FY 1986

Hydrothermal vents and polymetallic sulfides of the Galapagos and Gorda/Juan de Fuca Ridge systems and of submarine volcanoes

Malahoff, A.

Biol. Soc. Wash. Bull., 6, 19–41 (1985)

Active ocean-floor hydrothermal vents have been observed, to date, along ridge-crest segments of the Juan de Fuca and Explorer Ridges, located off North America, the East Pacific Rise, and the Galápagos Ridge, as well as on submarine volcanoes of the ridge-crests and submarine volcanoes of hot spots such as the Hawaiian Ridge. Vents that are currently generating polymetallic sulfide mounds and chimneys with "smoker" activity are found to be active in ridge-crests or segments with medium (5 to 9 centimeters per year) and fast (9–16 centimeters per year) spreading rates. A detailed submersible-based study was carried out over large inactive hydrothermal polymetallic sulfide deposits located along the faults of the axial rift valley along the crest of the Galápagos Ridge. The geological study of the Galápagos polymetallic sulfide deposits suggests that prolonged hydrothermal activity on a ridge-crest, especially that found along the fault boundaries of well-developed rift valleys, can develop large-volume, massive sulfide bodies on the contemporary oceanic crust. The geology, size and mineralogy of the massive sulfide body of the Galápagos resembles massive sulfide ore-bodies found on subaerial segments of fossil oceanic crust. The study also suggests that the size of massive sulfide bodies found along the crest of the mid-ocean ridge systems may vary from a few meters to two thousand meters in length. Commercially viable polymetallic sulfide deposits, however, may be rare. Detailed studies of the distribution of hydrothermal vents located along the Juan de Fuca Ridge system suggest that the number and size of hydrothermal deposits presently increase toward the north as a result of increased tectonic deformation of the ridge due to decreasing distance from the neighboring continental margin of North America. To date, contemporary oceanic analogues of massive sediment-hosted, ore-bodies have not been detected along the mid-ocean ridge-crests but may well be found along the marginal basins of the western Pacific in the future.