Palaeohydrogeological Evidences from Fracture Filling Minerals - Results from the Äspö/Laxemar Area

Abstract

ABSTRACTTwo different EU projects: the EQUIP project (Evidences from Quaternary Infills from Palaeohydrogeology) running from 1997 to 2000 and the ongoing PADAMOT-project (Palaeohydrogeological Data Analysis and Model Testing) have addressed the possibility of using fracture minerals as recorders of past hydrochemical and hydrogeological environments. The Swedish contribution in these two projects has concentrated on studies of fracture filling calcites from the Äspö/Laxemar area, southeast Sweden.The analyses applied in the two projects comprise stable isotope ratios of carbon and oxygen and strontium together with trace element contents and textural studies. The results obtained so far (mainly from the EQUIP project) show that several generations of calcite can be identified, chemical zoning is common, and the influence on calcite precipitation of fresh and marine water decreases with depth. It can be concluded that fine scale zoning, possible dissolution/redistribution of calcite, and the disturbances caused by drilling (where loose material which may contain young calcite precipitates were lost), introduce uncertainties in the recognition of different calcite generations. However, despite these problems it is indicated that calcite fracture fillings in Precambrian bedrock environments can add information e.g. concerning changes in groundwater chemistry and redox conditions in the past. The possibilities and problems with palaeohydrogeological interpretations are discussed based on the available data.