A NEW METHOD FOR THE INVESTIGATION OF NOBLE GASES DISSOLVED IN THE PORE WATER OF SEDIMENTARY ROCKS: FIRST RESULTS FROM COAL AND SALT MINES IN GERMANY

摘要

A new sampling technique has been developed for the analysis of noble gases dissolved in the pore waters of consolidated sedimentary rock samples. The analysis of the accumulated radiogenic ~4He and ~(40)Ar yields information on the porewater age in low permeable formations, where groundwater is not accessible by pumping. This dating technique is of particular interest for studies of nuclear waste disposal in geological formations. Newly broken rock samples from mine galleries or from sediment cores are rapidly packed into helium-tight stainless steel containers and then directly evacuated. Within three to five weeks storage time, depending on the size of the rock sample, the noble gases are released by molecular diffusion from the pore water into the evacuated container volume. From there they can easily be transferred into the mass spectrometer. In addition, vacuum distillation of aliquots of the rock samples yield representative pore water samples for analysis of the 5D and δ~(18)O content. Furthermore, the main chemical components can be obtained by leaching the rock sample with distilled water as is already done in the Konrad iron mine [1].