THE STORY OF PHOSPHORITE DEPOSITS ON THE GEORGIA SHELF: FROM PRIMARY ORIGIN AS PELLETS TO ECONOMIC SCALE PHOSPHATE RESOURCES, PAVEMENTS, AND NUCLEI FOR FERROMANGANESE NODULES

The shelf off Georgia was established as a major site of occurrence of offshore phosphorite deposits in the late 1980s. The discoveries emerged from research on a group of eight 100 m. foundation borings on the Georgia Shelf. These cores were made available by the U.S. Navy Tactical Air Command, Charleston, to the U.S. Geological Survey. The cores and associated geophysical data became part of a cooperative research project by scientists from USGS, the Geological Survey of Georgia, Georgia State University (including Vernon Henry), and other persons, partly supported by the U.S. Minerals Management Service.

Integration of petrographic and chemical analyses with regional geophysics and stratigraphy led to the conclusion that the shallow sediments on the Georgia shelf contain potentially economic deposits of phosphorite. Of special scientific interest was finding cores with rare well-preserved evidence of primary formation of the phosphorite pellets inside foraminiferal tests. The sediments contained all stages of phosphorite development from primary pellets to subsequent enrichment through winnowing, phosphatization of bones and carbonate tests and formation of aggregates of pellets. Other studies around the Charleston Bump (offshore South Carolina and Georgia) showed that recementation of phosphatic layers under high-energy conditions beneath the Gulf Stream had led to formation of cobbles to massive pavements of phosphorite that covered thousands of square kilometers on the Blake Plateau.

The formation and evolution of phosphorite pellets found in the Georgia deposits offer interpretive clues to formation of phosphorites in other areas where pelletal phosphorites are found. These range from the Miocene Monterey Formation of California, to oolitic phosphorites on Nauru Island, and Paleozoic deposits from various classical localities.