522 



UNITED STATES MINERAL RESOURCES 



thin beds of shales and limestones in rocks of Ordo- 

 vician, Devonian, Pennsylvanian, Permian, and 

 Cretaceous ages in the midcontinent area of the 

 United States. Phosphate particles are also concen- 

 trated as lag gravels at unconformities in this area. 

 Although the amount of phosphate per unit area is 

 small, the aggregate amount of phosphate most be 

 large, and it is possible that some of these rocks 

 may be mined as local sources of phosphate in the 

 future. 



LATIN AMERICA 



Large tonnages of phosphate are knov^^n in the 

 Jurassic of Peru and the Cretaceous of Colombia. 

 The phosphate-bearing rocks may extend through 

 Peru, Bolivia, and Ecuador into Colombia, and the 

 deposits in most of this area represent a large hypo- 

 thetical resource. Miocene rocks of the Sechura area 

 in Peru and in Falcon State in Venezuela contain 

 phosphorite deposits. The Miocene rocks of the w^est- 

 ern and northern coasts of South America should 

 be examined to determine if additional resources 

 are present. Along the Pacific Coast of Colombia the 

 Miocene rocks are so thick that discovery of eco- 

 nomic phosphate is not likely, but Miocene rocks in 

 Ecuador and Peru and the northern coast, particu- 

 larly in Venezuela, are thinner and may contain 

 additional resources. 



Deposits of the Florida type may be present in 

 Upper Cretaceous and Tertiary rocks on the east 

 coasts of continents. Deposits of this type occur in 

 Cretaceous rocks of the Recife area in Brazil, but 

 the potential is small because of the small area 

 underlain by marine Cretaceous rocks. Deposits 

 may also be present in Upper Cretaceous and Ter- 

 tiary rocks along the present east coast of South 

 America in Argentina. 



AFRICA AND THE NEAR EAST 



A very large area including much of the northern 

 half of West Africa and all of North Africa and 

 the contiguous parts of the Near East (Israel, Jor- 

 dan, Saudi Arabia, Turkey, etc.), is a sedimentary 

 basin in which the identified and hypothetical re- 

 sources of phosphate are extremely large. The po- 

 tential of this area is enormous. Deposits have been 

 found in recent years in almost all parts of the 

 sedimentary basin that have been examined. As 

 details of the stratigraphy, structure, and paleo- 

 geography are worked out, additional deposits will 

 probably be found. No tonnage figures have been 

 computed, but the total resources must be much 

 larger than the numbers shown on table 106. 



Not a great deal of specific information is avail- 

 able on this part of the world, but it is known 

 that large sedimentary basins that contain rocks 

 ranging in age from Cambrian to Cretaceous con- 

 tain phosphorite deposits, and it is likely that ex- 

 ploration will uncover additional large reserves. The 

 potential for this area is great. 



AUSTRALIA 



Australia has identified and hypothetical resources 

 of phosphate of Cambrian age in a large sedimentary 

 basin in the interior of the continent. The total re- 

 sources in this basin probably are extremely large — 

 several times the combined total of the identified 

 and hypothetical resources shown in table 106. 



GUANO AND RELATED DEPOSITS 



Little hope remains for finding additional re- 

 sources of the guano type of deposit such as typify 

 the Pacific Islands. All the Pacific Islands have 

 bsen searched, and although additional reserves may 

 be found they will, in all probability, be small. 



IGNEOUS APATITES 



Additional resources of igneous apatite are at best 

 moderate, particularly in comparison with the total 

 resources of the sedimentary phosphorites. Reserves 

 in undiscovered alkaline rock suites probably will 

 be hundreds of millions of tons in maximum size; 

 many will be much smaller. Reserves of this type 

 might be utilized as local sources in the future, and 

 the possibilities of finding deposits of apatite should 

 not be overlooked. 



SPECULATIVE RESOURCES 



Very little in the way of truly speculative re- 

 sources of phosphate remain to be found. We can 

 refine ideas and theories of the formation of marine 

 phosphorite, but the positions of the shelf, craton, 

 sedimentary basins, and geosynclines are known at 

 least in broad outline for most periods of geologic 

 time throughout the world. Not all the prospective 

 areas have been searched for phosphate, and sedi- 

 mentary basins where phosphate is known have not 

 all been thoroughly and exhaustively studied. New 

 deposits, then, remain to be discovered but all are 

 considered to belong to the hypothetical class rather 

 than the speculative. The total amount of phosphate 

 rock in the world, as identified or hypothetical, is 

 potentially so enormous that the assumption that 

 truly speculative resources are small has little 

 meaning. 



