The Velkua gold prospect in the high metamorphic grade area of south-western Finland

The Velkua Au prospect is situated in the high metamorphic grade Paleoproterozoic Svecofennian (1.9-1.8 Ga) bedrock of Southwestern Finland. Gold is enriched in an amphibolite formation surrounded by migmatitic mica gneiss (cordierite-garnet-K-feldspar) and coarse grained granites. Regional metamorphism corresponds to upper amphibolite or granulite facies. Gold occurs as native grains associated with silicate minerals and as inclusions and composite grains with sulphides. Larger gold grains are locally zoned, the core being an Ag-Au alloy and the border pure gold. No retrograde features are observed in silicate mineralogy of the host rock.