Compositional Variation of Major Elements in Groundwater Caused by Water-Rock Interaction (I)

Chemical Equilibrium and Mass Balance

Abstract

Compositional variation of groundwater interacting with Na Ca-feldspar was derived based on the mass balance and chemical equilibrium theory. The theoretical trend on (logmca²⁺+2pH)-_H4siO4 diagram was compared with chemical compositions of groundwater in granitic rock area. It was found that the compositional variation of the groundwater can be explained by this theoretical consideration and groundwaters are sometimes in equilibrium with secondary minerals (chalcedony, quartz, Camontmorillonite, kaolinite), but sometimes deviate from equilibrium. The mineralogical weathering profile of granitic rocks is also in accordance with this theory.