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Abstract
The Boviksgruvan deposit, situated 18 km northeast of Falun, is a gold-bearing magnesian skarn deposit which was mined for iron and zinc during the 18th and 19th centuries. Magnetite, sphalerite, galena, chalcopyrite, pyrite, and pyrrhotite dominate the ore mineral assemblage. In addition, gold, native bismuth, galenobismutitc, cosalite, joseite A, and joseite B are specific constituents recognized in the Boviksgruvan deposit. The ore can be divided into two mineralogical types. Ore type 1 consists of a biotite-magnetite assemblage with disseminated galena and Pb-Bi-sulphosalts. Ore type 2 consists mainly of iron sulphides, base metal sulphides, and anthophyllite. Gold is often intergrown with native bismuth, as inclusions in galena or as cavity fillings in magnetite. According to the cross-cutting relations recognized between magnetite and Pb-Bi-sulphosalts in ore type 1, these sulphosalts, as well as gold, are considered to represent a younger ore forming epoch in relation to the magnetite. Furthermore, the host rock of the goldbearing assemblage can be compared with mica-amphibole rich ‘sköl’ zones in certain stratiform sulphide deposits in Bergslagen, which may imply a tectonic control for ore type 1. However, the lead isotopic composition of cosalite and galena in this epigenetic ore type is comparable with isotopic data reported for volcanogenic sulphide deposits elsewhere in Bergslagen, which indicates that the gold-bearing assemblage in Boviksgruvan was formed very shortly after the volcanogenic sulphides.