SOME GENERAL GEOCHEMICAL FEATURES OF PHOSPHORITES

Based on 154 chemical analyses of phosphate ores from main world deposits some general geochemical features are evidenced. Chemical data belong to phosphorites of different ages and genetically types. Statistical and R-mode factory analysis were applied.

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.