ULTRAMICROSTRUCTURES OF PHOSPHATE PELLETS OF MICROGRANULAR PHOSPHORITES FROM THE STANDARD BASIN KARATAU (KAZAKSTAN)

A detailed study of pellets has been carried out for microgranular pho sphorites from the standard phosphorite-bearing basin Karatau, Kazakhs tan, in order to refine ideas of genesis of this basic industrial type of phosphate ores. Large magnifications reached by means of a scannin g electron microscope permitted us to see that the phosphate grains ar e chiefly made up of phosphatized remains of bacterial-algal mass and accumulations of microsclers of spongae (spongolites). The bacterial-a lgal organics in the phosphate matter is dominated by ball-, bacillus- , and cone-shaped forms. Coated grains of concentric (oolithic) struct ure are widespread. They may be considered oncolites, i.e. varieties o f bacterial-algal and partly sponge biotas, the source for phosphate g rains, which formed in other environments and in other places. The lat ter were much shallower than the settings where mechanical accumulatio n of grains proceeded and where phosphorites themselves came into exis tence.