Discovery of high-temperature hydrothermal mineralisation at Hatiba Mons volcano in the Red Sea

Hatiba Mons is the largest axial dome-shaped volcano in the ultra-slow spreading Red Sea rift. It hosts recently discovered (2022) widespread hydrothermal activity consisting of extensive iron deposits in the form of iron mounds. Two of these vent fields were investigated in detail during an expedition in 2023, with ROV observations as well as gravity coring of metalliferous sediments, massive sulfides, and background carbonates. A multidisciplinary approach was applied to first establish a geochemical and mineralogical framework of the new system, which is then linked to microbiological and pore fluid analyses of the sediments. This was achieved through the implementation of X-ray fluorescence, instrumental neutron activation analysis, inductively coupled plasma mass spectrometry, X-ray diffraction, petrological microscopy, electron-microprobe analysis, sulfur isotope analysis, and microthermometry. Whole-genome metagenomic sequences and morphological studies (scanning electron microscopy) are currently analyzed to elucidate the role of microbial communities in mound formation and/or degradation and mineral precipitation. The pore fluid chemistry will further enhance our understanding of the formation of the hydrothermal system at Hatiba Mons and the processes responsible for the chemical variability within the mounds.

Our study provides the first detailed description of an active Red Sea hydrothermal vent system outside the metalliferous brine-pool muds such as those of the Atlantis-II Deep. Hydrothermal precipitates at Hatiba Mons resemble MOR basalt-hosted deposits elsewhere. However, given the close proximity (<10km) of Miocene evaporites, the presence of small brine-filled depressions at the volcano summit and near-saturation salinities in fluid inclusions indicate a substantial contribution of dissolved evaporites to the hydrothermal system, influencing metal solubility, transport, and precipitation. This is reflected in some unusual high metal concentrations (e.g., Zn, Au, Ag, Cd, Sb). The mineral composition and paragenetic sequence, as well as microthermometric results suggest a waning hydrothermal system that experienced high-temperature hydrothermalism (250-300°C) in the past and current temperatures within the mounds (130-150°C) that are well above the currently measured in situ temperatures of 31°C and 51°C venting and core temperatures, respectively. Furthermore, we provide a detailed assessment of the first polymetallic massive sulfide occurrence associated with active hydrothermal venting in the Red Sea.

The deposit at Hatiba Mons formed at high temperatures, clearly showing that the fundamentals of hydrothermal activity in the Red Sea are not entirely different from other mid-ocean ridges; however, the elevated salinities may provide evidence that the geological setting allows for greater variability in the mineral deposits currently not observed in other modern seafloor hydrothermal systems, but common in the fossil rock record. The Red Sea spreading center remains an exploration target for the discovery of further sulfide occurrences and/or high-temperature vent sites. The presence of current low-temperature fluid venting and microbial mats, along with high-temperature precipitates within the mound, suggests a complex and dynamic hydrothermal activity at Hatiba Mons volcano and in the Red Sea. These findings contribute to a deeper understanding of the formation of marine mineral deposits, the evolution of hydrothermal systems, and their broader implications for deep-sea geochemistry and microbial ecology.