Exploration of critical elements in the concealed North Estonian basement and its Eastern Fennoscandian context

 

by Juan David Solano-Acosta ^{* a,1,} Sophie Graul ^a,2, Alvar Soesoo ^a,b,c,3, Rutt Hints ^a,4, Johannes Vind ^b,5, Sirle Liivamägi ^b,6

^a   Department of Geology, Tallinn University of Technology, Ehitajate tee 5, Tallinn, 19086, Estonia

^b  Geological Survey of Estonia, F. R. Kreutzwaldi 5, Rakvere, 44314, Estonia

^c   Department of Geology, University of Tartu, Ravila 14a, Tartu, 50411, Estonia 

 

¹ juan.solano@taltech.ee / 0000-0002-4341-644X

² sophie.graul@taltech.ee / 0000-0002-6396-5534 

³ alvar.soesoo@taltech.ee / 0000-0002-5711-1727

⁴ rutt.hints@taltech.ee / 0000-0001-6764-8037                                                                                                                                 

⁵ johannes.vind@egt.ee / 0000-0002-3025-8163 

⁶ sirle.liivamagi@egt.ee / 0009-0001-5180-200 

*  Corresponding author: juan.solano@taltech.ee  

Abstract

This study evaluates the mineral potential of the NE Tallinn-Alutaguse-Jõhvi Estonian Paleoproterozoic corridor, composed of amphibolite- to granulite-facies gneisses and metal-rich volcanic-sedimentary units. Mesoproterozoic rapakivi bodies were also analysed. Borehole geochemistry reveals that the Alutaguse metavolcanic suites have high concentrations of Cu (2230 ppm), Zn (2650 ppm), and Pb (4030 ppm), hosted in magnetite-rich and sulphide-graphite gneisses, similar to those found in ore systems in Sweden and Finland. Data suggest that the metalliferous Alutaguse target zones are linked to intrusive bodies and/or hydrothermal-skarn processes akin to those at Jõhvi. Automated MSCL-XYZ scanning of drill cores reveals associations of critical metals, including Ni-Co-Cr, Mo-W-Bi, Sn-Zn-Cd, Cu-Ni, Nb-Y-P, and Au-Ag-As-Sb-Bi-W-Se-Sn, identifying new prospective intervals. Analyses of the Märjamaa rapakivi pluton reveal REE concentrations of up to 3600 ppm in the Si-poor Fe-Ti-P-rich Phase I, indicating potential exploration targets. Geophysical data also highlight zones of high magnetic susceptibility, possibly inferring altered or mineralised target zones.

Keywords

Critical Raw Minerals (CRM) exploration; Estonian Precambrian basement; Geophysical potential analysis; drill-core Geochemistry.

Note:

Papers published in this special issue of the European Geologist journal have undergone a thorough peer-review process but have not been copy-edited. Authors bear full responsibility for the linguistic accuracy of their contributions.

This work is licensed under a Creative Commons Attribution 4.0 International License.

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1. Introduction

The Baltica or East European Craton in northeastern Europe comprises Archean-Paleoproterozoic to Neoproterozoic cratons, including Fennoscandia, Volgo-Uralia, and Sarmatia, which developed independently prior merging around 1.8-1.7 Ga [1-8] (Fig. 1a). Seismic and paleomagnetic data indicate that Baltica played a pivotal role in forming the Nuna supercontinent, characterised by substantial latitudinal movement and interactions among arc systems, microcontinents, and magmatism [3, 6-7]. In Fennoscandia (Fig. 1b), this is represented by the Paleoproterozoic Svecofennian Orogen (SO), which shows large-scale accretionary growth through multiple subduction-collision events, resulting in NW-SE-trending tectonic domains [1-12], and later Mesoproterozoic reactivation during Gothian and AMCG (Anorthosite-Mangerite-Charnockite-Granite) magmatism (1.6-1.4 Ga), mainly marked by rapakivi granites dated between 1.64 and 1.44 Ga, indicating a major intracontinental magmatic phase overlying the Svecofennian crust [13-18].

The Estonian Precambrian crystalline basement is a hidden continuation of the Fennoscandian Shield (Fig. 1b), mainly consisting of Paleo- to Mesoproterozoic metamorphic and igneous rocks (around 1.9-1.5 Ga) buried under 100-900 metres of Neoproterozoic to Devonian sediments that thicken southward (Figs. 1c-e), which structure, lacking outcrops, is inferred from drill cores, gravity and magnetic data, seismic surveys, and geochronology [2,8-12,18-26]. Six structural-petrological zones: Tallinn, Alutaguse, Jõhvi, West-Estonian, Tapa, and South-Estonian, are identified based on lithology, metamorphic grade, and geophysical signatures, each with distinct features (Fig. 1c) [8-12,18-22].

Data from the Trans-Baltic region show that the Paleoproterozoic crust beneath Estonia originated in the southern SO, a zone characterised by successive accretion of arc complexes, microcontinents, and sedimentary basins, forming the current mosaic of tectonic belts and oroclinal structures [1-8,18-26]. The Southern Svecofennian (SS) area in Finland, encompassing the Häme and Uusimaa belts and the Saimaa and Ladoga zones, exhibits interactions between juvenile arc crust and Archean basement, with arcuate contours interpreted as the Bothnian and Saimaa oroclines. Data suggest the Uusimaa belt extends beneath the Gulf of Finland toward the Tallinn zone. In contrast, the Ladoga zone continues southeast along the Archean boundary, marking the southeastern edge of the Svecofennian margin. These domains link south to the Bergslagen microcontinent and its ore province in south-central Sweden, forming a continuous Paleoproterozoic structural and magmatic corridor [2,4,8-12,18-29].

This corridor, spanning 1.91–1.87 Ga (Fig. 1f), encompasses the Tallinn, Alutaguse, and Jõhvi domains [2, 18-28]. It features Fe-S-Si-rich gneisses, magnetite units, and polymetallic systems, which are linked to Bergslagen-type successions in Finland and Sweden [2, 8, 19-25, 27, 28]. The units are associated with 1.91-1.89 Ga felsic volcanic and subvolcanic rocks, carbonates, turbidites, skarns, and later 1.79 Ga granites and migmatites linked to the late Svecofennian belt [2,8,11,12,19-25]. Notably, the Alutaguse region, comprising aluminous and graphitic gneisses, quartzites, carbonates, and metavolcanic suites, is thought to be a rifted back-arc basin segment within the Uusimaa-Tallinn arc system, later compressed and sealed, creating conditions for VMS-type Cu-Pb-Zn and polymetallic deposits (i.e., Critical Raw Materials (CRM)) [2,8,19-25].

In the Baltic countries, rapakivi intrusions are largely buried beneath the Phanerozoic cover; their distribution and architecture are inferred from seismic and potential-field data [2, 3, 6, 8, 10, 14-17]. In Estonia, the rapakivi suite comprises the large Riga Batholith and smaller, older intrusions, such as Märjamaa, Kloostri, Naissaare, Taebla, Neeme, and Ereda (Fig. 1c), as well as A-type stocks (e.g., Abja, Muhu, Virstu) [8, 10, 30]. Mainland plutons are mainly pink, coarse monzogranite-syenogranite, locally cut by aplitic and microsyenitic dykes. However, the classic rapakivi texture is rare; geochemical and isotopic signatures match those of the broader Fennoscandian rapakivi suite, emplaced along the Åland-PPDZ structural corridor. Geophysical, petrological, and geochemical work has shown that Märjamaa-Kloostri is a composite, structurally controlled system with three magmatic phases that display marked contrasts in petrophysical properties, oxidation state, fluorine content, and rare-earth enrichment, particularly in the early Fe-rich, silica-poor facies [13-17, 23, 24, 30].

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During the past century, more than 500 holes have been drilled to explore the crystalline basement. A significant portion of these drill cores is preserved and available in the Geological Survey of Estonia (EGT) rock archive. However, between 1990 and 2018, few studies of the crystalline basement were conducted [8]. Recent investigations have significantly enhanced our understanding of metal genesis and the overall characterisation of Precambrian units. Based on several geological, geochemical, and geophysical studies, this research integrates their results into a unified framework for the concealed Paleo- to Mesoproterozoic North Estonian basement and its position within the eastern Fennoscandian crust. By combining interpretation of legacy drill-core datasets, petrological analysis, automated Geotek MSCL-XYZ scanning, and Bouguer and magnetic data, the study reevaluates the distribution of critical-element associations within the Tallinn-Alutaguse-Jõhvi corridor, synthesises the lithological and structural controls on these systems, and considers rapakivi intrusions (especially the Märjamaa-Kloostri) in a tectono-magmatic and metallogenic context. Within Baltica’s geodynamic evolution, this synthesis ought to refine the metallogenic model of Estonia and identify new exploration targets.

2. Geological Setting

2.1 Fennoscandian Context

Within Baltica, the Paleoproterozoic crust of Fennoscandia consists of Archean blocks surrounded by Svecofennian supracrustal belts and granitoid complexes, segmented by major shear zones such as the Raahe-Ladoga system, the South Finland Shear Zone, and the Paldiski-Pskov Deformation Zone (PPDZ) [1-11,18-20] (Figs. 1a-c). Accretionary and collisional stages of the Svecofennian Orogen assembled arcs, microcontinents, and sedimentary basins into several provinces, including the SS zone (Häme, Uusimaa, Saimaa, Ladoga; Fig.1b), where juvenile arcs interacted with the Archean crust to develop oroclinal structures along the Bothnian and Saimaa trends [2,4,5]. Comparable processes shaped the Bergslagen province of Sweden, where 1.9–1.8 Ga volcanic-sedimentary-intrusive successions host extensive Fe-oxide and base-metal mineralisation [2, 18-24, 27, 28]. Seismic reflection-refraction experiments across the Baltic Sea, accompanied by gravity and magnetic modelling, reveal that the Svecofennian crust is organised into blocks bounded by steep, deeply rooted faults that remained mechanically weak into the Mesoproterozoic [3, 6, 18]. These inherited structures guided post-Svecofennian reactivation and, later, channelled AMCG magmatism along corridors such as the PPDZ [16,18], which continues to influence present-day intraplate seismicity [29].

2.2 Estonian Basement Domains

The Estonian crystalline basement represents the southeastern continuation of the Fennoscandian Shield. It is subdivided into structural-petrological domains bounded by long-lived shear systems such as the PPDZ and the Middle Estonian Fault Zone (MEFZ). These structures separate the amphibolite-facies crust in the north from granulite-facies blocks in the south and were repeatedly reactivated during the Mesoproterozoic [2,8-12,16]. In northern Estonia (Fig. 2), the Tallinn, Alutaguse, and Jõhvi domains host Paleoproterozoic volcanic-sedimentary successions that were later intruded by granitoids dated at 1.92-1.88 Ga. These domains include Fe-Si-rich gneisses, magnetite-bearing units, and sulphide-graphite horizons forming a part of the Bergslagen-Southern Svecofennian metallogenic corridor, with metamorphism dominated by amphibolite facies, locally reaching granulite conditions at ~3-5 kbar [2,8].

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The Tallinn Domain features negative free-air gravity and magnetic anomalies, indicating a relatively felsic crust [8, 11, 19]. The PPDZ bounds it to the southeast and contains amphibolite-facies metavolcanic rocks, amphibole-biotite-plagioclase gneisses, quartz-feldspar and Al-mica gneisses (biotite-cordierite-garnet-sillimanite), along with local sulphide-graphite gneisses and magnetite quartzites of the Jägala Complex [8,11,12]. Migmatisation is common, and structural-lithological correlations suggest that Tallinn is the southern extension of the Uusimaa Paleoproterozoic volcanic arc of Finland [2,8-12,16]. The Alutaguse Domain exhibits near-zero to slightly negative gravity and magnetic values, with local positive anomalies at Uljaste, Assamalla, and Haljala (Fig. 2). These anomalies are associated with sulphide-graphite gneisses, quartzites, skarnised carbonaceous rocks, and migmatised-pyroxene gneisses [8,11,12]. This domain is generally regarded as a rifted back-arc basin segment of the Uusimaa-Tallinn system, which was later compressed during post-Svecofennian deformation [8, 19-25]. The Jõhvi Domain is a narrower, distinct belt of alternating Fe- and S-rich garnet-pyroxene quartzites, high-Al garnet-cordierite-sillimanite gneisses, and Ca-rich to Ca-poor pyroxene, amphibole, and biotite gneisses. These rocks exhibit strong migmatisation and granite intrusions dating back to around 1.8 Ga, which aligns with late- to post-orogenic phases in southern Finland [2,5,8,18-25,34-36]. The Jõhvi province also exhibits some of Estonia’s strongest potential-field anomalies, mainly due to magnetite-rich units, highlighting it as a key part of the Bergslagen-type metallogenic corridor [24,25,31,32].

2.3 Mesoproterozoic AMCG and Rapakivi Magmatism

The Mesoproterozoic anorogenic magmatism of Fennoscandia consists predominantly of AMCG suites and rapakivi granites, emplaced between 1.64 and 1.44 Ga, within a broader 1.8–1.0 Ga intracontinental magmatic period [3,7,13–17]. These intrusions form batholiths and large plutons that overprint the Svecofennian architecture. They are spatially linked to crustal-scale faults, horst–graben structures, and zones of mafic underplating [16,37–40]. Paleomagnetic reconstructions suggest that this magmatism evolved in a long-lived intracontinental environment associated with Nuna breakup, plume trapping, and superswell activity beneath a thick lithosphere, rather than through simple rift or hotspot processes [3,7,16,37–40]. In this context, the Märjamaa–Kloostri granitoids plot predominantly within the continental-rift domain, consistent with rapakivi magmatism associated with intracontinental extension or transtensional reactivation within the Laurentia–Baltica framework [16,23,30]. Emplacement occurred during the final stages of the first Fennoscandian rapakivi AMCG event (Wiborg suite), driven by asthenospheric upwelling and mafic underplating linked to Nuna superswell activity [16,23].

The Fennoscandian rapakivi granites are grouped into four AMCG age clusters: 1.67-1.62, 1.59-1.56, 1.55-1.53, and 1.53-1.44 Ga; represented by the Wiborg, Åland, Salmi, and Ragunda suites, which together extend from southern Finland beneath the Gulf of Finland into Estonia, Lithuania, and Poland [7,13-16,38-40]. Seismic reflection profiles and potential-field inversions across the Baltic Sea indicate that rapakivi magmas were channelled along listric faults and dilatational ramps within NW-SE Svecofennian shear corridors, especially the Åland-PPDZ trend, producing tabular, sheet-like plutons marked by strong internal density and magnetic contrasts [16, 41, 42]. Thermal modelling further indicates that high-heat-production granites and sustained lithospheric weakening governed the emplacement and longevity of AMCG magmatism [16, 35, 37].

A-type and rapakivi granites are increasingly recognised as important sources for economic mineral systems. The intracontinental rift-superswell environments that produced the AMCG suite globally favour SEDEX, stratabound Cu, and IOCG-style deposits, driven by oxidised, volatile-rich, mantle-derived or lithosphere-fertilising fluids [16,37,43]. Halogens, such as F, also enhance metal transport, promote silicate dissolution, increase permeability, and generate characteristic greisen and skarn assemblages [16, 37, 43]. In the Wiborg Batholith and related intrusions of southern Finland, mineralisation includes In-bearing magnetite-sphalerite ores, Zn-Cu-Pb-Ag-In polymetallic veins, and Sn-W-Be greisen systems, controlled by late, evolved rapakivi phases and strike-slip/transtensional structures [16, 37-39, 44].

In Estonia, the Wiborg Suite is represented by the concealed Riga Batholith (also in Saaremaa) as well as several smaller intrusions: Märjamaa, Kloostri, Naissaare, Taebla, Neeme, and Ereda, which are emplaced along the Åland-PPDZ corridor [13,16,39,42]. Geophysical and petrological studies indicate that the Märjamaa-Kloostri intrusions form a composite, structurally controlled plutonic system comprising three magmatic phases with pronounced contrasts in density, susceptibility, oxidation state, and trace-element enrichment [16, 17, 23]. Recent work documents anomalously elevated REE contents, up to several thousand parts per million (ppm), locally in early Fe-rich, silica-poor phases, together with elevated F and other volatiles. Moreover, a clear spatial relationship with inherited Svecofennian shear structures was highlighted [16, 17, 23].

3. Materials and datasets

3.1 Geochemical datasets

Alutaguse and SS metasedimentary and metavolcanic units’ whole-rock compositions integrate three complementary datasets, analysed in previous articles [19,20,22-24]: (i) legacy major-element analyses (216 samples; Kivisilla et al. (1999) [33]); (ii) high-quality major-trace-REE data (16 samples; Solano-Acosta et al. [19]); (iii) new EGT trace-element data (149 samples) from Uljaste and adjacent cores [20,22-24]. Together, these define the major-, trace-, and REE variability of the Alutaguse units, supporting provenance and tectonic interpretations. Comparative Svecofennian data include 206 filtered major-trace samples from the GTK (Finnish Geological Survey) Rock Geochemical Database for Uusimaa, Häme, and Saimaa [44], supplemented by Ladoga siliciclastic (26) and metavolcanics (8), from Kotova et al. [26]. These datasets provide a robust regional framework for evaluating North Estonian arc-back-arc affinities with SS, as presented in Solano-Acosta et al. (2025) [19, 20, 22]. CRM associations are derived from MSCL-XYZ multi-spectral scanning of 22 drill cores from NE Estonia (Tallinn-Alutaguse) conducted by the EGT as reported by Nirgi et al. [25] (Fig. 2a). Inferred results reported certain elemental groups of polymetallic prospective systems, including Ni-Co-Cr, Cu-Ni, Ti-V-Fe, Mo-W-Bi, Sn-Zn-Cd, Nb-Y-P, K-Sn-Rb-Ga, and As-Sb-Bi-W-Se-Sn.

Rapakivi compositions are constrained using: (i) Legacy major-element data for Estonian rapakivi granitoids from Kivisilla et al. (1999) [33]. (ii) Märjamaa major-trace-REE dataset (62 samples) from Potagin (2024) [39], and (iii) Wiborg Suite data, extracted from the GTK Rock Geochemical Database [44]. 

3.2 Geophysical datasets

The geophysical component uses EGT Bouguer gravity anomaly and magnetic grids (https://gis.egt.ee/). Processed residual Bouguer and RTP magnetic datasets were used for the Alutaguse and Jõhvi domains (Figs. 3a–c) [23]. The Jõhvi dataset additionally includes a high-resolution ground magnetic survey acquired using a G-856AX proton-precession magnetometer [32]. For the Märjamaa–Kloostri intrusions, EGT gravity and magnetic grids were used (Figs. 3d–e) [16,23].

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4. Discussion

4.1 The Alutaguse back-arc basin and its relation to Southern Svecofennian domains

4.1.1 Metasedimentary signatures (High-SiO₂ > 63 wt.% and Low-SiO₂ ≤ 63 wt.%)

The plots of major, trace, and REE elements (Figs. 4a-c) indicate that the Alutaguse metasediments retain the fundamental compositional separation between the High- and Low-SiO₂ groups.

High-SiO₂ metasediments plot near UCC-like felsic trends, comparable to Uusimaa [19,20,22-24,33,44]. Yet, they consistently show higher Fe₂O₃, MgO, SO₃, and K₂O and lower Al₂O₃ and Na₂O, thus reflecting enhanced contributions from mafic detritus and basin-scale fluid circulation rather than a purely felsic arc-sourced sediment supply. Trace elements reinforce this interpretation: transition metals (V, Cr, Co, Ni, Cu, Zn), and Ba-Sr are higher than in Uusimaa and Saimaa, and REE patterns show elevated ΣREE: strong LREE enrichment, and subdued Eu anomalies in SS domains [19-22]. Compared to Häme and Saimaa’s High-SiO₂ metasediments, Alutaguse remains more Fe-Mg-S enriched. Häme and Saimaa show higher Al₂O₃ and Na₂O and more balanced REE distributions with stronger Eu anomalies, consistent with mature arc-front or intra-arc basins (Fig. 1f) that experienced less mafic influx [19,20,22,26]. Ladoga High-SiO₂ metasediments represent the quartz-rich, REE-poor endmember of the system, with the lowest Al₂O₃ and weakest metal enrichment, reflecting a more distal, Karelian-influenced provenance [2,54].

Low-SiO₂ metasediments sharpen these contrasts further. Alutaguse exhibits the lowest SiO₂ and Al₂O₃, the highest Fe₂O₃, MgO, and SO₃, and the broadest CaO-MgO ranges with Uusimaa (Fig. 4a). These units also contain high metal concentrations (Ni 385 ppm; Cu 1060 ppm; Zn 4100 ppm; Pb 1430 ppm), far exceeding Uusimaa, Häme, Saimaa, or Ladoga [19,20,22,26]. ΣREE remains elevated, yet shows pronounced HREE dominance, consistent with strong felsic-volcanic detrital input superimposed on mafic-rich basin fill. In contrast, Uusimaa and Saimaa Low-SiO₂ samples are more siliceous, higher in Al₂O₃ and HFSE (Zr, Hf, Y), and exhibit better balanced REE patterns with stronger Eu anomalies, reflecting derivation from more evolved arc-margin sources [19,20,22].

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4.1.2 Metavolcanic suite sources, magmatic affinities, and alteration

Major-element trends (Fig. 4a) show that the Alutaguse metavolcanic suites define a tholeiitic array, with increasing MgO and P₂O₅ and decreasing Na₂O toward mafic compositions, consistent with juvenile magmas produced in an extensional arc-proximal to back-arc basin setting [19,20,22,26,27]. Relative to all SS domains, the Alutaguse suite is systematically enriched in TiO₂, Fe₂O₃, MgO, and CaO and depleted in Al₂O₃, Na₂O, K₂O, and P₂O₅, indicating derivation from a hotter, more depleted mantle source and subsequent hydrothermal modification. CaO and MnO are highest in the Alutaguse and Uusimaa metavolcanic suites. Low A/CNK values and Fe-Ti-rich compositions further support a back-arc tholeiitic affinity [19, 20, 22, 23, 26].

Trace-element signatures (Fig. 4b) reinforce these distinctions. Alutaguse metavolcanics exhibit low La/Yb and high Zr/Nb ratios, consistent with the partial melting of a depleted asthenospheric mantle. In contrast, Ladoga volcanics yield higher La/Yb and lower Zr/Nb, indicating a more slab-modified source [19,20,22,23,26]. Elevated Th/Nb and depleted Ba/Th and U/Th in Alutaguse indicate a minimal slab-fluid contribution, in contrast to Häme and Saimaa, which display stronger subduction signatures [19,20,22,23,26].

Base-metal concentrations in the Alutaguse suite: Ni 210 ppm, Cu 2230 ppm, Zn 2650 ppm, and Pb 4030 ppm, are among the highest in the entire corridor and exceed both Alutaguse metasedimentary maxima and all SS metavolcanic fields [19-23,25,27,31-36]. This combination of tholeiitic major-element chemistry, asthenospheric mantle signatures, and high Cu-Zn-Pb enrichment parallels those of Bergslagen-type back-arc basin volcanic centres [21,22,23,27,28].

REE patterns (Fig. 4c) indicate moderate LREE enrichment and subdued HREE in the Alutaguse metavolcanics, with average REE contents exceeding most SS suites except Saimaa, consistent with melts derived from amphibolitic sources and later modified by hydrothermal circulation [19,20,22]. A positive Eu anomaly in Alutaguse may reflect high-temperature hydrothermal processes under reducing conditions; however, further sampling is required to confirm this observation. In contrast, SS metavolcanics, particularly from Saimaa and Häme, are enriched in Zr, Hf, and Y (Fig. 4b), consistent with more evolved intra-arc or continental-margin magmatic sources.

4.2. MSCL-XYZ element associations and implications for targeting

The MSCL-XYZ scanning of selected drill cores from the Geological Survey of Estonia’s archive refines understanding of the distribution of critical metals in the Tallinn-Alutaguse domains (Fig. 2a) [22, 25]. Core selection relied on digitised historical data and prioritised CRM [21, 22, 25]. Because basement lithologies differ strongly in background chemistry, anomalous Ni-Co in felsic or metasedimentary rocks, or REE, are particularly diagnostic of hydrothermal or metasomatic processes [21, 22, 25].

Scanning at 5-15 cm spacing along selected intervals allowed identification of key element associations: Ni-Co-Cr, Ti-V-Fe, Mo-W-Bi, Sn-Zn-Cd (In), Cu-Ni (PGM), Nb-Y-P (REE), K-Sn-Rb-Ga (Li), and As-Sb-Bi-W-Se-Sn (Au-Ag) [25]. Ni-Co-Cr and Cu–Ni are mainly linked to mafic–ultramafic intrusions; Ti-V-Fe is concentrated in the Haljala area; Mo-W-Bi occurs in both Haljala and the Tallinn structural zone; and Sn-Zn-Cd anomalies cluster in Uljaste and Viru-Nigula [25]. Other associations (Nb-Y-P, K-Sn-Rb-Ga, As-Sb-Bi-W-Se-Sn) span multiple lithologies, reflecting varied magmatic and hydrothermal controls [21, 22, 25, 31].

Scanner data reveal stronger heterogeneity than suggested by legacy descriptions, exposing abrupt changes in rock character and metal content [25]. This directly improves exploration targeting by identifying previously unrecognised mineralised zones and linking them to specific geophysical anomalies and lithologies. To fully assess these signals, detailed laboratory geochemical and petrographic–mineralogical studies are required [19-25].

4.3 Exploration significance: Critical-metal systems in the Tallinn-Alutaguse-Jõhvi corridor

The Tallinn domain represents the felsic arc front of the 1.92–1.89 Ga Tallinn-Uusimaa-Bergslagen system. It also forms the metallogenic core of the corridor, hosting the highest Cu-Pb-Zn enrichments in Low-SiO₂ and metavolcanic units (Fig. 3b), consistent with sustained volcanogenic and intrusive inputs and focused hydrothermal circulation, similar to fertile Bergslagen-type back-arc systems [19-22, 25, 27, 28]. At the eastern end of the corridor, the Jõhvi magnetite province provides the Fe-oxide endmember, with magnetite-rich gneisses (15-46 wt.% Fe; 1-6 wt.% Mn) and polymetallic sulphides representing metamorphosed volcanic-sedimentary protoliths rather than a typical skarn or BIF systems [8,21,31,32]. Magnetite compositions (Ti+V vs. Ca+Al+Mn) fall near the skarn-IOCG spectrum, and exceptionally strong remanent magnetisation reflects abundant sub-micrometre magnetite grains, a signature shared with Bergslagen and Orijärvi [2, 5, 21, 31, 32].

Geophysical enhancement of this scenario, with the residual Bouguer and RTP high-potential values, coincides with metal-rich lithologies across Alutaguse and Jõhvi (Fig. 2a-b; [8,18,21-23]), and cross-gradient SimPEG inversion (Fig. 3c) resolves ~10 km depth tabular zones of high susceptibility and low density corresponding to Fe-oxide-sulphide bodies at Haljala, Assamalla, and Uljaste; flanked by weakly magnetic graphite-rich horizons marking consolidated back-arc stratigraphy (e.g., density contrasts). The zones with lower magnetic signals are interpreted as graphite-rich gneisses, possibly formed during the consolidation of the back-arc basin. In contrast, the metalliferous Alutaguse zones are likely linked to intrusive bodies and hydrothermal-skarn enrichment, like those at Jõhvi [23, 31, 32].

 Plado et al. (2020) [32] provide a geological insight into the Jõhvi magnetic anomaly in NE Estonia. The investigation revealed that the three magnetic peaks, with maximum amplitudes of 19,290 nT (western), 15,880 nT (eastern), and 8,080 nT (northern) (Fig. 5b), are primarily caused by strong remanent magnetisation directed roughly vertically downward. The direction aligns with the dip of the iron ore formation. Strong remanence indicates a significant presence of small magnetite grains (<1 μm) in the Jõhvi ore, which warrants future (magneto)mineralogical studies. Petrophysical measurements of Mag-quartzites revealed that the residual magnetisation was about ten times greater than the induced magnetisation [32].

Together, Tallinn defines the felsic arc source, Alutaguse the metal-rich, tectonically focused back-arc basin, and Jõhvi the Fe-oxide-sulphide pole, establishing a continuous and concealed Cu-Pb-Zn-C-S-Fe-oxide metallogenic belt along the NW-SE Svecofennian structures. MSCL-XYZ scanning (5-15 cm resolution; Fig. 2a) further corroborates this framework by revealing heterogeneous Ni-Co-Cr, Ti-V-Fe, and Sn-Zn-Cd associations related to mafic influx and hydrothermal-metasomatic overprinting [21-25], thus refining exploration targets across the corridor. The MSCL-XYZ-derived CRM elemental associations, corresponding host lithologies, and representative drill-core intervals are synthesised in Supplementary Table S1.

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4.4 Geophysical and Petrogenetic Insights from the Märjamaa-Kloostri Rapakivi Intrusions

4.4.1 Geophysical Architecture, Structural Controls, and Emplacement Framework

High-resolution residual Bouguer and RTP magnetic datasets (Fig. 3d) delineate a sharply zoned intrusive system characterised by strong density-susceptibility contrasts, which record the multiphasic Märjamaa-Kloostri assembly [13, 16, 17, 23]. Phase I forms a dense, magnetite-bearing core, expressed by coincident gravity and magnetic highs, surrounded by a lower-density, weakly magnetic Phase II shell, and an outer Phase III domain marked by a Bouguer low and a subtle NW RTP high. This is consistent with an evolved, oxide-poor, Na-rich composition [16,23]. SimPEG cross-gradient inversions to 10 km depth (Figs. 3d-e) resolve these three bodies as a steep, vertically elongated high-susceptibility Phase I column, a positive-density/low-susceptibility Phase II envelope, and a NW-shifted Phase III satellite with susceptibility increasing at depth. Linear susceptibility ridges at the Phase I-II boundary likely represent feeder zones or collapsed blocks, providing the first 3D evidence for piston-cauldron mechanisms beneath North Estonia [16,23].

The derivative grids define a composite structural pattern in which nested radial and arcuate gradients outline the internal roof collapse of the intrusive chamber [16], revealing rims marking contacts and ring-fault geometries. In contrast, lineament analysis reveals that the pluton is situated at the intersection of Riedel-type fabrics-oriented NW-SE and NE-SW, which are linked to the PPDZ [2, 8, 16, 18]. Dense lineament clusters at the margins of Phases II and III correspond to reactivated strike-slip bands, whose organisation in R, R′, and P geometries indicates dextral transtensional [16]. This shear regime enhances different deformation events, governs magma ascent pathways, facilitates roof fragmentation, and produces the NW-directed trapdoor behaviour observed in both derivative grids and inversion sections.

The combined geophysical and structural evidence supports a model in which Märjamaa-Kloostri was positioned as a steep, shear-guided magma chamber that developed ring-fault collapse and asymmetric subsidence along the PPDZ corridor. Its timing (1.67-1.53 Ga) places it within the AMCG superswell phase, characterised by mantle upwelling, slab stagnation, mafic underplating, and enhanced lithospheric heat flow along long-lived shear zones [3, 7, 16, 37-40]. These conditions favoured the generation of oxidised, volatile-rich A-type magmas. They facilitated the structural trapping of the pluton, with PPDZ reactivation providing both vertical permeability and lateral dilation required for cauldron-style subsidence. SimPEG sections showing a cylindrical high-susceptibility core at ~3 km (Fig. 3e) depth, consistent with a long-lived thermal-mechanical anchor and the progressive evolution of a resurgent cauldron [16,23].

4.4.2 Petrogenetic Evolution: Oxidised A-Type Signature and Trace-Element-REE Systematics

Major-element indices (Fig. 6) highlight the distribution of Estonian rapakivi intrusions relative to the Wiborg body, indicating a mostly oxidised character for the mainland suites and more reduced values in the Wiborg and Riga intrusions. Märjamaa shows the highest Ti-Fe-Mg-Ca-P contents among the bodies studied [30]. These signatures align with oxidised A-type magmatism (Fig. 6b) that crystallises near the NNO (nickel-nickel oxide) buffer [13, 16, 17, 23]. Märjamaa-Kloostri granitoids contain high levels of normative magnetite and titanite [45], along with biotite-hornblende assemblages that differentiate from the more reduced Finnish rapakivi Wiborg suite bodies (e.g., Wiborg, Bodom, Obbnäs, Ahvenisto), which are richer in fluorine yet less oxidised [7,13-17,39,44].

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The trace-element and REE datasets (Fig. 7), reorganised by magmatic phase, reveal systematic differentiation throughout the intrusive sequence [16, 17, 23, 39]. Phase I is notably enriched in trace elements and LREE, with total REE content reaching approximately 3600 ppm in the most ferroan, silica-poor samples [16,17,23]. Phase II has intermediate compositions with peak K₂O, decreasing Fe-Ti-P, and declining oxide-phosphate modal fractions, while Phase III forms a Na-rich leucogranite with high SiO₂ and minimal Fe-Ti oxide content [16,17]. These trends suggest fractional crystallisation, varying degrees of crustal assimilation, and a change in oxygen fugacity during chamber development. All phases fall within the A₂-type granite field, characteristic of post-collisional to post-orogenic settings, where mantle-derived heating and crustal remelting interact within an intraplate, thick lithosphere environment [16, 17, 30, 45].

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4.4.3 Metallogenic Zoning and Exploration

Similar rift and superswell environments to those that formed the Fennoscandian AMCG suite are common in SEDEX, stratabound Cu, and Fe Oxide-Cu-Au-U (IOCG) deposits, which involve lithospheric thinning, mantle upwelling, and magmatism with oxidised, volatile-rich fluids [9, 16, 37, 38, 45]. These systems originate from a fertilised lithospheric mantle and deep-sourced fluids, characterised by phases of F and S that enhance metal solubility, promoting wall-rock alteration and greisenisation, which in turn form complex polymetallic assemblages [23, 27, 28, 32-34, 41, 42]. In southern Finland, rapakivi batholiths such as Wiborg, Åland, and Vehmaa, contain ores with magnetite-sphalerite, Zn-Cu-Pb-Ag-In veins, Sn-W-Be greisens, often in later phases (topaz granites, greisen caps, pegmatites) controlled by reactivated Svecofennian shear zones [12,17,19-21,29-31,36,41,42] (Figs. 3d–e). In the Märjamaa–Kloostri complex, SimPEG-derived density and susceptibility contrasts clearly distinguish phase-specific petrophysical signatures (Fig. 3e). In the X12–15 and Y15 zones of the northeastern sector (Fig. 3d), these anomalies suggest a structurally controlled subsurface feature that warrants targeted mineralogical and geochemical follow-up, potentially indicative of skarn-type alteration [16,17].

The Märjamaa-Kloostri intrusion constitutes a high-potential metallogenic system within northern Estonia. Its oxidised A-type affinity, emplacement along a major shear zone, and pronounced REE-HFSE enrichment, particularly in Phase I (Fig. 7), are consistent with fertile AMCG magmatic provinces. Phase I ferroan granodiorites host the highest REE contents, abundant Fe-Ti oxides, phosphate-rich domains, and the strongest magnetic-gravity responses (Fig. 3d), defining the primary REE-HFSE investigation target. Phase II margins are associated with ring-faulting and shear reactivation, providing favourable pathways for hydrothermal fluid flow and potential greisenisation, REE enrichment, or Fe-oxide-apatite enrichment (Table S1). Trapdoor structures in Phase III coincide with petrophysical anomalies indicative of late-stage fluid circulation. At a regional scale, superswell-driven extension and plume-related heating enhance the metallogenic fertility of the Wiborg Suite Estonian rapakivi intrusions, increasing the likelihood of concealed IOCG-like or HFSE-enriched A-type granite-related systems.

5. Conclusions

The Tallinn-Alutaguse-Jõhvi corridor defines a coherent arc-back-arc system, with Tallinn as the felsic arc front, Alutaguse as a base-metal-rich volcanic back-arc basin that represents the metallogenic core, and Jõhvi as a Fe-oxide-sulphide skarnised member. Elevated Cu-Pb-Zn enrichment in Alutaguse reflects sustained mafic intrusion and hydrothermal activity analogous to Bergslagen systems. Integrated geophysical signatures, including high susceptibility, low-density bodies, and strong remanent magnetisation, delineate this architecture and reveal the concealed geometry of mineralised zones. At the same time, MSCL-XYZ scanning and geochemical data identify multi-element associations. The High-Fe-Ti-P Märjamaa-Kloostri granitoids exhibit oxidised A-type characteristics, HFSE-REE enrichment, and geophysical evidence for piston-cauldron emplacement along the PPDZ, thus consistent with Mesoproterozoic magmatism and localised host-rock alteration in the northeastern sector. Together, these results establish a robust crustal and metallogenic framework for northern Estonia, highlighting the concealed Precambrian basement as a significant target for CRM exploration and focused future studies.

Supplementary Materials: The following are available online at https://eurogeologists.eu/wp-content/uploads/2026/03/Solano_Table_S1_CRM_Associations_Estonia.pdf. Table S1: Summary of CRM elemental associations, host lithologies, and representative drill-core intervals across the NE Estonian basement domains and the Märjamaa–Kloostri rapakivi system.

Author Contributions: Conceptualisation: Juan David Solano Acosta and Sophie Graul; Methodology: Juan David Solano Acosta; Validation: Juan David Solano Acosta, Sophie Graul, Tarmo All, Sirle Liivamägi, and Johannes Vind; Formal analysis: Juan David Solano Acosta and Sophie Graul; Investigation: Juan David Solano Acosta and Sophie Graul; Resources: Juan David Solano Acosta, Sophie Graul, Sirle Liivamägi, and Johannes Vind; Data curation: Juan David Solano Acosta and Sophie Graul; Writing—original draft preparation: Juan David Solano Acosta; Writing—review and editing: Juan David Solano Acosta and Sophie Graul; Visualisation: Juan David Solano Acosta and Sophie Graul; Supervision: Alvar Soesoo and Rutt Hints; Project administration: Sophie Graul and Johannes Vind. All authors have read and agreed to the published version of the manuscript.

Funding: This research was funded by the European Union’s Horizon Europe Programme, grant HORIZON-CL4-2024-RESILIENCE-01-01, and supported by the DEXPLORE Horizon Research Funds (document number VHE24051). Additional support was provided through the EU Funding & Tenders Portal, project ID 101178897. The same sources funded the APC.

Conflicts of Interest: The authors declare no conflict of interest.

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References

1. Bogdanova, S., Bingen, B., Gorbatschev, R., Kheraskova, T.N., Kozlov, V.I., Puchkov, V.N., & Volozh, Y.A. (2008). The East European Craton (Baltica) before and during the assembly of Rodinia. Precambrian Research, 160(1–2), 23–45. https://doi.org/10.1016/j.precamres.2007.04.024
2. Bogdanova, S., Gorbatschev, R., Skridlaite, G., Soesoo, A., Taran, L., & Kurlovich, D. (2015). Trans-Baltic Palaeoproterozoic correlations towards the reconstruction of supercontinent Columbia/Nuna. Precambrian Research, 259, 5–33. https://doi.org/10.1016/j.precamres.2014.11.023
3. Salminen, J., Lehtonen, E., Mertanen, S., Pesonen, L.J., Elming, S.-Å., & Luoto, T. (2021). The Precambrian drift history and paleogeography of Baltica. In Ancient Supercontinents and the Paleogeography of Earth (pp. 155–205). Elsevier. https://doi.org/10.1016/B978-0-12-818533-9.00015-1
4. Lahtinen, R., Johnston, S.T., & Nironen, M. (2014). The Bothnian coupled oroclines of the Svecofennian orogen: a Palaeoproterozoic terrane wreck. Terra Nova, 26(4), 330–335. https://doi.org/10.1111/ter.12107
5. Nironen, M. (2017). Bedrock of Finland at the Scale 1:1,000,000 – Major Stratigraphic Units, Metamorphism and Tectonic Evolution. Geological Survey of Finland. https://tupa.gtk.fi/julkaisu/specialpaper/sp_060.pdf
6. Bogdanova, S., Gorbatschev, R., Grad, M., Janik, T., Guterch, A., Kozlovskaya, E., Motuza, G., Skridlaite, G., Starostenko, V., Taran, L., et al. (2006). EUROBRIDGE: new insight into the geodynamic evolution of the East European Craton. Geological Society, London, Memoirs, 32(1), 599–625. https://doi.org/10.1144/GSL.MEM.2006.032.01.36
7. Salminen, J., Elming, S.-Å., Mertanen, S., Wang, C., Almqvist, B., & Oveisy Moakhar, M. (2021). Paleomagnetic studies of rapakivi complexes in the Fennoscandian Shield – Implications to the origin of Proterozoic massif-type anorthosite magmatism. Precambrian Research, 365, 106406. https://doi.org/10.1016/j.precamres.2021.106406
8. Soesoo, A., Nirgi, S., & Plado, J. (2020). The evolution of the Estonian Precambrian basement: geological, geophysical and geochronological constraints. Proceedings of the Karelian Research Centre of the Russian Academy of Sciences, (2), 18–33. https://doi.org/10.17076/geo1185
9. All, T., Puura, V., & Vaher, R. (2004). Orogenic structures of the Precambrian basement of Estonia as revealed from the integrated modelling of the crust. Proceedings of the Estonian Academy of Sciences, Geology, 53, 165–189. https://doi.org/10.3176/geol.2004.3.03
10. Raukas, A., & Teedumäe, A. (Eds.) (1997). Geology and Mineral Resources of Estonia. Estonian Academy Publishers. https://geoloogia.info/geology/index.html
11. Soesoo, A., Puura, V., Kirs, J., Petersell, V., Niin, M., & All, T. (2004). Outlines of the Precambrian basement of Estonia. Proceedings of the Estonian Academy of Sciences, Geology, 53, 149–164. https://doi.org/10.3176/geol.2004.3.02
12. Kirs, J., Puura, V., Soesoo, A., Klein, V., Konsa, M., Koppelmaa, H., Niin, M., & Urtson, K. (2009). The crystalline basement of Estonia: rock complexes of the Palaeoproterozoic Orosirian and Statherian and Mesoproterozoic Calymmian periods, and regional correlations. Estonian Journal of Earth Sciences, 58(4). https://doi.org/10.3176/earth.2009.4.01
13. Ahl, M. (1997). Rapakivi Granites and Related Rocks in Central Sweden: 7th International Symposium on Rapakivi Granites, July 24–26, 1996, University of Helsinki, Finland: Excursion July 16–23, 1996. Sveriges geologiska undersökning, vol. 87.
14. Kirs, J., Haapala, I., & Rämö, O.T. (2004). Anorogenic magmatic rocks in the Estonian crystalline basement. Proceedings of the Estonian Academy of Sciences, Geology, 53, 210–225. https://doi.org/10.3176/geol.2004.3.05
15. Puura, V., & Flodén, T. (2000). Rapakivi-granite–anorthosite magmatism; a way of thinning and stabilisation of the Svecofennian crust, Baltic Sea Basin. Tectonophysics, 305, 75–92. https://doi.org/10.1016/S0040-1951(99)00019-0
16. Solano-Acosta, J.D., Soesoo, A., & Hints, R. (2025). Integrated geophysical and emplacement modelling of the Märjamaa and Kloostri rapakivi granitoids, Estonia: insights into intrusion geometry and tectonic controls. Precambrian Research, in press. https://doi.org/10.1016/j.precamres.2025.107938
17. Potagin, C. (2024). Geology, geochemistry, and geochronology of the Märjamaa rapakivi granitoid intrusion. Master’s thesis, Tallinn University of Technology. https://digikogu.taltech.ee/et/Item/9a9e82c5-ec6c-4918-9f14-6b1ae4a24bc8
18. Solano-Acosta, J.D., Soesoo, A., & Hints, R. (2023). New insights into the crustal structure across Estonia using satellite potential fields derived from WGM-2012 gravity data and EMAG2v3 magnetic data. Tectonophysics, 846, 229656. https://doi.org/10.1016/j.tecto.2022.229656
19. Solano-Acosta, J.D., Soesoo, A., & Hints, R. (2025). Geochemistry, provenance, and tectonic setting of Paleoproterozoic metasedimentary and metavolcanic units of the Estonian Alutaguse region, eastern Fennoscandia. Estonian Journal of Earth Sciences, 74, 61–82. https://doi.org/10.3176/earth.2025.05
20. Solano-Acosta, J.D., Graul, S., Soesoo, A., Hints, R., All, T., Vind, J., Maala, L., & Liivamägi, S. (2025). Comparative geochemistry, provenance, and tectonic evolution of Paleoproterozoic metavolcanic and metasedimentary units in the Alutaguse Zone (North Estonia) and Southern Svecofennian domains. Precambrian Research (under review).
21. Nirgi, S., & Soesoo, A. (2021). Geology and geochemistry of a Paleoproterozoic iron mineralisation in North-Eastern Estonia. Proceedings of the Karelian Research Centre of the Russian Academy of Sciences, (10), 25–43. https://doi.org/10.17076/geo1492
22. Solano Acosta, J.D., Soesoo, A., Hints, R., Graul, S., All, T., Vind, J., Maala, L., & Liivamägi, S. (2025). Exploration of critical mineral resources in the North Estonian basement, Eastern Fennoscandia: Regional and local perspectives with analogies to the Southern Svecofennian Finnish terranes and the Swedish Bergslagen region. 5th International Professional Geology Conference (IPGC 2025), Zaragoza, Spain. https://doi.org/10.13140/RG.2.2.18847.01449/1
23. Solano-Acosta, J.D. (2026). Crustal structure, tectonics, and magmatic evolution of the Estonian Proterozoic basement: Geophysical and geochemical insights. Doctoral thesis, Tallinn University of Technology. https://doi.org/10.23658/taltech.9/2026
24. Solano Acosta, J.D., Soesoo, A., Hints, R., & Graul, S. (2025). Exploration of critical mineral resources in the North Estonian basement, Eastern Fennoscandia: A geochemical and geophysical investigation of a region akin to the Southern Svecofennian Finnish terranes and the Swedish Bergslagen Province. Goldschmidt 2025, Prague. https://doi.org/10.7185/gold2025.28444
25. Nirgi, S., Maala, L., & Kont, R. (2024). Kriitiliste toormete ja nendega assotsieeruvate elementide tuvastamine ning uuringupotentsiaali hindamine Eesti aluskorras [Identification of Critical Raw Materials and Associated Elements in Estonian Crystalline Basement Rock]. https://doi.org/10.23679/1032
26. Kotova, L.N., Kotov, A.B., Glebovitskii, V.A., Podkovyrov, V.N., & Savatenkov, V.M. (2009). Source rocks and provenances of the Ladoga Group siliciclastic metasediments (Svecofennian Foldbelt, Baltic Shield): results of geochemical and Sm–Nd isotopic study. Stratigraphy and Geological Correlation, 17, 1–19. https://doi.org/10.1134/S0869593809010018
27. Hanski, E. (2015). Synthesis of the geological evolution and metallogeny of Finland. In Mineral Deposits of Finland (pp. 39–71). Elsevier. https://doi.org/10.1016/B978-0-12-410438-9.00002-9
28. Beunk, F.F., & Kuipers, G. (2012). The Bergslagen ore province, Sweden: Review and update of an accreted orocline, 1.9–1.8 Ga BP. Precambrian Research, 216, 95–119. https://doi.org/10.1016/j.precamres.2012.05.007
29. Soosalu, H., Uski, M., Komminaho, K., & Veski, A. (2022). Recent intraplate seismicity in Estonia, East European Platform. Seismological Research Letters, 93, 1800–1811. https://doi.org/10.1785/0220210277
30. Solano Acosta, J.D., Soesoo, A., Hints, R., & Sula, C. (2025). Oxidised rapakivi magmatism and crustal architecture in the earliest AMCG suite: Geochemical and geophysical insights from Estonian intrusions along the Paldiski–Pskov Shear Zone (PPDZ), Wiborg-Suite Complex, Fennoscandia. 5th International Professional Geology Conference (IPGC 2025), Zaragoza. https://doi.org/10.48726/1mv94-7qc33
31. Soesoo, A., Nirgi, S., Urtson, K., & Voolma, M. (2021). Geochemistry, mineral chemistry, and pressure-temperature conditions of the Jõhvi magnetite quartzites and magnetite-rich gneisses, NE Estonia. Estonian Journal of Earth Sciences, 70(2). https://doi.org/10.3176/earth.2021.05
32. Plado, J., Kiik, K., Jokinen, J., & Soesoo, A. (2020). Magnetic anomaly of the Jõhvi iron ore, northeastern Estonia, controlled by subvertical remanent magnetisation. Estonian Journal of Earth Sciences, 69(4), 189–199. https://doi.org/10.3176/earth.2020.13
33. Kivisilla, J., Niin, M., & Koppelmaa, H. (1999). Catalogue of chemical analyses of major elements in the rocks of the crystalline basement of Estonia. Eesti Geoloogiakeskus. https://kirjandus.geoloogia.info/en/reference/21247
34. Kähkönen, Y. (2005). Svecofennian supracrustal rocks. In Developments in Precambrian Geology, Vol. 14, 343–405. https://doi.org/10.1016/S0166-2635(05)80009-X
35. Kukkonen, I.T., & Lauri, L.S. (2009). Modelling the thermal evolution of a collisional Precambrian orogen: high heat production migmatitic granites of southern Finland. Precambrian Research, 168, 233–246. https://doi.org/10.1016/j.precamres.2008.10.004
36. Kara, J. (2021). Evolution of the Svecofennian Bedrock in Southern Finland – Spatial and temporal changes in the mantle-derived magmatism and mantle-crust interaction. Doctoral thesis, University of Turku. http://urn.fi/URN:ISBN:978-951-29-8474-9
37. Pirajno, F., & Santosh, M. (2015). Mantle plumes, supercontinents, intracontinental rifting, and mineral systems. Precambrian Research, 259, 114–142. https://doi.org/10.1016/j.precamres.2014.12.016
38. Rämö, O.T., & Haapala, I. (2005). Rapakivi granites. In Developments in Precambrian Geology, Vol. 14, 533–562. https://doi.org/10.1016/S0166-2635(05)80013-1
39. Grabarczyk, A., Wiszniewska, J., Krzemińska, E., & Petecki, Z. (2023). A new A-type granitoid occurrence in southernmost Fennoscandia: geochemistry, age, and origin of rapakivi-type quartz monzonite from the Pietkowo IG1 borehole, NE Poland. Mineralogy and Petrology, 117(1), 1–25. https://doi.org/10.1007/s00710-022-00799-7
40. Bonin, B. (2007). A-type granites and related rocks: evolution of a concept, problems and prospects. Lithos, 97, 1–29. https://doi.org/10.1016/j.lithos.2006.12.007
41. Karell, F., Ehlers, C., Airo, M.-L., & Selonen, O. (2009). Intrusion mechanisms and magnetic fabrics of the Vehmaa rapakivi granite batholith in SW Finland. Geotectonic Research, 96, 53–68. https://doi.org/10.1127/1864-5658/09/96-0053
42. Nordbäck, N., Skyttä, P., Engström, J., Ovaskainen, N., Mattila, J., & Aaltonen, I. (2024). Mesoproterozoic strike-slip faulting within the Åland rapakivi batholith, southwestern Finland. Tektonika, 2(1), 1–26. https://doi.org/10.55575/tektonika2024.2.1.51
43. Valkama, M., Sundblad, K., Nygård, R., & Cook, N. (2016). Mineralogy and geochemistry of indium-bearing polymetallic veins in the Sarvlaxviken area, Lovisa, Finland. Ore Geology Reviews, 75, 206–219. https://doi.org/10.1016/j.oregeorev.2015.12.001
44. Rasilainen, K., Lahtinen, R., & Bornhorst, T.J. (2007). The Rock Geochemical Database of Finland: Manual. Geological Survey of Finland.
45. Klein, V., Konsa, M., & Niin, M. (1994). On mineralogy of the porphyraceous potassium granites of small massifs in the northern Estonian basement. Proceedings of the Estonian Academy of Sciences: Geology, 43(4), 165–176. Estonian Academy Publishers. https://doi.org/10.3176/geol.1994.4.01

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This article has been published in European Geologist journal 60 – 5th IPGC Special Edition 1