Composition and origin of phosphorite deposits of the Blake Plateau
An area of about 22 000 km 2 on the N Blake Plateau contains an estimated 2 billion tonnes of phosphorite concretions, and about 1.2 billion tonnes of mixed ferromanganese-phosphorite pavement. The phosphorite consists primarily of carbonate-fluorapatite, some calcite, minor quartz and other minerals. Drilling and other evidence show that the phosphorite is a lag derived from Miocene strata correlatable with phosphatic M Tertiary sediments on the continent. It has undergone variable cycles of erosion, reworking, partial dissolution and reprecipitation. Its present form varies from phosphatized carbonate debris, loose pellets, and pebbles, to continuous pavements, plates, and conglomeratic boulders. No primary phosphatization is currently taking place on the Blake Plateau.