ABSTRACT
The Långban mines in the Palaeoproterozoic Bergslagen ore province in south central Sweden, are well known for their complex and unique mineralogy, particularly within Pb-Mn-As-Sb-bearing fissure systems. Fluid inclusion data from fissure minerals suggest a formation for these assemblages at, or close to, atmospheric pressure, from aqueous NaCl-CaCl2-MgCl2 solutions of moderately high salinity at temperatures of initially c. 180°C via a sequence of boiling events at temperatures fluctuating between c. 80-120°C. This resulted in boiling-induced rapid formation of alternating fissure species at high pH conditions. Characteristic for the process is extensive precipitation of radial baryte and subsequent calcite and major Pb-Mn-As-minerals. It is proposed that the solutions responsible for the specific fissure mineralization in Långban were introduced in a very shallow post-Svecokarelian brittle tectonic environment, in conjunction with a late tectonic episode. The absence of similar mineralized brittle fissure or fault systems on a regional scale suggests that the metals in the Långban fissure system were derived very locally.
