Abstract

Recent marine phosphorite deposits occur at low latitudes on continental shelves where major gyrals of surficial oceanic currents, such as the south equatorial-Brazil-Benguela gyral of currents in the South Atlantic, flow close to the continental shorelines and are diverted seaward causing upwelling of deeper ocean waters near the shore. An analysis of both economic and uneconomic ancient phosphorites of this type shows that they occur at the edges of cratons, most commonly in early, deep-water, starved-basin stages of the adjoining miogeosynclines. Phosphorite deposits are also found at the edges of reconstructed ancient continents at low paleo-latitudes. Thus there is a relation between the paleogeographic and paleotectonic positions of Recent and ancient phosphorites, and the Recent deposits give the key to understanding the ancient ones. Using this understanding, several deposits of potentially economic phosphate rock have been found, and many areas suitable for future exploration for phosphate rock deposits are suggested.