A three-dimensional seismic reflection survey was conducted in 2010 in northern Finland over the Kevitsa mafic-ultramafic intrusion that hosts a large, disseminated Ni–Cu–PGE sulfide deposit. In the seismic data, layered subhorizontal reflections are observed within a constrained region inside the intrusion, in the vicinity of the Kevitsa resource area. In this study, we use seismic attribute analysis to study this reflectivity. Based on the attribute analysis, an earlier three-dimensional model of lithological contacts and near mine structures is validated and updated. The attribute analysis delineates the internal reflectors more precisely and reveals structures not seen in conventional amplitude displays earlier. These later structures have cut the originally continuous internal reflectors into piecewise packages. Better understanding of the spatial distribution of the reflective packages is significant for targeted mineral exploration at depth and the structures can potentially be critical for geotechnical planning of the Kevitsa open pit. We discuss a possible scenario for the genetic link between the internal reflectivity and magmatic layering, country rock contamination, hydrothermal alteration and sulfide mineralization. The existence of subhorizontal seismically reflective layers is attributed to successive magma pulses within the Kevitsa resource area, affected by country rock contamination and hydrothermal alteration. Overall, our interpretation is that the internal reflectors within the Kevitsa intrusion represent altered and possibly mineralized parts of the magma pulses.
The Pyhäsalmi Volcanogenic Massive Sulfide (VMS) deposit, hosted by volcanic rocks of the 1.93–1.91 Ga Vihanti–Pyhäsalmi–Rautalampi belt, is the largest base metal sulfide deposit in Finland (75.7 Mt at 0.9 wt.% Cu, 1.9 wt.% Zn, 0.4 g/t Au, and 14.1 g/t Ag, production 1962–2022). Although significant geological research and mineral exploration projects have been conducted since the 1950s, a comprehensive reconstruction of the volcanic setting and the linkages between volcanism and ore-forming processes has been missing. Based on outcrop mapping and relogging of old drill core in the Pyhäsalmi area, we identify 18 volcanic, sedimentary, and intrusive lithofacies with distinctive lithological and structural characteristics. The study area is dominated by rhyolitic lavas and/or domes, mafic lavas and intrusions, and a volcanogenic sedimentary facies composed of interbedded mudstone and sandstone turbidites. Volcanic facies associations suggest that the eruptive style of felsic volcanism was submarine and non-explosive, forming coherent rhyolitic flows and dome complexes with quench-fragmented hyaloclastic dome margins. Minor resedimented autoclastic volcanic breccias are also found. Volcaniclastic rocks were emplaced as turbiditic mass transport deposits in a submarine slope environment, and are intercalated with hemipelagic sediments, indicating a deep water below-wave-base depositional environment. The Pyhäsalmi ore formation is linked to the permeable autobrecciated facies of rhyolite domes/lavas which are found in contact with sedimentary facies. In contrast, the adjacent Mullikkoräme deposit (1.15 Mt) may represent a less-permeable dome/lava setting with no associated sedimentary facies. Volcanic facies associations (e.g., peperites and hyaloclastites) suggest shallow intrusive (cryptodome) to extrusive felsic volcanism in both the Pyhäsalmi and Mullikkoräme successions, followed by (extension-related) extrusive and locally weakly pyroclastic mafic magmatism on the seafloor. The study highlights new belt-scale exploration potential in areas of similar volcanic and sedimentary lithofacies associations and allow more detailed comparison with other base metal sulfide deposits and occurrences within Vihanti–Pyhäsalmi–Rautalampi belt.
The Kovela Granitoid Complex (KGC) in southern Finland hosts a minor deposit of Th and rare earth elements (REE) associated with crustal melting and magmatic differentiation processes. Such critical element deposits have a high economic and scientific importance. In this paper we deal with the geochemistry, ages and petrogenesis of the KGC rocks. The KGC comprises three main lithologies: garnet-alkali syeno-monzogranitegranodiorite (Grt-ASMG), monazite-rich pegmatitic tonalite-trondhjemite dikes (MnzPTT) and biotite-sillimanite gneiss (Bt-Sil-Gn) xenoliths. Whole-rock geochemistry reveals that Grt-ASMG rocks are peraluminous, high in potassium and silica, and display characteristics of S-type granitoids. Mnz-PTT dikes exhibit significantly higher REE and Th concentrations, with total contents reaching up to 42 000 ppm, with strong negative europium anomalies (Eu/Eu*=0.01–0.05). These geochemical trends, coupled with field observations, suggest that liquid immiscibility played a role in the separation of REE- and Th-enriched tonalite pegmatitic melts from the parent granitic magma. Monazite grains exhibit complex Th- and LREE-rich zoning, indicative of multiple crystallization and metamorphic events. U-Pb dating of monazite and zircon yields ages ranging from 1.92 Ga to 1.72 Ga, reflecting a prolonged history of magmatic and metamorphic activity. Garnet compositions suggest high crystallization temperature. Peak crystallization conditions, estimated using GB-GPBQ geothermobarometers, indicate granulite-facies conditions at temperature of ~780 °C and pressure of 4–5 kbar. The results suggest that the KGC formed through a combination of crustal melting and liquid immiscibility processes. These findings provide new insights into the enrichment mechanism of Th- and REE-enrichment in the granitic and pegmatitic systems and enhance our understanding of the metallogeny of similar granitoid complexes.
We describe three previously unknown or poorly studied mafic-ultramafic intrusions (Matokulma, Palojärvi, Hongonniittu) from the south-central part of the Paleoproterozoic Central Finland Granitoid Complex (CFGC). The ore potential and petrogenesis of the intrusions, with the focus on Matokulma and Palojärvi, are discussed based on petrography and geochemistry and, possible relationships with the Ni-Cu ore potential Vammala–Kotalahti type intrusions are examined. The poorly exposed Hongonniittu intrusion is likely genetically related to the Palojärvi intrusion. Median Mg-numbers for Matokulma and Palojärvi are 72 and 49, respectively. They consist of cumulus clinopyroxene, orthopyroxene and plagioclase, in case of Palojärvi also Fe-Ti oxide, and oikocrystic magmatic amphibole enclosing the cumulus phases. In Matokulma, mafic dikes cut the surrounding granitoids. A late leucogabbro dike with a U-Pb zircon age of 1882 ± 5 Ma constrains the minimum age for the Palojärvi intrusion. The Palojärvi leucogabbro has relatively radiogenic Nd isotope composition and is, in this respect, similar to Kotalahti-type mafic-ultramafic intrusions farther northeast. The parental magmas of the Matokulma and Palojärvi intrusions contained approximately 4–6 wt.% and 2–4 wt.% MgO, respectively. Magmatic amphibole, enrichment in large ion lithophile elements (LILE) and depletion in high field strength elements (HFSE) indicate crystallization from hydrous, evolved basaltic magmas. Owing to their evolved nature, the intrusions are not potential for magmatic Ni-Cu mineralizations, but Palojärvi could potentially host a Fe-Ti-V mineralization in deeper, concealed parts of the intrusion.
The targeting till geochemical dataset of Finland was collected during the 1970s and early 1980s by the Geological Survey of Finland (GTK). The dataset covers central Finnish Lapland and some areas in Ostrobothnia and eastern Finland. A subset of data from central Lapland has been examined in this study. The goal of this study is to present a detailed description of the high-resolution targeting till geochemical data, together with data preprocessing and preliminary data analysis. The geochemical data are considered to be compositional data. Box plots, original concentration maps, and quantile-quantile (Q-Q) plots were used to explore the data and original and centred log-ratio (clr) transformed concentration maps with lithological units, heat maps and principal component analysis (PCA) plots were used as analytical tools. The data analysis revealed mismatches between neighbouring map sheets which were caused by the problems related to till sampling, analytical methods, and the complex levelling problems of elements. A better insight into the data could be obtained by analysing clr-transformed data rather than by analysing raw data. A PCA biplot is a powerful tool for identifying the important patterns in the area and correlating them to the underlying geology.
The Svecofennian orogeny in southern Finland has traditionally been divided into two broadly defined compressional stages, the 1.89–1.87 Ga “synorogenic” stage and the ca 1.84–1.81 Ga “lateorogenic” stage. The term “intraorogenic” is used to describe a less studied stage that occurred between these two, with some overlap with both. Mafic and intermediate intrusions collectively named as the Kaiplot gabbros are situated on a number of islands and islets in Nagu (Nauvo) in the southwestern archipelago of Finland. The outcrops occur as dykes as well as plutonic bodies and have been emplaced in at least two separate pulses. Net-veining and other structures suggesting incomplete mixing between mafic and felsic magmas are found. The main plutonic body is a hornblende gabbronorite. U-Pb dating (TIMS, zircon) gives it an age of 1865 ± 2 Ma. Geochemically, the most primitive Kaiplot gabbros are tholeiitic and show affinity to back-arc basin basalts, indicating generation in an extensional tectonic environment. Their parental magmas appear to have originated from relatively high-degree partial melting of a shallow spinel-bearing and slightly subduction-modified depleted mantle. During transport and emplacement, both differentiation and assimilation of crustal material have taken place. The Kaiplot gabbros endorse an extensional tectonic episode of the Svecofennian orogeny at around 1865 Ma, possibly as a result of tectonic switching propagating southwestwards.
In the southernmost part of the Svecofennian province in Finland, leucogranites and migmatites stemming from both igneous and sedimentary protoliths reflect the complex magmatic history of the Svecofennian orogeny between 1.89 and 1.82 Ga. Although the migmatites and leucogranites in southernmost Finland display similar ages as their counterparts elsewhere in the Southern Finland Subprovince, they differ in field appearance and composition. Field and petrographical observations reveal K-feldspar megacrysts of varying sizes in the migmatized early Svecofennian (c. 1.89–1.87 Ga) supracrustal rocks and granitoids. Whole-rock geochemical analyses likewise display anomalously high K-contents in the early Svecofennian granitoids. Zircon U-Pb dating of migmatites and related leucogranites shows that a late Svecofennian partial melting event occurred at 1.84–1.82 Ga, possibly in several pulses. The morphological features of the migmatites as well as neosome mineralogy indicate a formation mechanism different from the dehydration melting prevalent elsewhere in the Subprovince.
In this short communication, we present new detrital single grain zircon U-Pb data for six metasedimentary rock samples from Jämsä, Central Finland. Four samples are from the southern parts of the Central Finland granitoid complex and two from metasedimentary rocks mixed with the volcanic belts bordering it to the south. Based on the obtained results, the detrital zircon populations of all the samples are similar, i.e. they are bimodal with peaks at 2.05–1.95 Ga and 2.90–2.70 Ga. The maximum depositional ages of the individual samples are interpreted as 1.93–1.90 Ga. Thus, the zircon populations are similar to both the Pirkanmaa migmatite belt, which borders the granitoid complex to the south, and the lowermost members of the volcano-sedimentary Tampere group to the west from our study area. The results further strengthen the similarities between the volcano-sedimentary successions in Tampere and Jämsä areas. Similarities between the detrital zircon populations within, and south of the Central Finland granitoid complex need to be taken into account in further refinements of regional tectonic models.
New U-Pb zircon ages reported for samples from the Maarianvaara granite and Tohmajärvi volcanic complex (TVC) corroborate previous estimates of their magmatic emplacement at ca. 1.85 Ga and 2.11 Ga, respectively. The ca. 1.85 Ga age of the largely undeformed Maarianvaara granite, which cuts the Proterozoic protomylonitic foliation in the Archean basement gneisses, sets a minimum age for the basementinvolved thrusting in North Karelia. Geological evidence and geochemical data for the Kylmäkallio sill, dated at ca. 2.11 Ga from Tohmajärvi, indicate it is cogenetic/coeval with mafic metavolcanic/hypabyssal intercalations occurring in both the TVC and the surrounding black schist layered metasedimentary rocks of the Tohmajärvi suite. Thus, burial of organic carbon in the sedimentary protoliths of the Tohmajärvi succession was evidently occurring at ca. 2.11 Ga, about 50 Ma earlier than has been assumed in some recent time-stratigraphic interpretations.
Fifteen post-orogenic, basic to acidic High-Barium-Strontium (HiBaSr) intrusions of shoshonitic affinity have been recognized in central and southern Finland. Most of the intrusions are found in a 500 km long E–W-trending belt in the Southern Finland Subprovince, with three of them in the Western Finland Subprovince. These rocks have distinctive field, mineralogical, chemical, geochronological and isotopic characteristics compared to the other plutonic rocks in the area. New zircon U-Pb LA-ICP-MS data for two of the intrusions confirm their post-orogenic age: 1805 ± 4 Ma for the Tistronskär biotite-hornblende monzodiorite and 1794 ± 13 Ma for the fluorite-bearing Loukee biotite granite. These rocks plot predominantly in the shoshonitic field and have relatively high K2O (~2.3 wt.%) in the basic varieties, increasing to ~5.0 wt.% in more acidic types. The Tistronskär monzodiorite and Loukee granite show similar geochemistry (high K, Ti, P, Ba, Sr and LREE) to other shoshonitic rocks in southern Finland. These geochemical characteristics, along with an initial 87Sr/86Sr value of 0.70322 and initial εNd value of -0.4 ± 0.4 at 1805 Ma for Tistronskär monzodiorite, indicate that subcontinental lithospheric mantle source may have been metasomatized by subducted sedimentary material before the 1.80 Ga melting event.
The Beck mine, located in the Republic of Karelia, Russia, is an abandoned mining site with significant potential for environmental contamination due to the presence of potential pollutants in its waste rocks. In this study, we investigated the chemical composition of mine waters and waste rocks and developed a theoretical model to understand waterrock interactions and the release of potential pollutants. Water samples collected from various locations on the Beck mine property were analyzed for chemical composition and showed low concentrations of total dissolved solids with pH values ranging from 6.42 to 7.74. The chemical composition of natural waters was determined by ICP-MS, ICP-AES, ion chromatography, potentiometric titration, and spectrophotometry. Equilibrium kinetic modeling was used to simulate water-rock interactions. The model predicted the concentrations of major and trace elements, demonstrating that dissolution-precipitation and complexation are the primary mechanisms shaping the chemical composition of mine waters. The dynamics of dissolution-precipitation of Fe-containing minerals highlighted the importance of the duration of water-rock interaction, with stagnant mine waters exhibiting higher concentrations of heavy metals. In addition, the presence of dissolved organic matter played a critical role in the accumulation of iron and arsenic in the studied mine waters. Overall, this study highlights the utility of equilibrium kinetic modeling in understanding the behavior of heavy metals during water-rock interactions and provides valuable insights into the potential environmental impacts of abandoned mine sites such as the Beck mine.
We present a geochemical dataset and cathodoluminescence images of apatite from the Neoarchean (2610 Ma) glimmerite-carbonatite rocks from the Siilinjärvi complex, Eastern Finland. The subhedral, tapered prismatic grains are compositionally fluorapatite, with limited substitution of Ca by Sr, Na and low REE and Si contents. The Sr/Y ratios are among the highest in a global apatite comparison, comparable to those from other calcite carbonatites, dolomite carbonatites, and phoscorites. Some grains show evidence of late- or post-magmatic interaction with a carbonatite magma or a hydrothermal fluid, resulting in REE-rich overgrowth rims or recrystallized grains with abundant fluid inclusions. We interpret the high Sr/Y ratios combined with low REE contents and depleted heavy REE+Y to represent crystallization from a mantlederived carbonatite parental magma. We show that the Siilinjärvi apatite is chemically heterogeneous but with a limited range in compositions. There are noticeable compositional differences on all spatial scales from micrometer to tens of meters, i.e., within a single crystal, between crystals in a sample, between samples and the two individual sampling locations. We conclude that the intra-crystal geochemical variability in apatite is a suitable tracer of the magmatic and post-magmatic evolution of carbonatite complexes.
Four quartz monzonite – granite intrusions forming the Sorsakoski granite lithodeme, are found within the Raahe-Ladoga suture zone in Central Finland. The prevailing potassium feldspar megacrystic quartz monzonites and granites form a bimodal association with diorites and gabbros. The granitoids are mainly calc-alkaline, ferroan, per- to metaluminous, and have high Zr and REE contents. Dominant mafic minerals are biotite and hornblende, clinopyroxene and orthopyroxene are locally present. The mafic units display effects of fractionation of clinopyroxene. In our interpretation, these intrusions were emplaced during regional late stages of deformation and postcrystallisation deformation partitioned into major shear zones leaving bulk of the intrusions relatively undeformed. Based on one new (1876 ± 6 Ma) and one pre-existing (1882 ± 5 Ma) U-Pb zircon age determination, the crystallisation age of the granitoids can be assumed at ca. 1880 Ma. Based on mineralogy, petrography, geochemistry, bimodal nature of magmatism and age, we correlate these intrusions to the A-type rocks of the previously described Saarijärvi suite. This shows that the syn-orogenic A-type magmatism extended eastwards beyond the Central Finland Granitoid Complex.
A widely spread ridge relief complex was formed by the last ice cover in the northeastern part of the Kola Peninsula. The complex belongs to the ice-marginal formations of the ice streams of the north-eastern Fennoscandian Ice Sheet. The applied morphometric research technique (including the analysis of the digital elevation model) has allowed identifying the ridge relief complex to make a sub-longitudinal belt. The belt comprises frontal and radial ridges, ridges and hills of the distal part of the belt, and complex-shaped ridges. These landforms were studied in eight outcrops and trenches. The frontal and some complex-shaped ridges consist of basal and ablation tills and glaciofluvial deposits deformed by the east- and north-eastward advancing glacier. The radial ridges composed of glaciofluvial sediments are the eskers. Glaciofluvial deposits with a thin cover of ablation and flow tills form the ridges on the distal part of the belt. They mark the limits of glacier expansion at an individual glacial stage. Some complex-shaped ridges are composed only of the ablation melt-out till and formed in crevasses of dead ice massifs. The ridge relief complex shows morphological similarities with the Veiki moraine in North Sweden, Pulju moraine in Finland, and ridges of the “ice-walled-lake plains” in North America. The location of the moraine ridge landforms is controlled by the topography of crystalline bedrock. During the last glaciation, the glacier retreated in several stages marked by belts of the ridge landforms. Each stage was followed by a series of oscillations corresponding to chains of frontal moraine ridges. The correlation of the ice-marginal forms in other parts of the Kola and Karelia regions allows the authors to refer them to the Neva Stage (other names are Keiva I, Syamozero), which took place in the Older Dryas Stadial.
Fracture studies commonly lack data for the length range between 10 m to 1 km. For this reason, scaling laws are required to extrapolate fracture properties, for example in discrete fracture network models. This study focused on analysis and correlation of topology, orientation and length distribution of multiscale fracture datasets to assess their scalability. The used datasets comprise UAV-derived photogrammetric models from natural outcrops and lineaments mapped using airborne LiDAR, bathymetry and aerogeophysical data, in several contrasting scales and resolutions. This study highlights challenges in acquiring uncensored and coherent brittle structural datasets from source data characterized by a large span of resolutions between the remote sensing datasets and models of the fractured outcrop. In specific, collected data was found to be potentially biased and affected by uncertainties related to both the censoring by sedimentary cover and the scale of observation. Our results revealed differences between lineament and outcrop fracture orientations, as well as difficulties in assessing topological parameters from lineament datasets. The 1:200000 resolution was found best suited to the mapping of lineament length and resulted in a length distribution power law exponent of -1.92. For outcrop fractures that are less than 2 m long, the lognormal length distribution provided the only good fit to our data, while the longer outcrop fractures fitted relatively well with a power law exponent of -2.26.
Mining industry generates a significant amount of waste including waste rock and tailings. The disposal of mine tailings has environmental impacts, such as the releasing of heavy metals to surface and underground waters. Therefore, adequate rehabilitation of mining waste storage facilities is essential. Abandoned tailings ponds may contain significant amounts of valuable minerals, including critical raw materials, and offer opportunities as secondary mineral resources. In this study geochemical and mineralogical characterization were made for the diverse mine tailings of the Rautuvaara tailings pond which was the final disposal site for different ore deposits. The samples were collected from two different locations in the tailings pond, preconcentrated and analysed with several methods including PSA, XRD, FE-SEM, EPMA, pXRF, WD-XRF and AAS. The geochemical results indicate substantially elevated Cu, As, Ni and Zn concentrations in the tailings. Mineralogical investigations revealed that the tailings contain valuable minerals such as gold, cobaltite, and W-bearing rutile. The last could be used as an indicator mineral in tailings classification and possibly also in future ore exploration. The study of secondary mineralogy revealed that the most weathered top layers of the tailings show secondary alteration rims on the surfaces of mineral particles, and the enrichment of As and Ni in the Fe- and Mn-oxide minerals.
Modern techniques for detrital mineral provenance were applied to sediment core 96/12-1pc from the Lomonosov Ridge in the central Arctic Ocean. The techniques include quantitative clay mineralogy analysis combined with determination of Nd, Pb, and Sr isotopes from clay fraction. The clay mineral assemblage and the isotope signatures depict distinct changes during the Marine Isotope Stage (MIS) 4-3 transition corresponding to the Middle Weichselian deglaciation. This transition is characterised by a homogenous, 48 cm thick, dark grey, silty clay layer with a distinctive IRD concentration, forming a prominent marker bed for the central Arctic Ocean sediments. The elevated smectite and kaolinite contents in the transitional interval are possible weathering products of the Siberian basaltic rocks, such as the Putorana Plateau, feeding the shelves of the Kara Sea and the western Laptev Sea. The Nd and Sr isotope values are compatible with input from the basaltic rocks and fall within the isotopic range of sediments from these shelves. The abrupt changes in the Nd, Pb and Sr isotopic data from the distinct grey layer attributed to the MIS 4-3 transition likely mark a pronounced deglaciation event. An increase in coarse debris in the grey layer indicates a change in the sedimentation regime with a strong iceberg rafting component. This change may also be related to a sudden release of meltwater from a large ice-dammed lake in the northern Siberia.
Digital elevation models, based on laser scanning imageries (LiDAR-DEM) and aided by ground penetrating radar (GPR) data, were used to study glaciofluvial Gilbert-type ice-contact deltas in the Younger Dryas Salpausselkä end-moraine zone in southern Finland. The geomorphological data analysed were used to reconstruct the water-level drop of the late glacial Baltic Ice Lake to the early Holocene Yoldia Sea and tie these changes to a wider stratigraphic context. The results indicate that the sudden drainage event at around 11 650 cal. yrs BP left its imprint not only on the varved sediments but also on ice-contact glaciofluvial deltas in the Second Salpausselkä zone throughout southern Finland. This morphostratigraphic boundary can be placed at locations where the ice-contact deltas occur at two different levels; the higher-level deltas formed during the Baltic Ice Lake B III water-level stage and the lower-level deltas during the Yoldia Sea Y I water-level stage. This morphostratigraphically defined boundary in southern Finland marks the Pleistocene/Holocene chronostratigraphic boundary in southern Finland and shows the corresponding positions of the Scandinavian Ice Sheet’s Finnish Lake District Ice Lobe and the Baltic Sea Ice Lobe.
Established international soil classification systems have not properly accommodated acid sulfate soils (ASS) and soil materials in Finland and Sweden because: (1) in these soils some diagnostic ASS properties are too deep to meet the depth requirements, and (2) there is a lack of defined diagnostic soil classification criteria for acidic and potentially acidic soil materials that do not completely fulfill the diagnostic pH criterion of pH < 4.0. In this paper, two new ASS materials are introduced with the prefix “para” for parasulfuric material (oxidized material) and parahypersulfidic material (reduced material). These materials have diagnostic pH-criteria of pH 4.0–4.5 and 3.0–3.5 (field-pH for parasulfuric material and incubation-pH for parahypersulfidic material) for mineral and organic soil materials (here defined as > 20% organic matter; peat and gyttja), respectively. The term “para-acid sulfate soil (para-ASS) material” is introduced for soil materials which may have a considerable environmental impact due to mobilization of acidity and dissolved metals. Because organic acids may lower pH to values below the established pH-value of < 4.0 for ASS materials, a pH of < 3.0 is used in the Finnish-Swedish ASS classification for organic soil materials. These changes and new additions to existing diagnostic ASS materials have consequently also led to a slight modification of the required field-pH values of the existing terms “hypersulfidic material” and “sulfuric material”. The Finnish-Swedish ASS classification further includes a systematic way for classification of the entire soil profile and no depth requirements for diagnostic ASS materials are present; what matters is the current or potential environmental impact that the soil has or may have. It is proposed that the Finnish-Swedish ASS classification may serve as a framework for establishing a unified ASS classification globally and that the new diagnostic ASS materials are included in relevant international soil classification systems.
