24 Springs in the Water Cycle: Supply, Water-rock Interaction, and History

Tuesday, 15 March 2005
1:00 PM - 4:00 PM

MODEL SIMULATIONS OF THE SARATOGA SPRINGS: RESULTS AND UNCERTAINTIES

Paper number: 24-4
Program: THEME SESSIONS
Time: 2:00 PM – 2:20 PM

Authors

Abstract

The d13C (-5.8 to +0.8 ‰ VPDB) of dissolved inorganic carbon and elevated dissolved 3He/4He ratios show a mantle or magmatic origin for the CO2 in the saline Saratoga mineral springs. The stable isotopic content of the spring water and Sr isotopic composition (dissolved Sr) define mixing lines between modern local meteoric waters and a probable Canadian Shield-type brine under the Adirondack Mountains. We used NETPATH, a U. S. Geological Survey chemical mass-balance model, and PHREEQCI, a geochemical water-rock reaction model, to heuristically test whether water-rock interactions at Saratoga could broadly be simulated from plausible end-member compositions of reactive minerals, brine, and meteoric water. Waters are generally nearly equilibrated with calcite and dolomite and undersaturated with respect to gypsum, halite, and silica.

For the mass balance model, we diluted a plausible Canadian Shield Brine to match the chlorinity of the most saline Saratoga Water, and then balanced the model by stochiometrically dissolving; 6 mmol of dolomite, 35 mmol of sodium feldspar, and 3 mmol of potassic feldspar per kg, consuming 67 mmol of carbon dioxide, and precipitating 6 mmol/kg of calcite. We used these results as input to PHREEQCI to test whether the resulting solution would calibrate to major solute concentrations in the spring water. The forward reaction simulations were equivocal, poorly calibrated to observations of spring water chemistry in the field. We think this result probably reflects uncertainty with respect to the brine composition in crystalline rocks under the Adirondack Mountains.