Origin of fluids in the shallow geothermal environment of Savo, Solomon Islands

Smith, D.J., Jenkin, G.R.T., Boyce, A.J. , Naden, J. and Petterson, M.G. (2006) Origin of fluids in the shallow geothermal environment of Savo, Solomon Islands. Geochimica et Cosmochimica Acta, 70(18), A598. (doi:10.1016/j.gca.2006.06.1111)

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Abstract

Savo is a recently emergent volcano. An active geothermal system has been present for at least 50 years, expressed at the surface by numerous hot springs, fumaroles and steaming ground. Samples of water and steam were collected from geothermal features and non-thermal springs and wells, and representative samples of altered rocks and precipitates were collected from geothermal areas.

Analysis of the waters for anion, cation and stable isotope composition shows that the waters discharging at the surface fall into two groups (see Table).

Reoka type fluids have the high sulfate, low pH, and enriched δ18O and δD values typical of steam heated acid sulfate waters, where shallow groundwater is heated by rising steam and gas. Isotopically light H2S is oxidised in the near surface environment to produce the sulfate content.

Rembokola type fluids have chemistry distinct from the Reoka type fluids, despite the two being found within close proximity (<10 m). Rembokola Type fluids produce a carbonate sinter, so are assumed to be saturated with bicarbonate. The aqueous sulfate has heavy δ34S, suggesting that it is not exclusively produced by the oxidation of H2S in the near surface environment. We suggest that condensation of volcanic gases (including CO2 and isotopically heavy SO2) into meteoric-derived groundwater in the upper levels of the volcanic edifice produces these carbonate–sulfate waters. The presence of SO2 suggests that there is a degassing magma at depth, and potentially a high sulfidation-type epithermal system beneath the steam heated zone.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Boyce, Professor Adrian
Authors: Smith, D.J., Jenkin, G.R.T., Boyce, A.J., Naden, J., and Petterson, M.G.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Geochimica et Cosmochimica Acta
Publisher:Elsevier Ltd.
ISSN:0016-7037
ISSN (Online):1872-9533

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