FY 1984

The geological setting and chemistry of hydrothermal sulfides and associated deposits from the Galapagos Rift at 86°W

Malahoff, A., R.W. Embley, D.S. Cronan, and R. Skirrow

Mar. Mining, 4(1), 123–137 (1983)

A multibeam, narrow-beam ocean floor survey using the U.S. Navy S.A.S.S. system was conducted over the axial region of the Galápagos Rift crest between 85°10′W and 86°15′>W. The survey data over the ridge crest at 85°50′W and 0°45′W show the presence of a double rift, with axial rift elements striking in an east-west direction. The south wall of the northern rift was surveyed in detail, using visual observations and sampling with the submersible ALVIN. Dives 1001 and 1002 showed the presence of recent volcanic extrusions along the axis of the rift valley and the presence of an extinct hydrothermal vent system at the base of a 40-m high marginal fault system. The hydrothermal vent system is located at a water depth of 2,850 m and extends for at least 1 km along the base of the fault scarp. Iron oxide mounds with up to 34% Fe and inactive sulfide chimneys with up to 27% Cu and a maximum of 7 m in height are underlain by cemented talus with Fe-Cu sulfide forming the cementing matrix. The geological association suggests that these hydrothermal vent deposits were formed in situ along the fault system in an analogous manner to the Cyprus Fe-Cu sulfide deposits of the Troodos Complex.