Thermal and fluid evolution during contact metamorphism around the Kevitsa and Satovaara intrusions: implications for sulfur and metal mobilization in the host black schist

Contact metamorphism of carbon- and sulfur-rich black schists can play a critical role in the genesis of magmatic sulfide deposits. This study investigates the metamorphic evolution of the Matarakoski formation black schist surrounding the Kevitsa and Satovaara intrusions in northern Finland. Raman spectroscopy of carbonaceous materials and Ti-in-biotite thermometry indicate peak contact metamorphic temperatures of 500–600 ± 50 °C. Biotite-scapolite alteration during contact metamorphism indicates influx of Cl-rich fluids, which mobilized Cu and Co within the black schist and possibly into the Kevitsa intrusion. These fluids were channelized in porous zones created by the sills adjacent to the Kevitsa intrusion. During contact metamorphism, pyrite decomposition to pyrrhotite released sulfur, potentially contributing to the Kevitsa Cu-Ni-PGE deposit. Minor hydrothermal sulfides, including Co-rich pyrite, chalcopyrite, and arsenopyrite, suggest fluid-mediated metal redistribution during retrograde metamorphism. These findings support a multi-stage model of ore formation involving partial melting, devolatilization, and hydrothermal fluid transport, emphasizing the significance of contact aureole processes in magmatic sulfide systems. • The black schist reached peak contact metamorphic temperatures of 500–600 ± 50 °C. • Cl-rich fluids mobilized Cu and Co during peak contact metamorphism. • Hydrothermal sulfides formed as fluid activity continued during retrograde stage. • Hydrothermal processes are important in mobilizing metals around intrusions.