PGEs behaviour and Os isotopes in hydrothermal-magmatic fluids

S. G. Tessalina, M. A. Yudovskaya

Research output: Contribution to journalMeeting abstract

Abstract

PGEs behaviour is still little known in hydrothermal and
magmatic fluids due to their low concentrations, approaching
the detection limit. In this work, the PGEs behaviour and Os
isotopes were studied in the high-temperature mainly
magmatic fluids from the Kudrivay volcano, as well as in
hydrothermal ore facies from three distinctly different Urals
VHMS deposits.
The Kudryavy volcano in the Kurile Islands (Russia) is
passively degassing with fumarole temperatures of up to 940°
C, offering the possibility for the direct study of magmatic
volatiles. The concentration of each of the PGE does not
exceed 1 ppb, with the highest Os and Pt contents reaching
907 and 490 ppt, and the Pt/Pd ratio ranging from 0.3 to 2.3.
The Os is the most vapor-compatible element. While Pt and
Pd are the less vapor-compatible, they are still enriched by 2–3
orders of magnitude in the volatile phase relative to the
volcanic rocks. Fumaroles have relatively unradiogenic
187Os/188Os isotope ratios in a range from 0.122 up to 0.152,
similar to these of peridotite xenoliths from the underlying
mantle wedge within the Kurile–Kamchatka subduction zone.
The modern hydrothermal fluids have unradiogenic Os
isotopes pointing to a nearly complete domination of osmium
isotopes from the host volcanics (mostly basalts). The Os
concentration in fluids is typically buffered at seawater
concentration. In Urals VHMS deposits, the PGEs are
enriched in first-stage high-temperature portions of
hydrothermal systems and correlate with Co and Au contents.
187Os/188Os ratio increases with depth in the hydrothermal
system in the following order: seafloor altered sediments –
clastic sulphides – massive sulphides – stockwork zone –
sulphide chimney. The straight line correlation between initial
187Os/188Os and 1/Common Os shows the mixture of two
components, which could be identified as hydrothermal fluid
and seawater.
In conclusion, even little contribution of PGEs-rich
magmatic fluid into hydrothermal system will significantly
influence the Os isotope composition.
Original languageEnglish
Pages (from-to)A1322-A1322
Number of pages1
JournalGeochimica et Cosmochimica Acta
Volume73
Issue number13 supplement
DOIs
Publication statusPublished - Jun 2009
Externally publishedYes
EventGoldschmidt Conference (19th : 2009) - Davos, Switzerland
Duration: 21 Jun 200926 Jun 2009

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