Kirsti Loukola-Ruskeeniemi

Environmental impact of metalliferous black shales at Talvivaara in Finland, with indication of lake acidification 9000 years ago

Abstract Environmental impact of metalliferous black shales was studied in the Talvivaara area in eastern Finland with 194 lake sediment and 48 organic stream sediment samples and 57 surface water and 9 ground water samples. The samples were analysed using a combination of ICP–MS and ICP–AES methods. Continuous undisturbed lake sediment cores were obtained from seven lakes. Cores from three of the lakes penetrated through the sediment column into the underlying clay, which was deposited in a late glacial ice-dammed lake between 12,000 and 9000 years ago. The concentrations of Ni, Zn, and Cd in surface water and organic stream and lake sediments were significantly greater if the bedrock of the catchment area consisted of black shales than if it consisted of gneiss granite or quartzite. It appeared that this was also the case in the past. The influence of bedrock chemistry is particularly pronounced in the Lake Harkalampi profile at a depth of 358 cm, which records the abrupt isolation of the lake from the Sotkamo ice-dammed lake 9000 years ago. At this time, the metalliferous black shales of the catchment area were exposed to prolonged wave action and erosion, and pH dropped to as low as 3.8. Following isolation of the lake the organic content of the sediment steadily increased, attaining a maximum value of 13% at a depth of 310 cm. Maximum Ni (0.1%), Cu (0.03%), Zn (0.5%), and Al (3.4%) concentrations are recorded shortly after isolation, when the proportion of organic material was still as low as 2.7%. Evidently vegetation effectively reduces bedrock weathering even in cool climate, since Ni, Cu, Zn, and Al concentrations decreased and pH increased in Lake Harkalampi due to colonization of tundra vegetation.

Geochemical evidence for the hydrothermal origin of sulphur, base metals and gold in Proterozoic metamorphosed black shales, Kainuu and Outokumpu areas, Finland

Metamorphosed black shale formations 120–150 m thick with median concentrations of 7% non-carbonate carbon and 6–8% sulphur are abundantly met in drill cores in the Kainuu and Outokumpu areas. Carbon isotope δ3C values are comparable to the average isotopic composition of non-carbonate carbon in sedimentary rocks. The rare earth element patterns show cerium depletion, indicating a marine origin. Base metal concentrations in black shales are high in the Talvivaara mineralization (ore estimate: 300 Mt with 0.26% Ni, 0.14% Cu and 0.53% Zn) and in the vicinity of ophiolite complexes. In the Kainuu schist belt, the median value for gold is 35 ppb (max 170 ppb) in the western part and 16 ppb (max 180 ppb) in the east. Highest platinum and palladium concentrations encountered are 60–70 ppb. It is shown that in the Kainuu black shales, concentrations of sulphur, base metals and precious metals have been increased by hydrothermal processes, as indicated by positive europium anomalies, elevated mercury concentrations (max 7.5 ppm), high sulphur isotope δ34S values and the enrichment of sulphur and base metals relative to carbon. The processes operative during the deposition of these shales find an analogy in recent processes in ocean ridge spreading axes.

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.

Leaching of Dissolved Organic Carbon and Trace Elements After Stem-Only and Whole-Tree Clear-cut on Boreal Peatland

The aim of this work was to study the short-term effect of clear-cut harvest on concentrations of dissolved organic carbon (DOC), B, Al, Zn, Cu, Ni, Cr, Cd and Pb in drainage water from northern peatland catchments in Finland underlain by granitic or black shale bedrock, the latter having higher concentrations of several trace elements, such as Ni and Zn. Stem-only harvest (SOH) or whole-tree harvest (WTH) with stump removal were carried out at coniferous sites. Controls were left unharvested. DOC and trace element concentrations were monitored during one pre-treatment and two post-treatment years. There was no constant increase in the element concentrations. However, there were signs that both SOH and WTH clear-cut harvest on northern peatland catchments increases the concentrations of DOC, B, Al, Zn and Ni in ditchwater in some sites irrespective of the bedrock type. The greatest increases were observed in WTH sites but the study does not allow us to assess the statistical significance of the magnitude of the difference between SOH and WTH. We conclude that the element concentrations in ditchwater depend largely on site characteristics masking the possible effect of harvest.

Nickel isotopic variation in black shales from Bohemia, China, Canada, and Finland: a reconnaissance study

We present δ60Ni values for black shales, determined by double-spike MC-ICP-MS. The samples comprise Paleoproterozoic Talvivaara Ni–Zn–Co–Cu black shales from Finland, Neoproterozoic black shales from the Teplá-Barrandian Unit, Czech Republic, Early Cambrian Ni–Mo-rich black shales from the Yangtze Craton, and Devonian Ni–Zn–PGE black shales from Yukon, Canada. In addition, the sample set includes a black smoker sample from the Logatchev hydrothermal field, Mid-Atlantic Ridge. The δ60Ni values vary from − 0.84 ± 0.09 to + 0.62 ± 0.04‰ (2SD) with a median of − 0.10‰ (n = 28). Ni isotopic compositions were predominantly lighter than those of abiotic terrestrial and extraterrestrial samples (0.15 and 0.27‰), mantle (0.23‰, Gall et al. 2017), present-day seawater (1.44‰, Cameron and Vance 2014), dissolved Ni from riverine input (0.84‰, Cameron and Vance 2014), ferromanganese crusts (0.9–2.5‰, Gall et al. 2013), Devonian/Mississippian organic-rich marine sediments, lower Jurassic organic-rich marine sediments (0.2–2.5‰, average 0.92‰, n = 18, Porter et al. 2014), and euxinic sediments of the Black Sea (0.14–0.51‰, Vance et al. 2016). However, the range of δ60Ni values in our black shale samples was close to that of the weathering products of mafic/ultramafic rocks (ore and soil samples) ranging from − 0.60 to + 0.30‰ (Ratié et al. 2015; Spivak-Birndorf et al. 2018), Ni-sulfide ores hosted by Archean komatiites from Australia and Canada (− 0.10 to − 1.03‰, average − 0.70‰, n = 8, Gueguen et al. 2013), and Archean Ni-rich magmatic sulfides from Zimbabwe (− 0.28 to − 0.47‰, n = 6, Hoffman et al. 2014). Based on our observations and considering the extremely low contribution of direct biological uptake of Ni, and a dominant Ni residence in early Fe/Ni-sulfides, we suggest that our mostly light Ni isotopic compositions in metal-rich black shales result from sulfidization of organic matter and Ni removal into sulfides.