GEOCHEMISTRY OF SALINE SUBSURFACE WATER SALINE COUNTY (MISSOURI)

An investigation of saline subsurface water in central Missouri has shown that the chemical character of this water is largely governed by mineralogical controls. Although the water is supersaturated with respect to quartz, the silica concentration is held constant at approximately 9 p.p.m. apparently by the dissolution of illite. A series of scatter diagrams for the water samples indicates that potassium and hydrogen ion have a markedly different relationship to variations in salinity than do other group Ia elements. The K+ H+ activity ratio ranges from approximately 103.8 to 104.0 and is apparently controlled by the presence of illite or illite plus kaolinite. Calculation of the ion activity products [Ca2+][CO32-] and [Ca2+][Mg2+][CO32-]2 indicates that the saline water is approximately saturated with respect to calcite and dolomite. The mean Ca2+ Mg2+ activity ratio, 1.51, is in agreement with the value obtained by Hsu (1963) for water from dolomitic limestones. The variations in the Ca/Na and Mg/Na ratios in the Missouri water samples can be predicted using a model in which the concentration of Na is affected only by the addition or removal of water from the system whereas the concentrations of Ca and Mg are additionally affected by equilibration with calcite and dolomite. The ion activity products [Sr2+][CO32-] and [Ba2+]CO32-] are constant at 10-10.3 and 10-12.4 respectively. This suggests that the water is saturated with respect to SrCO3 and BaCO3 in some form and that the Sr/Ba activity ratio, 102.1, is mineralogically controlled. Because the chemistry of the saline water is now controlled to a large extent by its mineralogical environment the compositional characteristics of the water cannot be used to determine the origin of the salinity. © 1969.