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Copper speciation in vapor phase fluid inclusions from the Mole Granite, Australia

J.A. Mavrogenes, A.J. Berry, M. Newville1 and S.R. Sutton1
1
Consortium for Advanced Radiation Sources, University of Chicago

X-ray fluorescence elemental maps and copper K-edge X-ray absorption spectra were recorded for single vapour and brine phase fluid inclusions from the Mole Granite, NSW, Australia. The maps indicate that copper is concentrated in the vapour inclusions and at room temperature uniformly distributed in the condensed fluid. Opaque precipitates in these inclusions do not contain copper. The absorption spectra identify the stable complexes as [Cu(OH2)6]2+ at 25°C, [CuCl2]- at 200°C, and [CuCl(OH2)] at the homogenisation temperature of around 400°C. This change in copper coordination and oxidation state is fully reversible. The results suggest that copper is transported in the vapour phase as a neutral chloride complex. We aim to identify the factors that control copper partitioning between a vapour phase and high density brine. This work has implications for understanding the metal distribution between epithermal and porphyry type environments in hydrothermal systems.