Hydrogeochemical characterization of the Sakatti mine prospecting area, Sodankylä, Finnish Lapland

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Titel: Hydrogeochemical characterization of the Sakatti mine prospecting area, Sodankylä, Finnish Lapland
Författare: Lahtinen, Tatu
Medarbetare: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta, Geotieteiden ja maantieteen laitos
University of Helsinki, Faculty of Science, Department of Geosciences and Geography
Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten, Institutionen för geovetenskaper och geografi
Utgivare: Helsingin yliopisto
Datum: 2017
Språk: eng
Permanenta länken (URI): http://urn.fi/URN:NBN:fi-fe2017121155634
Nivå: pro gradu-avhandlingar
Ämne: Geology
Abstrakt: In 2011, Anglo American Sakatti Mining Oy published an ore discovery in Sodankylä, Finnish Lapland. The rich Ni-Cu-PGE orebody, named Sakatti ore, is partially underlying Viiankiaapa-mire’s Natura 2000 protection area. This sets additional challenges for the utilization of the resource without compromising the fragile nature of the area. To estimate the impacts of possible future mining operations, the complex hydrochemical and hydrogeochemical conditions at Viiankiaapa must be well understood. Most water samples from the research area show a chemical composition close to the natural Finnish groundwater composition Ca–HCO3. However, in four groundwater observation wells, located south from Kiimakuusikko, Na–HCO3 type waters were detected. These sites were GA300 (8.26 ppm of Na), GA202 (17.34 ppm of Na), GA202 deep (15.23 ppm of Na) and GA201 (7.92 ppm of Na). Source for the anomaly is likely lithological due to lack of chloride in the samples. One possible source could be weathering of albite to kaolinite. Albite is hosted in the breccia unit, located close to the site. Albite-kaolinite weathering could release Na+ ions into the surrounding soil solution, which would provide a source for the high sodium concentrations. Kitinen river shows slightly higher Al, Li and Cu contents compared to other waters from the research area. This could possibly be used to distinguish river water from groundwater at sites where river water infiltrates the groundwater system. On the other side, Na, K and DSi have higher concentrations in groundwaters compared to surface waters. This could make them useful groundwater indicators. Sakattioja and the other smaller streams draining the mire, are characterized by very high isotope values, low amounts of DSi and low EC. These characteristics likely reflect the hydrogeochemistry of the water on the surface of the mire. The hydrogeochemical similarity of these streams is also highlighted by the hierarchical cluster analysis, where the samples from these sites form a clear cluster of their own. Stable isotope results are mixed and difficult to interpret. The most striking features are the low values observed at the mire near Kiimakuusikko and the high values observed in Sakattioja. Many groundwater samples show signs of evaporated source water component or re-infiltration of surface waters. This could be due to water from the mire infiltrating the groundwater system and then re-emerging in the observation wells and springs close to Kitinen. Overall, based on the results, the hydrogeochemistry at the research area can be considered to be very complex. The samples represent multiple different water compositions residing in poorly connected groundwater and surface water systems. This makes interpreting the results particularly difficult and is also reflected in the statistical analyzes which produce somewhat mixed results.
Subject: hydrogeologia

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