Chemical Composition and Petrogenetic Implications of Eudialyte-Group Mineral in the Peralkaline Lovozero Complex, Kola Peninsula, Russia

Lovozero complex, the world’s largest layered peralkaline intrusive complex hosts gigantic deposits of Zr-, Hf-, Nb-, LREE-, and HREE-rich Eudialyte Group of Mineral (EGM). The petrographic relations of EGM change with time and advancing crystallization up from Phase II (differentiated complex) to Phase III (eudialyte complex). EGM is anhedral interstitial in all of Phase II which indicates that EGM nucleated late relative to the main rock-forming and liquidus minerals of Phase II. Saturation in remaining bulk melt with components needed for nucleation of EGM was reached after the crystallization about 85 vol. % of the intrusion. Early euhedral and idiomorphic EGM of Phase III crystalized in a large convective volume of melt together with other liquidus minerals and was affected by layering processes and formation of EGM ore. Consequently, a prerequisite for the formation of the ore deposit is saturation of the alkaline bulk magma with EGM. It follows that the potential for EGM ores in Lovozero is restricted to the parts of the complex that hosts cumulus EGM. Phase II with only anhedral and interstitial EGM is not promising for this type of ore. Nor is the neighboring Khibiny complex despite a bulk content of 531 ppm of Zr. Khibiny only has interstitial and anhedral EGM. The evolution of the Lovozero magma is recorded in the compositions EGM up through a stratigraphy of 2400 m in Phase II and III of the complex, and distinct in elements like rare earth elements (REE), Sr, Ba, Th, U, Rb, Mn, Fe. The compositional evolution reflects primarily fractional crystallization processes within the magma chamber itself in combination with convective magma flow and layering by precipitation of minerals with different settling velocities. The suggested mechanism for the formation of the EGM deposits is flotation of very small, suspended EGM crystals in the convective magma and concentration below the roof of the magma chamber. Phase III EGM is enriched in total REE (1.3%) and in HREE (Ce/Yt = 8.8) and constitutes a world class deposit of REE in the million tons of Phase III eudialyte lujavrites.


Introduction
High-field strength elements (HFSE) including the rare earth elements (REE) are strategic and critical for high-tech industry and green technologies. Their consumption and economic importance is progressively growing up. REE are for the most part mined in a restricted number of carbonatite-related deposits in which the REE are hosted in a large group of carbonate-and phosphor-bearing minerals including, bastnaesite, parisite, and monazite. A very different resource for HFSE (e.g., Zr, Hf, Nb, Ta, REE) is large-volume alkaline syenitic complexes rich in Eudialyte-Group Mineral (EGM) and other HFSE bearing minerals. The aim of this contribution is to improve our understanding of the formation The alkaline rocks of Lovozero divide into three distinct phases. Phase I is preserved in the lowermost parts of the complex and as xenoliths throughout the complex. Phase I is composed of poikilitic, even-grained feldspathoidal syenite. Their bulk composition is miaskitic, i.e., have an agpaitic index (molar (Na2O + K2O)/Al2O3) > 1. The rock-forming minerals are K-Na feldspar, nepheline, nosean, aegirine-diopside, and magnesio-riebeckite with accessory ilmenite, magnetite, titanite, apatite group mineral and mosandrite (Ce).
Phase II, also known as the differentiated complex, is formed by repeated three-layer successions composed of urtite, followed by foyaite and lujavrite. Urtite is a syenite with a nepheline to pyroxene ratio > 0.7, foyaite is a nepheline-rich syenite, and lujavrite is a green peralkaline syenite rich in alkali pyroxene and feldspathoids. The transitions between the three rock types are mostly gradational. Sharp contacts only occur between the urtite and underlying lujavrite of the previous three-layers succession. The layered units of Phase II range in thickness from a few centimeters to hundreds of meter and sum to a total of app. 2000 m. The bulk compositions of Phase II nepheline syenites have an agpaitic index > 1 and are more alkaline than rocks of Phase I. The rock-forming minerals are nepheline, microcline, sodalite, aegirine, and arfvedsonite with accessory phases typomorphic for peralkaline syenites including EGM, lamprophyllite, lomonosovite, murmanite, apatite-group mineral, loparite-(Ce), villiaumite, titanite, sodalite, and lorenzenite (Table 1). Cumulus loparite-(Ce) locally appear concentrated into stratigraphically well constrained thin layers.
The nepheline syenites of Phase III comprise 15-18% of the volume of the Lovozero complex and forms the upper sheet-like part of the Lovozero. The complex contains more than 120 pegmatites. The contact to the Phase II is conformable and sharp with dips shallowing toward the center of the complex. The eudialyte lujarites are exposed in the summits of the Lovozero Massif, have a maximum thickness of 450 m, of which an increasing part is lost to erosion toward the southeast. Phase III is composed of repeated units of urtite, juvite, eudialyte foyaite, and leucocratic, mesocratic, and melanocratic eudialyte lujavrites [1]. Juvite is a strongly nepheline-dominated rock with ~20 modal % alkali feldspar. The alkaline rocks of Lovozero divide into three distinct phases. Phase I is preserved in the lowermost parts of the complex and as xenoliths throughout the complex. Phase I is composed of poikilitic, even-grained feldspathoidal syenite. Their bulk composition is miaskitic, i.e., have an agpaitic index (molar (Na 2 O + K 2 O)/Al 2 O 3 ) > 1. The rock-forming minerals are K-Na feldspar, nepheline, nosean, aegirine-diopside, and magnesio-riebeckite with accessory ilmenite, magnetite, titanite, apatite group mineral and mosandrite (Ce).
Phase II, also known as the differentiated complex, is formed by repeated three-layer successions composed of urtite, followed by foyaite and lujavrite. Urtite is a syenite with a nepheline to pyroxene ratio > 0.7, foyaite is a nepheline-rich syenite, and lujavrite is a green peralkaline syenite rich in alkali pyroxene and feldspathoids. The transitions between the three rock types are mostly gradational. Sharp contacts only occur between the urtite and underlying lujavrite of the previous three-layers succession. The layered units of Phase II range in thickness from a few centimeters to hundreds of meter and sum to a total of app. 2000 m. The bulk compositions of Phase II nepheline syenites have an agpaitic index > 1 and are more alkaline than rocks of Phase I. The rock-forming minerals are nepheline, microcline, sodalite, aegirine, and arfvedsonite with accessory phases typomorphic for peralkaline syenites including EGM, lamprophyllite, lomonosovite, murmanite, apatite-group mineral, loparite-(Ce), villiaumite, titanite, sodalite, and lorenzenite (Table 1). Cumulus loparite-(Ce) locally appear concentrated into stratigraphically well constrained thin layers. International Mineralogical Association (2020) [21].
The nepheline syenites of Phase III comprise 15-18% of the volume of the Lovozero complex and forms the upper sheet-like part of the Lovozero. The complex contains more than 120 pegmatites. The contact to the Phase II is conformable and sharp with dips shallowing toward the center of the complex. The eudialyte lujarites are exposed in the summits of the Lovozero Massif, have a maximum thickness of 450 m, of which an increasing part is lost to erosion toward the southeast. Phase III is composed of repeated units of urtite, juvite, eudialyte foyaite, and leucocratic, mesocratic, and melanocratic eudialyte lujavrites [1]. Juvite is a strongly nepheline-dominated rock with~20 modal % alkali feldspar.
A coarse layering is developed in the eudialyte lujavrites. Their bulk rock compositions are very alkaline with an agpaitic index of~1.50 and they are rich in high field strength elements (HFSE) such as zirconium that reaches a bulk rock maximum of 1.66 wt. % ZrO 2 [8]. Bodies of porphyritic lujavrite are located at the contact to the underlying Phase II syenites. They are believed to be partly quenched melts or mushes of eudialyte lujavrite magma. The eudialyte lujavrites host a suite of later intrusive lithologies including veins of lovozerite and murmanite and lamprophyllite porphyritic lujavrite, (about 2 vol. % of Phase III). They are interpreted as residual melts of Phase III are up to several kilometers in length and up to 50 m wide. Other late intrusive bodies are composed of poikilitic sodalite syenite and tawite (sodalite dominated rock). Titanite, apatite-group mineral, and amphibole-rich rocks in the eastern part of the complex are formed in a reaction between the Phase III magma and host rocks in the roof of the Lovozero complex [1].
The main rock-forming minerals of eudialyte-lujavrites are nepheline (23%), aegirine (17%), alkali-amphibole (15%), microcline (20%), and EGM (about 25%). EGM occurs as euhedral crystals and grain cores, a distinctive characteristic that sets EGM of Phase III apart from the EGMs of Phase II. The common accessory minerals include lamprophyllite, lomonosovite, murmanite, loparite-(Ce), lovozerite, pyrochlore supergroup minerals, and sodalite. The modal proportion of EGM crystals increases significantly to 30-40 vol. % in upper parts of Phase III. These EGM-rich rocks of ore grade are found in the apical part of the eudialyte complex as layers and meter-size lenticular bodies. Horizons defined as eudialyte ore are almost monomineralic with up 95 vol. % EGM with minor nepheline, aegirine, microcline, and arfvedsonite. EGM ores are a significant resource for especially the heavy rare earths elements (HREE), zirconium, and hafnium. In addition, the ores are also enriched in manganese, niobium, scandium, uranium, and thorium.

Samples and Analytical Method
Most of the samples in this study were collected from seven drill cores (numbers 469, 904, 521, 178, 144, 272B and 905) that cover a complete stratigraphic section through the Lovozero complex (~2400 m) except for the middle part of Phase II. Hand samples completed the vertical section of Lovozero.
The EGM analyses were made using Cameca SX50 and CAMECASX 100 electron microprobes with four wavelength-dispersive spectrometers at the Natural History Museum, London, and at Vernadsky Institute, Moscow. Operating conditions were in both cases an accelerating voltage of 15 kV and a 20 nA probe current. A combination of natural minerals, synthetic compounds, and pure metals, which included synthetic NaNbO 3 , SrTiO 3 , CaTiO 3 , ZrSiO 4 and individual REE-doped glasses for the major components were used as standards.
Trace element analyses were performed in Frankfurt University, Max Plank Institute in Mainz, Germany, and Vernadsky Institute, using Thermo Scientific Element 2 ICPMS instruments coupled with a Resonetics Resolution M-50 excimer laser. The laser spot size varied from 20 to 60 µm. NIST glasses and Zircon 91500 were used as standards. To minimize the influence of later rimming and equilibrations of first crystallized EGM, only the cores of EGM grains and crystals were analyzed. The full data set includes analyses from 650 grains in 213 samples.

Petrographic Characteriatics of EGM
Detailed accounts of the petrography of the lithologies of the Lovozero complex can be found in Vlasov et al. [14], Gerasimovsky et al. [1], and Bussen and Sakharov [22]. The rock-forming paragenesis remains the same throughout Lovozero, and includes nepheline, potassium feldspar, aegirine, and alkali-amphibole. Only the relative proportion and the compositions of the rock-forming minerals vary. The present work focusses on the petrographic relations and compositions of EGM.
Eudialyte is not present in Phase I lithologies, which therefore will not be described further. In the lower miaskitic part of Phase II the accessory phases include zircon, manganese-rich ilmenite, mosandrite-(Ce), keldyshite, lavenite, titanite, apatite group minerals, and no EGM. Zircon is the mineral that hosts the Zr. EGM is found higher in Phase II in association with agpaitic minerals such as lorenzenite, lamprophyllite, villiaumite, murmanite, and lomonosovite. In these rocks, EGM occurs as interstitial and anhedral grains. The size of EGM grains varies from tens to 1-2 mm. Individual EGM grains display very complex zoning that shows well in back-scattered electron images ( Figure 2). Minerals 2020, 10, x FOR PEER REVIEW 5 of 20 metals, which included synthetic NaNbO3, SrTiO3, CaTiO3, ZrSiO4 and individual REE-doped glasses for the major components were used as standards.
Trace element analyses were performed in Frankfurt University, Max Plank Institute in Mainz, Germany, and Vernadsky Institute, using Thermo Scientific Element 2 ICPMS instruments coupled with a Resonetics Resolution M-50 excimer laser. The laser spot size varied from 20 to 60 µm. NIST glasses and Zircon 91500 were used as standards. To minimize the influence of later rimming and equilibrations of first crystallized EGM, only the cores of EGM grains and crystals were analyzed. The full data set includes analyses from 650 grains in 213 samples.

Petrographic Characteriatics of EGM
Detailed accounts of the petrography of the lithologies of the Lovozero complex can be found in Vlasov et al. [14], Gerasimovsky et al. [1], and Bussen and Sakharov [22]. The rock-forming paragenesis remains the same throughout Lovozero, and includes nepheline, potassium feldspar, aegirine, and alkali-amphibole. Only the relative proportion and the compositions of the rockforming minerals vary. The present work focusses on the petrographic relations and compositions of EGM.

Compositions of EGM
The EGM composition shows continuous upwards decrease in Fe and a complementary increase in Mn from Phase II to the Phase III. The Mn/Fe ratios (apfu) increase upward from 0.76 in the Phase II to 0.87 in EGM of Phase III (Figure 9, Tables 2 and 4, average values in Tables 5 and 6). Shilling et al. [25] considered Mn/Fe ratio to be the most suitable fractionation indicator. The difference in Mn/Fe ratio in EGMs of Phase II and Phase III is insignificant. Consequently, the values of the Mn and Fe distribution coefficients of surrounding minerals mainly affected this ratio. Trace element compositions normalized to primitive mantle ( Figure 8)

Arrival of EGM on Liquidus
The timing of crystallization of EGM relative to that of the liquidus paragenesis of its host, and the compositional variations of the EGMs provide constrains to the genesis of large deposits of EGM with high concentrations of valuable HREE. In Phase II of Lovozero, EGM is an interstitial and poikilitic phase. It has anhedral grain shapes and shows significant and non-systematic chemical zonation (Figure 2). This type of EGM is typical for all parts of Phase II, with modal proportion of EGM, lamprophyllite, murmanite, and lomonosovite increasing upwards toward Phase III. The petrographic relations suggest that the anhedral EGM grains crystallized from late stage melts in Phase II crystal mushes, and that local geochemical variation, coexisting with HFSE-bearing accessory phases, and diffusion of HFSE account for the compositional variability in, e.g., LREE/ HREE (Figure 7). The petrographic relations are very different for EGM in Phase III and the eudialyte deposits. EGM grains are euhedral (Figures 3 and 4), and some are composed of amalgamated fragments of EGM crystals ( Figure 5). The EGM crystals are understood as liquidus crystals that crystallized in equilibrium with the lujavritic liquidus paragenesis, that includes nepheline, aegirine, and alkali-amphibole. Support for EGM as liquidus phase in melt of Phase III and eudialyte ores is provided by the porphyritic lujavrites. In these partly quenched rocks very small euhedral EGM crystals are enclosed other liquidus phases ( Figure 10).
Although the LREE/ HREE ratios and concentrations vary and outliers occur, the ratios of Phase III EGMs are in the 2-3 range and suggest a general equilibration with a single and large volume of melt. That is a characteristic of liquidus phases, and the main control on the formation of EGM ores in Lovozero is therefore, suggested to be saturation of agpaitic magma in components necessary for nucleation of, liquidus eudialyte i.e., in the melt with 1-2% ZrO 2 . Such concentrations are found in quenched and homogenized melt inclusions in the minerals of EGM ores and experiments [13].
EGM grains are euhedral (Figures 3 and 4), and some are composed of amalgamated fragments of EGM crystals ( Figure 5). The EGM crystals are understood as liquidus crystals that crystallized in equilibrium with the lujavritic liquidus paragenesis, that includes nepheline, aegirine, and alkaliamphibole. Support for EGM as liquidus phase in melt of Phase III and eudialyte ores is provided by the porphyritic lujavrites. In these partly quenched rocks very small euhedral EGM crystals are enclosed other liquidus phases ( Figure 10). Although the ∑LREE/∑HREE ratios and concentrations vary and outliers occur, the ratios of Phase III EGMs are in the 2-3 range and suggest a general equilibration with a single and large volume of melt. That is a characteristic of liquidus phases, and the main control on the formation of EGM ores in Lovozero is therefore, suggested to be saturation of agpaitic magma in components necessary for nucleation of, liquidus eudialyte i.e., in the melt with 1-2% ZrO2. Such concentrations are found in quenched and homogenized melt inclusions in the minerals of EGM ores and experiments [13].

Genesis of the Lovozero EGM Ore
The timing of arrival of EGM on the liquidus in the Lovozero complex is here estimated from the relative volumes of the phases of the complex, and assuming a continuum of fractionation and melt evolution. Phase III comprises the last 15 vol. % that crystallized in Lovozero, and the bulk magma apparently saturated with EGM after ~85% of the initial volume of Lovozero had solidified. Following Gerasimovsky et al. [1] the initial ZrO2 content of the bulk liquid Lovozero complex was 0.35 wt. %. With crystallization and evolution of Lovozero, the ZrO2 content is modelled to have reached 1.66 wt. %. in Phase III [7]. This corroborates the experimentally estimated concentration of 1.4-2 wt. % ZrO2 needed to bring EGM on the liquidus of alkaline agpaitic magma [13], and thus a classic fractional crystallization scenario.
Crystals of EGM form mats in the uppermost parts of in Phase III. The density of eudialyte is in the order of 2.8. The agpaitic magma of Ilimaussaq intrusion is and a proxy for that of Lovozero has a modelled density of ~2.3. It does not seem reasonable to assume the EGM mats to be simple floatation cumulates. The small euhedral crystals with sizes in the hundredths of a millimeter, in particular in the porphyritic lujavrites, would be in suspension and be carried along in convective

Genesis of the Lovozero EGM Ore
The timing of arrival of EGM on the liquidus in the Lovozero complex is here estimated from the relative volumes of the phases of the complex, and assuming a continuum of fractionation and melt evolution. Phase III comprises the last 15 vol. % that crystallized in Lovozero, and the bulk magma apparently saturated with EGM after~85% of the initial volume of Lovozero had solidified. Following Gerasimovsky et al. [1] the initial ZrO 2 content of the bulk liquid Lovozero complex was 0.35 wt. %. With crystallization and evolution of Lovozero, the ZrO 2 content is modelled to have reached 1.66 wt. %. in Phase III [7]. This corroborates the experimentally estimated concentration of 1.4-2 wt. % ZrO 2 needed to bring EGM on the liquidus of alkaline agpaitic magma [13], and thus a classic fractional crystallization scenario.
Crystals of EGM form mats in the uppermost parts of in Phase III. The density of eudialyte is in the order of 2.8. The agpaitic magma of Ilimaussaq intrusion is and a proxy for that of Lovozero has a modelled density of~2.3. It does not seem reasonable to assume the EGM mats to be simple floatation cumulates. The small euhedral crystals with sizes in the hundredths of a millimeter, in particular in the porphyritic lujavrites, would be in suspension and be carried along in convective magma. The here preferred genesis is therefore floatation of tiny crystals of EGM to the top of Phase III melt volume, where they are envisaged to have stuck together and re-crystallize to larger crystals in a type of ripening process (Figure 4). A similar mechanism for the accumulation and concentration of heavier apatite-group mineral and lighter nepheline was envisaged in the model proposed for the Genesis of Apatite ores in the Khibiny complex [26].
The EGMs of Phase III lujavrites and eudialyte ores have elevated HREE contents compared to EGMs of Phase II. The anhedral Phase II EGMs are confined to interstitial volumes of melt which evolved relative to the contemporaneous bulk liquid. Interstitial EGM would start to crystallize in mushes of Phase II, before the arrival of EGM on the liquidus of the bulk liquid of Phase III. The EGMs of Phase II would be trapped in small volumes of melt and not be able to scavenge HFSE elements from a larger bulk magma. They would have compositions controlled by the bulk composition of the interstitial melts, and as suggested in Figure 7, the paragenesis of coexisting HFSE-bearing phases.
On the contrary we suggest that the euhedral and idiomorphic liquidus crystals of EGM of Phase III crystalized in a large convective volume of melt in equilibrium with the rock-forming liquidus paragenesis and layering in Phase III lujavrites. They also formed after crystallization of loparite-(Ce) and formation of the loparite ores. Loparite-(Ce) is very strongly enriched in LREE and the effect would be a relative enrichment in HREE over LREE in melts of Phase III.
Consequently, a required condition for the formation of a EGM deposit with high concentration of HREE is the saturation of alkaline magmas with respect to EGM at a stage in the magmatic evolution when the LREE/ HREE ratio was already lowered because of the fractionation of LREE-rich phases, e.g., loparite-(Ce). In addition, equilibration and scavenging from a large volume of melt would favor higher concentrations of REE in EGM. If the concentration of the elements needed for saturation are significantly lower at the liquidus of the melt, then the crystallization of the ore mineral would occur at sub-liquidus conditions in small and possible partly isolated volumes of interstitial melt. Such a scenario would not facilitate the formation and accumulation of the EGM. It seems evident that the potential for viable EGM ores in the large Lovozero complex, is restricted to Phase III in which EGM crystallized as the liquidus phase in the lujavritic magma. From this follows that anhedral and interstitial EGM of the neighboring Khibiny complex EGM is unlikely to form eudialyte ore deposits, despite a bulk concentration of 531 ppm Zr [27].

Consequences for Layered Agpaitic Complexes
The evolutionary trend recorded in the EGM compositions is consistent with a continuous and closed system evolution of Lovozero intrusion and feeder system exemplified, e.g., in parageneses and clinopyroxene compositions [7]. The same is suggested for kakortokites of the Ilimaussaq intrusion based on the stratigraphic variation in EGM compositions and core to rim fractionation during in situ fractionation in crystal mushes [15].
Much information has, however, emerged over the past decade and two very different models are advocated for the development of igneous layering in Ilimaussaq, including: (1) A classic closed system evolution with layering caused by gravitational accumulation, and e.g., crystal mat formation [16,26,[28][29][30]; and (2) a crystallization model based on repeated replenishment of the magma chamber [31]. The latter model, however, require that the magmas or mushes evolved along evolutionary trends similar to those observed in Ilimaussaq. Such models relocate observed evolution to a not known or specified feeder chamber. The need for such an unspecified feeder chambers for the Ilimaussaq intrusion rests on petrofabric (CDS) studies, sometimes sharp contacts between repeated cyclic layers, and structural characteristics interpreted as the result of turbulent accumulation of new pulses of inclusion-bearing agpaitic mush in the kakortokites [31]. It is also argued that the classic gravitational settling (or flotation) mechanisms cannot explain the petrofabrics and the repetition of 29 tripartite cycles of black, red, and white kakortokites.
These models, however, appear to exclude liquidus crystallization under the roof and subsequent gravitational accumulation of crystal mushes in the floor of the magma chamber. Magmas cool through roof and walls and are better insulated at floor by accumulated crystal mush. Cooling would in most cases be most efficient at the roof and cause crystallization and mush formation. The mushes, that would be variable affected by interaction with rafts of roof rocks, sink to the floor, and simulate being new magma pulses, although being the result of processes within the magma chamber itself. Such processes are well described from e.g., the Skaergaard intrusion [32]. At present, there is no indisputable evidence to suggest that the kakortokites of the Ilimaussaq intrusion should be anything but the result of crystallization of magma and density-controlled distribution of solids, crystal mushes, and melts within a magma chamber. The same may apply to the Lovozero complex and following Gerasimovsky et al. [1] and Kogarko et al. [17] there is no compelling evidence to suggest that the Lovozero complex represents rocks crystallized from multitude of replenishment events.

Conclusions
The conclusions of the study are:

1.
Eudialyte (EGM) of the Lovozero complex is enriched in HREE. EGM of the ore-bearing Phase III of the complex reaches an average of 1.3 wt. % total REEs (max 1.8), and a Ce/Yb = 8.88. In addition, EGM-ores are strongly enriched with Zr and many other HFSE elements commodities.

2.
The petrography shows that the time of crystallization of EGM relative to liquidus paragenesis changes upward and as the Lovozero complex crystallizes. The interstitial, anhedral EGM crystals in all of Phase II indicate that the bulk magma was not yet saturated in components needed for nucleation of EGM. Only after crystallization, about 85% of the volume of the initial magma was saturated and nucleation of EGM was reached and EGM changed the role to become a cumulus phase.

3.
Saturation of the bulk magma that leads to EGM nucleation is a prerequisite for eudialyte ores.
The ores formed as a result of the suspension and upward transportation of very small crystals and subsequent amalgamation growth below the roof of the magma chamber. The process compares to that suggested for the Khibina apatite-group mineral deposits [26]. 4.
EGM of the neighboring Khibiny complex is anhedral, interstitial, and unlikely to form eudialyte ore deposits, despite a bulk concentration of 531 ppm Zr.
Author Contributions: All scientific conceptualization, analytical work, and synthesis of the results have been carried out by the first author (L.K.), who also prepared an earlier version of the manuscript; T.F.D.N. revised the structure and wording of the manuscript, added resource perspective introduction, added petrographic definitions in description of Lovozero complex, added LREE/HREE calculation and illustration (Figure 7), added comparisons and general perspectives to the Discussion. All authors have read and agreed to the published version of the manuscript.
Funding: This work was supported by the Russian Federation represented by the Ministry of education and science of Russia № 075-15-2020-802.