Arsenic and antimony in geothermal waters of Yellowstone National Park, Wyoming, USA
Geochimica et Cosmochimica Acta, 1984
A total of 268 thermal spring samples were analyzed for total soluble As using reduced
molybdenum-blue; 27 of these samples were also analyzed for total Sb using name atomic absorption
spectrometry. At Yellowstone the Cl/As atomic ratio is nearly constant among neutral-alkaline springs
with Cl > 100 mgL-1, and within restricted geographic areas, indicating no differential effects of adiabatic
vs. conductive cooling on arsenic. The Cl/As ratio increases with silica and decreases with decreasing Cl/
ΣC03; the latter relationship is best exemplified for springs along the extensively sampled SE-NW trend
within the Lone Star-Upper-Midway Basin region. The relationship between Cl/As and Cl/ΣC03 at
Yellowstone suggests a possible rock leaching rather than magmatic origin for much of the Park's total
As flux. Condensed vapor springs are tow in both As and Cl. Very high Cl/As ratios (>1000) are associated
exclusively with highly diluted (Cl < 100 mgL-1) mixed springs in the Norris and Shoshone Basins and
in the Upper White Creek and Firehole Lake areas of Lower Basin. The high ratios are associated with
acidity and/or oxygen and iron; they indicate precipitation of As following massive dilution of the As-bearing
high-Cl parent water.
Yellowstone Sb ranged from 0.009 at Mammoth to 0.166 mgL-1 at Joseph's Coat Spring. Within
basins, the Cl/Sb ratio increases as the Cl/ΣC03 ratio decreases, in marked contrast to As. Mixed springs
also have elevated Cl/Sb ratios. WHITE (1967) and WEISSBERG (1969) previously reported stibnite (Sb2S3),
but not orpiment (As2S3), precipitating in the near surface zone of alkaline geothermal systems.
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