Arsenic chemistry in hot springs

Once hydrothermal fluids approach the surface, lower pressures cause the liquids to boil. As steam separates from hydrothermal water, arsenic preferentially remains in the liquid phase. Above 200 °C, only about 0.1-0.5% of the arsenic in surface and near-surface hot springs partitions into steam (Ballantyne and Moore, 1988, 477). Table 3.6 lists the arsenic concentrations in condensates of gases from various volcanoes and hot springs. 

Amorphous AS2S3 , which has an uncertain composition (Helz el al., 1995, 4602-4603), and orpiment often precipitate in hot springs and geothermal wells. The compounds are currently precipitating in hot 

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