Phosphatisation has widely occurred in oceanic Co_rich crusts and exerted a remarkable effect on the properties of Co-rich crusts. However, no agreement has so far been reached with regard to the genesis of phosphate. In this study，the upper and lower layers in the older portion of a crust from the Central Pacific WX seamount were systemically observed and tested by such means as reflecting microscope, scanning electron microscope, electron microprobe and X-ray diffraction, and their possible geneses and characteristics of formation were discussed. The upper layer, with homogeneous composition, is mainly composed of intact phosphatic foraminifer fossils and nannofossils as well as abiotic carbonate fluorapatites (CFA), representing the biologic and autogenic origin. However, the lower layer, with visible metasomatic texture and relatively high Si, Al, K and Fe, is notably different from the upper one, and seems to have been formed mainly by replacement of carbonates. Therefore, different phosphate layers in crusts have different geneses.