Abstract: Fluid inclusions in the progressively metamorphosed rocks of the Joroinen-Sulkava area, located in the south-eastern end of the Raahe-Ladoga zone near the Archaean-Proterozoic boundary, southeastern Finland, fall into four main categories: (1) H₂O-rich, (2) CO₂-rich, (3) mixed H₂O-CO₂ and (4) CH₄-N₂ inclusions. The samples were collected from quartz veins associated with different deformation phases (D₂-D₄) and from metapelites. The progressive stage of metamorphism took place mainly during the D₂ deformation. The age of metamorphism and D₂ deformation becomes younger with increase in metamorphic grade from amphibolite to granulite facies.

Regional distribution of the different fluid types indicates a change in fluid regime from H₂O to CO₂-dominant during the progressive stage of the metamorphism. H₂O entered preferentially into the anatectic melt. The possibility of CO₂ infiltration from deeper crust can not be excluded, because granulite facies rocks occur most probably below the lower grade zones. A zone enriched in CH₄-N₂ fluids is located near the lineament zones caused by the D₃ deformation. This fluid type dominates the Au-bearing D₂–D₃ quartz lenses in the K-feldspar-sillimanite zone. Density data of early CO₂ inclusions in combination with estimates of metamorphic temperatures (645–750°C) in the different metamorphic zones indicate a pressure range of 3.0–4.5 kbar, which is consistent with data derived from mineral geobarometry. The diversity of fluid types encountered in the D₂–D₄ quartz veins are a result of the passage of different fluids through veins at different times without re-equilibrating with the wall rocks. However, it is supposed that the CH₄-N₂ fluid is derived from a CO₂-rich fluid with X_CH4 ⩽ 0.4 by re-equilibration during its passage through the rocks.