Аннотация:INFLUENCE OF QUARTZ ON THE PYROCHLORE SOLUBILITY IN FLUORIDE SOLUTIONS (T=550-850OC, P=1 KBAR)
1KORZHINSKAYA V.S., 2KOTELNIKOVA Z.A., 1KOTELNIKOV A.R., 1SUK N.I. 1Institute of Experimental Mineralogy RAS, Chernogolovka, Moscow district, Russia; 2Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, RAS, Moscow
To estimate the influence of quartz (the most wide-spread mineral of ore rare-earth metal granitoid complexes) on pyrochlore solubility (Ca, Na)2(Nb, Ta)2O6 (O, OH, F) special runs (with quartz and without it) have been done. The runs lasted 7-15 days at 550o, 650o and 850oC and pressure 1 kbar in the solutions LiF (0.08 M), NaF (1M); KF (0.5 and 1M ) on hydrothermal devices with the external heating and cold valve and in “gas bombs”. To estimate phase fluid state we used a method of synthetic fluid inclusions in quartz. Quenching solution after the run was analyzed by ICP/MS and ICP/AES (mass-spectral and atomic-emission) method for the elements (Nb,Ta,Na,Ca,Mn,Fe,Ti etc.). Solid charge was analyzed on the electronic microprobe CamScan MV2300 (VGA TS 5130MM) and by the x-ray phase method.
Fluid Phase State for the runs with KF solution (concentration 0.5-1M): at 550oC and 1 kbar in case of the initial concentration of the solution 2.9 mass% (0.5M) a fluid is homogeneous: only G+L inclusions occur. If at the same P-T conditions the concentration of the initial solution increases up to 1M (5.8 mass %) then a fluid is heterogenized what testifies to the formation of different-type inclusions.
Solubility of pyrochlore. It is experimentally determined that at T = 550oC quartz presence decreases essentially Nb content in KF solutions (more than by 3 orders). For temperatures 650oC and 850oC quartz presence in the system increases the equilibrium content of Nb in the solution by an order of magnitude: at 650oC Nb content in 1mKF without quartz is 2.91*10-5, but in quartz presence it is 1.59*10-4 m/ kg H2O; at 850oC the number of Nb without quartz is 2.38*10-4, but with quartz (or with granite melt) is 2.39*10-3 mol/ kg H2O. The investigation of fluid inclusions in quartz has shown that under the conditions of the runs the reactions of high-temperature hydrolysis KF take place: KF + H2O = KOH↓+ HF↑; here the interaction with quartz takes place: SiO2 + 2KOH = K2SiO3 + H2O, with the formation of silicate glass phase (aqueous solution-melt).The phase of silicate glass was synthesized in the runs on pyrochlore solubility at 650o and 850oC and pressure 1 kbar (in the solution 1M KF). This phase of alkaline glass is a concentrator of Nb (Nb2O5 up to 16 mass %). The distribution coefficient of Nb between glass and fluid is equal to 500 (in favor of glass). It is shown that the phase of the alkaline silicate solution-melt can serve as an effective concentrator of the ore component (Nb) at the last low-temperature stages of crystallization of rare-metal granites.
This study was supported by RFBR, project № 15-05-03393.
