HR: 0800h
AN: V31A-1415    [Abstracts]
TI: Cu-Cl-Salt-Hydrate Melts and Their Possible Role in Ore-forming Systems
AU: * Renno, A D
EM: Axel.Renno@mineral.tu-freiberg.de
AF: Technische Universit\"{a}t Freiberg Institut f\"{u}r Mineralogie, Brennhausgasse 14, Freiberg, D-09596 Germany
AU: Franz, L
EM: Leander.Franz@mineral.tu-freiberg.de
AF: Technische Universit\"{a}t Freiberg Institut f\"{u}r Mineralogie, Brennhausgasse 14, Freiberg, D-09596 Germany
AU: Witzke, T
EM: witzke@iml.rwth-aachen.de
AF: RWTH Aachen Institut f\"{u}r Mineralogie und Lagerst\"{a}ttenlehre, W\"{u}llnerstrasse 2, Aachen, D-52056 Germany
AU: Herzig, P M
EM: pherzig@ifm-geomar.de
AF: Leibniz-Institut f\"{u}r Meereswissenschaften , Dienstgeb\"{a}ude Ostufer Wischhofstrasse 1-3, Kiel, 24148 Germany
AB: We found direct evidence for a Cu-Cl-salt-hydrate melt in equilibrium with a complex system of silicate melts in a magnesiohastingsite-dominant cumulate from the TUBAF Seamount near Lihir Island (Papua New Guinea). We observed four distinct exsolution-induced features in the trachyandesitic intercumulus melt: 1) exsolution of a Cu-Fe sulfide melt, 2) exsolution of a Cu-salt-hydrate melt, 3) exsolution of a second foiditic silicate melt, and 4) exsolution of a vapor phase. The Cu-Cl-salt-hydrate melt crystallized into polycrystalline monomineralic aggregates of clinoatacamite. The features, which testify the formation of the clinoatacamite as an exsolution from the silicate melt, are presented. There is no indication of late hydrothermal alteration or weathering in the sample. We compare different possibilities to explain the formation of the xenolith and show, that the xenolith had formed independently from its parent magma in the oceanic crust. Even though no data on the solubility in Cu-Cl-silicate melt systems are available we suggest, with respect to other salt-melt - silicate-melt systems, an upper temperature limit of 800 $\deg$C for the unmixing of the salt-hydrate-melt. The observation of these unmixing processes sheds new light on the modus operandi of how metal-enriched magmatic fluids enter hydrothermal systems. We present different scenarios, how these fluids may affect the formation of ore deposits, like epithermal gold deposits or copper porphyry systems.
DE: 9355 Pacific Ocean
DE: 3640 Igneous petrology
DE: 3655 Major element composition
DE: 1020 Composition of the crust
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting