Abstract: Sediments from DSDP 424, a core taken in a hydrothermal mound in the Galapagos Mounds Field, comprise biogenic oozes, siliceous ash-rich layers and two varieties of hydrothermal precipitates, an Fe-rich clay (nontronite), and Mn oxides. Compositionally, these sediments differ considerably from one another and vary in proportion down the core to basement. Geochemical partition studies on the sediments have indicated a variable fractionation of the elements that they contain between clays, carbonate, and Mn oxides with the hydrothermal phases being strongly depleted in trace elements. The hydrothermal sediments are thought to have been formed as a result of the fractional precipitation of Fe silicates and Mn oxides from ascending hydrothermal solutions which are depleted in trace elements due to subsurface precipitation of sulphides, and have had insufficient time to scavenge trace metals from sea water due to their rapid precipitation