Pertti Sarala

The Glaciation of Finland

Abstract Middle Pleistocene Glaciations . In Lapland and western Finland there are sites where till or glaciofluvial deposits underlie Eemian organic sediments. Many of them are correlative to the Saalian glaciation. At Naakenavaara a Holsteinian peat is underlain by the Elsterian till unit. These sites provide the basis for the general Quaternary stratigraphy of Finland. Late Pleistocene Glaciations . After the Eemian Stage interglacial two Early Weichselian stadials and two interstadials (Brorup, MIS 5c and Odderade, MIS 5a) have been found. The extent of the Middle Weichselian ice sheet is still unknown. Finland was ice covered during Late Weichselian Substage and was completely deglaciated by 10 ka ago.

Proxy comparison in ancient peat sediments: pollen, macrofossil and plant DNA

We compared DNA, pollen and macrofossil data obtained from Weichselian interstadial (age more than 40 kyr) and Holocene (maximum age 8400 cal yr BP) peat sediments from northern Europe and used them to reconstruct contemporary floristic compositions at two sites. The majority of the samples provided plant DNA sequences of good quality with success amplification rates depending on age. DNA and sequencing analysis provided five plant taxa from the older site and nine taxa from the younger site, corresponding to 7% and 15% of the total number of taxa identified by the three proxies together. At both sites, pollen analysis detected the largest (54) and DNA the lowest (10) number of taxa, but five of the DNA taxa were not detected by pollen and macrofossils. The finding of a larger overlap between DNA and pollen than between DNA and macrofossils proxies seems to go against our previous suggestion based on lacustrine sediments that DNA originates principally from plant tissues and less from pollen. At both sites, we also detected Quercus spp. DNA, but few pollen grains were found in the record, and these are normally interpreted as long-distance dispersal. We confirm that in palaeoecological investigations, sedimentary DNA analysis is less comprehensive than classical morphological analysis, but is a complementary and important tool to obtain a more complete picture of past flora.

Exploration using till geochemistry and heavy minerals in the ribbed moraine area of southern Finnish Lapland

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.

Rare earth element and gold exploration in glaciated terrain: example from the Mäkärä area, northern Finland

The Mäkärä Au-rare earth element (REE) prospect area is located in the Tana Belt, south of the 1.9 Ga Lapland Granulite Belt, in northern Finland. The Belt has prominent lanthanum (La) and yttrium (Y) anomalies in regional till and bedrock geochemical data. High Y indicates enrichment of heavy REE in the bedrock. At Mäkärä, promising narrow Au-hematite-quartz veins occur in connection with tensional fractures in the great shear zone. Under the latest ice divide of the last glaciation, subglacial erosion was weak and glacial transport distance short. High Au contents in saprolite and till together with deep weathering have a strong positive correlation with the positive electromagnetic anomalies caused by the sulphidic gneisses. The highest La and Y contents in till correlate well with the Th maxima of airborne-radiometric datasets. Locally, the <0.06 mm till size fraction contains up to 0.4% REE. A recent exploration project in Mäkärä revealed a 13 m wide Au-hematite-quartz vein with a mean of 3 ppm Au and 0.04–0.1% REE in kaolinitic saprolite derived from arkosic gneiss. The elevated REE content resembles that of ionic adsorption clays in China. Typical REE-rich minerals are monazite, rhabdophane, xenotime and kaolinite. Till geochemistry proved useful in REE exploration.

Gold exploration using till at Petäjälehto, northern Finland

ABSTRACT Till geochemistry, ground geophysics, heavy mineral studies and diamond drilling have been used for gold exploration at the Petäjälehto target, northern Finland. Geochemical anomalies of gold and its pathfinders Cu, Bi, Co and Te in detailed till sampling have encouraged further exploration at the target scale. In addition, tens of Au nuggets in heavy mineral concentrates of basal till and in pre-Quaternary regolith indicate significant Au mineralization in the target area. Preliminary lithological studies based on the outcrop observations and drill-cores proved the hydrothermally altered, brecciated shear zones in granite gneiss and amphibolite host rocks to be suitable for Au mineralization. The source for Au nuggets seems to be the quartz–carbonate and magnetite–pyrite–quartz veins. This research also strengthens the concept of effectiveness of surficial geological methods for tracing potential sources of mineralized debris and rock fragments in glaciated terrains.

First physical evidence for forested environment in the Arctic during MIS 3.

Old sedimentological and geochronological records can be preserved underneath the central parts of the continental ice sheets under non-erosive, cold-based subglacial conditions. Organic deposits that predate the last deglaciation are of particular value for the information held on glacial-time climate and environmental conditions. In this study, we present multiproxy data derived from a well-preserved MIS 3 interstadial (55–25 ka ago) organic layer from inside the Arctic Circle in the Finnish Lapland. Biological proxy evidence, namely coming from aquatic plant species, indicates July temperatures as high as 14.4 °C, i.e. higher than those of today for the study site. Macrofossil evidence demonstrates for the first time the presence of pines accompanied by tree birch during the MIS 3 interstadial in northern Fennoscandia. These results concur with contemporary insolation model outcomes but contradict with the previous proxy-based view of open tundra conditions during the MIS 3. The data suggest that there are highly dynamic interstadial continental ice-sheet dynamics following changes in orbital forcing. Warm climate enabled the establishment of forests on exposed landscape. Moreover, we suggest that in the light of these new data, previous MIS 3 pollen data could be re-interpreted.

Comparison of different portable XRF methods for determining till geochemistry

Three portable X-ray fluorescence (pXRF) methods were compared and tested in an exploration program using till in Sinoselkä, northern Finland. The use of one truck-mounted XRF unit and two handheld pXRF analysers were tested for basal till samples gathered using percussion drilling with a flow-through sampling bit. The datasets were compared to both conventional aqua regia based analyses and each other. The results prove that a correlation between the data generated by different pXRF methods was acceptable for some major (Ca, Fe) and most of the base metal elements (like As, Cr, Cu, Mn, Ni, Pb, Zn) in the Sinoselkä area. The pXRF analyses also correlate well with the aqua regia geochemical data of the same elements. Distribution of the elements was comparable to the lithological changes in the underlying bedrock that indicates a short glacial transport distance. It is also demonstrated that more than absolute values, the relative values and their changes are those which should be considered and carefully examined. The results reported here emphasize the usefulness of pXRF analysers in till geochemical exploration and demonstrate that they involve easy and fast methods to collect geochemical data for tracing sources of multi-metal mineralization. Furthermore, pXRF is applicable in gold exploration, although indicator elements like As, Bi, Cu, Mn and Sb have to be used instead of Au.

Gold exploration using heavy minerals in till and weathered bedrock in Petäjäselkä, northern Finland

As a part of a gold exploration project in Petäjäselkä, northern Finland, carried out by the Geological Survey of Finland, heavy mineral studies and detailed till geochemical and stratigraphical studies were used for mineral exploration. These studies covered c. 22 km2 in the Petäjäselkä area. The objective of this research was to find out how heavy minerals and till geochemistry can be used in gold exploration, and how they reflect the glacial dispersion in shallow till areas in Petäjäselkä. Furthermore, an automated mineralogical identification method (SEM-EDS) was tested in the indicator mineral research. Samples from till and underlying, pre-glacially weathered bedrock were collected from the test pits and trenches. A total of 381 heavy mineral and 713 geochemical samples were collected. The heavy mineral samples were concentrated with a spiral concentrator and a Knelson concentrator. The geochemical samples were analysed by ICP-AES and GF-AAS following aqua regia decomposition. The elevated gold contents and distinct anomalies found in till and weathered bedrock indicate the whole study area to have potential for gold mineralization. Based on microscopic and automated mineralogical studies, native gold was the only useful indicator mineral present in the heavy mineral samples for gold exploration in Petäjäselkä.The detailed till geochemical results show that the glacial transport distance in Petäjäselkä is short, only some tens of meters. Differences in the Au-Ag contents of the gold grains were noted between the three gold mineralized targets in Kerolaki, Selkä-Mäntypää and Ranta-Mäntypää. Arsenic, bismuth and tellurium proved to be pathfinder elements for gold mineralization both in till and weathered bedrock. The results of this study show that the heavy mineral studies, together with till geochemical studies, provide a useful method for identifying exploration targets in glaciated terrain. However, different methods of heavy mineral concentration affect the recovery of gold grains and thereby the final results of this study.