Stable isotope study of the igneous, metamorphic and mineralized rocks of the Edough complex, Annaba, Northeast Algeria
✍ Scribed by R. Laouar; A.J. Boyce; Y. Ahmed-Said; A. Ouabadi; A.E. Fallick; A. Toubal
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 335 KB
- Volume
- 35
- Category
- Article
- ISSN
- 1464-343X
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✦ Synopsis
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 d 34 S values of þ5:4 AE 2:2‰ (1r) and d 18 O between þ5:6‰ and þ6:9‰, with the most hydrothermally altered rocks having the lowest d 18 O values. This is indicative of seawater being a major component of the hydrothermal fluids. Seawater interaction with the granitoids produced enrichment in 34 S 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 d 34 S values of þ1.7‰ and þ 1.8‰. The basement amphibolites of Kef Lakhal indicate derivation from a basaltic magma with d 18 O ranging from þ4.9‰ to þ8.6‰. Locally altered amphibolite has the lowest d 18 O values suggestive of meteoric water interaction, whereas the highest d 18 O indicate the incorporation of crustal material during the genesis of the amphibolites. Crustal contamination is also reflected in their d 34 S of À18‰ to þ2.1‰, with the most contaminated rocks having the lowest d 34 S. Host Palaeozoic mica schists with d 18 O of þ12.7‰ and d 34 S of À13.2‰
and associated marbles (d 34 S À9.9‰ to À17.4‰) are thought to be the most likely contaminants. At the Ain Barbar Fe-Cu-Pb-Zn deposit, d 34 S values range between À9.6‰ and À10.8‰, 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, d 34 S values of the sulphide-sulphur extend from À1.2‰ to À8.1‰ indicative of magmatic sulphur with the incorporation of substantial amounts of sulphur derived from the host mica schists.