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 Pappilanm/iki prospects in the Kainuu schist belt and the Outokumpu rock assemblage.Indications of anomalously high base metal abundances were first obtained from the Kainuu schist belt in 1961 ( Fig. 1; Nenonen 1964). Subsequent studies undertaken by the Geological Survey of Finland established the existence of black shale rich in Ni, Cu and Zn in the Kainuu municipalities of Paltamo and Puolanka (Ervamaa 1971(Ervamaa , 1974Laajoki 1974). The metal-rich black shale (Ni=0.33%, Cu=0.11%, Zn=0.58%) occurs as zones in the ordinary black shale and in association with mafic volcanite. Ervamaa (1971Ervamaa ( , 1981 suggests that the metal concentration of the metal-rich black shale and the anomalous concentrations of the same metals in the volcanite-serpentinite complex at Jormua in Paltamo (prospect 1 in Fig. 2) may be genetically linked.The occurrences at Talvivaara were discovered in 1977 (prospect 2 in Fig. 2) and an evaluation of the ore reserves completed two years later indicated 300 Mt of base-metal-rich black shale averaging 0.14% Cu, 0.26% Ni, 0.02% Co, 0.53% Zn, 0.35% Mn, 10% Fe, 7% C, 630 ppm V,. 102 ppm Mo and 2.6 ppm Ag. The discovery of the Talvivaara deposits prompted an evaluation of the ore potential of other similar black shales nearby (Talvitie et al. 1980). The black shale formations in the Kainuu schist belt, as in the Outokumpu district, range in thickness from tens of metres to well over 100 m, except at Talvivaara where tectonic processes have thickened the strata and the maximum thickness observed in drill cores exceeds 400 m. The black shales in Kainuu enclose basemetal-rich layers, which often are close to serpentinite bodies. The prospects drilled indicate the existence of occurrences containing tens of million tonnes of basemetal-rich black shale but do not indicate any prospect as large as that at Talvivaara.In the course of studies undertaken in the southern part of the Kainuu schist belt, a rock assemblage typical of the Outokumpu Cu-Co-Zn-Au ores, and composed of serpentinite, skarn and quartz rock, was encount...
