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Published December 1991 | public
Journal Article

Partitioning of Cu, Sn, Mo, W, U, and Th between melt and aqueous fluid in the systems haplogranite-H_2O-HCl and haplogranite-H_2O-HF

Abstract

The partition coefficients K_D=c_(fluid)/c_(melt) of Cu, Sn, Mo, W, U, and Th between aqueous fluid and melt were measured in the systems haplogranite-H_2O−HCl and haplogranite-H_2O−HF at 2kbars, 750°C, and Ni−NiO buffer conditions using rapid-quench cold seal bombs, with many reversed runs. Concentrations of trace elements (1–1000 ppm) in the quenched aqueous fluid and in the glass were determined by plasma emission spectrometry (DCP). KD of F is close to 1 in the system studied. K_D of Cu and Sn strongly increases with increasing Cl concentration due to the formation of chloride complexes in the aqueous fluid, while HF has no effect. However, in 2M HCl, K_D of Cu approaches 100, while K_D of Sn is below 0.1 under the same conditions. The partition coefficients of Mo and W are high if water is the only volatile present (Mo: 5.5, W: 3.5), but strongly decrease with increasing HCl and HF, due to the destabilization of hydroxy complexes. K_D of U and Th is very low in the absence of complexing agents, but strongly increases with increasing HF concentration. KD of U also increases with increasing HCl concentration and with increasing CO_2 concentration in the system haplogranite-H_2O−CO_2, indicating the stability of chloride and carbonate complexes of U at magmatic temperatures. The data suggest a stoichiometric ratio of Cl: U=3:1 and of F:U=2:1 in these complexes. Cl-rich fluids are responsible for the formation of porphyry Cu deposits, but are much less effective in the transport of Sn. F appears not to be essential for the concentration of Mo and W in fluids evolving from a granitic magma. The different complexing behavior of U and Th in aqueous fluids may account for their fractionation during magma genesis.

Additional Information

© 1991 Springer-Verlag. Received November 22, 1991; Accepted May 13, 1991. We thank Phil Ihinger for making the design of his rapid-quench bombs available to us. E. Stolper allowed us access to the DCP laboratory and S. Newman introduced us to its operation. This research benefited from discussions with Tom LaTourette and Dimitri Vlassopoulos. H.K. wishes to thank Sieger van der Laan, John Stone, Laurinda Chamberlin and Mike Wolf for their hospitality and support. This work was supported by NSF grant No. 89-04375 (Peter Wyllie) and by NATO/German Academic Exchange Service (Hans Keppler). This is Caltech Division of Geological and Planetary Sciences contribution No 4945.

Additional details

Created:
August 22, 2023
Modified:
October 17, 2023