Xiong Xiaolin

Partitioning of F between aqueous fluids and albite granite melt and its petrogenetic and metallogenetic significance

The fluid/melt partitioning experiments on fluorine were carried out in the system albite-H2O-HF atP = 100 MPa, 770°C ≤T≤800°C: and wt = 2% −6% conditions. The concentrations of fluorine in quenched glasses (melt) were determined by electron microprobe and those of fluorine in the coexisting aqueous fluid were calculated by the method of mass balance. The result shows that the fluorine was concentrated in granitic melt relative to the coexisting fluid. The partition coefficient DF(wtFF1/wtFMt) ranges from 0.35 to 0.89. It increases with increasing fluorine content in the system. This means that there is not just one single value of partition coefficient for fluorine in the granitic melt-fluid system. The partitioning behavior of fluorine in this system depends critically on fluorine and proton (H+) concentrations. Our data suggest that F-rich granitic melts exist in nature and that fluorine may not be an important complexing agent of metal elements in F-bearing fluids.

Raman Investigation of BaWO4-II Phase under Hydrostatic Pressures up to 14.8 GPa

The BaWO4-II phase is synthesized at 5.0 GPa and 610°C with a cubic-anvil apparatus and identified by XRD. Raman scattering measurement is carried out to investigate the phase behaviour of a pure BaWO4-II phase (space group P21/n, Z = 8) under hydrostatic pressures up to 14.8 GPa at ambient temperature. In each spectrum recorded for this phase, 27 Raman modes are observed, and all bands shift toward higher wavenumber with a pressure dependence ranging from 3.8 to 0.2 cm−1/GPa. No pressure-driven phase transition occurs in the entire pressure range in this study. Our results indicate that the previously reported high pressure phase of BaWO4 at pressure above about 10 GPa and room temperature (Errandonea et al. Phys. Rev. B 73(2006)224103) is not the BaWO4-II phase.

Phase equilibria in the granite-H2O-HF system and effect of fluorine on granitic melt structure

Experiments carried out in the system granite-H2O-HF at 0.1 GPa show that the crystal-liquid equilibrium temperature of quartz rises and that of alkali-feldspar goes down with increasing F content. The calculated results of quartz and alkali feldspar crystal-liquid equilibrium show that the activity of SiO2 in melt increases and the activities of NaAlSi3O8(Ab) and KAlSi3O8(Or) decrease, with a greater decreasing extent for aAbL than aOrL. These systematic changes are believed to be caused by F complexing with Al, Na, K, but not Si in the melt, and are consistent with F decomposing AlO2− tetrahedra and more preferentially forming complexes with Na than K. The comparison between effects of F and H2O on phase equilibrium suggests that the maximum difference affecting melt structure between F and OH is F complexing without Si and OH complexing with Si in granitic melt.Experiments carried out in the system granite-H2O-HF at 0.1 GPa show that the crystal-liquid equilibrium temperature of quartz rises and that of alkali-feldspar goes down with increasing F content. The calculated results of quartz and alkali feldspar crystal-liquid equilibrium show that the activity of SiO2 in melt increases and the activities of NaAlSi3O8(Ab) and KAlSi3O8(Or) decrease, with a greater decreasing extent for a Ab L than a Or L . These systematic changes are believed to be caused by F complexing with Al, Na, K, but not Si in the melt, and are consistent with F decomposing AlO 2 − tetrahedra and more preferentially forming complexes with Na than K. The comparison between effects of F and H2O on phase equilibrium suggests that the maximum difference affecting melt structure between F and OH is F complexing without Si and OH complexing with Si in granitic melt.