GEOCHEMISTRY, AGE, AND ORIGIN OF THE HOGBERGET GRANITE, WESTERN BERGSLAGEN, SWEDEN

An undeformed Palaeoproterozoic granite pluton, located at Hogberget, 10 km north of Kopparberg in western Bergslagen, has been investigated with respect to petrology, geochemistry, and geochronology. The geochemistry indicates a leucocratic and peraluminous granite and a REE pattern characterized by a large negative Eu-anomaly and a slight enrichment of the light REEs. Age determination by means of the U-Pb in zircon method yielded 1750+/-10 Ma. The Hogberget granite is spatially and genetically related to the Wigstrom (Hogfors) tungsten skarn deposit and is comparable with other W-Mo related granites in western Bergslagen (e.g. Pingstaberg, Fjallberg, and Skalhojden), which traditionally are considered to have an anatectic origin. The data presented in this paper give further support to genetical models favouring a Late- to post-Svecofennian, granite-related origin for the W-Mo deposits in western Bergslagen and are in strong conflict with theories favouring a rift-related Early Svecofennian genesis for these ores. The recognition of c. 1.75 Ga Late Svecofennian granites in western Bergslagen indicates a large time interval between peak of regional metamorphism and granite formation, which makes a genetic relation between regional metamorphism and the Late Svecofennian granites in western Bergslagen uncertain.