| Summary: | The study follows previous work on Ermioni VMS and addresses in detail the formation and evolution of two adjacent VMS systems, Karakasi and Roro. It is based on a stable and radiogenic isotopic composition of sulfides and ganguefrom stringer (Karakasi) and massive (Roro) VMS ore. The isotopic geochemistry of Pb and noble gases (Ar-He) of pyrite from both sites indicates the development of a deep and evolved heat and possibly metal source attributed to subduction of radiogenic material (Pindos oceanic crust). The differences in the stable (Fe, S) and radiogenic (Sr, Ar) isotopic compositions between the two sites depict variation in the geologic environment of VMS formation, and in particular the effect of seawater. The higher δ<sup>57</sup>Fe and δ<sup>34</sup>S values of Roro massive pyrite are attributed to direct interaction of hot, ascending metal-bearing hydrothermal fluids with cold seawater. Karakasi stringer oreis characterized by higher <sup>87</sup>Sr/<sup>86</sup>Sr ratios and radiogenic Ar values (as <sup>40</sup>Ar/<sup>36</sup>Ar), indicating interaction of ore-bearing, hydrothermal fluids with crustal material (hanging-wall turbidites). During the approximate 0.5 Ma period separating the two systems, the hydrothermal system migrated from east to west, and at the same time evolved from free discharge on the seafloor (Roro—easterly), resembling contemporary seafloor style and mound-shaped massive sulfides, to a sediment-confined, subseafloor system (Karakasi—westerly).
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