Betechtinite and cobalt pentlandite, two minerals new for Långban, were observed coexisting with chalcocite, bornite, sphalerite, galena, and magnetite in a serpentinized skarn. Magnetite occurs in two generations, as euhedral crystals and as fracture fillings. This feature plus the textural relations of sulfides suggest an oxidation at very low temperature. The presence of chalcocite, bornite and minor amounts of native bismuth, and the absence of pyrite indicate a low sulfur activity during crystallization of these sulfides.