Natural rock containing one or more phosphate minerals (usually calcium 

 phosphate) is generally referred to as phosphate rock. Phosphate rock is nei- 

 ther constant in composition nor occurrence and consists of a variable mixture 

 of calcium phosphates and other minerals. X-ray studies have shown that the 

 dominant phosphate mineral in Florida deposits is fluor-apatite found in the 

 extensive bedded deposits of marine origin. Studies by the United States Geo- 

 logical Survey (USGS) have shown that the phosphates of the Bone Valley forma- 

 tion and the Hawthorn fonnation are of marine origin (Calver 1957). These 

 deposits are sedimentary beds of phosphate pebbles, sand, and clay located in 

 Hillsborough and nearby counties. The hard rock phosphate deposits, on the 

 other hand, were formed by weathering of surface rocks, and the deposition of 

 phosphate as replacement for limestone is not of marine origin. 



OFFSHORE 



Hydrocarbon-bearing formations in the Gulf of Mexico are generally asso- 

 ciated with sub-seabed vertical salt movements that form salt domes. Under 

 the weight of the overlying beds, salt is squeezed upwards, piercing sedimen- 

 tary beds, and arching. Those that are closer to the seabed surface form into 

 domes. The domes are typically topped by caprock. Oil and gas accumulates 

 along the flanks of these salt domes (U.S. Department of the Interior 1980a). 



The West Florida Shelf and Slope extends from the DeSoto Canyon in the 

 Gulf of Mexico eastward to The Straits of Florida in the Atlantic Ocean. Geo- 

 logically, it is considered the submerged extension of peninsular Florida. 

 Interest in Southwest Florida has been scattered in areas known as the Florida 

 Middle Ground, Tarpon Springs, the Elbow, Saint Petersburg, and Charlotte Har- 

 bor. Salt domes and anticlines within these areas are the principal explora- 

 tory drilling targets of industry seeking oil and gas fields. 



Industry's present interest in the Eastern Gulf of Mexico is focused on 

 the Howell Hook and Pulley Ridge areas on the Outer Continental Shelf. Both 

 of these areas are south of parallel 26°, about 161 km (100 miles) west of 

 Fort Myers in Lee County. It is theorized that a continuation of the geophys- 

 ical and geological characteristics in the Sunniland basin extend to the Outer 

 Continental Shelf, and that oil and gas resources there may be in commercial 

 quantity. 



Recently there has been speculation that an abundance of phosphate lies 

 in the Gulf of Mexico's continental shelf waters. Scientists from the Univer- 

 sity of South Florida believe that phosphate deposits may extend from the City 

 of Apalachicola to the Keys. The heaviest concentration appears to be between 

 16 km (10 miles) and 96 km (60 miles) off the coast of Clearwater. In June 

 1981 two USGS research vessels conducted additional studies on the phosphate 

 potential of the Gulf of Mexico (Tallahassee Democrat 1981). 



THE MINERAL INDUSTRY 



Minerals that are of economic importance in Southwest Florida are phos- 

 phate, petroleum, peat, limestone, cement, and sand. Other than phosphate and 

 petroleum, peat is perhaps the most important mineral. Major peat deposits 

 are the Everglades, and Corkscrew Marsh. The mining of peat historically 



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