LIQUID PHASE IMMISCIBILITY IN THE SYSTEM CA5(PO4)3F-SIO2-NAF-CAO-MGO AND ITS SIGNIFICANCE IN APATITE-ORE GENESIS

Abstract

We studied the possibility that the Khibiny apatite-nepheline ores were formed from immiscible liquid phases in a system composed of 13 main components - P2O5, SiO2, TiO2, Al2O3, Re2O3, Re2O3, FeO, CaO, MgO, SrO, Na2O, K2O and F, each of which contributed to the reaction producing such phases. To ascertain the role of CaO and MgO in the immiscibility process in this complex system, we studied its partial sections (Ca5 (PO4)3F-SiO2-NaF and Ca5(PO4)3F2-SiO2-NaF-CaO-MgO. The experimental work was done on synthetic material by the quenching method. It was found that in the system Ap-SiO2-NaF, there is a broad field of two immiscible liquid phases, silicate and phosphate-fluoride. Silicate melts, when quenched, readily form glass, but the phosphate-fluoride melts always crystallize. The morphology of the immiscible liquid phases (drops, layers and the like) persists in the quenched samples. Their mutual solubility is limited and, up to 1400° C, does not exceed 5 to 7 percent.