Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland

Abstract The Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt northeastern Finland. volcano-sedimentary sequence that hosts was intensely altered, deformed, and metamorphosed to greenschist facies during 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate temporal relationship between Co Au deposition of enrichment protolith composition alteration mineralogy by utilizing lithogeochemical data petrographic observations. We also nature fluids involved formation based on sulfide trace element sulfur isotope LA-ICP-MS together tourmaline mineral chemistry boron isotopes. Classification original protoliths made basis geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, felsic metavolcanic ultramafic sill. host rocks does not control type or intensity mineralization. Sulfur values (δ 34 S − 2.6 + 7.1‰) obtained for pyrite, chalcopyrite, pyrrhotite indicate two distinct ore types formed from different compositions origins. A reduced, metamorphic fluid responsible pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized deposited pyrite-dominant ore. main mineralization stages at follows: (1) widespread albitization predates both mineralization; (2) stage 1, associated chlorite (± biotite ± amphibole) alteration; (3) 2, related sericitization. Crystal-chemical suggest involvement evaporite-related deposit; allow conclusion. Results our research association spatially coincident multiple hydrothermal processes.