New geochemical and mineralogical data of Ogasawara phosphorites (northwestern Pacific)

A mineralogical and geochemical study of five phosphorite samples from the Ogasawara submarine plateau (Northwest Pacific) was performed using optical and scanning electron microscopy (SEM), X-ray diffraction analysis, and inductively coupled plasma spectrometry equipped with microanalysis systems. The total rare-earth elements (REE) content varied from 94 to 183 ppm, with an average of 145 ppm. Their distribution, distinct negative Ce anomalies and redox indices indicate the primary precipitation from oxygenated seawater under relatively oxic marine conditions during early diagenesis. From the point of view of economic potential, the studied phosphorites can be considered as a valuable source of phosphate flour with a low content of radioactive elements in the mineral composition.