peri-diapiric saline province of the Eastern Saharan Atlas, host polymetallic Zn–Pb–F–Ba–Sr mineralizations. These mineral concentrations develop either directly above the Triassic evaporitic bodies or within the overlying Albian–Aptian sedimentary cover. The paragenetic assemblage is more diverse in the Hameimat North massif, reflecting the greater extent and proximity of Triassic outcrops. Sulfur isotopic values obtained from Triassic gypsum (δ³⁴SCDT = +13.4 to +15.1‰, n=3) are consistent with the Triassic seawater sulphates and those of regional Triassic evaporites. Sulfate minerals (barite and celestine) display relatively high δ³⁴SCDT values (+18 to +24‰, n=6), consistent with a Triassic evaporitic sulphate source. In contrast, sulphide minerals exhibit lower δ³⁴SCDT values (−2.2 to +10.4‰, n=22), indicating that sulphide sulphur was derived from Triassic sulphates through thermochemical sulphate reduction (TSR), a process supported by fluid inclusion data, show hot fluids, with homogenization temperatures around 115°C. The carbon and oxygen isotopic compositions of the host carbonates (δ¹³CPDB= +0.2 to +4.7‰; δ¹⁸OSMOW= +20.6 to +23.1‰) reflect an inorganic carbon source and oxygen derived from the leaching of Cretaceous carbonates, implying significant fluid–rock interactions. Combined isotopic and metallographic evidence indicates that the ore-forming fluids were mainly of basinal origin, having circulated through Triassic evaporites and Cretaceous carbonates. Their isotopic signatures closely resemble those of Mississippi Valley-type (MVT) deposits, highlighting the major role of Triassic diapirism and fluid–carbonate interactions in the genesis of these polymetallic mineralizations.