Chemistry of groundwater in tuffaceous rocks central Nevada

Abstract

A flow path chemical model in tuffaceous rocks was developed using statistical, graphical, and computer methods. Forty nine springs which discharged from glassy, devitrified, and variably altered silicic rocks represent early stage recharge chemistry. Chemical analyses from Pahute Mesa and Yucca Mountain wells penetrating similar rock type and representing further chemically evolved waters, were compared. Common traits included pH, S04, HC03, Si02, TDS, and mineral saturation and stability. The trace elements (Fe, Mn, F, Li, and Sr), Cl, and cation concentrations, and temperature distinguished the two end member groundwaters. The difference in cation proportion between the Ca-HC03 type recharge chemistry and the Na-HC03 type well chemistry may reflect a decrease in divalent ions upon secondary mineral formation and/or ion exchange with clay and zeolite minerals (chiefly smectite and clinoptilolite).