Y. Xu et al., Sulfur geochemistry of hydrothermal waters in Yellowstone National Park: I. The origin of thiosulfate in hot spring waters, GEOCH COS A, 62(23-24), 1998, pp. 3729-3743
Thiosulfate (S2O32-), polythionate (SxO62-), dissolved sulfide (H2S), and s
ulfate (SO42-) concentrations in thirty-nine alkaline and acidic springs in
Yellowstone National Park (YNP) were determined. The analyses were conduct
ed on site, using ion chromatography for thiosulfate, polythionate, and sul
fate, and using colorimetry for dissolved sulfide. Thiosulfate was detected
at concentrations typically less than 2 mu mol/L in neutral and alkaline c
hloride springs with low sulfate concentrations (Cl-/SO42- > 25). The thios
ulfate concentration levels are about one to two orders of magnitude lower
than the concentration of dissolved sulfide in these springs. In most acid
sulfate and acid sulfate-chloride springs (Cl-/SO42- < 10), thiosulfate con
centrations were also typically lower than 2 mu mol/L. However, in some chl
oride springs enriched with sulfate (Cl-/SO42- between 10 to 25), thiosulfa
te was found at concentrations ranging from 9 to 95 mu mol/L, higher than t
he concentrations of dissolved sulfide in these waters. Polythionate was de
tected only in Cinder Pool, Norris Geyser basin, at concentrations up to 8
mu mol/L, with an average S-chain-length from 4.1 to 4.9 sulfur atoms.
The results indicate that no thiosulfate occurs in the deeper parts of the
hydrothermal system. Thiosulfate may form, however, from (1) hydrolysis of
native sulfur by hydrothermal solutions in the shallower parts (< 50 m) of
the system, (2) oxidation of dissolved sulfide upon mixing of a deep hydrot
hermal water with aerated shallow groundwater, and (3) the oxidation of dis
solved sulfide by dissolved oxygen upon discharge of the hot spring. Upon d
ischarge of a sulfide-containing hydrothermal water, oxidation proceeds rap
idly as atmospheric oxygen enters the water. The transfer of oxygen is part
icularly effective if the hydrothermal discharge is turbulent and has a lar
ge surface area. Copyright (C) 1998 Elsevier Science Ltd.