Immiscibility of NaF-Na_2SO_4-NaCl-containing fluids from a synthetic fluid inclusion study

摘要

Increased content of F and SO_4-ions in magmatic fluid is frequently related with concentration of REE, Mo, W, Sn, Ta, Nb, U, Th, Be, Li, Rb, Cs and other elements. The data about fluorine-containing fluids, their phase state under high temperature and pressure corresponding to separation of fluid from magma is practically absent. Fluorine is present in solutions in 0.1 to few wt percents, basing on studies of natural fluid inclusions. In order to obtain experimental evidence on fluorine-containing fluids, we synthesized fluid inclusions in natural quartz under T = 500-800℃ and P=0.5-2 kbar in solutions, containing NaF or NaF+NaCl, by cracks healing method. Inclusions of solutions containing Na_2SO_4+(NaF and NaCl) were synthesised at 300-800℃ and P=0.5-3 kb.We used ampullaceous technique. Fluid-generative mixture was 0.5M (2.1 wt %) NaF solution or dry-through solid NaF (solubility is 4.1 wt % under room temperature), Na_2SO_4 (solubility is 31.5 wt %) and water. NaCl was put as 1M or 2M solution. The measurement accuracy was ±50 bar for pressure and ±5° for temperature. Lead-in into experimental mode took 1.5-2 h, tempering - 5-8 min for exoclave and 20-30 min for autoclave. The overall experiment duration was 23-35 days.