Geochemistry of a fossil hydrothermal system at Barton Peninsula, King George Island
A fossil hydrothermal system on Barton Peninsula, King George Island, Antarctica, formed a series of lead-zinc- and pyrite + native sulphur-bearing epithermal quartz ± calcite veins, filling fault-related fractures in hydrothermally altered volcanic rocks of Eocene age. The lead-zinc veins occur wit...
| Published in: | Antarctic Science |
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| Main Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Cambridge University Press (CUP)
1995
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1017/s0954102095000101 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102095000101 |
| Summary: | A fossil hydrothermal system on Barton Peninsula, King George Island, Antarctica, formed a series of lead-zinc- and pyrite + native sulphur-bearing epithermal quartz ± calcite veins, filling fault-related fractures in hydrothermally altered volcanic rocks of Eocene age. The lead-zinc veins occur within argillic hydrothermal alteration zones, whereas the pyrite + native sulphur veins are found within advanced argillic alteration zones. Fluid inclusion data indicate that the vein formation occurred at temperatures between about 125° and 370°C (sphalerite deposition formed at 123–211°C) from fluids with salinities of 0.5–4.6 wt.% eq. NaCl. Equilibrium thermodynamic interpretation of mineral assemblages indicates that the deposition of native sulphur in the upper and central portions of the hydrothermal system was a result of the mixing of condensates of ascending magmatic gases and meteoric water giving rise to fluids which had lower pH (<3.5) and higher fugacities of oxygen and sulphur than the lead-zinc-depositing fluids at depth. The δ 34 S values of sulphide minerals from the lead-zinc veins (δ 34 S = −4.6 to 0.7‰) are much higher than the values of pyrite and native sulphur from the pyrite + native sulphur veins (δ 34 S = −12.9 to −20.1‰). This indicates that the fluids depositing native sulphur had higher sulphate/H 2 S ratios under higher fo 2 conditions. Sulphur isotope compositions indicate an igneous source of sulphur with a δ 34 S ΣS value near 0‰, probably the Noel Hill Granodiorite. Measured and calculated δ 18 O and δD values of the epithermal fluids (δ 18 O water = −6.0 to 2.7‰, δD water = −87 to −75‰) indicate that local meteoric water played an important role for formation of lead-zinc and native sulphur-bearing quartz veins. |
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