Eastern American phosphorite-bearing province

(Map) THE EASTERN AMERICAN PHOSPHORITE-BEARING PROVINCE

EASTERN AMERICAN PHOSPHORITE-BEARING PROVINCE (RU: Восточно-Американская фосфоритоносная провинция) is situated on the territory of the south-eastern states of the USA: Florida, Georgia, North Carolina, and South Carolina, within the limits of the Atlantic coastal plain, and on the adjacent parts of the coastal shelf of the Atlantic ocean. The length is approximately 1300 kilometres. The area is 200 thousand square kilometres. The reserves of the phosphorites (1980), including the forecasted reserves of the coastal shelf zone, are 19.1 billion tonnes, including 8.65 billion tonnes of the proven and probable reserves, and 4.2 billion tonnes for the opencast development (1.2 billion tonnes within the Florida state). The main industrial deposits are concentrated within the Central Florida (Polk County) and North Florida, and within the North Carolina (Lee Creek). The discovery of the first deposits on the territory of the Florida peninsula, and the start of their operation, belong to the 1867-93. The deposits are represented by the continental Pliocene-Quaternary phosphoritic pebbles and "hard" metasomatic ores. The major industrial depositions belong to the Bone Valley formation (Pliocene), and are distributed within the Central Florida (see the Map).

The Bone Valley formation (the average thickness is approximately 11 metres) is represented by the two horizons: the lower horizon (5.2 metres) with the rich ores (27-33% of the P2O5), and the upper horizon (6 metres) with the aluminophosphate ores (17-27% of the P2O5). The main phosphorite-controlling structure of the Florida state is the Ocala uplift, on the wings of which are placed the industrial phosphoritic deposits of the basin, with the slightly inclined or horizontal embedment of the productive horizon. The Lee Creek deposit is one of the largest deposits within the USA, this deposit has been discovered during the 1951, and is being developed since the 1966. This deposit is confined to the clayish-dolomitic Pango River formation of the Middle Miocene (up to 36 metres). There is prominent the productive horizon with the thickness of up to 12 metres, which has been formed of the alternating layers of the phosphate-containing dolom ites, clays, and phosphoritic sands, with the average content of the P2O5 of approximately 15%. The embedment of the strata is horizontal. The reserves of the phosphorites, which are accounted for the unit of the area, are by 5 times more, than at the deposits within the Florida state.

All the deposits are being developed using the opencast method. The thickness of the overburden is 6-30 metres. Approximately 80% of the quantity of the annual extraction of the phosphorites is accounted for the deposits within the Florida state, where are concentrated more than 25 open-pit mines with the productive capacity from 1 to 6.5 million tonnes per year. The ores, which are being developed, are subjected to the mechanical beneficiation at the first stage, and later are subjected to the flotation and calcined roasting at the temperature of 800-1000 degrees Celsius, with the obtainment of the marketable concentrates, which are containing more than 33-36% of the P2O5. The total extraction of the phosphorites within the province (1980) amounts to approximately 80% of the total annual extraction within the USA (42.5 million tonnes within the Florida state, and 4.2 million tonnes within the North Carolina state). More than 70% of the phosphorites, which are extracted within the Florida state, are used within the agriculture, 1% are used within the industry (for the obtainment of phosphorus), 26% are exported into the Canada, Japan, France, and other countries.