Chemical Equilibria in the Thermal Spring Waters of Virginia

Basic Information
Author: Helz, G.R. , Sinex, S.A.
Description:The composition of waters from 10 thermal springs located in western Virginia near the 38th parallel lineament have been analysed for major dissolved components and for Sr, Fe, Cu, Zn and Cd; from these analyses, free ion activities have been calculated. The temperatures of the springs range from 17 to 39C, the heat apparently being derived simply from deep circulation along synclinal, Middle Ordovician limestones. More than 95 percent of the dissolved solids consist of Calcium, Magnesium, HCO3, and Sulfate. The concentrations of these components, as well as the spring temperatures, have not changed appreciably in 140 year in some springs. The waters that have temperatures below 25C are all undersaturated with respect to calcite and dolomite, possibly because they have been contaminated by shallow ground waters. The waters with temperatures above 25C are in equilibrium with calcite and dolomite. Furthermore, in this latter group, the calcium-sulfate activity product and the sulfate-carbonate activity ratio are nearly constant, even though the waters are under saturated with respect to gypsum, anhydrite, celestite and strontianite. This can be explained if CaSO4 is coprecipitated in a mineral such as aragonite. The waters have absorbed some dissolved oxygen near the surface, but at depth they may be anoxic with Eh controlled by the oxidation of pyrite to goethite. The extremely low chloride concentrations of these waters clearly distinguish them from the brines which deposited Mississippi Valley and Appalachian type epithermal ore deposits. This resource is available for purchase for a downloadable PDF. For more information on this resource, please see the link provided.
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Organization Name: University of Maryland
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Geographic Extent
North Bounding Latitude: 40
South Bounding Latitude: 36
East Bounding Longitude: -75
West Bounding Longitude: -84