Hydrothermal deposits and associated basement rocks from the Galapagos spreading center

Relatively thick (up to 15 m) hydrothermal deposits from the southern flank of the Galapagos spreading center were drilled on a crust of about 0.62 myr old (magnetic age), during Leg 54 of the "Glomar Challenger" in the central Eastern Pacific Ocean. A stratigraphic sequence of ferrobasalt, pelagic oozes, and hydrothermal deposits of green clay-rich material and Fe-Mn concretions were recovered. The green clay-rich material (Fe-Si type of smectite) is also found interlayered between the pelagic ooze and filling veins, veinlets and vesicles in the drilled basement rocks. The low transitional metal content (Cu < 150 ppm). Ni < 100 ppm and Co < 200 ppm) and the nature of the green clay-rich material from the Galapagos deposits make them comparable to that of other hydrothermal products discovered from other oceanic ridges. In general, the basement rock has a higher transitional metal content than the overlying hydrothermal material. Hydrothermal fluids percolating from the basement through the sedimentary cover or precipitating from solutions emmanating from localized vents are proposed models for the origin of the hydrothermal layers