Chemical composition of smectite-bearing basal metalliferous sediments from DSDP Leg 9

The mineralogy and P, Fe and Mn contents of basal metalliferous and nonmetalliferous sediments of two Deep Sea Drilling Project cores (Sites 77 and 80) were investigated. When compared with superjacent nonmetalliferous material, basal metalliferous sediments are significantly enriched in P, Fe and Mn. Among the phases present in the metalliferous sediment samples are a poorly-crystalline Fe-rich smectite and X-ray amorphous Fe oxyhydroxides. P is associated primarily with the oxyhydroxides. Adsorption of phosphate on smectite does not seem to play any role in the uptake of P by metalliferous sediments. An estimate of the removal of P by on- and off-ridge metallogenic deposition suggests that this process strongly affects the overall geochemical balance of phosphorus in the World Ocean.