Mobility, speciation and distribution of platinum group elements in silicate melts and fluids at high pressure
Final Report Abstract
High pressure experiments were conducted at 200 MPa and 1250 °C to assess the effect of volatiles on Platinum (Pt) and Iridium (Ir) solubility in Fe-free silicate melts which can be considered as analog melts for basalts. Water dissolved in silicate melts does not influence the solubility of Pt and Ir. Under geologically relevant conditions, Pt and Ir are dissolved primarily in the 2+ valence state. Thus, Pt and Ir solubilities are dependent on oxygen fugacity and can be modeled by following equations [Pt](ppb) = 1389(fO2) + 7531(fO2)^1/2 [Ir](ppb) = 23714(fO2)^1/2 A novel technique was developed to synthesize fluids inclusions in equilibrium with silicate melts and was applied to assess the partitioning of Pt between an aqueous fluid and a hydrous diopside-anorthite melt. Although improvements of the technique still need to be done (the size of the inclusions is small), the analysis of melts and fluid inclusions using Laser Ablation ICP-MS indicates that the partition coefficient of Pt between hydrous fluids and melt is in the range 2 to 50. Chlorine and CO2 dissolved in the silicate melt have no or very little effect on Pt and Ir solubility in a Fe-free basaltic melt. Preliminary evidence of minor Cl-complexing of Ir is observed, but for extremely high Cl concentrations in the melt (~ 2 wt% Cl). Thus, the transport of Pt and Ir via Cl-bearing or CO2-bearing complexes in silicate melts is not expected to play a dominant role in geological processes. However, preliminary data indicate that the partition coefficient of Pt between CO2-rich fluids and melt is in the range 10^3- 10^4. Furthermore, the partition coefficient of Pt and Ir between Cl-bearing fluids and melt is high and is in the range 10^3- 10^4 and 10^2-10^3, respectively, indicating that Cl-bearing or CO2-rich fluids can be highly efficient in transporting PGEs in magmatic-hydrothermal systems.
Publications
- Internationales Symposium für Experimental Mineralogy, Petrology and Geochemistry (EMPG X) in Frankfurt, 2004. Crystallization entrapment method applied to fluid-melt partitioning of platinum in basaltic systems
Blaine, F. A.; Linnen, R. L.; Holtz, F.; Fryer, B.J. ; Brügmann, G. E.
- (2005). Platinum solubility in a haplobasaltic melt at 1250 °C and 0.2 GPa: the effect of water content and oxygen fugacity. Geochimica et Cosmochimica Acta, 69, 1265-1273
Blaine F.A., Linnen R.L., Holtz F., Brügmann G.E.
- Goldschmidt Conference 2005. Geochimica et Cosmochimica Acta, Volume 69, Issue 10, Supplement 1, Goldschmidt Conference Abstracts 2005, p.A736. Partitioning and vapour transport of Pt at magmatic conditions
Blaine, F. A.; Linnen, R. L.; Holtz, F.; Gagnon, J. E.; Brügmann, G. E.
- Goldschmidt Conference 2008. Geochimica et Cosmochimica Acta, Volume 72, Issue 12, Supplement 1, Goldschmidt Conference Abstracts 2008, p.A88. The effect of chlorine on the solubility of Pt in a haplobaslatic melt at 0.2 GPa and 1523K
Blaine, F. A.; Linnen, R. L.; Holtz, F.; Brügmann, G. E.
- (2010). The effect of Volatiles (H2O, Cl, CO2) on the Solubility and Partitioning of Platinum and Iridium in Fluid-Melt Systems. Dissertation, 162 p.
Blaine, F. A.
