Petrology, geochemistry and stable isotope studies of the Miocene igneous rocks and related sulphide mineralisation of Oued Amizour (NE Algeria)

摘要

The Oued Amizour granitoids of North Africa were studied in order to assess the role of magma processes in the formation of the large Zn-deposit in the region. Access to material from a similar to 800 m drillhole cutting the entire igneous succession greatly facilitated the investigation. The rocks reveal, from the top to the bottom, two distinct lithologies: volcanic, mainly pyroclastic rocks and sub-volcanic microgranitic - plutonic granodioritic rocks. Both lithologies were subject to hydrothermal alteration. The boundary between the two lithologies is marked by a massive, similar to 10 m thick anhydrite layer. The geochemistry of these rocks shows that they are intermediate to felsic in composition and exhibit high-K to shoshonitic talc-alkaline features with I-type signature. The negative Eu, Sr and Nb anomalies and the high LILE and LREE enrichment observed in the whole igneous suite indicate that the various volcanic and plutonic rocks are genetically related. The granitoids are considered to have formed under post-collisional geotectonic regime during the Miocene, similar to those described in the Alpine Belt of northern Africa.