EVOLUTION OF THE CHEMICAL COMPOSITION OF APATITE IN ORES OF THE SELIGDAR TYPE AS AN INDICATOR OF THE CONDITIONS OF ITS FORMATION

Abstract

The liberation of extraneous phases by cooling apatite is indicated by intramineral microscopic ingrowths, which have close chemical affinities with the host mineral. It has been shown that rare earths not only occur in the apatite lattice, but are also liberated in separate minerals. The microscopic ingrowths of this type include monazite, which is found only within apatite crystals. The chemistry of monazite of the Seligdar deposit has been studied previously but the conditions of its generation have not been interpreted. Calculations indicate that the monazite contains as much as 40 percent of rare earths and less than 2 to 3 percent of sulfur that was initially concentrated in the apatite. Most of the sulfur liberated from the apatite reacted with the CaO of carbonatite to form the anhydrite. The apatite-sulfate associations in carbonatite bodies of the Seligdar type are associated primarily with areas of present-day occurrence of nelsonite, camaphorite and redbergs. In the Seligdar deposit these parageneses were found in inner contacts of the ore bodies and also at depths of less than 350 m from the surface. Additional study results are discussed.