Geochemical peculiarities of mafic- and ultramafic-hosted VMS deposits

Seafloor massive sulfide (SMS) deposits on oceanic spreading centers have variable concentrations of base metals (mostly Cu, Zn), precious metals (Au, Ag), critical metals (Co, Ni), and other trace elements. The geological factors that control this geochemical variability are still a matter of debate. In particular, the role of the composition of substrate rocks (specifically mafic vs. ultramafic) has been variably considered to be decisive or subordinate. This work provides a detailed minero-petrographic and geochemical study of four Volcanogenic Massive Sulfide (VMS) deposits (Outokumpu, Ivanovka, Dergamysh, Ergani) from the OCT and SSZ. The studied deposits include both mafic and ultramafic-hosted types. Field samples from these deposits have been studied by classical minero-petrographic techniques and by major and trace elements geochemical analysis. The new geochemical data were compared with the abundant data on present-day ocean seafloor massive sulfide deposits by means of advanced multivariate statistical analysis, in order to highlight similarities or differences in element associations and related hydrothermal processes and geological constraints. This statistical approach appears to have predictive capabilities making it possible to relate specific element associations to specific geological settings