Submarine phosphorites: The deposits of the chatham rise, New Zealand, off Namibia and Baja California, Mexico-origin, exploration, mining, and environmental issues

Abstract

Rising consumption and increasing prices of phosphate fertilizers initiated the commercial exploration of offshore phosphorite deposits. Origin of the phosphorite, state of exploration, and mining concepts are described for three of the most advanced projects. The phosphorites of the Chatham Rise/New Zealand are located in 400 m water depth, about 500 km offshore and originated by Late Miocene phosphatization of a hemipelagic chalk. The gravel-sized phosphorites form a residual decimeter-thick layer with an inferred resource of 24 million tons. The authigenic, sand-sized phosphorites at the outer shelf of Namibia form a meter-thick layer with estimated resources of 60 million tons. The sand-sized phosphorites on the mid-shelf off the Baja California/Mexico contain an estimated resource of about 300 million tons. In all three projects, the phosphorites are planned to be recovered by a trailing suction hopper dredge and enriched by onboard size screening. Mining licenses were granted, but environmental considerations have delayed the economically feasible exploitation of these marine phosphorites.