Phase composition and U-Pb pitchblende systems of quartz-calcite-pitchblende veins at the Schlema-Alberoda deposit (Erzgebirge)

A link between the isotope age discordance of pitchblende from quartz-calci te-pitchblende (kku) veins and its phase heterogeneity has been established . As pitchblende inhomogeneities occur locally and are not accompanied by n oticeable changes of its optical properties, local analytical instruments s uch as an electron microscope and an electron microprobe have been used to reveal and to estimate the elemental composition of various mineral phases. An isotope study was carried out using a method of isotope dating of local microsamples. All these techniques allowed us to obtain isotopic data char acterizing primary zoning of pitchblende as well as to determine a trend an d the consequence of its epigenetic transformation. The wide range in isoto pe dares of pitchblende from (kku)-veins (about 100 Ma) is shown to be rela ted to its alteration during consequent stages of the hydrothermal process.