FLUORINE PARTITIONING BETWEEN GRANITIC MELT AND APATITE

Fluorine (F) is a common element found in magmas and emitted from volcanoes. It is important to learn the effect that F has on the magma in terms of density, viscosity, and the interaction between F and other elements in the magma. F has an effect on ore deposit formation, and knowledge gained on F behavior in magmas could be used to locate future deposits. F concentration in granitic rocks is not equal to the F that was in the magma because F gas is lost from the magma. Through experimentation the relationship between F concentration in granitic rocks and F concentration in the initial magma can be determined. Cold-seal experiments done with granitic gels of varied F content, between temperatures of 650-800C, at 200MPa, to determine the partition coefficient [DF(Ap/melt)=F(Ap)/F(Gl)] of F between apatite (Ap) and the hydrous melt (quenched to glass; Gl). New variations on previous experiments include higher starting temperatures up to 900C and different initial F content in the granitic gels. The chemical composition of apatite crystals formed in previous experiments also had a larger than normal percentage of F. Previously, F content was varied from 0.3, 1.0, and 1.3 wt.%. Current experiments are being run with initial F content in powders of 0.1, 0.3, and 0.75 wt.%. By decreasing the initial amount of F, less F will be available for incorporation into apatite, and the percentage of F in the apatite crystals should be similar to what is found naturally. In addition to varying the F content, water and quartz content also has been changed. Quartz was added to the gel, and less water was introduced than before. Quartz was added to make up 6 wt.% of the total gel. Water concentration was kept at 10 wt.% which is the saturation point. Previous experiments were done with water concentrations over 10 wt.%. These variables were introduced in order to grow larger crystals. Previous experiments did not consistently grow crystals large enough(>10 microns diameter) for proper analysis. These new variations on the initial experiments should provide crystals large enough to analyze and of useful melt compositions to get good results for the partition coefficient of F into apatite.