SULFOSALT MINERALOGY AND PARAGENETIC RELATIONS IN ZN-PB ORES FROM TUNABERG, BERGSLAGEN, SWEDEN

The high-grade metamorphic stratabound zinc-lead sulphide deposits of Tunaberg, Bergslagen, Sweden, are hosted by metatuffites, graphite sla tes and skarn-altered marbles. Galena-rich ores contain Ag-Sb-bearing galena with two groups of sulphosalts: A) early Cu-Pb-Sb-sulphosalts ( boulangerite, meneghinite, bournonite, manganoan jamesonite) occurring as up to 1 mm tabular or acicular crystals in early galena, and B) la te Cu-Ag-Sb-sulphosalts (Ag- and high-Ag-tetrahedrite, pyrargyrite, po lybasite, stephanite, diaphorite and andorite) occurring as anhedral i nclusions and as replacement rims and caps on the Cu - Pb - Sb - sulph osalts; Ag - Bi-bearing galena occurs associated with bismuthian meneg hinite and late Ag-Bi-sulphosalts of matildite and gustavite. The Tuna berg Zn - Pb ores crystallized from relatively Ag - Bi - Sb-rich, Zn-P b-Cu-Co-Ni-Fe-S-bearing metamorphogenic hydrothermal solutions, and is associated with formation of sillimanite-muscovite in hydrothermally altered metatuffites and of Cu - Co - sulphide skarn in marbles. Textu ral and mineralogical data suggest crystallization of the early galena - Pb - Sb - sulphosalt assemblages at temperatures of about 500-degre es-C. Reaction of the Pb-Sb-sulphosalts with Ag-Cu-enriched residual s olutions caused replacement of Pb-Sb-sulphosalts by Ag-Sb- and Cu-Ag-S b-sulphosalts; Ag - tetrahedrite is replaced by high-Ag - tetrahedrite , pyrargyrite and polybasite at temperatures down to below 190-degrees -C. The paragenetic sequence reflects a differentiation trend from Pb- rich to Cu - Ag-rich Sb - Bi-bearing solutions.