Long-Lived Mantle Plume and Polyphase Evolution of Palaeoproterozoic PGE Intrusions in the Fennoscandian Shield

The NE Fennoscandian Shield comprises the Northern Belt in Finland and the Southern Belt in Karelia. They host mafic-ultramafic layered Cu-Ni-Cr and Pt-Pd-bearing intrusions. Precise U-Pb and Sm-Nd analyses indicate the 130-Ma evolution of these intrusions, with major events at 2.53, 2.50, 2.45, and 2.40 Ga. Barren phases were dated at 2.53 Ga for orthopyroxenites and olivine gabbro in the Fedorovo-Pansky massif. PGE-bearing phases of gabbronorites (Pechenga, Fedorovo-Pansky, Monchetundra massifs) and norites (Monchepluton) are 2.50 Ga old. Anorthosites of Mt. Generalskaya (Pechenga), the Fedorovo-Pansky, and Monchetundra massifs occurred at 2.45 Ga. This event produced layered PGE-bearing intrusions in Finland (Penikat, Kemi, Koitelainen) and mafic intrusions in Karelia. The Imandra lopolith dikes occurred at the final phase (2.40 Ga). Slightly negative εNd and ISr values (0.703–0.704) suggest that intrusions originated from an enriched mantle reservoir. Low 3He/4He ratios in accessory minerals (ilmenite and magnetite) indicate an upper mantle source. Large-scale correlations link the Fennoscandian Shield with the Superior and Wyoming cratons.


Introduction
The NE Fennoscandian (Baltic) Shield covers the Archaean crust formed at 3.5-2.7 Ga [1,2].The post-Archaean evolution is mainly reflected in rifting and emplacement of mafic-ultramafic complexes along NE-trending structures.The NE Baltic Shield hosts the Southern (Fenno-Karelian) Belt (FKB) and the Northern (Kola) Belt (KB) that we studied in detail in our profound research [3].
KB strikes northwestwards for over 500 km.It borders the SW edge of the Archaean Kola-Norwegian Block and the Northern and Southern edges of the Palaeoproterozoic Pechenga-Imandra-Varzuga rift.There are several layered mafic-ultramafic bodies [7].Layered PGE-bearing pyroxenite-norite-gabbro-anorthosite intrusions occur at the boundaries between early Proterozoic rifts lying over the Archaean basement [9,10].
The purpose of this work is a complex study of Palaeoproterozoic Pt-Pd and Cu-Ni intrusions that are widespread in the NE Baltic Shield.We use a set of isotope techniques to define precision ages of formation of reefs, lower and upper parts of layered intrusions, host rocks, and cutting dyke series.We also aimed at studying sources of primary magmas and primary reservoirs.The main objective of this research is to compare new isotope data with those on other Palaeoproterozoic intrusions of the Finnish group, Northern America, and Canada.This would corroborate the model of the plume mantle source for all Palaeoproterozoic intrusions.
The current study continues our investigations [3], but substantiates it with new isotope geochronological data.It allowed us to define that PGE-bearing intrusions of the Fennoscandian Shield referred to the enriched mantle reservoir EM-1.This paper provides new data showing that magmatism in the Kola-Karelian Province correlates with the peak of mafic-ultramafic magmatism in the Superior and Wyoming provinces (2.45 Ga).
The purpose of this work is a complex study of Palaeoproterozoic Pt-Pd and Cu-Ni intrusions that are widespread in the NE Baltic Shield.We use a set of isotope techniques to define precision ages of formation of reefs, lower and upper parts of layered intrusions, host rocks, and cutting dyke series.We also aimed at studying sources of primary magmas and primary reservoirs.The main objective of this research is to compare new isotope data with those on other Palaeoproterozoic intrusions of the Finnish group, Northern America, and Canada.This would corroborate the model of the plume mantle source for all Palaeoproterozoic intrusions.
The current study continues our investigations [3], but substantiates it with new isotope geochronological data.It allowed us to define that PGE-bearing intrusions of the Fennoscandian Shield referred to the enriched mantle reservoir EM-1.This paper provides new data showing that magmatism in the Kola-Karelian Province correlates with the peak of mafic-ultramafic magmatism in the Superior and Wyoming provinces (2.45 Ga).

Geological Setting
The Palaeoproterozoic East Scandinavian Large Igneous Province (LIP) occurs in the NE Fennoscandian Shield (Figure 1).Its granulite and gneiss-migmatite basement originated at >2550 Ma.This province had several stages of magmatism and sedimentation separated by breaks (conglomerates).The Sumian stage (2550-2400 Ma) was crucial for the production of Pt-Pd ores [9,10].In FKB, the magmatism was most active at 2450 to 2400 Ma [4,[10][11][12][13][14][15][16].In KB, PGE-bearing intrusions formed at 2530-2450 Ma.The Fedorovo-Pansky Layered Complex strikes northwestwards for >60 km and dips Southwestwards at an angle of 30-35° (Figure 2).The Fedorov, Lastjavr, Western and Eastern Pansky are its major blocks [9].This complex is bordered by the Archaean Keivy terrain and the Palaeoproterozoic Imandra-Varzuga rift.In the North, the complex borders alkaline granites of the White Tundra intrusion.Their U-Pb age on zircon is 2654 + 15 Ma [17].The contact of the Western Pansky Block with the Imandra-Varzuga volcano-sedimentary sequence mostly has Quaternary deposits.However, drill and excavation works to the South of Mt.Kamennik reveal a strongly sheared and metamorphosed contact between the intrusion and overlying Palaeoproterozoic volcano-sedimentary rocks.The Fedorovo-Pansky Layered Complex strikes north-westwards for >60 km and dips Southwestwards at an angle of 30-35 • (Figure 2).The Fedorov, Lastjavr, Western and Eastern Pansky are its major blocks [9].This complex is bordered by the Archaean Keivy terrain and the Palaeoproterozoic Imandra-Varzuga rift.In the North, the complex borders alkaline granites of the White Tundra intrusion.Their U-Pb age on zircon is 2654 + 15 Ma [17].The contact of the Western Pansky Block with the Imandra-Varzuga volcano-sedimentary sequence mostly has Quaternary deposits.However, drill and excavation works to the South of Mt.Kamennik reveal a strongly sheared and metamorphosed contact between the intrusion and overlying Palaeoproterozoic volcano-sedimentary rocks.
The authors had earlier studied the Fedorovo-Pansky massif using a full set of geological, mineralogical, petrographical, and geochemical methods [3].This allowed us to identify the block structure of the massif and define zones with different composition, age, and mineralization.Provided below is a compilation of previously obtained data [3] and results of this study.The authors had earlier studied the Fedorovo-Pansky massif using a full set of geological, mineralogical, petrographical, and geochemical methods [3].This allowed us to identify the block structure of the massif and define zones with different composition, age, and mineralization.Provided below is a compilation of previously obtained data [3] and results of this study.
The Fedorov Block is a part of the Fedorovo-Pansky Complex.The Layered Lower Horizon (LLH) of its Main Gabbronorite Zone is composed of gabbronorite, norite, pyroxenite and interlayers of leucocratic gabbro and anorthosite, and reef-type PGE deposit.The Upper Layered Horizon (ULH) consists of olivine-bearing troctolite, norite, gabbronorite, and anorthosite.It comprises several layers of PGE-rich ore (Pd > Pt) [9].The U-Pb age of the ULH rocks on single-grain zircon and baddeleyite is 2447 + 12 Ma.This age shows that ULH rocks are the youngest in the Fedorovo-Pansky Complex.
The Fedorov Tundra Block is in the West of the Fedorovo-Pansky massif.It contains mafic and rare ultramafic rocks, mostly gabbronorites with highly heterogeneous mineral grains.The contacttype Cu, Ni, and PGE mineralization is economically valuable.
There are three mineral types of the sulfide mineralization: pyrrhotite, pyrrhotite-chalcopyrite, and pentlandite-chalcopyrite-pyrrhotite.The latter type is best-valued commercially, since it contains the complex PGE mineralization.

Materials and Methods
The Fedorov Block is a part of the Fedorovo-Pansky Complex.The Layered Lower Horizon (LLH) of its Main Gabbronorite Zone is composed of gabbronorite, norite, pyroxenite and interlayers of leucocratic gabbro and anorthosite, and reef-type PGE deposit.The Upper Layered Horizon (ULH) consists of olivine-bearing troctolite, norite, gabbronorite, and anorthosite.It comprises several layers of PGE-rich ore (Pd > Pt) [9].The U-Pb age of the ULH rocks on single-grain zircon and baddeleyite is 2447 + 12 Ma.This age shows that ULH rocks are the youngest in the Fedorovo-Pansky Complex.
The Fedorov Tundra Block is in the West of the Fedorovo-Pansky massif.It contains mafic and rare ultramafic rocks, mostly gabbronorites with highly heterogeneous mineral grains.The contact-type Cu, Ni, and PGE mineralization is economically valuable.
There are three mineral types of the sulfide mineralization: pyrrhotite, pyrrhotite-chalcopyrite, and pentlandite-chalcopyrite-pyrrhotite.The latter type is best-valued commercially, since it contains the complex PGE mineralization.
Besides pentlandite, chalcopyrite and pyrrhotite may also host minor PGE, though lower than pentlandite [18], i.e., kotulskite, merenskyite, braggite, stillwaterite, vysotskite, and sobolevskite for palladium; braggite, moncheite, merenskyite, and sperrylite for platinum; and gold-silver alloys for gold [19,20].In total, 29 PGE and gold minerals, as well as eight PGE phases with no status of individual minerals, have been recorded in the ore.Microprobe analyses of their chemical compositions have been conducted in the Geological Institute KSC RAS [20,21].

Isotope Analyses
The U-Pb concordia plot and Sm-Nd isochron methods are applied to define the age of crystallization of the rocks.U-Pb zircon and baddeleyite ages for the same sample are commonly coherent.They indicate a similar age of the magma crystallization and subsequent transformations.Coordinates of baddeleyites are near the concordia line.However, it is difficult to apply this method due to minor amounts of zircon and baddeleyite grains in these rocks.
Compared to the precise U-Pb systematics with an error of ca.0.1%, the Sm-Nd method is not an accurate geochronometer (error of ca.2-3%).However, it allows defining the crystallization age of mafic rocks using major rock-forming minerals.The method is especially important for dating rocks with syngenetic ore minerals.It has been used to date (2482 ± 36 Ma) the early gabbronorite and second anorthosite (2467 ± 39 Ma) ore bodies in the Fedorovo-Pansky deposit.This deposit is considered to be economically important [33].
Sm-Nd ages of the KB mafic-ultramafic intrusions overlap because of large errors.The estimations are compatible with U-Pb ages obtained on zircon and baddeleyite.They are especially important for marginal fast-crystallizing rocks of the Taxitic Zone within the Fedorovo-Pansky Complex.The ages of early barren orthopyroxenite and gabbro are 2521 ± 42 Ma and 2516 ± 35 Ma (Sm-Nd method) and 2526 ± 6 Ma and 2516 ± 7 Ma (U-Pb method).The ore-bearing norite of the Fedorov Block yields ages of 2482 ± 36 Ma (Sm-Nd method) and 2485 ± 9 Ma (U-Pb method) [34,35].
Importantly, the Sm-Nd method provides valuable petrological and geochemical markers, i.e., εNd(T) and TDM.The εNd value shows a degree of the mantle source depletion, while TDM indicates an approximate age of melt extraction from the mantle protolith [35].

LA-ICP-MS
The distribution of rare and precious metals in sulfide parageneses has been first studied in detail using the laser ablation inductively coupled magma mass spectrometry (LA-ICP-MS).It enables detecting regular patterns of the element distribution with a high degree of accuracy.The results indicate that pentlandite in sulfide parageneses of the Fedorov Tundra deposit has commercially valuable PGE mineralization.
The method of LA-ICP-MS (UP-213 laser, high-resolution Element-XR mass spectrometer with ionization) has been applied to analyze concentrations of Cr, Co, As, Se, Ru, Rh, Pd, Ag, Cd, Sb, Re, Os, Ir, Pt, Au, Tl, Pb, and Bi in sulfides.The following parameters have been accepted for the analysis: crater diameter is 40 µm, impulse frequency of laser radiation is 4 Hz.The samples have been analyzed by blocks, which were prepared using the Element XR software.Standard samples have been measured at the beginning and end of each block.Internal laboratory sulfide standards have been used for analysis.The deviation by calibration standards is 10-20%.Fe has been applied, having quite high concentrations in relation to background values.It occurs in all of the studied samples and is the most homogeneously distributed in phases.
Regional PGE-bearing deposits are represented by the basal and reef-like types.According to modern economic evaluation, the basal type is preferable for mining, even if the PGE content (1-3 ppm) is lower than in reef-type deposits (>5 ppm).Basal deposits are thicker and contain more Pt, Cu, and especially, Ni.
In the Eastern Fennoscandian Shield, the Palaeoproterozoic magmatic activity is associated with the formation of Cu-Ni (±PGE), Pt-Pd (Rh, ±Cu, Ni, Au), Cr, and Ti-V deposits [40,41].The Fedorov deposit is best-valued for PGE (Pt, Pd, Rh), but Ni, Cu, and Au are also economically important [10].Ore-forming magmatic and post-magmatic processes are closely related to the Taxitic Zone gabbronorite of the 2485 ± 9 Ma magmatic pulse.Reef-type deposits (Pt-Pd (±Cu, Ni, Rh, Au) and ore occurrences of the Western Pansky Block (Fedorovo-Pansky Complex) are genetically associated with pegmatoid leucogabbro and anorthosite rich in late-stage fluids.Portions of this magma produce additional injections of ca.2500 Ma, ca.2470 Ma (the Lower, Northern PGE reef) and ca.2450 Ma (the Upper, Southern PGE reef of the Western Pansky Block and PGE-bearing mineralization of Mt.Generalskaya intrusion).These magma injections are quite similar in their prevalence of Pd over Pt, ore mineral composition [9] and isotope geochemistry of the Sm-Nd and Rb-Sr systems.εNd values for these rocks vary from −2.1 to −2.3.This may indicate a single long-lived enriched magmatic source.

Fedorovo-Pansky Massif: U-Pb and Sm-Nd Isotope Data
Several large samples have been selected in the Fedorovo-Pansky Complex for further isotope analyses.Medium-and coarse-grained gabbronorite have been sampled in LLH of the Eastern Kievey area.Three types of zircons (transparent, with a vitreous luster) have been separated [3]: Pan-1, regular bipyramidal-prismatic crystals of up to 120 µm; Pan-2, fragments of prismatic crystals; and Pan-3, pyramidal apices of crystals of 80-100 µm.In immersion view, all the zircons display a simple structure with fine zoning and cross jointing.
The previously obtained data show that the crystallization time of the main gabbronorite phase of LLH is 2491 ± 1.5 Ma, since the upper intersection age is 2491 ± 1.5 Ma (MSWD = 0.05) and the lower intersection is at zero and indicates the loss of Pb (Figure 3a, Table 1) [3,7,44].The same zircon sample has been analyzed at the Royal Ontario Museum laboratory (Canada).It proved slightly older (2501.5 ± 1.7 Ma) [45].
deposit is best-valued for PGE (Pt, Pd, Rh), but Ni, Cu, and Au are also economically important [10].Ore-forming magmatic and post-magmatic processes are closely related to the Taxitic Zone gabbronorite of the 2485 ± 9 Ma magmatic pulse.Reef-type deposits (Pt-Pd (±Cu, Ni, Rh, Au) and ore occurrences of the Western Pansky Block (Fedorovo-Pansky Complex) are genetically associated with pegmatoid leucogabbro and anorthosite rich in late-stage fluids.Portions of this magma produce additional injections of ca.2500 Ma, ca.2470 Ma (the Lower, Northern PGE reef) and ca.2450 Ma (the Upper, Southern PGE reef of the Western Pansky Block and PGE-bearing mineralization of Mt.Generalskaya intrusion).These magma injections are quite similar in their prevalence of Pd over Pt, ore mineral composition [9] and isotope geochemistry of the Sm-Nd and Rb-Sr systems.εNd values for these rocks vary from −2.1 to −2.3.This may indicate a single long-lived enriched magmatic source.

Fedorovo-Pansky Massif: U-Pb and Sm-Nd Isotope Data
Several large samples have been selected in the Fedorovo-Pansky Complex for further isotope analyses.Medium-and coarse-grained gabbronorite have been sampled in LLH of the Eastern Kievey area.Three types of zircons (transparent, with a vitreous luster) have been separated [3]: Pan-1, regular bipyramidal-prismatic crystals of up to 120 μm; Pan-2, fragments of prismatic crystals; and Pan-3, pyramidal apices of crystals of 80-100 μm.In immersion view, all the zircons display a simple structure with fine zoning and cross jointing.
The previously obtained data show that the crystallization time of the main gabbronorite phase of LLH is 2491 ± 1.5 Ma, since the upper intersection age is 2491 ± 1.5 Ma (MSWD = 0.05) and the lower intersection is at zero and indicates the loss of Pb (Figure 3a, Table 1) [3,7,44].The same zircon sample has been analyzed at the Royal Ontario Museum laboratory (Canada).It proved slightly older (2501.5 ± 1.7 Ma) [45].
In the framework of this research, the authors have conducted new measurements using single zircon grains from the main PGE gabbronorite phase from the old collection (Figure 3b, Table 2) and obtained the similar age of 2500 ± 3 Ma.The isotope Sm-Nd data show the age of the same gabbronorite on the main rock-forming minerals and whole-rock is 2487 ± 51 Ma (MSWD = 1.5) [16].
In contrast with the zircon age, the rock-forming minerals originate at the post-magmatic stage.However, considering measurement errors, Sm-Nd ages are suggested to be close to the U-Pb ones.   1 All ratios are corrected for blanks of 0.1 ng for Pb and 0.04 ng for U, mass discrimination 0.17 ± 0.05%. 2 Correction for common Pb has been determined for the age according to [25].
In the framework of this research, the authors have conducted new measurements using single zircon grains from the main PGE gabbronorite phase from the old collection (Figure 3b, Table 2) and obtained the similar age of 2500 ± 3 Ma.The isotope Sm-Nd data show the age of the same gabbronorite on the main rock-forming minerals and whole-rock is 2487 ± 51 Ma (MSWD = 1.5) [16]. 1 Ratios are corrected for blanks of 1 pg for Pb and 10 pg for U, mass discrimination 0.12 ± 0.04%. 2 Correction for common Pb has been determined for the age according to Reference [25].
In contrast with the zircon age, the rock-forming minerals originate at the post-magmatic stage.However, considering measurement errors, Sm-Nd ages are suggested to be close to the U-Pb ones.
Analyses of whole-rock and rock-forming silicate and sulfide minerals from gabbro pegmatite give a Sm-Nd age of 2467 ± 39 Ma, MSWD = 1.8.εNd(T) is negative with −1.4 ± 0.5 (Figure 4a, Table 3).Noteworthy, these ages are quite similar within the measurement error.
Analyses of whole-rock and rock-forming silicate and sulfide minerals from gabbro pegmatite give a Sm-Nd age of 2467 ± 39 Ma, MSWD = 1.8.εNd(T) is negative with −1.4 ± 0.5 (Figure 4a, Table 3).Noteworthy, these ages are quite similar within the measurement error.The U-Pb age is identical to the Sm-Nd one.Hence, we can suggest a very narrow closure temperature in the U-Pb (zircon) and Sm-Nd (rock-forming and sulfide minerals) systematics.The U-Pb age is identical to the Sm-Nd one.Hence, we can suggest a very narrow closure temperature in the U-Pb (zircon) and Sm-Nd (rock-forming and sulfide minerals) systematics.

Content, ppm
Isotope analyses of these samples using the whole rock, pyroxene and plagioclase yield ages that correspond to the respective U-Pb ages on zircon (Figure 6d-f).Table 5 provides a compilation of the previously obtained results [3] and new results of isotope geochemical research.A similar age is obtained from Sm-Nd data on rock-forming minerals of ULH anorthosite, i.e., 2442 ± 74 Ma with slightly negative εNd(T) = −1.8± 0.5, MSWD = 0.24 (Figure 5b, Table 4).The U-Pb zircon age of early barren orthopyroxenite (F-3) from the Fedorov Block (2526 ± 6 Ma) marks the emplacement time (Figure 6a, Table 1).The similar U-Pb age (Figure 6b, Table 1) has also been obtained using zircon from barren olivine gabbro (F-4).Cu-Ni-PGE-bearing taxitic gabbronorites (F-2) from the Fedorov Block (Figure 6c, Table 1) yield a U-Pb age on zircon of 2485 ± 9 Ma [34].Isotope analyses of these samples using the whole rock, pyroxene and plagioclase yield ages that correspond to the respective U-Pb ages on zircon (Figure 6d-f).Table 5 provides a compilation of the previously obtained results [3] and new results of isotope geochemical research.

Fedorovo Tundra Deposit: Trace Element Compositions
Three samples from different areas of the Fedorovo Tundra deposit have been investigated: sample BGF-237-132 from olivine-bearing gabbronorite of the Bolshoy Ikhtegipakhk, samples BGF-487-50.5 and BGF-495-76.5 from gabbronorite of the Pakhkvaraka area.
Mantle normalized diagrams (Figures 7 and 8, Table 6) show ratios of the obtained contents for each measured component normalized to the primitive mantle.Dashed areas indicate dispersion of the obtained results.

Fedorovo Tundra Deposit: Trace Element Compositions
Three samples from different areas of the Fedorovo Tundra deposit have been investigated: sample BGF-237-132 from olivine-bearing gabbronorite of the Bolshoy Ikhtegipakhk, samples BGF-487-50.5 and BGF-495-76.5 from gabbronorite of the Pakhkvaraka area.
Mantle normalized diagrams (Figures 7 and 8, Table 6) show ratios of the obtained contents for each measured component normalized to the primitive mantle.Dashed areas indicate dispersion of the obtained results.
Pentlandite is the main concentrator of Co and PGEs (Pd, Ru, and Pt).Since Pt and Pd are the best-valued commercial minerals of the Fedorovo Tundra deposit, pentlandite can be considered the most important among economic sulfide minerals of this deposit, along with PGMs.However, the abundance of pentlandite is much higher.
Pyrrhotite has a significant content of Cr and PGEs (Ir and Os).Pyrrhotite is the major concentrator of As and Bi.
Chalcopyrite accumulates almost all Ag and a significant proportion of Au.This mineral has high contents of Pb and Rh either.
Se, Re, Sn, and Ta are quite homogeneously distributed in all of the three mineral phases.Pentlandite is the main concentrator of Co and PGEs (Pd, Ru, and Pt).Since Pt and Pd are the best-valued commercial minerals of the Fedorovo Tundra deposit, pentlandite can be considered the most important among economic sulfide minerals of this deposit, along with PGMs.However, the abundance of pentlandite is much higher.
Pyrrhotite has a significant content of Cr and PGEs (Ir and Os).Pyrrhotite is the major concentrator of As and Bi.
Chalcopyrite accumulates almost all Ag and a significant proportion of Au.This mineral has high contents of Pb and Rh either.
Se, Re, Sn, and Ta are quite homogeneously distributed in all of the three mineral phases.9b,c, Table 7).The Sm-Nd isotope ages of rock-forming and sulfide minerals are much coeval to the U-Pb zircon data that suggested a very narrow closure temperature at the time of origination. 1 Ratios are corrected for blanks of 1 pg for Pb and 10 pg for U, mass discrimination of 0.12 ± 0.04%. 2 Correction for common Pb has been determined for the age according to Reference [25].
The whole rock, silicates and sulfides of the Penikat intrusion have a Sm-Nd age of 2426 ± 38 Ma (MSWD = 0.2) (Figure 9a, Table 8).It agrees with the Sm-Nd age of 2410 ± 64 Ma determined for the Penikat intrusion earlier [51].Importantly, sulfide data lie on the isochron as well.It testifies to the coincidence of sulfide formation and the rock crystallization.Table 9 provides compiled isotope data obtained in previous [3] and the current research.  Ratios are corrected for blanks of 1 pg for Pb and 10 pg for U, mass discrimination of 0.12 ± 0.04%. 2 Correction for common Pb has been determined for the age according to Reference [25].
The Sm-Nd isotope ages of rock-forming and sulfide minerals are much coeval to the U-Pb zircon data that suggested a very narrow closure temperature at the time of origination.
The whole rock, silicates and sulfides of the Penikat intrusion have a Sm-Nd age of 2426 ± 38 Ma (MSWD = 0.2) (Figure 9a, Table 8).It agrees with the Sm-Nd age of 2410 ± 64 Ma determined for the Penikat intrusion earlier [51].Importantly, sulfide data lie on the isochron as well.It testifies to the coincidence of sulfide formation and the rock crystallization.Table 9 provides compiled isotope data obtained in previous [3] and the current research.

Discussion
A full set of advanced isotope geochronological methods has been applied to study the largest and ore-richest deposits of the Fedorovo-Pansky Complex.Table 10 is a data base of U-Pb and Sm-Nd ages of PGE layered intrusions in the Fennoscandian Shield.It includes both available and new data obtained by the authors of this study.
Previously, the authors had suggested that these PGE intrusions occurred at the same interval [3].Based on U-Pb and Sm-Nd data, the authors defined zones with different ages in the Fedorov Block, Western Pansky Block of the Fedorovo-Pansky Complex, Monchetundra massif, Mt.Generalskaya and Imandra lopolith [3].This study corroborates and substantiates results of the previous research.New data prove that, in the suggested hypothesis, there were four pulses of the magmatic activity associated with the formation of PGE intrusions of the Fennoscandian Shield in the interval 2.53-2.40Ga.
The Fedorov Block of the Fedorovo-Pansky Complex represents an independent magma chamber.Its rocks and ores differ significantly from those of the Western Pansky Block [3,10].A 2 km-thick rock sequence stretches from as a layered or differentiated syngenetic series.The age of melanocratic pyroxenite-norite-gabbronorite-gabbro between the Marginal Zone to the Lower Gabbro Zone is 2526 ± 6 and 2516 ± 7 Ma.The Taxitic Zone is intruded by concordant Cu-Ni-PGE-bearing gabbronorite (Fedorov deposit) of the second-pulse magmatic injection (2485 ± 9 Ma).
Isotope 4 He/ 3 He ratios are another reliable isotope tracer of mantle plume processes [56,70,71].Their use in the Precambrian study requires further consideration.He isotope data on rocks and minerals of the KB intrusions show that the 4 He/ 3 He isotope ratios of n × 10 6 and n × 10 5 correspond to ratios of the upper mantle and differ from those of the crust (n × 10 8 ) and lower mantle (n × 10 4 ) [3,12,71].According to these data, crustal contamination was local.
The LIP layered intrusions are directly related to the Fennoscandian Shield metallogeny [39].The evolution of the two belts of layered mafic complex (2.53 to 2.40 Ga) encompasses a group of younger (2.44 Ga) intrusions within FKB [5,72].
Isotope 4 He/ 3 He ratios are another reliable isotope tracer of mantle plume processes [56,70,71].Their use in the Precambrian study requires further consideration.He isotope data on rocks and minerals of the KB intrusions show that the 4 He/ 3 He isotope ratios of n × 10 6 and n × 10 5 correspond to ratios of the upper mantle and differ from those of the crust (n × 10 8 ) and lower mantle (n × 10 4 ) [3,12,71].According to these data, crustal contamination was local.
The LIP layered intrusions are directly related to the Fennoscandian Shield metallogeny [39].The evolution of the two belts of layered mafic complex (2.53 to 2.40 Ga) encompasses a group of younger (2.44 Ga) intrusions within FKB [5,72].
We consider a LIP as a product of a vast long-lived plume, according to geochemical data (Table 10).The studied East-Scandinavian LIP, or mafic LIP, has the following features: • gravity anomalies caused by a crust-mantle layer at the bottom of the crust; • riftogenic (anorogenic) structural ensembles with multipath extensional fault tectonics identified by the distribution of grabens and volcanic belts, dike swarms, and intrusive belts; • protracted polyphase tectonics and magmatism, continental discontinuities and erosion with early stages of tholeiitic-basalt (trappean), boninite-like, and subalkaline magmatism in the continental crust, possible closing stages of the Red Sea-type spreading magmatism; • intrusive sills, lopoliths, sheet-like bodies, large dikes and dike swarms.The intrusions are often layered and differ from rocks formed in subduction and spreading zones, with trends of thin differentiation layering, limited development of intermediate and felsic rocks, often with leucogabbro and anorthosite ends and abundant pegmatoid mafic varieties; • typical mantle geochemistry of rocks and ores, as registered by isotope mantle tracers: 143 Nd/ 144 Nd, 87 Sr/ 86 Sr, 187 Os/ 188 Os, and 3 He/ 4 He; • large orthomagmatic Cr, Ni, Cu, Co, PGE (±Au), Ti, and V deposits [18,69,72,75,76].

Figure 1 .
Figure 1.Sketch map of the Palaeoproterozoic East Scandinavian LIP in the Northern Fennoscandian Shield [15].

Figure 1 .
Figure 1.Sketch map of the Palaeoproterozoic East Scandinavian LIP in the Northern Fennoscandian Shield [15].

Table 4 .
Sm-Nd data on whole rock and rock-forming minerals from ULH anorthosite of the Fedorovo-Pansky massif.

Figure 6 .
Figure 6.Isotope U-Pb ages on zircon (A-B-C) and Sm-Nd isochrones (D-E-F) for rock-forming minerals from the Fedorov Block of the Fedorovo-Pansky massif.

Figure 6 .
Figure 6.Isotope U-Pb ages on zircon (A-C) and Sm-Nd isochrones (D-F) for rock-forming minerals from the Fedorov Block of the Fedorovo-Pansky massif.

Figure 7 .
Figure 7. Mantle normalized diagram showing the distribution of PGEs, Au, and Re in sulfides (composition of the primitive mantle is according to Reference [48]).

Figure 7 .
Figure 7. Mantle normalized diagram showing the distribution of PGEs, Au, and Re in sulfides (composition of the primitive mantle is according to Reference [48]).

Figure 8 .
Figure 8. Mantle normalized diagram showing the distribution of some trace elements in sulfides (composition of the primitive mantle is according to References [49,50]).

Figure 8 .
Figure 8. Mantle normalized diagram showing the distribution of some trace elements in sulfides (composition of the primitive mantle is according to References [49,50]).

Figure 9 .
Figure 9. Mineral Sm-Nd isochron for PGE-bearing gabbronorites (a), the U-Pb age on single zircon (b) from the Penikat intrusion and the U-Pb age on single zircon grains (c) from the Kemi intrusion (Finland), FKB.

Figure 9 .
Figure 9. Mineral Sm-Nd isochron for PGE-bearing gabbronorites (a), the U-Pb age on single zircon (b) from the Penikat intrusion and the U-Pb age on single zircon grains (c) from the Kemi intrusion (Finland), FKB.

Figure 10 .
Figure 10.Plot of εNd-ISr for the KB and FKB layered intrusions.Grey color indicates an EM-1 reservoir at the time of the layered intrusions formation.Sm-Nd and Rb-Sr isotope data are provided in Table9.

Figure 10 .
Figure 10.Plot of εNd-ISr for the KB and FKB layered intrusions.Grey color indicates an EM-1 reservoir at the time of the layered intrusions formation.Sm-Nd and Rb-Sr isotope data are provided in Table9.

Table 1 .
Isotope U-Pb data on baddeleyite (Bd) and zircon (Zr) on the Western-Pansky and Fedorov Blocks of the Fedorovo-Pansky massif.

Table 4 .
Sm-Nd data on whole rock and rock-forming minerals from ULH anorthosite of the Fedorovo-Pansky massif.

Table 5 .
Sm-Nd data on whole rock and rock-forming minerals from the Fedorov Block of the Fedorovo-Pansky massif.

Table 5 .
Sm-Nd data on whole rock and rock-forming minerals from the Fedorov Block of the Fedorovo-Pansky massif.

Table 6 .
Contents (ppm) of different elements in sulfide parageneses of the Fedorovo Tundra deposit.
4.3.Penikat (Sompuyarvi reef) and Kemi Intrusions: Sm-Nd and U-Pb GeochronologyGabbronorites (about 30 kg) were sampled in a geological field trip headed by M. Iljina (Geological Survey of Finland) to the Penikat and Kemi intrusions in 2008.The concordant age on 2 types of zircon from gabbronorite is 2430 ± 2 Ma.The concordant age on three types of zircon from the Kemi sample is 2447 ± 4 Ma (Figure9b,c, Table7).Sompuyarvi reef) and Kemi Intrusions: Sm-Nd and U-Pb Geochronology Gabbronorites (about 30 kg) were sampled in a geological field trip headed by M. Iljina (Geological Survey of Finland) to the Penikat and Kemi intrusions in 2008.The concordant age on 2 types of zircon from gabbronorite is 2430 ± 2 Ma.The concordant age on three types of zircon from the Kemi sample is 2447 ± 4 Ma (Figure

Table 7 .
U-Pb data on single zircon from layered PGE intrusions in Finland.

Table 8 .
Sm-Nd data on whole rock, rock-forming and sulfide minerals from ore-bearing gabbronorite of the Penikat layered intrusion.

Table 7 .
U-Pb data on single zircon from layered PGE intrusions in Finland.

Table 8 .
Sm-Nd data on whole rock, rock-forming and sulfide minerals from ore-bearing gabbronorite of the Penikat layered intrusion.

Table 9 .
Sm-Nd and Rb-Sr data on whole rock from layered Palaeoproterozoic complexes of the Fennoscandian Shield.