520 



UNITED STATES MINERAL RESOURCES 



CONCENTRATION AND ENRICHMENT 

 OF MARINE DEPOSITS 



The richest of the marine deposits have been con- 

 centrated or enriched by secondary processes. For 

 example, the deposits in the Bone Valley Formation 

 of Florida were formed by submarine reworking of 

 a phosphate-rich residuum. Leaching related to 

 Pleistocene and modern weathering has further up- 

 graded the deposits. The occurrence of phosphate 

 gravels at unconformities is caused by weathering 

 and reworking. 



River-pebble deposits occur as bars and in the 

 flood plains of streams that drain phosphate areas 

 in Florida, Georgia, and South Carolina. The 

 streams concentrate coarse-grained phosphate par- 

 ticles because of their size and specific gravity. 

 Fine-grained phosphate particles, quartz sand, and 

 clay are carried downstream, and the river-pebble 

 deposits consist of coarse-grained phosphate nodules 

 and quartz grains. The phosphate particles are low 

 in P2O5 content because of leaching by the acid 

 waters of the stream. 



Chemical weathering of phosphatic limestone in 

 a humid climate results in the removal of the solu- 

 ble calcium carbonate and the consequent enrich- 

 ment and concentration of the phosphate. The 

 "brown rock" phosphates of Tennessee and Ken- 

 tucky are examples. Individual deposits are not 

 large but they are grouped in such a way that the 

 mined material can be hauled to a central recovery 

 plant. The composition of the phosphate particles 

 and their mineralogy are about the same as the 

 composition and mineralogy of the marine phos- 

 phorite from which they were derived. 



The apatite mineral of sedimentary rocks is taken 

 into solution by acid ground water, and P2O5 may 

 be precipitated if the solutions pass through 

 aluminum- or iron-bearing rocks or through lime- 

 stone. Secondary deposits in limestone areas, such 

 as the white rock of Tennessee and the hardrock of 

 Florida, consist of phosphate incrustations or ir- 

 regular replacement. The P2O5 content depends on 

 the degree of replacement; some replacement de- 

 posits are very high in phosphate content. Deposits 

 are irregular in shape and are generally small. 



OTHER TYPES OF PHOSPHATE DEPOSITS 



Other sources of phosphate include bone piles, 

 glauconite, and phosphatic iron ores that yield a 

 basic slag in the Bessemer or basic open-hearth 

 manufacture of steel. Bone piles are no longer an 

 important source of phosphate. Glauconite (green 

 sand) contains both K2O and P2O5 and has some 

 use as a fertilizer; reserves and resources in the 



Cretaceous and Paleocene of the Atlantic Coastal 

 Plain are very large. Phosphatic iron ore includes 

 marine deposits like the Red Mountain Formation 

 of Alabama as well as apatite-magnetite deposits. 

 Basic slag (Thomas Meal) made in processing these 

 ores contains about 8 percent P205, and is used as 

 a fertilizer. 



Phosphatic lake beds of Eocene age are known 

 from intermontane basins of Wyoming and Utah. 

 The beds that contain phosphate range in thickness 

 from less than 1 to about 6 feet and contain an 

 average of about 2 percent P2O5. The maximum 

 P2O5 is about 19 percent. 



RESOURCES 

 IDENTIFIED AND HYPOTHETICAL RESOURCES 



Phosphorite deposits are known throughout the 

 world and throughout the geologic column from the 

 Precambrian to the Holocene. Data for tonnages of 

 identified phosphorite in tables 105 and 106 are 

 from all possible sources. Most of the figures for 

 the United States are from unpublished data of the 

 U.S. Geological Survey, including information from 

 R. L. Detterman (written commun., 1972) for 

 Alaska. Tonnages are computed in different ways 

 for different deposits in the United States. For the 

 unconsolidated phosphate sands of the Atlantic 

 Coastal Plain, they are computed on the basis of 

 recoverable product that contains a given percent 

 BPL (bone phosphate of lime). In Tennessee, re- 

 serves are computed as tons of rock that contain 

 a certain percent P, and in the Western United 

 States tonnage is phosphate rock, in the ground, of 

 a given percent P2O5. Percent P2O5 times 2.185 

 equals percent BPL [equals Ca3(P04)2], and per- 

 cent P2O5 times 0.436 equals percent P. 



Tonnages for the United States shown in table 

 105 are in metric tons of rock that contain more 

 than 24 percent P2O5, and total tons for the Eastern 

 and Western United States are changed to metric 

 tons of percent P to conform with the tonnage fig- 

 ures for other countries of the world in table 106. 



Tonnage estimates are fairly good for the United 

 States, Africa, the Near East, and the Pacific 

 Islands, but it is almost certain that the estimates 

 are low, and perhaps very low, for Latin America 

 and Australia. The resource estimates for Asia are 

 probably low because of lack of detailed data, par- 

 ticularly for China. 



SEDIMENTARY PHOSPHORITE 



UNITED STATES 



Hypothetical resources for the United States 

 shown in table 105 are those for which reasonable 



