Publication Date:
2017-04-04
Description:
This paper documents arsenic concentrations in 157 groundwater samples from the island of Ischia and the Phlegrean Fields,
two of the most active volcano-hosted hydrothermal systems from the Campanian Volcanic Province (Southern Italy), in an attempt
to identify the environmental conditions and mineral-solution reactions governing arsenic aqueous cycling. On Ischia and in the
Phlegrean Fields, groundwaters range in composition from NaCl brines, which we interpret as the surface discharge of deep
reservoir fluids, to shallow-depth circulating fluids, the latter ranging from acid-sulphate steam-heated to hypothermal, cold,
bicarbonate groundwaters. Arsenic concentrations range from 1.6 to 6900 μg·l−1 and from 2.6 to 3800 μg·l−1 in the Phlegrean
Fields and on Ischia, respectively. They increase with increasing water temperature and chlorine contents, and in the sequence
bicarbonate groundwatersbsteam-heated groundwatersbNaCl brines. According to thermochemical modeling, we propose that
high As concentrations in NaCl brines form after prolonged water–rock interactions at reservoir T, fO2 and fH2S conditions, and
under the buffering action of an arsenopyrite+pyrite+pyrrhotite rock assemblage. On their ascent toward the surface, NaCl brines
become diluted by As-depleted meteoric-derived bicarbonate groundwaters, giving rise to hybrid water types with intermediate to
low As contents. Steam-heated groundwaters give their intermediate to high As concentrations to extensive rock leaching promoted
by interaction with As-bearing hydrothermal steam.
Description:
Published
Description:
313–330
Description:
reserved
Keywords:
Arsenic geochemistry
;
Hydrothermal systems
;
Water–rock interaction
;
Hydrogeochemistry
;
Arsenopyrite
;
03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Format:
1251413 bytes
Format:
application/pdf
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