An iron-rich deposit from the Northeast Pacific

An iron-rich deposit dredged from the upper flank of Dellwood Seamount in the Northeast Pacific has been analyzed for major and trace elements, rare-earth contents and uranium isotopic composition. In terms of mineralogy and overall chemical composition, the deposit resembles other iron-rich deposits variously attributed to volcanic hydrothermal activity. Both the relative concentrations of the rare-earth elements and the isotopic composition of uranium rule out seawater as the sole source of elements in this deposit. The rare-earth element pattern indicates that these elements were derived from the underlying basalt. The²³⁴U/²³⁸U ratio is significantly higher than in seawater and can best be explained by preferential leaching of²³⁴U generated by decay from its parent²³⁸U in the underlying rock and subsequent redeposition of the excess²³⁴U together with the Fe and minor metals. These data are consistent with a model for the origin of submarine metal-rich solutions involving mobilization of elements from the interior of slowly cooling basalts by circulating seawater.