Stable isotope study of the igneous, metamorphic and mineralized rocks of the Edough complex, Annaba, Northeast Algeria

Abstract

The petrogenesis of igneous, metamorphic and mineralized rocks in the Edough massif, NE Algeria, indicates an interplay between crustal and magmatic sources, and magmatic and surface fluids, as determined by sulphur and oxygen isotopic analyses. The Tertiary igneous rocks (microgranites and rhyolites) show a tendency towards I-type granitoids with δ 34S values of +5.4±2.2 ‰ (1 σ) and δ 18O between +5.6 ‰ and +6.9 ‰, with the most hydrothermally altered rocks having the lowest δ 18O values. This is indicative of seawater being a major component of the hydrothermal fluids. Seawater interaction with the granitoids produced enrichment in 34S of sulphide-sulphur in both the microgranites and associated skarn mineralization. However, in the Beleleita W–Sn–(Au) deposit, magmatic fluids dominated the mineralization, reflected by δ 34S values of +1.7 ‰ and +1.8 ‰. The basement amphibolites of Kef Lakhal indicate derivation from a basaltic magma with δ 18O ranging from +4.9 ‰ to +8.6 ‰. Locally altered amphibolite has the lowest δ 18O values suggestive of meteoric water interaction, whereas the highest δ 18O indicate the incorporation of crustal material during the genesis of the amphibolites. Crustal contamination is also reflected in their δ 34S of −18 ‰ to +2.1 ‰, with the most contaminated rocks having the lowest δ 34S. Host Palaeozoic mica schists with δ 18O of +12.7 ‰ and δ 34S of −13.2 ‰ and associated marbles ( δ 34S −9.9 ‰ to −17.4 ‰) are thought to be the most likely contaminants. At the Ain Barbar Fe–Cu–Pb–Zn deposit, δ 34S values range between −9.6 ‰ and −10.8 ‰, indicating that the sulphide-sulphur and base-metals were likely leached from the host Cretaceous flysch and/or the underlying mica schists, with local Tertiary magmatic rocks providing the heat for local convection cells. At Boumaiza Fe-deposit, δ 34S values of the sulphide-sulphur extend from −1.2 ‰ to −8.1 ‰ indicative of magmatic sulphur with the incorporation of substantial amounts of sulphur derived from the host mica schists.