Report of Investigation 196 - arkisto.gsf.fi - Geologian tutkimuskeskus

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Geologian tutkimuskeskus, Tutkimusraportti 196 – Geological Survey of Finland, Report of Investigation 196, 2012 High pre-mining metal concentrations and conductivity in peat around the Talvivaara nickel deposit, eastern Finland Conductivity Spearman’s correlation coefficient Spearman’s correlation coefficient Spearman’s correlation coefficient 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 C Co M1 M2 M3 Depth pH Pb S Cu U WaterCont. pH Mn Pb Ni DryDensity Humification Humification Cu DryDensity U Ni WaterCont. Ash Fig. 31. The statistically most significant correlations between conductivity and the other measured parameters at study sites M1, M2 and M3. C Ash WaterCont. C Co Fe Co Ash U Zn Cu pH Humification Pb Zn Mn DryDensity Conductivity Zn Fe Pos. correlation is significant at the 0.01 level (2-tailed). Pos. correlation is significant at the 0.05 level (2-tailed). Neg. correlation is significant at the 0.01 level (2-tailed). Neg. correlation is significant at the 0.05 level (2-tailed). S S Depth Mn Ni Depth Conductivity Fe Conductivity 31
Geologian tutkimuskeskus, Tutkimusraportti 196 – Geological Survey of Finland, Report of Investigation 196, 2012 Markku Mäkilä, Kirsti Loukola-Ruskeeniemi and Heikki Säävuori was observed between sulphur and pH, manganese, conductivity and iron, but a significant negative correlation between sulphur and lead. At the mica schist study site M1, pH values displayed a positive correlation with sulphur, copper, nickel and uranium and a negative correlation with conductivity (Fig. 29). At study site M2 there was no marked association between pH and any of the analysed elements, although a negative correlation with cobalt was observed. At study site M3, pH was positively correlated with S, Mn and conductivity and negatively with Pb and Co. At study site M1 there was a marked correla- 32 tion between the ash content and iron, lead and pH (Fig. 30). At study site M2, a marked positive correlation was observed between the ash content and conductivity, sulphur, nickel, iron, zinc and uranium. There was a strong negative correlation between electrical conductivity and depth, pH, S and Cu at study site M1 (Fig. 31), and a clearly positive correlation of conductivity with depth, nickel, sulphur, iron and zinc at M2. Conductivity was positively correlated with iron, depth, manganese, sulphur and pH at study site M3. 5 APPLICATION OF ELECTRIC CONDUCTIVITY MEASUREMENTS IN ENVIRONMENTAL STUDIES The logging probe (Fig. 9, p. 10) can be used for mapping the electrical conductivity and temperature of peatlands and underlying unconsolidated sediments. Conductivity data have been applied in the interpretation of electromagnetic (AEM) maps, and for tracing pollutants within peatlands. Electric conductivity also reflects the nutrient conditions (salinity, acidity), which, together with temperature, control the growth and decay processes within peatlands (Puranen et al. 1997, Puranen et al. 1999). Electrical conductivity correlates with the temperature and acidity (pH value) of peatland waters. A rise in temperature of one degree Celcius increases the electrical conductivity of the solution by approximately 2% (Hem 1985). Electrical conductivity measurements provide a reliable indication of anomalies in peat, and can be used as a preliminary indicator of peat conductivity (Puranen et al. 1996). The method is also more cost-effective than other geophysical techniques. The high sulphur content of peatlands in the black schist area had an effect on the high conductivity, especially in the sedge-dominated bottom and middle layers (Lerssi & Virtanen 2006). The peat layers investigated in the Talvivaara area contain high Zn, Cu and Ni concentrations but low Pb concentration compared with the values from western Finland reported by Virtanen (2005). This is because at Talvivaara the black schist has high Ni, Cu, and Zn concentrations but does not contain more Pb in average than the ad- 6 DISCUSSION Higher acidity of peat layers and increasing metal contents enhances the conductivity of peat. Highly conductive runoff and groundwaters in poorly conducting peat is an optimal research target for conductivity probing (Puranen et al. 1996, Mäkilä & Toivonen 1998). A high sulphur concentration lowers the pH and increases the conductivity in Carex peat. In the acidic surface layers at the study sites the hydrogen ions significantly increase or even dominate the electric conductivity of peat. For pH values lower than 3.5 the conductivity effect due to hydrogen ions is at least 10 mS/m (e.g. Kivinen 1935). At the black schist study sites M2 and M3, the effect of bedrock composition on the metal (Fe, Ni, Zn) and sulphur concentration of the peat as well as the conductivity can be seen in the basalmost peat layers (Figs. 13, 15 and 18). At the mica schist study site M1 the metal concentrations were lower and the change in acidity from the about 3.1. in the surface layer to 4.4 in the bottom layer is the principal cause of the observed reduction in conductivity from 13 mS/m to 3 mS/m. jacent granitic rocks. According to Virtanen et al. (1997), the basal peat layer overlying the Pampalo gold-arsenic ore deposit at Ilomantsi, in easternmost Finland, contains 100 times more arsenic than than the average background value for peat in the area. Such high values arise from upwards migration of metals in groundwater or gaseous
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Report of Investigation 196 - arkisto.gsf.fi - Geologian tutkimuskeskus

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