DO MARINE MOLDS INFLUENCE HG AND SI PRECIPITATION IN THE HYDROTHERMALJADE FIELD (OKINAWA TROUGH)

Several massive sulfide smoker fragments from the JADE field (Okinawa Trough, Japan) yielded filamentous aggregates of both cinnabar (HgS) a nd amorphous silica (SiO2), resembling fungal hyphens. For this simila rity, polished and thin sections of filaments were compared with recen t moulds that had formed on sulfide samples. Since the influence of ma rine moulds on mineral precipitation is poorly known, studies on bacte rial and algal mineralization mechanisms were reviewed to generally id entify microbial metabolism processes that could lead to the formation of the observed filaments. The development of HgS pseudomorphs is lik ely to have occurred through methylation reactions, while the filament replacement by silica probably happened via an intermediate formation of silica-carbon compounds, followed by a successive breakdown of the se phases under changing geochemical conditions.