The upper Cretaceous Ermioni VMS deposit, Argolis Peninsula, Peloponnese, Greece: Type, genesis, and geotectonic setting

Abstract

The age, type and geotectonic setting of the Ermioni VMS are explored. Although obscured by post-ore deformation and metamorphism, the Ermioni VMS is genetically and spatially related to hydrothermally altered volcaniclastic rocks and arkoses at the footwall, and turbidites at the hangingwall. The Ermioni VMS deposits occur at Karakasi, Roro and Cambrorosso mine sites, and in close proximity to each other. At Karakasi, the identified hydrothermal alteration zones include a lower and innermost grunerite zone, succeded by an intermediate silica-chlorite zone which shows the largest spatial development and surrounded by a silica-epidote-chlorite zone at the flanks, whereas an albite-prehnite zone is developed at the top of the VMS system. The Ermioni VMS comprises nearly monomineralic pyrite with elevated Cu and Co content, and Cu/(Cu + Zn) and Co/Ni ratios typical for “Mafic-Pelitic”-type VMS deposit. Two ore stages are recognized, Stage I euhedral and coarse-grained pyrite (major Co carrier) with minor chalcopyrite, magnetite and pyrrhotite was followed by Stage II pyrite and minor chalcopyrite and sphalerite. Rubidium-Sr and Os-Re radiogenic pairs on pyrite from the Roro massive and Karakasi stringer ores define an upper Cretaceous age of VMS formation (65.58 ± 0.9 to 66.02 ± 0.1 Ma and 64.96 ± 0.9 to 65.12 ± 0.1 Ma, respectively). This age debunks the previously proposed classification as Cyprus-type. The stable isotope compositions of the hydrothermal fluids, including δ18OΗ2Ο, δDΗ2Ο, δ13CCO2, δ30SiNBS, point to mixing between subduction related hydrothermal fluids, seawater and seafloor turbidites, which accords well with the proposed classification. The δ34SH2S and δ57Fe values confirm a magmatic origin of sulfur and leaching of the footwall volcaniclastic rocks with contributions from seawater and turbidites. Radiogenic isotope and trace element geochemistry indicate that the Ermioni “Mafic-Pelitic” VMS was formed at a partly sediment-covered, upper Cretaceous back-arc spreading center above a retreating subduction zone setting within the “Adheres Melange unit”. The Ermioni VMS is the only known upper Cretaceous sulfide ore identified in Greece. The findings of this work may be used in expanding future research on the metallogenic potential of Greece.