Isotopic and geochemical data of the Pingstaberg Mo-bearing granite in Bergslagen, South Central Sweden

Abstract

An isotopic and geochemical investigation of the Pingstaberg Mo-occurrence in the Bergslagen region, south-central Sweden, has been undertaken. The mineralization is of an intra-granitic type, and is situated within an undeformed granite of a minimum melt composition. In comparison with a 'normal granite', the mineralized part of the Pingstaberg granite is enriched in Y, Nb, Rb, U, Th and HREE, and depleted in Zn, Cu, Zr, Sr and Ba. Several of its characteristic isotopic and geochemical features are probably due to the Mo-mineralizing solutions, and these are likely also to have caused the strongly corroded structure of the analyzed zircons. As a result the U-Pb zircon and Rb-Sr whole-rock isotopic systems have been affected in various ways. The achieved U-Pb zircon age of 1781 ± 46 Ma is, however, considered to be essentially undisturbed, and this age is considered to represent both the time of granite emplacement and the mineralization episode. The Rb-Sr whole rock age of 1.53 Ga, on the other hand, has been reset and is interpreted as reflecting a post-crystallization hydrothermal event. The results presented in this study suggest that the Pingstaberg granite was formed at a late-orogenic stage (1.80-1.75Ga) of the Svecokarelian orogeny.