SOME GENERAL GEOCHEMICAL FEATURES OF PHOSPHORITES
The average content of world phosphorites is of about 29% P2O5. Small positive and negative correlations between the age and different compounds have been discovered. P2O5 has high positive correlations with F, CaO and negative with SiO2, MgO, CO2. CaO has high negative correlations with SiO2, Al2O3, K2O and MgO. F has positive correlations with P2O5, CaO and negative with MnO, CO2. SiO2 has high positive correlation with Al2O3, K2O, TiO2. Many correlations of high coefficients there are discovered in terrigenous glauconite phosphorites, in phosphate shells and concretions, while in weathered, metamorphised, aluminum-bearing dolomite phosphorites and in iron-manganese phosphate rocks correlations are less expressed. In weathered phosphorites primary correlations between main components are lost.
Five factors are determined and interpreted: 1) The antagonism between chemical components (P2O5, CaO, F) and detritic components (SiO2, Al2O3, Fe2O3, MgO, Na2O, K2O). This is: factor of Ph and Total Alcality indexes (TA) of environment of sedimentation. 2) Factor of CO2 reduction. 3) Redox cycle (Eh) and MgO inhibition for Francolite precipitation. 4) Factor of stable sulfur isotope or factor of sulfate precipitation. 5) Factor of Fluorine arrangement.
The above mentioned factors in cooperation and mutual influence have contributed to the formation of Francolite, chemical and detritic minerals in anoxic, suboxic and oxic zones and later during diagenetic processes. Common feature in phosphorites it is the antagonism of chemical elements: P, Ca, F with detrite elements: Si, Al, Fe, Mg, Mn. As conclusion, phosphorites there are characterized by their common laws of the environment of formation.