Base-metal-rich metamorphosed black shales associated with Proterozoic ophiolites in the Kainuu schist belt,Finland: a genetic link with the Outokumpu rock assemblage

Metamorphosed black shale is an essential component of the Early Proterozoic Outokumpu rock assemblage, together with serpentinite, calc-silicate rock and quartz rock. This rock assemblage, hosting the major Cu-Co-Zn deposits of Outokumpu and considered ophiolitic in origin, has also been encountered to the northwest in the Kainuu schist belt. The rift basin encompassing the two areas was intruded by ophiolite complexes 1.96–1.97 billion years ago. Remnants of ultramafites are met as serpentinite and talc-carbonate rock lenses bounded by faults along the western margin of the Kainuu schist belt. The black schist formations range in thickness from tens of metres to 400 m. Metal-rich layers occur close to the serpentinite bodies. The most extensive formations of metal-rich black schist (300 Mt, 0.26% Ni, 0.14% Cu, 0.53% Zn) have been encountered at Talvivaara. The lithological, mineralogical and geochemical results indicate a genetic link between the Jormua, Talvivaara, Alanen and Pappilanmäki prospects in the Kainuu schist belt and the Outokumpu rock assemblage.