Davidson, Donald M., Jr.
M.S. (Master of Science)
Department of Geology
Fluorine; Phosphate minerals--North Carolina--Beaufort County; Mineralogy--North Carolina--Beaufort County; Phosphate rock--North Carolina--Beaufort County
Pelletal, intraclastic, and skeletal grains from phosphorites in the Neogene Pungo River and Lower Yorktown formations of the Aurora Phosphate District, North Carolina, were analyzed by electron microprobe for F, P, and associated elements. F/P₂O₅ values calculated from the analytical data were observed to consistently increase from core to margin within the pelletal grains, but not in the other grain types. The data support previous studies which noted that a gradual uptake of fluorine, presumably by carbonate fluorapatite, occurred during diagenesis of modern phosphatic sediments. The microprobe data also show that phosphate grains within carbonate lithofacies have higher F/P₂O₅ values than grains in terrigenous (siliciclastic) lithofacies. X-ray fluorescence and ion-selective electrode analyses of bulk sediment samples corroborate the microprobe data and further show that depth (age) is not a factor in the fluorine distribution through the stratigraphic column of the Aurora Phosphate District. The observed difference in fluorine distribution among pellets, intraclasts, and skeletal grains supports the theory that the different phosphate grain types formed in different environments and by different mechanisms. The occurrence of all three grain types together within every stratigraphic horizon, despite their diverse origins, indicates that mechanical reworking and winnowing of sediments were important processes in the genesis of the Aurora phosphorite. It is inferred that fluoridation played an important role in rendering stable phosphorite grains that led to their mechanical concentration as lag deposits.
Ong, Reynaldo G., "Fluorine distribution in the neogene phosphorites, Aurora Phosphate District, Beaufort County, North Carolina" (1991). Graduate Research Theses & Dissertations. 3160.
v, 69 pages, maps
Northern Illinois University
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