Abstract Lake sediments were studied from four lakes in environmentally different areas in northern Finland. Lakes Pyykösjärvi and Kuivasjärvi are situated near roads with heavy traffic and the city of Oulu. Lakes Martinlampi and Umpilampi are small lakes in a forest area with no immediate human impact nearby. The concentration of Pb increases in the upper parts of the sedimentary columns of Lake Kuivasjärvi and Lake Pyykösjärvi. This is interpreted as being an anthropogenic effect related to heavy traffic in the area and use of Lake Pyykösjärvi as an airport during World War II. High Ni and Zn concentrations in the Lake Umpilampi sediments are caused by weathered black schists. Sediments in Lake Martinlampi show high Pb and Zn contents with increasing Pb concentrations up through the sedimentary column. The sources of these elements are probably Pb-Zn mineralization in the bedrock, Pb-Zn-rich boulders and anomalous Pb and Zn contents in till in the catchment area of the lake.
The geochemistry of different till size fractions and studies of heavy minerals have been used in mineral exploration in the ribbed moraine terrain in southern Finnish Lapland. The Peräpohja Schist Belt and layered intrusions along its southern margin have known potential for economic Au, Co, Cu, Fe, Zn, U and PGE mineralization. In till, high element concentrations related to mineralization in the local bedrock preferentially occur in the near-surface (less than 2 to 3 m depth) of ribbed moraine ridges. The ridges formed subglacially by gouging of local bedrock, which favoured the deposition of rock material derived from the local bedrock surface into till on the surficial part of ridges. The short distance of glacial transport (<500 m) is indicated by clast angularity, the abundance of locally derived boulders in the upper till and at the surface, and by the preservation of euhedral pyrite and chalcopyrite crystals and native Au grains in the heavy mineral concentrates. Detailed studies show that ribbed moraine ridge tops can be used for mineral exploration because they are more likely to be composed of local bedrock than are the sediments comprising the ridge core.
Abstract White and yellowish precipitates were found in a gravel pit in the Kumpuselkäesker chain during the summers of 2004—2007. The esker is located in northern Finland, in the northern Ostrobothnia schist area which contains mica schists with quartz veins, which are locally enriched in Co, Cu, Au, Zn, Pb and Ni. A thin till bed lies between the esker gravel and bedrock. Precipitates were found as small grains on the till surface, encrusting twigs and around small pebbles. Ground-water ponds in the pit measured in the summer of 2006 were very acidic as was the till material. The precipitates comprise secondary sulphates, such as gypsum, pickeringite and Mg-sulphates, which are all water-soluble.
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