The ~1.62 Ga Märjamaa and Kloostri rapakivi intrusions of western Estonia record a tripartite magmatic evolution during the late stages of the Wiborg rapakivi suite, emplaced in a transtensional pull-apart setting related to shear-zone reactivation during Nuna breakup and constructed through piston cauldron-subsidence processes. Whole-rock major-element geochemistry, complemented by CIPW normative phase relations, is used to constrain melt evolution, redox conditions, and crystallization patterns across three magmatic phases. Phase I formed as a deeply rooted intrusion that evolved into a piston cauldron structure through roof collapse and block assimilation, and comprises ferroan granodioritic to quartz-monzonitic compositions with lower silica and alkalis and elevated Ca and Fe–Ti–P-bearing components, reflecting relatively less evolved melts. Phase II intruded as a concentric granite ring during continued subsidence and represents the most fractionated stage, characterized by higher silica and alkalis, pronounced Ca depletion, and minimal normative Fe–Ti oxides and apatite. Phase III corresponds to the late Kloostri body emplaced by asymmetric subsidence and represents a Na-rich leucogranitic melt with the highest silica contents and the lowest abundances of Ca-bearing, Fe–Ti-bearing, and P-bearing components. Progressive differ entiation from Phase I to Phase III is reflected by systematic Fe-Mg trends, whereas redox conditions are more robustly constrained by iron speciation, indicating reduced conditions in Phase II, intermediate values in Phase I, and more oxidized conditions in Phase III. Decreasing normative Fe–Ti oxides from Phase I to Phase III primarily reflect progressive differentiation rather than solely oxygen-fugacity variations, emphasizing the semi-quantitative nature of redox constraints derived from major-element data. Theoretical thermobarometric estimates indicate mid-crustal crystallization at ~3–5 kbar with progressive cooling from Phase I to Phase III.

The supplementary material is designed to provide complementary figures and plots enhancing the geochemical distribution patterns described in this research.

The similar to 1.62 Ga buried M & auml;rjamaa and Kloostri rapakivi granitoids in western Estonia consist of three magmatic phases. This study utilizes processed Bouguer gravity and magnetic anomaly data to model the internal architecture and emplacement geometry of the granitic bodies, testing how inherited crustal structures influenced these processes within the context of the Mesoproterozoic Anorthosite-Mangerite-Charnockite-Granite (AMCG) magmatism in Fennoscandia. Potential-field data were processed through spectral separation and derivative filters (TDR, TDX, AS), complemented by lineament extraction and density mapping. A cross-gradient joint inversion using the SimPEG Python module, conducted down to 10 km, delineates three-dimensional density and susceptibility contrasts. Potential lineaments align with Riedel shear patterns along the NW-trending, dextral-oblique & Aring;land-Paldiski-Pskov Deformation Zone (PPDZ), indicating transtensional pull-apart reactivation that focused magma ascent and suggesting that 1.6-1.4 Ga AMCG rapakivi granites and coeval basins formed through reactivation of Svecofennian fabrics. Phase I rooted deeply, formed as a steep-sided tabular granodiorite body that evolved into a piston-cauldron structure through roof collapse and block assimilation, producing positive magnetic and Bouguer anomalies. Phase II intruded as a surrounding granite ring during continued subsidence, associated with negative gravity anomalies. Phase III represents a late-stage trachytic Kloostri leucogranite emplaced by asymmetric subsidence, characterized by positive magnetic and negative Bouguer signatures. The phases were placed during the final stages of the first Fennoscandian rapakivi AMCG event (i.e. Wiborg suite), driven by asthenospheric upwelling and mafic underplating from superswell activity, within Nuna's breakup configuration. Overall, the results support a crustal structure-controlled emplacement in which shear-zone reactivation affect the geometry of the Fennoscandian rapakivi intrusions.

This study combines geochemical, structural, and geophysical data to constrain the geometry, tectonic controls, and petrogenetic evolution of Estonian rapakivi intrusions within the first Wiborg Suite.

This research explores the geochemistry of Paleoproterozoic metasedimentary and metavolcanic units in the Alutaguse region of North Estonia and the South Svecofennian (SS) zones, including Ladoga, Saimaa, Häme Belt, and Uusimaa Belt, to better understand the tectonic evolution of the Svecofennian Orogeny in Eastern Fennoscandia. Metasedimentary units consist of micaceous gneisses (± Grt ± Crd ± Sil), while metavolcanics include amphibolites and pyroxenic gneisses. Historical and new data show that High-SiO₂ (>63 wt%) metasediments have felsic origins similar to the Upper Continental Crust (UCC), whereas Low-SiO₂ (≤63 wt%) metasediments, resembling graywackes and shales, indicate mafic to intermediate origins similar to post-Archean Australian Shale (PAAS). Various weathering indices, including CIA, PIA, CIW, and ICV for metasediments, and AI, CCPI, WIP, and SI for metavolcanics, were applied to reveal these geochemical trends. The metavolcanics are classified as sub-alkaline, with geochemical signatures pointing to asthenospheric mantle origins for Alutaguse and subducted oceanic crust origins for SS. Tectonic affinity analyses indicate a predominant oceanic arc setting across both regions. High CaO and MnO concentrations in Alutaguse and Uusimaa metasediments suggest a genetic link, positioning Alutaguse as a 1.90–1.89 Ga back-arc to the Uusimaa belt, followed by the accretion of Uusimaa and Häme belts around 1.87 Ga, marking the closure of the Svecofennian ocean. The Alutaguse zone likely developed as a back-arc to the Tallinn-Uusimaa belt after the accretion of the Bergslagen microcontinent. This interpretation is supported by geophysical anomalies correlated with Zn-Pb-Fe mineralisation. The assemblages found in Alutaguse province comprises high proportions of highly deformed sulphides (pyrite, pyrrhotite, arsenopyrite) and sphalerite disseminated in graphitic amphibolitic-gneisses, which shows similarities with Bergslagen's VMS (SEDEX?) provinces and warrants further investigation. Figure 1. Crustal structure in the central and southern parts of the Svecofennian orogen as integrated across the Baltic Sea, after Bogdanova et al. (2015) and Geochemical relations from the Alutaguse and SS metasedimentary units include major elemental tectonic discriminant functions.

This research focuses on the geochemical analysis of Paleoproterozoic metasedimentary and metavolcanic units in the Alutaguse region of northern Estonia, shedding light on the geodynamic evolution during the Svecofennian orogeny in eastern Fennoscandia. The metasedimentary units consist of micaceous gneisses (+/- Grt +/- Crd +/- Sil), and the metavolcanic units include amphibolites and pyroxenic gneisses. Geochemical analyses utilized both historical and new whole-rock geochemical data. Weathering indices indicated their applicability for provenance studies and tectonic setting analyses. Metasediments are classified by their silica content: high-SiO2 (>63 wt%) metasediments resemble litharenites, implying higher maturity and felsic origins akin to the upper continental crust reference; low-SiO2 (<63 wt%) metasediments align with graywackes and shales, indicative of mafic to intermediate origins, similar to the post-Archean Australian shale, with TiO2-Ni suggesting sedimentary trends. Discriminant tectonic parameters associated these metasedimentary groups with a continental rift domain. Total alkali-silica classified the metavolcanics as subalkaline units. Geochemical ratios, such as La/Yb vs. Zr/Nb and La/Sm vs. Sm/Yb, crossing the spinel-lherzolite trend, were closest to the primitive mantle reference. The Th/Nb and Th/Zr ratios revealed asthenospheric mantle origins for the basaltic magma sources in Alutaguse. Tectonic settings derived from Y/15-La/10-Nb/8 and TiO2-10(MnO)-10(P2O5) ratios suggested a predominant oceanic arc affinity. It is proposed here that the Alutaguse structural zone developed as the back-arc of the Tallinn-Uusimaa belt(s), following the accretion of the Bergslagen microcontinent at 1.9-1.87 Ga, concluding with the closure of the paleo-Svecofennian ocean.

Titanium-containing minerals serve a variety of industrial applications. Iron and titanium oxides, ilmenite (Fe2+TiO3), pseudorutile (Fe23+Ti3O9), and rutile/anatase (TiO2) are notably used in the production of paint, plastic and paper pigments; moreover, titanium metal is considered as a Critical Raw Material (CRM). Grande Côte Operation (GCO), a subsidiary of Eramet, has been operating the Senegalese Grande Côte heavy minerals (HM) placers for zircon and Fe-Ti oxides since 2014. Senegal's placer deposits extend over 100 km in length and 5 km in width and lie alongside the country's north coast. These Quaternary ore-bodies resulted from the erosion of the Mauritanian belt and repetitive episodes of marine transgression and regression, as well as from aeolian dune formations, leading to significant heterogeneity. Related distribution trends in impurities and heavy minerals are yet not anticipated or understood.This study explores the mineralogical heterogeneities to investigate variations in terms of the distribution and alteration of the titanium-bearing phases. Ten drill cores were selected to investigate three synthetic profiles based on high-resolution sampling. Heavy minerals from composite samples were recovered using dense liquid. The obtained concentrates were prepared as representative thick sections for textural analysis. Semi-quantification investigations were conducted by means of QEMSCAN® analyses.The heavy minerals content was not related to sand facies or depth, and the average concentration ranged from 0.1% to 4.2%, with an average of 0.9. From the concentrate, it could be inferred that Fe-Ti phases represented 14.4% for ilmenite, 57.1% for pseudorutile, 1.8% for anatase and 3.7% for rutile. Pseudorutile was the predominant phase, indicating an advanced alteration. A decrease in ilmenite/pseudorutile ratio was observed with increasing depth in all profiles.Based on these findings, the alteration rate in the ilmenite series was investigated by adding a finely spaced range of Fe/Ti ratios and impurities content (mainly Al) to the QEMSCAN® database. The weathering process is initiated by the oxidation of Fe2+ into Fe3+, progressively leading to the formation of pseudorutile, marked by grains with cracking patterns due to topotaxial reactions. The following stage is driven by iron-lixiviation and implies hydroxylian pseudorutile apparition due to intense hydration and hydroxylation processes. Dissolution and reprecipitation reactions led to a final alteration, creating highly Ti-enriched, impurities-rich and porous grains. The evolution with depth of the coefficient of variation between the content of Fe-Ti phases illustrated an authigenic Ti-enrichment. A substantial drop (-40%) in unaltered ilmenites was observed at surface levels. A downward enrichment of pseudorutile proportion (5 to 10%) was observed up to 13m, where the sharp increase (up to 40%) in Ti-rich phases correlates to the water-table depth above 18m, advanced alteration led to the transformation of almost all ilmenite phases into pseudorutile.QEMSCAN® analyses contributed to a better understanding of the Grande Côte placer deposits, highlighting the significance of spatial variability and local water table settings for Fe-Ti oxide distribution and alteration processes, allowing a first ore body modelling and a global assessment of HM content.

Determining the local versus global influence on the metallogeny of redox-sensitive trace-metal-enriched black shales remains challenging despite extensive geochemical research in related topics. A set of local triggers or modifiers of syngenetic metal enrichment, still poorly understood, impedes the ability to adequately predict the potential distribution of metal resources. This study of the Lower Ordovician T & uuml;risalu Formation examines the stratigraphic trends of Mo and U isotopes in Mo-U-V hyper-enriched thin transgressive black shales and associated beds from the inner shelf of the Baltic Palaeobasin (Aseri PH012B drillcore, NE Estonia) to reveal underlying connections between isotopic fractionation, palaeoenvironmental changes, and metal enrichment processes. Twenty samples from the basal 28-cm-thick Unit I and overlying 66-cm-thick Unit II were analysed by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and interpreted within a recently developed high-resolution chemostratigraphic framework. The tested samples yielded variable delta 98Mo (from -0.89 to +2.03 %o) and delta 238U values (from -0.27 to +0.52 %o). Unit I, which is Mo-enriched, yielded the highest delta 238U and lowest delta 98Mo values, whereas Unit II, which is U-enriched, is marked by sharply lower delta 238U values. This black shale succession was deposited under a prolonged sea-level transgression. Variations in delta 98Mo and delta 238U suggest that the mechanism of Mo and U sequestration changed depending on facies during the transgression. Metal enrichment was influenced by a combination of ultra-slow sedimentation rates (0.6-1.0 mm kyr- 1), relative sea-level changes, and shallow redox stratification maintained in part by surface heating under a super-greenhouse climate. Extremely slow sedimentation prolonged seawater-sediment interactions, facilitating diffusion-controlled uptake of U and Mo under euxinic conditions. Landward expansion of the subpycnoclinal oxygen-depleted watermass and related redox shifts from suboxic to euxinic conditions near the seafloor drove the selective hyper-enrichment of Mo, and U. Isotopic trends highlight efficient Mo sequestration in euxinic settings likely aided by recycling of Fe-Mn near redoxcline and U hyper-enrichment under Mo-depleted watermasses.

The importance of rare earth elements (REEs) in high-tech industries and the growing demand for raw materials have spurred interest in exploring unconventional deposits. Sedimentary phosphorite deposits are among the most prospective, with REE extraction as a P by-product. However, these ores are highly diverse regarding ΣREE content, distribution, and nature of phosphatic materials. This study focuses on the Estonian phosphorites of the Baltic paleobasin, which constitute one of Europe's largest phosphate rock reserves and are characterised by phosphatic shell fragments deposited in nearshore settings. Geochemical investigations were conducted on carbonate-cemented phosphorites from Toolse and Aseri deposits. The determination of REE distribution and uptake mechanisms within apatites and carbonates was addressed by LA-ICP-MS in situ imaging technique developed by Drost et al. (2018), which allows identification and discrimination of mineral phases by integrating semiquantitative compositional data through the stepwise elemental distribution. Diagenetic enrichment stages were assessed using the following pathfinder elements as pooling channels: Sr and U. Shelly apatites have homogenous REE-distribution patterns, MREE-enriched up to 15-fold compared to the PAAS, with positive Y and Ce anomalies indicative of an early digenetic overprint traceable by the Sr distribution. The average REE content in studied apatite is 2149ppm. However, the extent of diagenetic overprint and enrichment varies locally. In Toolse, shells show lesser recrystallised textures, and the Sr- and U-depleted stages allow the tracing of pristine signals prior to deposition. In Aseri, U-sorting reveals a second, alteration-driven enrichment in which fragment edges present a ΣREE up to 7020ppm. This alteration stage is less pronounced in Toolse, where REE content reaches only 4150ppm. The distinction between Sr and U-driven enrichment is less evident due to the lower input of hydrogenic or lithogenic REE carriers. The carbonates from both localities were found to be REE depleted compared to PAAS. Based on these observations, the compositions of the apatite species could be distinguished and modelled to characterise the deposit. The diagenetic enrichment of REE was mainly driven by the upwelling of nutrient-rich waters, Fe and Mn-(oxyhydr)oxide reductive desorption, and secondary phosphatisation and homogenisation of shells. Fluctuations of redox gradients and Fe-Mn cycles led to slight local REE variability. Developing euxinic conditions and lithogenic input endorsed a later alteration-driven uptake, resulting in highly REE-rich edges. Despite differences in enrichment level, the two deposits' REE distribution patterns are similar. Main REEs are Ce (33%), Y (21%), La (12%), Nd (16%) and Dy (3%), and are considered among the most critical elements. On average, U concentrations are 92ppm in Aseri and 31ppm in Toolse, and toxic elements (Cd, Zn, Th) are found in trace amounts. The study introduces a combined technique based on LA-ICP-MS and empirical distribution function data analyses as a powerful, accurate, cost-effective tool for determining REE distributions. It allows visualisation at different scales, representative measurements and a first approach to semi-quantifying elements. The method could provide insights into factors that control genesis in low-grade sedimentary ores and determine their potential valorisation routes.

The changes in the thermal behavior of shelly phosphorite ore from Toolse deposit along the drill-core PH014B (depth 21.1–26.7 m) cut into sub-samples with a length of 0.1 m have been studied. The primary phosphorus-bearing mineral in Estonian phosphorite is fluorcarbonate apatite (francolite) originated from lingual brachiopod shells which during the following millions of years of deposition has partially transformed into fluorhydroxyl apatite. The experiments on a Setaram Labsys Evo 1600 thermoanalyzer coupled with Pfeiffer Omnistar Mass Spectrometer were carried out under non-isothermal conditions at the heating rate of 10 °C min−1 up to 1200 °C in an oxidizing atmosphere containing 79

Global WGM-12 gravity data and EMAG2v3 magnetic data were used to give new information of the Estonian crust. The Estonian Precambrian crystalline basement, composed of Paleo-Meso Proterozoic metamorphic and igneous rocks, is covered by a Paleozoic sedimentary rock deposit 100 – 800 m thick. To visualise crustal layers of the Estonian basement, we employed spectrum analysis of magnetic and gravity data. The gravimetric data was used to identify the depth of the Moho and Conrad discontinuities. The magnetic data has been evaluated to calculate the Curie point depth (CPD), which was then utilized to predict heat flow values over the study area. The subsurface of Estonia is divided into six petrological-structural zones: Tallinn, Alutaguse, Jõhvi, West-Estonian, Tapa and South-Estonian. Potential lineaments in each zone delineates a NW-SE trend. In order to assess the structural variations of the crust over Estonia, different profiles are presented showing contrasting values of potential field, CPD and heat flow, particularly in the Precambrian Rapakivi granitic plutons and the Paldiski-Pskov deformation zone. The depth of the Curie point reveals a mean value of 15 km, while the depth of the Moho suggests a mean value of 60 km, while the mean depth of the Conrad discontinuity is around 18 km.

Tremadocian highly metalliferous black shales and associated grey shales from the Aseri PH012B drill core (NE Estonia) in the innermost part of the Baltic Palaeobasin were targeted to record their nitrogen and organic carbon isotope variance combined with the total organic carbon and total nitrogen record. The obtained molar C/N ratios of black shales from 26 to 52 indicate a considerable loss of N compared to primary biomass. The recorded δ15N values from –2.5 to 0.2‰ likely evolved due to isotopic fractionation related to N2 fixation by primary producers, superimposed by later anoxic ammonium oxidation processes within the uppermost sediments. The high net primary productivity, which controlled the accumulation of organic-rich shallowwater complexes, was fuelled by the internal cycling of P in the sea basin and combined with intensive N exchange between marine and atmospheric pools.

Sedimentary phosphorites in Cambrian-Ordovician boundary beds in Estonia are among Europe's most extensive phosphate rock reserves, with a tonnage of approximately three billion tonnes. In addition, they are potential sources of rare earth elements and yttrium (REE + Y). The ore consists of sandstone rich in phosphatic brachiopod fragments deposited in a shallow marine peritidal environment of the Baltic Paleobasin. A detailed geochemical and mineralogical investigation was conducted on the northern part of the Toolse deposit based on three drill core cross-sections. The REE sequestration model was developed based on the correlation of the sedimentary facies of the members of the Kallavere formation. Analyses were conducted on 140 whole-rock samples and 14 discrete black shale samples. Inductively coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence (XRF) and X-ray diffraction (XRD) measurements were performed for each sample. Textural analyses were conducted with field-emission scanning electron microscopy (FE-SEM), and quantitative wavelength dispersive spectrometer (WDS) analysis of major and trace elements was performed with an emission electron probe microanalyser (EPMA). The PAAS normalised REE + Y patterns were relatively homogeneous throughout the deposit except for the cerium and yttrium contents. The REE + Y contents of the phosphorites indicate a distinctive 'bell-shaped' pattern enriched with middle-REE (MREE) enriched. In the lower part of the deposit, the FREE + Y concentration is enriched up to 12-fold, compared to the average shale, reaching up to 1234 ppm. LREE enrichment is observed in these horizons, with a 9-fold peak at neodymium. In terms of absolute values, the most prevalent REEs are, in order, Ce, Y, Nd, and La, which respectively reach maximum mean values of 296 ppm, 248 ppm, 164 ppm and 135 ppm. The profiles indicate multistage uptake during transport, deposition, and early diagenesis of brachiopod detritus. The sedimentation was associated with a steep redox gradient in the porewater in a coastal environment during the beginning of marine transgression. The near-shore upwelling of oxygen-poor deeper water rich in dissolved nutrients and Mn, combined with the input of lithogenic Fe, helped create favourable conditions for REE sequestration. Positive Y anomalies indicate an initial uptake of REE + Y by hydroxyapatite through Ca substitution in an oxic environment near the sediment-water interface. The sediment burial induced the formation of carbonate fluorapatite (CAF) and a shift to the REE adsorption uptake mechanism, reinforced by the significant intercrystalline porosity of the shells. The transition to a suboxic environment below the surface layers resulted in the reductive dissolution of Mn-(oxyhydr)oxides and the release of LREE in the porewater system, resulting in an overprint of the original REE pattern to the point of inducing positive Ce anomalies. A late enrichment in MREE occurred during early diagenesis as a result of desorption of REE from the Fe-(oxyhydr) oxides and organic-rich particles under relatively anoxic conditions.

Furongian-Tremadocian phosphorites of Estonia are sandstone rich in biogenic apatite, repre-sented by brachiopod detritus. The study focuses on the mineralogical and micro-analytical characterisation of phosphorites from the Aseri, Toolse, and Kabala deposits based on FE-SEM and EPMA analyses. The shell fragments are composed of alternating compact and porous laminae, but with considerably poor preservation of pristine textures, superseded by the formation of authigenic CAF-apatite during the early diagenesis. In all settings, the shells showed preferential uptake of Sr into the porous cryptocrystalline laminae. The altered areas are composed of massive apatite crystallites with Mn-enriched layers. They are frequently covered with pyrite, indicating progressive recrystallisation under the influence of interstitial fluids and fluctuations in redox gradients in coastal environments.

The essential role of the fine mineral fraction in V hyper-enrichment in black shales has been suggested in previous studies; however, 'the operational details' of such metallogenic systems remain poorly understood. This study addresses the syngenetic enrichment pathways of V in black shales from the Lower Ordovician in the inner shelf of the Baltic Palaeobasin, showing very high content of redox-sensitive elements, including that of V. X-ray fluorescence spectroscopy (XRF) and organic element analysis (CHNS-O), combined with bivariate and multi-variate data analyses, were employed to analyse high-resolution geochemical profiles (> 360 samples) of ther-mally immature black and grey shales, as well as black shale containing siltstones, from two drill cores from NE Estonia. The detected V (up to 2300 ppm), Mo (up to 4500 ppm), and U (up to 500 ppm) enrichment lacked well-defined co-variance, indicating a complex redox environment and element-specific enrichment pathways. While the maximum V and Mo concentrations were confined to the basal part of the black shale-black shale complex, V hyper-enrichment was also observed in the Mo-U-poor black shale interbeds in the siltstones. Co-variance ana -lyses in metalliferous horizons revealed strong positive relationships between V and organic matter, Al, Ti, and K. Cr, characterised by a high affinity for natural sorbents, demonstrated an almost perfect correlation with V (r = similar to 95), despite its low concentrations. These patterns are hypothesised to reflect V capture via reduced V(IV)-organic complexes adsorbed to fine clay particles after reduction of V(V) in the seawater column rich in dis -solved organic matter. These data suggest that the specific surface area of clay particles acted as the primary limiting parameter for V capture, and the particle flux to the shallow sea bottom defined the degree of V hyper-enrichment in the studied settings.

Lower Paleozoic black shales from Estonia, Sweden, and Russia were analyzed for major and trace elements to reconstruct the provenance, tectonic setting, and paleoweathering conditions of these shales. The black shale is highly enriched in U, V, Mo, and Pb (except in samples from Sweden where Pb is slightly enriched), slightly enriched in SiO2, Fe2O3, K2O, and TiO2 and highly depleted in CaO, Na2O, and MnO, with respect to average shales. The provenance signatures (Th/Sc versus Zr/Sc, Al2O3 versus TiO2, Zr versus TiO2 plots, and Zr/Sc ratio) of the Baltoscandian black shales suggest that they were derived from rocks of intermediate to felsic composition and from recycled sediments. The likely provenance region was the Paleoproterozoic igneous and metamorphic basement of southern central and southern Finland, which consists predominantly of felsic to intermediate metamorphic (acidic to intermediate gneisses, felsic volcanics, microcline granites and migmatites) and igneous rocks (small granitic intrusions and large rapakivi granite intrusions), and reworked older Ediacaran and Lower Cambrian sediments; however, the proportion of clastic input from these sources is not uniform in the three regions studied. The discrimination of the tectonic settings of source materials of the black shale using the SiO2 versus K2O/Na2O plot and a new discriminant method (APMdisc) favors a passive margin setting. The Chemical Index of Weathering (CIW) indicates that the clastic material in the black shale of the studied regions has experienced an intense degree of chemical weathering. Weathering indices (Chemical Index of Alteration CIA and CIW) also show that the black shale has experienced significant secondary potassium enrichment.