Isotopic studies of epigenetic features in metalliferous sediment, Atlantis II Deep, Red Sea

The unique depositional environment of the Atlantis II Deep brine pool in the Red Sea produces a stratiform metalliferous deposit of greater areal extent than deposits formed by buoyant-plume systems typical of the midocean ridges because of much more efficient metal entrapment. Isotopic analyses of strontium, sulfur, carbon, and oxygen from the metalliferous sediments indicate that three major sources contribute dissolved components to the hydrothermal system: seawater, Miocene evaporites, and rift-zone basalt. An areally restricted magnetite-hematite-pyroxene assemblage formed at high temperatures, possibly in response to hydrothermal convection initiated by intrusion of basalt into the metalliferous sediment. A correlation between smectite Fe/(Fe+Mg) ratios and oxygen isotope temperatures suggests that smectite is a potentially important chemical geothermometer, and confirms geochemical calculations indicating that Mg-rich smectite is more stable than Fe-rich smectite at elevated temperatures.