FE-RICH MINERALIZED MICROBES FROM HYDROTHERMAL VENTS AT TAGORO SUBMARINE VOLCANO, EL HIERRO ISLAND (CENTRAL EAST ATLANTIC)

Hydrothermal iron‐rich crusts have been recovered from Tagoro submarine volcano (El Hierro, Canary Islands) in the central Atlantic. A novel hydrothermal field was discovered and filmed by ROV at the summit (89-120 m depth) of the new volcano formed in 2012. Iron- and silica-rich gelatinous deposits pool over and between basanites in hornito-like structures and surrounding areas. The rocks are capped by red and yellow mm to cm thick hydrothermally derived Fe-oxyhydroxide layered crusts; micro-cracks and degasification vesicles on basanite are filled by pyrite and anhydrite. The crusts consist of ferrihydrite and minor anhydrite, with sparse pyrite at their base. The ferrihydrite has a mean particle size of 1–5 nm indicating rapid deposition. The crusts display wide variability in bulk composition between ROV sampling stations. Fe-oxyhydroxide crusts show high contents of Fe₂O₃ (28-58 wt%) moderate SiO₂ (up to 11.3 wt%) and P₂O₅ (1.4-4.8 wt%). Mn (Fe/Mn >700) and combined Co, Ni and Cu contents are very low. These deposits plot in the Fe‐rich endmember of the ternary diagram of Bonatti et al. (1972) indicating a hydrothermal origin. Normalized REE patterns of samples show a negative Ce anomaly and a strongly positive Eu anomaly, suggesting rapid deposition of the iron oxyhydroxide near the hydrothermal vent. Precipitation from the hydrothermal solution was caused by mixing with seawater. Electron microprobe studies revealed mineralized microbes that include filamentous, coccoids and helical fibrils coated by Fe-rich and silica precipitates, reflecting possible bacterial oxidation of iron from the hydrothermal fluids. The rDNA analysis indicates the abundance of Fe²⁺-oxidizing and sulfur- reducing and oxidizing bacteria commonly found at deep-sea hydrothermal vents. Preservation of the microbes indicates rapid mineralization with a stable supply of supersaturated fluids to the microbe surface nucleation sites. The mineralization styles evident in the microbes are similar to other mineralized microbes found in marine and terrestrial hot spring deposits in the deep Atlantic Ocean, Iceland and Yellowstone. The hydrothermal system formed at Tagoro volcano provides an excellent opportunity to study the evolution of hydrothermal fluids and mineralization processes in a shallow-water hotspot volcano setting