HR: 0800h
AN: V31D-0684    [Abstracts]
TI: Experimental Constraints on Pt-Pd-Au Partitioning in an H2O-Haplogranite-Sulfide-Oxide phase assemblages
AU: * Bell, A
EM: bella19@unlv.nevada.edu
AF: Dept. of Geoscience, UNLV, 4505 Maryland Parkway, Las Vegas, NV 89154-4010, United States
AU: Simon, A C
EM: adam.simon@unlv.edu
AF: Dept. of Geoscience, UNLV, 4505 Maryland Parkway, Las Vegas, NV 89154-4010, United States
AU: Guillong, M
AF: Institute Isotopengeologie/Mineral. Rohstoffe, ETH Zentrum, NW F86.1, Zurich, 8092, Switzerland
AU: Heinrich, C
EM: heinrich@erdw.ethz.ch
AF: Institute Isotopengeologie/Mineral. Rohstoffe, ETH Zentrum, NW F86.1, Zurich, 8092, Switzerland
AB: We performed experiments to to elucidate the role of sulfide and magnetite crystallization on the Pt, Pd and Au metal budgets of a water-saturated haplogranite magma. Experiments were carried out by equilibrating a NaCl- KCl +/-HCl aqueous solution, haplogranite melt, magnetite and two sulfide assemblages with elemental Pt, Pd, and Au. Oxygen fugacity was buffered at approximately Ni-NiO by the intrinsic buffering capacity of the experimental apparatus, and fS2 was fixed at Ni-NiO by sulfide phase assemblages of pyrrhotite (po) plus intermediate solid solution (Iss), and at a second fS2 by an Iss plus bornite assemblage. The experiments were carried out at 800C and 150 MPa, slightly higher than the critical pressure in the NaCl-KCl-H2O system for varying durations. Experimental run products were analyzed for major elements by using wavelength dispersive spectrometry electron probe microanalysis (EPMA) at UNLV and for trace elements via laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) at ETH in Zurich Switzerland. Resultant data were used to calculate Nernst-type partition coefficients for Pt, Pd and Au between the silicate melt and all solid phases. Calculated partition coefficients for Pt and Pd between all sulfides and melt suggest that po more efficiently sequesters Pd relative to Pt from the melt. Sulfide saturation of a melt and subsequent crystallization of po, Iss and bn will decrease significantly the concentration of Pd, Pt and Au in the melt. Po and Iss effectively fractionates Pd from Pt by at least one of magnitude resulting in a strong decrease in the Pt/Pd ratio of the melt. Additionally, moderate to high concentrations of Pd (1-2 wt%) in Iss at both fS2 values decreases Au solubility in Iss by an order of magnitude from the Au solubilities reported by Jugo et. al. (1999, Lithos). The presence of HCl in the assemblage has no statistically meaningful effect on the solubilities and partitioning behavior of the investigated elements. The results will be used to model the Pt, Pd, Au budget of an evolving magmatic system.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3618 Magma chamber processes (1036)
DE: 3630 Experimental mineralogy and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting