A large Miocene phosphorite deposit on the Atlantic Coastal Plain in Beaufort County, North Carolina, contains estimated reserves of 10 billion tons. The phosphorite zone, where examined, is 60 feet thick, and the P2O5 content of the untreated ore is about 18 per cent. The sediment consists of phosphate pellets, sand-sized quartz grains, and clay, with thin beds of indurated coquina and phosphatic dolomite.
The phosphate pellets contain quartz grains, glauconite, carbonaceous matter, and organic remains. Although most of the pellets are structureless, some show concentric layering around a nucleus.
Chemical, X-ray-diffraction, infrared-spectral, and other data demonstrate that the phosphorite mineral is francolite, and that CO2 is an integral part of the apatite structure.
The clay fraction of the phosphorite includes montmorillonite, illite and clinoptilolite. The clay minerals and zeolite probably originated through alteration of volcanic detritus from an undetermined source.
Studies indicate origin of the phosphorite to have been in a shallow marine basin characterized by a reducing environment, phosphate replacement of calcareous sediments, local reworking and alteration of certain of the pellets, and coincidence of phosphorite deposition with pyroclastic activity.