Paleohydrogeological events in Forsmark, central Sweden, recorded by stable isotopes in calcite and pyrite

摘要

A large data set of stable isotopes in fracture filling calcite and pyrite has, together with detailed studies of thin sections, been applied to interpret the paleohydrogeology in Forsmark, central Sweden. Four major fracture mineral generations have been distinguished. An early period of precipitation of epidote, quartz and chlorite followed by a period of hydrothermal precipitation of calcite together with adularia, hematite, prehnite and laumontite correlating with the Sveconorwegian (Grenvillian) orogeny in western Sweden. A later period of precipitation of calcite together with e.g. quartz, pyrite and asphaltite displays an organic influence of the formation fluid and has been interpreted to be the result of circulation of fluids originating from an organic rich sedimentary cover during the Paleozoic. The youngest calcites are found in hydraulically conductive fractures and zones and may have precipitated during a long period including the present.