Sampling of brine in cores of Precambrian granite from northern Illinois

Abstract

The composition of groundwater in deep‐seated rocks is of great interest, both geochemically and in connection with the disposal of radioactive waste. However, sampling of deep‐seated groundwater is expensive and often difficult. We describe here a simple technique for the elution of pore fluid (groundwater) from cores of igneous rocks, and we describe brine eluted from a core of Precambrian granite from Northern Illinois drill hole UPH‐3. The brine is predominantly NaCl and CaCl₂, with a Ca/Na mole ratio of about 0.05 to 0.1. From analysis of soluble chloride in a crushed sample the chloride concentration in the pore water is estimated as 2.3 M. The brine is similar to brine in the Illinois Basin, and it was probably derived from the overlying sediments.