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EFFECT OF PHOSPHORUS ON THE BEHAVIOR OF REE IN THE HYDROTHERMAL PROCESS (THERMODYNAMIC MODELLING)
G. N. Shironosova 1, I. R. Prokopyev 1,2,3
1 Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia; 2 Novosibirsk State University, Novosibirsk, Russia; 3 Tuvinian Institute for Exploration of Natural Resources SB RAS, Kyzyl, Russia
Apatite and phosphates of rare earth elements are widely distributed in corresponding deposits, primarily embedded in carbonatite-phoscorite complexes, that indicates the enrichment of hydrothermal fluids with phosphorus and necessitates the study of the phosphorus role in the evolution of REE. For the first time, thermodynamic calculations were performed for the entire series of lanthanides, as well as yttrium, on the effect of phosphorus concentration during cooling of hydrothermal fluid from 500 to 100 °C, affected the association of monazite with calcite. With a decrease in the added phosphorus concentration, the formation of not only fluorapatite and xenotime was determined, but also a wide stability field of bastnasite and parisite in the low–temperature area; with an increase in the added phosphorus concentration the situation is converse: the area of bastnansite formation decreases in slightly acid and weak-alkaline conditions and parisite disappears in a slightly acid fluid. The presence of saline agent in fluid is accompanied by an increase in the concentration of rare earths and phosphorus in it. At the same time, the concentration of light rare earth elements in the high-temperature area is higher than that of heavy ones, while heavy lanthanides predominate in the lowtemperature area. Phosphate complexes contribute significantly to the transportation of rare earths; at high temperatures, the main contribution is made by chlorocomplexes of light lanthanides, and at low temperatures by fluorocomplexes of heavy elements.
Keywords: rare earth elements, monazite, xenotime, bastnasite, parasite, thermodynamic modelling.
DOI 10.20403/2078-0575-2025-1-75-84