Klassifikation av leptiter i malmstråket mellan Ö. Silvberg och Vallberget, Dalarna
1986
Hellström, Carina
Ö. Silvberg och Vallberget are two sulphide-ore mines immediately to the west of the town Säter in Dalarna. They are found in a NE-SW trending orebearing zone in the Leptite-formation. An area extending about 6 km in the NE-SW and 2 km in the perpendicular direction has been mapped. It consists of different types of volcanics, which chemically correspond to rhyolites (Na-rich, K-rich and alkali-intermediate) and basalts. The last-mentioned rocks occur as small lenses in the rhyolites. The texture of the volcanics varies as a function of the distance to the volcanic centers, from coarse-grained leptites with agglomeratic texture through fine-grained ones with porphyric texture to fine-grained laminated volcanics (tuffites). The ore-bearing zone is surrounded by acid alkali-intermediate rhyolites. Na-rich leptites (rhyolites) in the north-west and K-rich leptites in the south delimit the occurrence of the alkali-intermediate leptites. The K-rich leptites gradually pass over into carbonate-rich sediments. The Ö. Silvberg are (Pb-ore, rich in Ag) and the Vallberget-ore (Cu-and Zn-ore) are both surrounded by similar volcanic rocks. Mapping and chemical analyses support the conclusion that the ores have been formed under similar conditions at the same stratigraphic level but independently of each other.
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