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.

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 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.

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 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 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.

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.

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.

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.