SVECONORWEGIAN POLYMETALLIC QUARTZ VEINS IN SWEDEN

A widely distributed system of partly gold-bearing polymetallic quartz veins occurs in the Southwest Scandinavian Domain of the Fennoscandia n Shield. The veins are localized to the west of the Mylonite Zone, wi th the majority forming a belt extending from lake Mjosa, southeastern Norway, to lake Vanern, southwestern Sweden. Granitoids, gneisses and metasediments with ages of c. 1.6-1.1 Ga constitute the host rocks fo r the investigated veins, which display cross-cutting relationships re lative to these rocks and are inferred to be of Sveconorwegian origin, i.e. around 0.9 Ga old. The veins show variable chemical and mineralo gical compositions and four types can be distinguished: Cu-dominated v eins with chalcopyrite and/or bornite; Pb-Cu-bearing veins with pyrite as well as occasional galena and chalcopyrite; Zn-Pb-dominated veins with sphalerite and galena as well as occasional pyrite and chalcopyri te; Mn-bearing vein(s) with galena, chalcopyrite and hausmannite. In a ddition, native gold and a number of rare minerals including argyrodit e, hessite, tellurobismuthite and altaite are present, preferently in the two first mentioned types. The ore lead isotopic composition is mo re complex than previously reported and two separate source rock syste ms appear to have contributed to the vein deposits. One system was res ponsible for the complex metalliferous veins in Dalsland and westernmo st Varmland, whereas the other system was responsible for the veins in the Varmskog area. In spite of the chemical, mineralogical and isotop ic variations recognized, overlapping characteristics between the vein types do exist and a common origin in general is envisaged for all ve ins.