Calcite fracture fillings as indicators of paleohydrology at the Aspo Hard Rock Laboratory, Sweden

Isotopic compositions of carbon ({delta}{sup 13}C), oxygen ({delta}{sup 16}O) strontium ({delta}{sup 87}Sr) in calcite fracture fillings are being used to reconstruct the source and evolution of the groundwater at Aespoe and Laxemar, at the Aespoe Hard Rock Laboratory (AEHRL), south-eastern Sweden. These calcites precipitated from groundwater in the fractured crystalline rocks at some time in the past, and {delta}{sup 13}C, {delta}{sup 18}O and {delta}{sup 87}Sr values of the calcites reflect those of the source waters. The fracture fillings mark the pathways of past fluid movement so an understanding of their genesis is particularly important for understanding the paleohydrology in the area. The utility in applying the multiple-isotope approach to groundwater and fracture minerals derives from the fact that the different systems represent different processes. Studies of the groundwater chemistry suggest a very complicated history, however, the isotope data demonstrate that it is possible to postulate mixing of different groundwater members to explain the isotopic systematics of the calcite fracture fillings at Aespoe and Laxemar.