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Article

Zr-Th-REE Mineralization Associated with Albite–Aegirine-Bearing Rocks of the Burpala Alkaline Intrusion (North Baikal Region, South Margin of the Siberian Craton)

by
Ivan Aleksandrovich Izbrodin
1,2,
Anna Gennadievna Doroshkevich
1,2,
Anastasia Evgenyevna Starikova
1,2,
Alexandra Vladislavovna Malyutina
2,
Tatyana Nikolaevna Moroz
2 and
Igor Sergeevich Sharygin
3,*
1
Department of Geology and Geophysics, Novosibirsk State University, 630090 Novosibirsk, Russia
2
Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia
3
Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, 664033 Irkutsk, Russia
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(7), 742; https://doi.org/10.3390/min15070742
Submission received: 14 June 2025 / Revised: 11 July 2025 / Accepted: 13 July 2025 / Published: 16 July 2025
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Abstract

The rocks of the Burpala alkaline intrusion contain a wide range of rare minerals that concentrate rare earth elements (REEs), Nb, Th, Li, and other incompatible elements. One of the examples of the occurrence of such mineralization is albite–aegirine rocks located at the contact zone between the intrusion and the host terrigenous–sedimentary rock. In albite–aegirine rocks, cubic crystals of “metaloparite”, partially or completely substituted by bastnäsite-(Ce) and polymorphic TiO2 phases (anatase and rutile) mainly represent the rare metal minerals. In albite–aegirine rocks, trace element minerals are predominantly represented by cubic crystals of “metaloparite”, which are partially or completely replaced by bastnäsite-(Ce) and polymorphic TiO2 phases such as anatase and rutile. Additionally, Th-bearing zircon (up to 17.7 wt% ThO2) and a variety of unidentified minerals containing REEs, Th, and Nb were detected. The obtained data indicate that bastnäsite-(Ce) is the result of the recrystallization of “metaloparite” accompanied by the formation of Th-bearing zircon and Nb-bearing rutile (up to 9.9 wt% Nb2O5) and the separation of various undiagnosed, unidentified LREE phases. Our studies show that remobilization of LREEs, HFSEs, and local enrichment of rocks in these elements occurred due to the effects of residual fluid enriched in fluorine and carbon dioxide.

1. Introduction

Post-magmatic hydrothermal mobilization of rare earth elements, zirconium, and niobium has been recorded in a number of alkaline intrusions [1,2,3]. This phenomenon is typically associated with albitization caused by the high solubility of sodium in natural fluids, making sodium a critical element in metasomatic transformations. Aegirinization, which frequently accompanies albitization, plays a crucial role in the formation of rare metal deposits of niobium, tantalum, zirconium, uranium, and thorium [4]. Aegirinization has been recognized as the dominant metasomatic process associated with U and Th enrichment in Ukrainian uranium deposits [5]. The concentrations of Zr, Nb, and REEs in pegmatites and metasomatic zones in the Burpala alkaline intrusion reach levels that are of significant economic importance for commercial production [6].
The Burpala alkaline intrusion is located in the North Baikal region of Russia and is a part of the North Baikal alkaline province in the similarly named Late Paleozoic riftogenic zone. It represents one of the key igneous complexes within this zone, along with the Synnyr ultrapotassic and some small alkaline intrusions. The intrusion (56°32′ N, 110°41′ E) hosts more than 80 mineral species, including rare and recently described minerals [7,8], and exhibits mineral diversity comparable to that of well-known complexes such as Lovozero and Khibiny [8,9].
The first mineralogical studies of the Burpala intrusion were carried out by A.S. Portnov and co-authors [10,11,12], who provided a detailed characterization of its mineral assemblages. Further research has since focused on rare minerals, such as loparite, melanocerite, strontium perrierite, britholite, and rinkite [13,14,15,16], which are predominantly hosted in nepheline syenites and late- to post-magmatic formations—including alkaline pegmatites, syenite pegmatites, and metasomatic rocks [8]. These rock types occur both within the intrusion and along its northwestern contact zone with country rocks, forming narrow bodies enriched in rare-metal mineralization. In these zones, zirconium (~1–5 vol.%) and titanium mineralization are widespread, represented by rutile, ilmenite, loparite, catapleiite, astrophyllite, burpalite, and lavenite. Research by Mitchell and Chakhmouradian [17] shows that loparite is capable of incorporating significant amounts of thorium (up to 18.4 wt% ThO2), which leads to compositional changes and the formation of structural vacancies. Notably, loparite in metasomatic zones is often replaced by a poorly investigated mineral phase known as “metaloparite” [14]. Although occurrences of “metaloparite” have also been reported from other alkaline provinces (e.g., the Kola Alkaline Province, Schryburt Lake complex, Ontario), it has not yet been approved as a valid mineral species by the International Mineralogical Association (IMA). This is related to the lack of data on its chemical composition and crystal structure and, additionally, because its samples occur as complex aggregates of several minerals [14].
The study of zircon is no less intriguing, as both its morphology and composition can be significantly altered during interaction with aqueous (hydrothermal), magmatic, and metamorphic fluids [18]. Zircon crystallization is controlled by temperature, fluid composition, and the presence of coexisting mineral phases enriched in REEs, U, Th, and Hf [19]. For example, the authors of study [20] reported direct precipitation of hydrothermal zircon in peralkaline granites of the Corupá Pluton (Southern Brazil), characterized by elevated HFSEs, L-, and MREEs and high Th/U ratios—all indicative of fluid–rock interaction. Moreover, zircon is known to undergo dissolution and reprecipitation in fluid-rich environments [21,22,23].
This study presents new mineralogical and petrographic data on albite–aegirine rocks occurring in an ore zone near the contact between the Burpala alkaline intrusion and weakly metamorphosed sandstones. These rocks are enriched in rare minerals that concentrate rare earth elements (REEs), Nb, Th, Li, and other incompatible elements. Their investigation allows for the identification of specific geochemical conditions during their formation. In addition, the results open new perspectives for understanding fluid–mineral interaction mechanisms, as well as processes of element mobilization, redistribution, and localization.

2. Materials and Methods

All analytical studies were conducted at the Center for Collective Use of Multielement and Isotope Studies (CCU MIS) of IGM SB RAS, Novosibirsk.
Petrographic analysis of albite–aegirine rocks was carried out on an Olympus BX51 microscope (Olympus Corporation, Tokyo, Japan) equipped with a Luminera InfinityX 32 digital camera.
Backscattered electron (BSE) imaging, elemental mapping, and qualitative and quantitative mineral analyses were carried out using a TESCAN MIRA 3 LMU scanning electron microscope (TESCAN, Brno, Czech Republic) equipped with an Aztec Energy/INCA Energy 450+ XMax-80 energy-dispersive spectrometer (Oxford Instruments NanoAnalysis, High Wycombe, UK). The measurements were performed at an accelerating voltage of 20 kV, a probe current of 1 nA, and a beam diameter of 10 nm, with an acquisition time of 20–40 s per spectrum. Metallic cobalt (Co) was used for quantitative normalization and beam energy calibration of the spectrometer. Matrix corrections were applied using the XPP method within the INCA Suite software package version 5.05.
Raman scattering spectroscopy was used to study the degree of distortion of the zircon crystal lattice. The Raman scattering spectra for minerals were obtained on a Horiba LabRAM HR800 spectrometer (Horiba Jobin Yvon, Palaiseau, France) equipped with a 1024 pixel LN/CCD detector in backscatter geometry, using an Olympus BX41 microscope (Olympus Corporation, Tokyo, Japan) with 100× objective (WD = 0.37 mm, aperture 0.75), which provided a focal spot diameter of ~2 µm. For excitation, Nd:YAG laser radiation with a wavelength of 532 nm was used at a power of 0.25 mW to prevent heating of the samples. The absence of thermal effects was verified by comparing spectra at power levels of 7 and 0.25 mW. The spectra were recorded in the wave number range of 100 to 3800 cm−1 with signal acquisition times varying from 20 to 100 s. The system was calibrated using the 520.7 cm−1 silicon line, with a measurement accuracy of ±0.5 cm−1 and a spectral resolution of 1–1.5 cm−1.
Additionally, 2D mapping of Th-bearing zircon was conducted using the automated confocal Raman scattering system WITec Apyron (Oxford Instruments NanoAnalysis, Abingdon, Oxon, UK). Excitation of the sample was achieved using a laser with a wavelength of 488 nm (50 mW), while the spectra were recorded in the range of 100–4000 cm−1.
Trace element compositions of zircon were analyzed using laser ablation–split-flow–inductively coupled plasma–mass spectrometry (LA-SF-ICP-MS) with an Element XR high-resolution mass spectrometer (Thermo Fisher Scientific, Waltham, MA, USA), coupled to an Analyte Excite excimer laser ablation system (Teledyne Cetac, Omaha, NE, USA), equipped with a HelEx II dual-volume ablation cell. Scanning was performed on the masses following isotopes: 31P, 49Ti, 88Sr, 89Y, 91Zr, 93Nb, 138Ba, 139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 157Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 172Yb, 175Lu, 178Hf, 232Th, and 238U. The analyses were carried out in E-scan mode. Signal detection was conducted in counting mode for all isotopes except for 31P, 89Y, 91Zr, 178Hf, 232Th, and 238U, which were measured in triple detection mode. The laser beam diameter was 25–35 μm, with a pulse repetition rate of 5 Hz and a laser energy density of 3 J/cm2. Data processing was performed using the “Glitter” software package, version 4.4 (GEMOC, [24]). Element concentrations in zircon were calibrated externally using NIST SRM 610 glass standard (National Institute of Standards and Technology, Gaithersburg, MD, USA), with 91Zr used as the internal standard. The natural zircon GJ-1 [25,26,27] was used as a secondary reference material to monitor analytical accuracy.
Mineral abbreviations follow the symbols approved by the International Mineralogical Association (IMA) [28], except for phases associated with loparite—metaloparite (m-Lop) and x-metaloparite (X-Lop).

3. Geological and Mineralogical Background

The Burpala alkaline intrusion located in the North Baikal region, together with the Synnyr and Tassky intrusions, is part of the Late Paleozoic North Baikal alkaline province. Their formation is coeval with the manifestation of the Late Paleozoic post-orogenic magmatism (alkaline, basitic, and granitoid) related to plume activity within the Transbaikal segment of the Central Asian fold belt [29,30,31,32,33]. The tectonic position of the intrusion is determined by its location at the boundary between the western segment of the Baikal–Vitim belt within the COAB and the marginal zone of the Siberian craton (Figure 1). The marginal part is composed of the Marekta basement bench and Neoproterozoic rift structures of the Olokit zone [34]. The western segment of the Baikal–Vitim belt consists of the Early Baikal high-grade metamorphic volcanogenic–carbonate–terrigenous complexes and overprinted Late Baikal tectono-metamorphic associations, including ultramafic rocks and a polymetamorphic suite of migmatites, tonalites, and amphibolitized metabasites. The intrusion has a pronounced zonality: the outer part consists of quartz (more than 5% quartz) and quartz-bearing syenites, while the central part is composed of alkaline and nepheline syenites (Figure 1a). Lenticular bodies of nepheline syenite with a foyaitic texture (4 × 0.5 km2) and various vein-like bodies of granites, aplites, and pegmatites are also observed in the central part [35]. The intrusion is hosted by weakly metamorphosed sedimentary-terrigenous rocks, predominantly sandstones, silt–sandstones, and siltstones, with rare interbeds of limestone. Various metasomatic rocks with complex mineral composition are the products of intense post-magmatic processes and occur in the contact zone of the intrusion [36]. The most common varieties are feldspar metasomatites (albitites, microclinites, microcline–albitite and albite–aegirine rocks), and the contact zones of phenitization with significant accumulation of Nb, Ti, Zr, REEs, U, and Th. In addition, monomineral zones consisting of britholite (ore zone 3 in Figure 1a) and fluorite (ore zone 4 in Figure 1a) are occasionally formed.
The first detailed studies of the intrusion [36] revealed five ore zones with rare-metal mineralization (Table 1). The studies showed that the most widespread rocks in the NW part of the intrusion are phenites (ore zone 2), which are observed along the contact with the host rocks, while ore zone, 1 which is composed of albite–aegirine and aegirine–microcline metasomatites, is traced parallel to ore zone 2, 200–400 m westward of the contact (Figure 1a). These zones have similar ore mineralization represented by loparite/metaloparite, zircon, ilmenite, catapleiite, lavenite, and aeschynite. Ore mineralization within the central part of the intrusion is confined to alkaline trachytoid and nepheline syenites. Three zones with different mineral compositions were identified: pegmatoidal syenites with britholite mineralization (zone 3); fluoritized and albitized syenites with apatite and leucophane (zone 4), and altered syenites (zone 5) with zircon, loparite, thorite, chevkinite, eudialyte, and other minerals (Table 1). The geological survey works suggest the two- or three-phase formation of the intrusion. Geochronologic data (U-Pb zircon) obtained for the main intrusive phases (quartz, alkaline, and nepheline syenites) vary in the range of 300–289 Ma [37,38]. The U-Pb age of ore-bearing metasomatic rocks from ore zone 2 (295 ± 3 Ma) was determined by the marginal zones of zircon, which indicates that the nature of ore formation is syngenetic to the main stage of the intrusion formation [39]. Its petrological aspects are described in [6,40,41,42].

4. Results of the Study of Albite–Aegirine Rocks

Samples of coarse-grained albite–aegirine rocks (metasomatites), including pegmatoidal varieties represented by thin (up to 2 m) lenses in fine-grained quartz syenites (ditch 8, Figure 1b), were analyzed. The contacts of these rocks with syenites are sharp, sinuous, and frequently contain monomineral rims of albite (Figure 2a) or aegirine. This zone is located on the watershed between the Trekhozerny and Obryvisty creeks (tributaries of the Kudushkit River) in close proximity to the contact of the intrusion with weakly metamorphosed sandstones. The groundmass is composed of columnar, sheaf-like aggregates of aegirine with the length of individual crystals up to 2 cm and late albite (relative to aegirine) (Figure 2). Semi-rounded or polygonal voids are present in the rock structure, accounting for 1%–5% of the total rock volume. The distribution of aegirine and albite in the rock varies unevenly, with the areas enriched in either albite (40–60 vol.%) or aegirine (up to 90 vol.%). Apatite, monazite, fluorite, potassium feldspar, natrolite, zircon, tainiolite, “metaloparite”, bastnäsite, rutile, anatase, cesarolite (?), and aeschynite (?), as well as unidentified phases of variable composition Th-REE-Ti, Pb-Mn(OH?), Pb-Ce(OH?), etc., were found in the rocks. These phases preferentially fill cavities and form discrete aggregates 5–10 μm in size, mainly near Th-bearing zircon. However, significant deviations in analytical totals (up to 25%) and the uncertainty of the Raman spectra significantly complicate their accurate identification.

Mineral Chemistry

Clinopyroxene exhibits a homogeneous aegirine composition with a minor hedenbergite component (close to Hd2Ae98). Admixtures of TiO2 and Al2O3 (0.2–1.2 wt%) and ZrO2 (0.2–1.4 wt%) are consistently present.
Feldspars are represented exclusively by Na-rich alkali feldspar (albite), whereas potassium feldspar is rare and occurs closer to the contact zone (samples k8-2a, k8-4). At least two generations of albite were optically identified: early albite crystallized after aegirine, and late albite developed in crosscutting veinlets. However, no significant differences in their chemical composition were detected.
“Metaloparite” is represented by cubic crystals and their aggregates up to 2 mm in size (Figure 2a–c). The primary loparite is preserved only as individual relics within the “metaloparite” and most likely was transformed into it at the early stages of metasomatic processes. It contains scarce aegirine inclusions (Figure 3a). The alteration of “metaloparite” led to the formation of bastnäsite-Ce and titanium oxides (Figure 3b,c). There are instances where “metaloparite” is replaced by unidentified mineral phases (Figure 3a, light gray) with SiO2 (3.5–9.7 wt%) and BaO (2.1–2.5 wt%) or SiO2 (7.5–9.5 wt%), PbO (4.2–8.8 wt%), and ThO2 (17.5–19.0 wt%). A common feature of these mineral phases is low sums (Table 2) of component concentrations (85–80 wt%), which is mostly due to their high water content. The preserved zones of “metaloparite” contain low concentrations of SrO (0.0–1.5 wt%), Nb2O5 (2.5–4.7 wt%), and CaO (0.1–1.0 wt%) with a complete lack of Na2O (Table 2). The predominance of Ce over La and enrichment in ThO2 (2.5–7.0 wt%), with a deficiency of the sum up to 7 wt% are noted.
The main rare earth mineral in the rocks is bastnäsite-(Ce), while monazite-(Ce) occurs in smaller amounts. In addition, unidentified cryptocrystalline or amorphous phases containing combinations of Th-REE-Ti, Pb-Mn-REE, and Pb-Ce elements were detected along the fractures and along the grain boundaries of “metaloparite”, Th-bearing zircon, and bastnäsite, and in the voids (Figure 3d). However, the exact chemical composition of these phases remains uncertain, as the analytical results show a significant deficit of the total amount (73–85 wt%), which complicates their identification.
Bastnäsite-(Ce) is generally formed by “metaloparite” (Figure 3) and occurs less frequently in later aggregates in association with Th-bearing zircon (Figure 2d) or in aggregates filling cavities in the rock.
Bastnäsite-(Ce) typically forms at the alteration of “metaloparite” (Figure 3). It is less commonly found in later mineral aggregates, where it occurs in association with Th-bearing zircon (Figure 2d), or within aggregates that fill cavities in the rock. Bastnäsite contains small amounts of ThO2 (0.4–4.5 wt%). The Ce/(Ce + La) ratios vary from 0.57 to 0.67, which corresponds to an intermediate series of solid solutions between bastnäsite-(La) and bastnäsite-(Ce). In addition to the above elements, it contains SiO2, CaO, and SrO and occasionally TiO2, PbO, and ZrO2 in concentrations of 1–2 wt% (Table 3), which is probably due to the presence of various microinclusions.
The main minerals are titanium oxides accompanying bastnäsite. Raman spectroscopy revealed two polymorphic modifications of TiO2. According to the Raman bands in the wave number region of 144, 390, 516, and 640 cm−1 (Figure 4), the mineral developing at the initial stage by “metaloparite” (point 168 in Figure 3a) was identified as anatase [43,44]. This polymorphic modification was detected exclusively within the “metaloparite” and it forms close intergrowths with bastnäsite (Figure 3a,c,d). The Raman spectrum of the TiO2 phase developing along the cracks or edges of “metaloparite” grains (e.g., point 172 in Figure 3a) shows bands near 143, 440, and 613 cm−1 corresponding to rutile [43,44]. Rutile, the same as anatase, forms in paragenesis with bastnäsite, but it produces relatively larger segregations localized along fractures or closer to the “metaloparite” grain boundaries (Figure 3). In addition, rutile was found on the periphery of Th-bearing zircon grains (point 106 in Figure 5; Figure 4), and was also observed in the form of idiomorphic grains in association with aegirine. The chemical composition of Ti-oxides reveals variable contents of Nb2O5 (0.5–9.9 wt%), SiO2 (0.28–0.8 wt%), and FeO (0.8–2.5 wt%).
Individual grains of fluorapatite are commonly observed in association with “metaloparite” (Figure 3c). Fluorapatite has an irregular internal structure expressed in a varying composition of Na2O (0.22 to 1.35 wt%), La2O3 + Ce2O3 (0.8 to 5 wt%), and SrO (2.5 to 8 wt%). Apatite is characterized by the belovite isomorphism scheme 2Ca2+ = Na+ + REE3+ [45]. It is worth noting that some fluorapatite grains contain abundant monazite inclusions and fewer bastnäsite inclusions.
Zircon is represented by two types in the rock. Zircon of the first (predominant) type forms a fine dissemination (grain size up to 20 µm) in aegirine (Figure 5a). The mineral lacks crystallographic facets and has a round or irregular shape. The chemical composition is close to stoichiometric (Table 4, Figure 6). Impurities are represented by HfO2 up to 2 wt%.
Zircon of the second type is high-Th one. It forms large (up to 200 μm) interstitial grains oriented along the direction of rock banding (Figure 2b,c and Figure 5). Zonality in the internal structure can be occasionally observed (Figure 5b). A combined study involving EPMA and Raman spectroscopy revealed a distinct internal heterogeneity of zircon of this type (Figure 5c,d). They show variable ThO2 content (from 0.2 to 17.7 wt%) and elevated contents of Ti, Fe, Mn, Ca, Nb, Y, and light rare earth elements (LREEs) (Table 5, Figure 6), as well as decreasing totals with increasing Th concentrations. Elemental maps for such zircon indicate strong chemical heterogeneity even within a single grain (Figure 5c). The zircon heterogeneity is also effectively distinguishable by Raman mapping (Figure 5d). Obviously, Th is unevenly distributed within the grain of newly formed zircon and does not form independent thorium phases (e.g., thorite).
The trace element composition (LA-ICP-MS) was obtained for type II zircon with ThO2 content not exceeding 1 wt% (9 grains examined) (Table 4).
Despite the explicit heterogeneity of zircon grains of this type, their REE patterns have a similar flat and weakly differentiated shape (Figure 7). The distinctive features are a weak positive Ce anomaly (Ce/Ce* = 1.1–2.5) and a virtually absent negative Eu/Eu* anomaly. Such patterns drastically contrast with the previously obtained characteristics of magmatic zircon in the Burpala alkaline intrusion [39], which exhibit a steep positive slope, depletion in light rare earth elements (LREEs), and significant positive Ce anomaly (Ce/Ce* = 6–427) and negative Eu anomaly (Eu/Eu* = 0.37–0.93). The obtained spectra demonstrate similarities with those for the central parts of zircon extracted from phenites of ore zone 2.
While examining Raman scattering in type II high-Th zircon, different zones that are distinguished by contrast in BSE images were investigated. The light regions visible in the BSE image are characterized by high Th content (up to 14 wt% ThO2, the same as at point 109 in Figure 5), while there is a deficiency of up to 20 wt% of the sum of elements. In contrast, the dark zones in the BSE image are characterized by low Th content (0.5–2 wt% ThO2) and less significant sum deficiencies to 10 wt%. In the case of zircon zones with up to 2 wt% ThO2, the Raman spectrum shows significant changes in the structure of peaks. As shown in Figure 8a (spectra 1 and 2), the characteristic peaks are shifted to 987 cm−1 and 984 cm−1, respectively, as compared to zircon with an undisturbed crystal structure with characteristic Raman bands 1008, 439, and 355 cm−1 [47]. This shift is accompanied by significant broadening of the bands. Their full width at half maximum (FWHM) is about 27 and 30 cm−1, respectively, with a shoulder of about 952 and 955 cm−1 observed on the side of smaller wave numbers (Figure 8a, inset). This is characteristic of disordered zircon and indicates partial amorphization of zircon structure [48,49,50].
Most of the studied zircon grains with ThO2 contents higher than 10 wt% do not show peaks of the ν3 mode (SiO4) on the spectra owing to significant radiation damage and superimposed fluorescence. The Raman spectra (Figure 8b) of moderately metamict zircon (points 87 and 90 in Figure 8c) with low ThO2 content (0.5 wt% and deficiency of the sum of elements about 10 wt%) in the wave number range of 100–1100 cm−1 show bands typical of zircon: 350 cm−1 ((Eg) M-O oscillations), 439 cm−1 (ν2), 965 cm−1 (ν1), and 1000 cm−1 (ν3) Si-O oscillations. In the zones with high-Th zircon (Figure 8a, spectrum 109), the peak of the ν3 (SiO4) mode on the Raman spectra is shifted to 993 cm−1 (FWHM 24 cm−1), the bands of symmetric strain vibrations are wider and more intense, and there are no bands in the region of lattice modes. The above-mentioned features of the spectra may be related to the effects of photoluminescence [51]. Additional bands resulting from REEs’ luminescence are also observed in the spectra, which are experimental artifacts (see Figure 8c).

5. Discussion

5.1. Genesis of Albite–Aegirine Rocks of the Burpala Alkaline Intrusion: The Role of Magmatic and Hydrothermal Processes

Some features of the albite–aegirine rocks from the Burpala alkaline intrusion indicate that these rocks are of metasomatic origin, which is consistent with the data obtained in previous studies [14]. Similar formations are widespread in the classic agpaitic intrusions such as the Lovozero and Ilimausak [52]. These rocks are a result of the complex interaction between magmatic and hydrothermal processes.
The age of magmatic rocks in the Burpala alkaline intrusion, including quartz, alkali, and nepheline syenites, is 300–289 Ma [37,38], while the age of metasomatic rocks was determined to be about 295 ± 3 Ma [39]. These data indicate syngenetic formation of metasomatic rocks and intrusion emplacement. Doroshkevich and co-authors [42] report that the intrusion formed through prolonged fractional crystallization of the alkaline mafic melt. The similar Sr–Nd–Pb isotopic characteristics of the rocks suggest their common magmatic source, but assimilation of the upper crust material favored the transition from nepheline to quartz syenites, which reflects the complex magmatic system evolution [42].
The major volume of rare-earth mineralization within the intrusion is associated with hydrothermal activity. Anomalously high concentrations of REEs, Zr, Y, and Nb were found in pegmatites [6]. Their concentrations are substantially lower in phenites and in zones of albitized rocks. Migration of rare metal-rich fluids from the deep parts of the intrusion to its periphery and into host rocks could have resulted in mineralization. This is confirmed by the specific features of post-magmatic ore minerals, replacement textures, and spatial association with linear distribution zones. Fluid penetration occurred predominantly along the zones of weakness, which contributed to the local enrichment of rocks in rare earth elements, thorium, zirconium, niobium, and other incompatible elements. Albite–aegirine rocks reveal zonality in their distribution, owing to which, in places, mainly loparite and minerals of the wöhlerite group (burpalite and lavenite) and catapleite are formed [35]. In other parts, only “metaloparite” is formed (Figure 3) while zirconium silicates are represented by zircon (Figure 5).

5.2. Formation of “Metaloparite” Under Hydrothermal Conditions

“Metaloparite” is a major Th-bearing mineral in the aegirine–albite rocks of the Burpala alkaline intrusion. Its thorium content is comparable to that of loparite from the intrusive igneous rocks within the intrusion. The mineral formed through metasomatic replacement of primary loparite by alkali- and REE-rich hydrothermal fluids during late-stage fluid–rock interactions [14]. Typically, loparite does not contain such high Th concentrations, except for that found in Eveslogchorr, Khibiny Complex (up to 18.5 wt% ThO2), and in phenitized rocks of the Parana carbonatite complex (up to 6.5 wt% ThO2) [17]. In other alkaline complexes, the Th content in loparite is low, and it shows a tendency of enrichment in Na2O and Nb2O5 and depletion in LREEs 2O3 and TiO2 towards the grain margin, reflecting the melt evolution [17]. In the studied albite–aegirine rocks of the Burpala alkaline intrusion, unaltered loparite is practically not preserved. Instead, “metaloparite” is found (see Figure 3). The reason why “metaloparite” occurs only in certain parageneses is probably related to the change in sodium leaching rate, which depends on the alkalinity of the fluid. A decrease in alkalinity (pH 4.5–6.0) increases the rate of Na leaching from the loparite structure [14]. Our data indicate that alteration of “metaloparite” with the participation of F-containing fluids leads to the formation of a localized environment enriched in Ti, Na, Nb, and REEs and is accompanied by the formation of bastnäsite-(Ce) and Nb-bearing rutile and anatase, as well as Th-rare earth phases at the periphery of grains. Studies show that this mineralization is often associated with REE remobilization from minerals under the influence of fluids circulating during the late hydrothermal stage of the evolution of alkaline or carbonatite complexes [53,54,55]. These minerals form in the presence of precursor minerals, providing the necessary anions and/or cations for their formation. Thorium can be used as one of the main indicators of late remobilization [54]. The behavior of REEs and Zr in hydrothermal systems depends on the complex interaction of physicochemical factors such as pH, temperature, and the concentration of complexing ions (e.g., Cl−, F−, and OH−) [2].

5.3. Zircon Formation in Albite–Aegirine Rocks

Fluid-affected zircon has been the subject of numerous studies [39,56]. They have attracted attention due to their peculiar structures, diverse trace element composition, and distribution patterns of rare earth elements. The latter are considered to be the result of fluid changes and indicate changing conditions during fluid migration and evolution. There is a sufficient number of examples demonstrating the transformation of primary zircon with changes in its composition and texture [4,57]. As a result of this transformation, the newly formed zircon often develops a porous internal structure. An important factor leading to this transformation is the disruption of the zircon structure caused by α-decay radiation damage, e.g., [57]. Hydrothermally altered or deposited zircon is commonly enriched in LREEs, Sr, Y, Th, U, and other elements [20,58,59], although ThO2 contents in typical zircon generally do not exceed 1 wt% [60]. However, significantly higher Th concentrations, reaching up to 10 wt% ThO2, have been reported in zircon from alkaline granites (e.g., Um Ara, Egypt; Yanshan, China) and pegmatites (e.g., Emeishan, China) [21,61,62]. These values notably exceed the experimentally determined solubility limit of ThO2 in the zircon structure (~5.5 ± 0.5 wt%) [63].
Investigations obtained by us show that the albite–aegirine rocks of the Burpala alkaline intrusion contain two types of zircon. The first type of zircon as inclusions in aegirine likely formed via recrystallization of the latter. The second type observed in rims of “metalloparite” grains was formed as the result of the alteration of loparite-(Ce). The results of our study indicate that the residual fluid present after crystallization of the major minerals (aegirine and albite) was enriched in thorium and REEs. This is confirmed by a specific REE distribution in zircon of the second type demonstrating elevated content of these elements compared to zircon from the igneous rocks of the Burpala alkaline intrusion [39].
A weakly positive Ce anomaly and the absence of an Eu anomaly are characteristic features of the second type of zircon. The positive Ce anomaly in zircon is attributed to the fact that Ce4+ is more compatible in the zircon structure than Ce3+ and other LREEs [19]. Its magnitude is determined by the Ce4+/Ce3+ ratio, which is, in turn, controlled by the oxygen fugacity [64,65], i.e., redox conditions of the environment. The low values of the cerium anomaly in hydrothermally altered zircon may indicate reducing conditions and high alkalinity of a hydrothermal fluid [64]. In our opinion, the most probable reason for the occurrence of a reducing environment during mineral crystallization is mass aegirine crystallization, which changes the redox equilibrium in the mineral-forming medium towards reduced conditions [66]. Aegirine formation requires significant amounts of Fe3+, at the expense of Fe2+ oxidation under fluid-saturated conditions. This process is accompanied by the release of free electrons, leading to a decrease in oxygen fugacity and a shift in redox equilibrium towards more reduced conditions. It is likely that the reducing conditions during the formation of zircon from albite–egirine rocks were the reason for the absence of a positive Ce anomaly in them. A similar process is described in the work of [67], in which it is shown that newly formed metasomatic minerals can inherit the REE patterns from the replaced minerals. Despite certain differences in compositions, including REEs (Figure 7), the predominant part of the figurative points of zircon from this group on the discrimination diagrams La vs. (Sm/La)n and (Sm/La)n vs. Ce/Ce* [59] are shifted towards the fields of zircon formed under hydrothermal conditions (Figure 9).
It is well known that metasomatic processes are characterized by a combination of dissolution and precipitation of minerals, resulting in both changes in the mineral composition of rocks and alterations of the macro- and micro-elemental composition of the minerals. Combined dissolution of thorite and zircon allows for simultaneous enrichment of the fluid with thorium and zirconium [60]. This is possible under certain physicochemical conditions in which leaching and dissolution of pre-existing accessory phases occur through the interaction with F−, CO2, and OH−- containing fluids enriched in Th, Y + HREE, Zr, and/or U, which are generally thermodynamically unstable [60]. The diffusion–reaction process involving dissolution and redeposition reactions is accompanied by the formation and growth of new “pure” zircon without significant trace element impurities, as well as in situ precipitation of MSiO4 phases such as thorite (ThSiO4) or coffinite (USiO4) [56]. Despite the fact that the rocks contain “pure” Th-free zircon of the first type in the form of inclusions in aegirine, we did not find phases such as thorite or zircon with a “porous” structure comprising numerous micron-sized thorite inclusions. Substitution of alkaline pyroxenes or amphiboles with high ZrO2, TiO2, and REE contents in the rocks of alkaline magmatic complexes may be an important source of these elements for newly formed minerals [53]. It is likely that the formation of the first type of zircon occurred during the recrystallization of aegirine initially enriched in Zr.
The textural position of type II zircon suggests that this zircon crystallized at late stages. It contains no significant thorite segregations, which implies that it was not affected by dissolution and re-deposition processes. The indicator of the influence of fluid on zircon is its elevated content of non-formula elements, Ca, Sr, Ba, and some others [56]. Elemental mapping (Figure 7) confirms that the high contents of Th, REEs, Nb, Fe, and a number of other non-formula elements in zircon are most likely due to the incorporation of these elements into the structure of the mineral, rather than the presence of small mineral inclusions. The significant negative correlation (R = −0.98) between the non-formula elements and Zr(+Hf) and its absence with Si (R = 0.46) confirm that these elements predominantly occupy the Zr site (Figure 6). The presence of a peak of the ν3 (SiO4) mode shifted to 993 cm−1 (FWHM 24 cm−1) in the Raman spectra of zircon and the absence of bands in the region of the lattice modes are probably due to the presence of areas with high radiation damage and high Th content, which resulted in the metamictization of the mineral. It has been found that metamict zircon may contain significant amounts of Ca, Fe, Al, and H2O [58]. Thus, metamictization of zircon is one of the reasons for the appearance of various impurity elements in its composition, although it is also possible that the process of metamictization of the zircon structure enhances as its chemical composition changes. Several isomorphism schemes can be assumed for the occurrence of non-formula elements, the most important of which is Th4+(+U4+) → Zr4+. The appearance of trivalent cations (Y, REE) can be compensated according to the scheme (Y, REE)3+ + Nb5+ → 2Zr4+ [19]. However, the incorporation of divalent cations (Ca, Mn) remains unbalanced. It was found that even in zircon with low radiation damage to the structure, H+ can be incorporated to compensate charge imbalance [69]. Taking into account the low sums of high-Th zircon (deficiencies of sums up to 20 wt%) and their metamictization, we can assume the possibility of incorporation of a larger molecule such as a hydroxonium (H3O+). Metamict zircon crystals were previously found to be extremely reactive even under near-surface low-temperature conditions, facilitating fluid access to radiation-damaged areas [70]. The occurrence of blurred boundaries between the areas with different Th contents (see Figure 5) may indicate the presence of damaged zones in the zircon crystal lattice, which favored penetration of fluids into the original grain, which was accompanied by repeated changes in its composition. Some researchers [59,71] have established that high water (up to 5 wt%) and fluorine (up to 1 wt%) contents in zircon have a positive correlation with LREEs and the content of other incompatible elements, which may indicate exposure to fluid and/or fluid-saturated melt.

6. Conclusions

The changed redox conditions that occurred during the formation of aegirine may have favored the precipitation of rare earth and Th-bearing minerals. The studied Th-bearing zircon from aegirine–albite rocks of the Burpala alkaline intrusion has high and anomalous concentrations of thorium, OH− or H2O, and, in some cases, other incompatible elements (Nb, Al, Ca, Fe, Ti, and Ce). Such high thorium contents were previously observed only in zircon from alkaline granites subjected to both high- and low-temperature hydrothermal alterations caused by fluorine- and carbon dioxide-rich solutions [21,60,72]. The formation of Th-bearing zircon in albite–aegirine metasomatites of the Burpala alkaline intrusion occurred under similar conditions due to the impact of residual fluid enriched in Na, F, and CO2 on the “metaloparite”. This leads to its complete dissolution and remobilization of Th, LREEs, and HFSEs with significant local fluid enrichment in these elements. This results in the formation of bastnäsite, anatase, rutile, Th-bearing zircon, and rare earth phases.

Author Contributions

I.A.I. conceived and designed the project, conducted fieldwork, and prepared the original draft. A.G.D. participated in fieldwork and data curation. A.E.S. contributed to the methodology and drafted the section on mineral chemistry. A.V.M. performed EPMA analysis and provided mineralogical descriptions. T.N.M. carried out Raman analysis and provided relevant descriptions. I.S.S. reviewed and edited the entire manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

The geology of the region was studied within the framework of the state assignment of IGM SB RAS (22041400241-5), while mineralogical studies were supported by the Russian Science Foundation (RSF) under grant #22-17-00078-P (https://rscf.ru/en/project/22-17-00078/, accessed on 12 July 2025).

Data Availability Statement

The data presented in this study are contained within the article.

Acknowledgments

The analytical work was carried out using equipment provided by the Analytical Center for Multi-Elemental and Isotope Research, Siberian Branch of the Russian Academy of Sciences (Novosibirsk, Russia). We thank the two anonymous reviewers for their constructive comments, suggestions, and corrections, which helped us to improve the manuscript.

Conflicts of Interest

The author declares no conflicts of interest.

References

  1. Sheard, E.R.; Williams-Jones, A.E.; Heiligmann, M.; Pederson, J.C.; Trueman, D.L. Controls on the Concentration of Zirconium, Niobium, and the Rare Earth Elements in the Thor Lake Rare Metal Deposit, Northwest Territories, Canada. Econ. Geol. 2012, 107, 81–104. [Google Scholar] [CrossRef]
  2. Gysi, A.P.; Williams-Jones, A.E.; Collins, P. Lithogeochemical Vectors for Hydrothermal Processes in the Strange Lake Peralkaline Granitic REE-Zr-Nb Deposit. Econ. Geol. 2016, 111, 1241–1276. [Google Scholar] [CrossRef]
  3. Chakrabarty, A.; Mitchell, R.H.; Ren, M.; Pal, S.; Pal, S.; Sen, A.K. Nb–Zr–REE Re-Mobilization and Implications for Transitional Agpaitic Rock Formation: Insights from the Sushina Hill Complex, India. J. Petrol. 2018, 59, 1899–1938. [Google Scholar] [CrossRef]
  4. Liu, S.; Fan, H.-R.; Yang, K.-F.; Hu, F.-F.; Rusk, B.; Liu, X.; Li, X.-C.; Yang, Z.-F.; Wang, Q.-W.; Wang, K.-Y. Fenitization in the Giant Bayan Obo REE-Nb-Fe Deposit: Implication for REE Mineralization. Ore Geol. Rev. 2018, 94, 290–309. [Google Scholar] [CrossRef]
  5. Cuney, M.; Émertz, A.; Mercadier, J.; Mykchaylov, V.; Shunko, V.; Yuslenko, A. U Deposits Associated with Sodium Metasomatism from Central Ukraine: A Review of Some of the Major Deposits and Genetic Constraints. Ore Geol. Rev. 2012, 44, 82–106. [Google Scholar] [CrossRef]
  6. Vladykin, N.V.; Sotnikova, I.A. Petrology, Geochemistry and Source Characteristics of the Burpala Alkaline Massif, North Baikal. Geosci. Front. 2017, 8, 711–719. [Google Scholar] [CrossRef]
  7. Semenov, E.I.; Es’kova, E.M.; Kapustin, Y.L.; Khomyakov, A.P. Mineralogy of Alkaline Massifs and Their Deposits; Nauka: Moscow, Russia, 1974; p. 251. [Google Scholar]
  8. Portnov, A.M. Burpala—A Mineralogical Reserve? Priroda 2018, 5, 73–82. [Google Scholar]
  9. Arkhangel’skaya, V.V. Rare-Metal Alkaline Complexes of the Southern Margin of the Siberian Platform; Nedra: Moscow, Russia, 1974; p. 128. [Google Scholar]
  10. Portnov, A.M. Calcium Catapleiite—A New Variety of Catapleiite. Dokl. Akad. Nauk USSR 1964, 154, 603–609. [Google Scholar]
  11. Portnov, A.M.; Nikolaeva, L.V.; Stolyarova, T.I. Calcium Seidocerite—A New Variety of Seidocerite. Dokl. Akad. Nauk USSR 1964, 156, 338–340. [Google Scholar]
  12. Portnov, A.M.; Nikolaeva, L.V.; Stolyarova, T.I. Landauite, a New Titanium Mineral. Dokl. Akad. Nauk USSR 1966, 166, 1420–1421. [Google Scholar]
  13. Merlino, S.; Perchiazzi, N.; Khomyakov, A.P.; Pushcharovskii, D.Y.; Kulikova, I.M.; Kuzmin, V.I. Burpalite, a New Mineral from Burpalinskii Massif, North Transbaikalia, USSR: Its Crystal Structure and OD Character. Eur. J. Miner. 1990, 2, 177–185. [Google Scholar] [CrossRef]
  14. Chakhmouradian, A.R.; Mitchell, R.H.; Pankov, A.V.; Chukanov, N.V. Loparite and ‘Metaloparite’ from the Burpala Alkaline Complex, Baikal Alkaline Province (Russia). Miner. Mag. 1999, 63, 519–534. [Google Scholar] [CrossRef]
  15. Macdonald, R.; Baginski, B.; Kartashov, P.; Zozulia, D.; Dzierzanowski, P. Chevkinite-Group Minerals from Russia and Mongolia: New Data from Fenites, Metasomatites and Ore Deposits. Miner. Mag. 2012, 76, 535–550. [Google Scholar] [CrossRef]
  16. Stachowicz, M.; Bagiński, B.; Macdonald, R.; Kartashov, P.M.; Oziębło, A.; Wożniak, K. Structure of Sr-Zr-Bearing Perrierite-(Ce) from the Burpala Massif, Russia. Miner. Mag. 2014, 78, 1647–1659. [Google Scholar] [CrossRef]
  17. Mitchell, R.H.; Chakhmouradian, A.R. Th-Rich Loparite from the Khibina Alkaline Complex, Kola Peninsula: Isomorphism and Paragenesis. Miner. Mag. 1998, 62, 341–353. [Google Scholar] [CrossRef]
  18. Skublov, S.G.; Li, S.-H. Anomalous Geochemistry of Zircon from the Yastrebetskoye Rare-Metal Deposit (SIMS and TOF Study). Zap. Gorn. Inst. 2016, 222, 798–802. [Google Scholar]
  19. Hoskin, P.W.O.; Schaltegger, U. The Composition of Zircon and Igneous and Metamorphic Petrogenesis. Rev. Miner. Geochem. 2003, 53, 25–104. [Google Scholar] [CrossRef]
  20. Vlach, S.R.F. On the Morphology and Geochemistry of Hydrothermal Crypto- and Microcrystalline Zircon Aggregates in a Peralkaline Granite. Minerals 2022, 12, 628. [Google Scholar] [CrossRef]
  21. Abd El-Naby, H.H. High and Low Temperature Alteration of Uranium and Thorium Minerals, Um Ara Granites, South Eastern Desert, Egypt. Ore Geol. Rev. 2009, 35, 436–446. [Google Scholar] [CrossRef]
  22. Abd El-Naby, H.H. Alteration and Non-Formula Elements Uptake of Zircon from Um Ara Granite, South Eastern Desert, Egypt. Minerals 2024, 14, 834. [Google Scholar] [CrossRef]
  23. Starikova, A.E.; Doroshkevich, A.G.; Sklyarov, E.V.; Donskaya, T.V.; Gladkochub, D.P.; Shaparenko, E.O.; Zhukova, I.A.; Semenova, D.V.; Yakovenko, E.S.; Ragozin, A.L. Magmatism and Metasomatism in the Formation of the Katugin Nb-Ta-REE-Zr-Cryolite Deposit, Eastern Siberia, Russia: Evidence from Zircon Data. Lithos 2024, 472–473, 107557. [Google Scholar] [CrossRef]
  24. Griffin, W.L.; Powell, W.J.; Pearson, N.J.; O’Reilly, S.Y. GLITTER: Data Reduction Software for Laser Ablation ICP-MS. In Laser Ablation ICP-MS in the Earth Sciences: Current Practices and Outstanding Issues; Mineralogical Association of Canada, Short Course Series; Sylvester, P., Ed.; Mineralogical Association of Canada: Québec City, QC, Canada, 2008; Volume 40, pp. 307–311. [Google Scholar]
  25. Jackson, S.E.; Pearson, N.J.; Griffin, W.L.; Belousova, E.A. The Application of Laser Ablation-Inductively Coupled Plasma Mass Spectrometry to In Situ U-Pb Zircon Geochronology. Chem. Geol. 2004, 211, 47–69. [Google Scholar] [CrossRef]
  26. Yuan, H.-L.; Gao, S.; Dai, M.-N.; Zong, C.-L.; Günther, D.; Fontaine, G.H.; Liu, X.-M.; Diwu, C.R. Simultaneous Determination of U-Pb Age, Hf Isotopes and Trace Element Compositions of Zircon by Excimer Laser-Ablation Quadrupole and Multiple-Collector ICP-MS. Geostand. Geoanal. Res. 2008, 32, 405–419. [Google Scholar] [CrossRef]
  27. Piazolo, S.; Belousova, E.; La Fontaine, A.; Corcoran, C.; Cairney, J.M. Trace Element Homogeneity from Micron- to Atomic Scale: Implications for the Suitability of Zircon GJ-1 as a Reference Material. Chem. Geol. 2017, 456, 10–18. [Google Scholar] [CrossRef]
  28. Warr, L.N. IMA–CNMNC Approved Mineral Symbols. Miner. Mag. 2021, 85, 291–320. [Google Scholar] [CrossRef]
  29. Jahn, B.M.; Litvinovsky, B.A.; Zanvilevich, A.N.; Reichow, M. Peralkaline Granitoid Magmatism in the Mongolian–Transbaikalian Belt: Evolution, Petrogenesis and Tectonic Significance. Lithos 2009, 113, 521–539. [Google Scholar] [CrossRef]
  30. Litvinovsky, B.A.; Tsygankov, A.A.; Jahn, B.M.; Katzir, Y.; Be’eri-Shlevin, Y. Origin and Evolution of Overlapping Calc-Alkaline and Alkaline Magmas: The Late Palaeozoic Post-Collisional Igneous Province of Transbaikalia (Russia). Lithos 2011, 125, 845–874. [Google Scholar] [CrossRef]
  31. Doroshkevich, A.G.; Ripp, G.S.; Izbrodin, I.A.; Savatenkov, V.M. Alkaline Magmatism of the Vitim Province, West Transbaikalia, Russia: Age, Mineralogical, Geochemical and Isotope (O, C, D, Sr and Nd) Data. Lithos 2012, 152, 157–172. [Google Scholar] [CrossRef]
  32. Tsygankov, A.A.; Burmakina, G.N.; Khubanov, V.B.; Buyantuev, M.D. Geodynamics of Late Paleozoic Batholith-Forming Processes in Western Transbaikalia. Petrology 2017, 25, 396–418. [Google Scholar] [CrossRef]
  33. Izbrodin, I.; Doroshkevich, A.G.; Rampilov, M.; Elbaev, A.; Ripp, G. Late Paleozoic Alkaline Magmatism in Western Transbaikalia, Russia: Implications for Magma Sources and Tectonic Settings. Geosci. Front. 2020, 11, 1289–1303. [Google Scholar] [CrossRef]
  34. Andreev, A.A.; Rytsk, E.Y.; Velikoslavinskii, S.D.; Tolmacheva, E.V.; Bogomolov, E.S.; Lebedeva, Y.M.; Fedoseenko, A.M. Age, Composition, and Tectonic Setting of the Formation of Late Neoproterozoic (Late Baikalian) Complexes in the Kichera Zone, Baikal-Vitim Belt, Northern Baikal Area: Geological, Geochronological, and Nd Isotope Data. Petrology 2022, 30, 345–378. [Google Scholar] [CrossRef]
  35. Andreev, G.V. Petrology of the Formation of Potassic, Nepheline, and Alkaline Syenites; Nauka: Novosibirsk, Russia, 1981; p. 85. [Google Scholar]
  36. Pak, A.S.; Mikov, N.A.; Bushuev, V.P.; Mikhalev, D.F.; Tokar’, N.V.; Yudovskii, A.G. Report on the Results of Geological Exploration Work by the Sol’ Party in the Maigunda River Basin for 1960–1961; Buryat Geological Department: Ulan-Ude, Russia, 1962; p. 213. [Google Scholar]
  37. Kotov, A.B.; Vladykin, N.V.; Yarmolyuk, V.V.; Sal’nikova, E.B.; Sotnikova, I.A.; Yakovleva, S.Z. Permian Age of the Burpala Alkaline Intrusion (Northern Baikal Area): Geodynamic Implications. Dokl. Akad. Nauk 2013, 453, 295–299. [Google Scholar]
  38. Izbrodin, I.A.; Doroshkevich, A.G.; Malyutina, A.V.; Semenova, D.V.; Radomskaya, T.A.; Kruk, M.N.; Prokopev, I.R.; Starikova, A.E.; Rampilov, M.O. Geochronology of the Rocks of the Burpala Alkaline Complex (Northern Baikal Area): New U-Pb Data. Geodin. Tektonofiz. 2024, 15, 741. [Google Scholar] [CrossRef]
  39. Starikova, A.E.; Malyutina, A.V.; Izbrodin, I.A.; Doroshkevich, A.G.; Radomskaya, T.A.; Isakova, A.T.; Semenova, D.V.; Korsakov, A.V. Mineralogical-Petrographic and Geochemical Characteristics of Zircon as an Indication of Its Formation Conditions Based on Zircons from Rocks of the Burpalinsky Massif, Northern Baikal Region. Geodin. Tektonofiz. 2024, 15, 787. [Google Scholar] [CrossRef]
  40. Vladykin, N.V.; Sotnikova, I.A.; Kotov, A.B.; Yarmolyuk, V.V.; Sal’nikova, E.B.; Yakovleva, S.Z. Structure, Age, and Ore Potential of the Burpala Rare-Metal Alkaline Massif (Northern Baikal Area). Geol. Rudn. Mestorozhd. 2014, 56, 272–290. [Google Scholar]
  41. Malyutina, A.V.; Doroshkevich, A.G.; Starikova, A.E.; Izbrodin, I.A.; Prokop’ev, I.R.; Radomskaya, T.A.; Kruk, M.N. Composition of Mafic Rock-Forming Minerals in the Rocks of the Burpala Alkaline Massif (Northern Baikal Area). Russ. Geol. Geophys. 2025, 66, 299–315. [Google Scholar] [CrossRef]
  42. Doroshkevich, A.G.; Savatenkov, V.M.; Malyutina, A.V.; Izbrodin, I.A.; Prokopiev, I.R.; Starikova, A.E.; Radomskaya, T.A. Petrogenesis and Sources for Rocks of the Alkaline Rare-Metal Burpala Intrusion (Northern Baikal Region). Petrology 2025, 33, 45–67. [Google Scholar] [CrossRef]
  43. Lafuente, B.; Downs, R.T.; Yang, H.; Stone, N. The Power of Databases: The RRUFF Project. In Highlights in Mineralogical Crystallography; De Gruyter: Berlin, Germany, 2015; pp. 1–30. [Google Scholar]
  44. Sacco, A.; Mandrile, L.; Tay, L.-L.; Itoh, N.; Raj, A.; Moure, A.; Del Campo, A.; Fernandez, J.F.; Paton, K.R.; Wood, S.; et al. Quantification of Titanium Dioxide (TiO2) Anatase and Rutile Polymorphs in Binary Mixtures by Raman Spectroscopy: An Interlaboratory Comparison. Metrologia 2023, 60, 05501. [Google Scholar] [CrossRef]
  45. Pasero, M.; Kampf, A.R.; Ferraris, C.; Pekov, I.V.; Rakovan, J.; White, T.J. Nomenclature of the Apatite Supergroup Minerals. Eur. J. Miner. 2010, 22, 163–179. [Google Scholar] [CrossRef]
  46. Sun, S.-S.; McDonough, W.F. Chemical and Isotopic Systematics of Oceanic Basalts: Implications for Mantle Composition and Processes. Geol. Soc. Lond. Spec. Publ. 1989, 42, 313–345. [Google Scholar] [CrossRef]
  47. Hoskin, P.W.O.; Rodgers, K.A. Raman Spectral Shift in the Isomorphous Series (Zr1−xHfx)SiO4. Eur. J. Solid State Inorg. Chem. 1996, 33, 1111–1121. [Google Scholar]
  48. Nasdala, L.; Irmer, G.; Wolf, D. The Degree of Metamictization in Zircon: A Raman Spectroscopic Study. Eur. J. Miner. 1995, 7, 471–478. [Google Scholar] [CrossRef]
  49. Zhang, M.; Salje, E.K.H.; Farnan, I.; Graeme-Barber, A.; Daniel, P.; Ewing, R.C.; Clark, A.M.; Leroux, H. Metamictization of Zircon: Raman Spectroscopic Study. J. Phys. Condens. Matter 2000, 12, 1915–1925. [Google Scholar] [CrossRef]
  50. Zamyatin, D.A. Application of Raman Spectroscopy for Studying Shocked Zircon from Terrestrial and Lunar Impactites: A Systematic Review. Minerals 2022, 12, 969. [Google Scholar] [CrossRef]
  51. Zeng, Z.; Liu, Y. Magmatic–Hydrothermal Zircons in Syenite: A Record of Nb-Ta Mineralization Processes in the Emeishan Large Igneous Province, SW China. Chem. Geol. 2022, 589, 120675. [Google Scholar] [CrossRef]
  52. Kostyleva-Labuntsova, E.E.; Borutskii, B.E.; Sokolova, M.N.; Shlyukova, Z.V.; Dorfman, M.D.; Dudkin, O.B.; Kozyreva, L.V. Mineralogy of the Khibiny Intrusion; Nauka: Moscow, Russia, 1978; Volume 2, p. 586. [Google Scholar]
  53. Feng, Y.; Samson, I. Replacement Processes Involving High Field Strength Elements in the T Zone, Thor Lake Rare-Metal Deposit. Can. Miner. 2015, 53, 31–60. [Google Scholar] [CrossRef]
  54. Giebel, R.J.; Gauert, C.D.K.; Marks, M.A.W.; Costin, G.; Markl, G. Multi-Stage Formation of REE Minerals in the Palabora Carbonatite Complex, South Africa. Am. Miner. 2017, 102, 1218–1233. [Google Scholar] [CrossRef]
  55. Kozlov, E.; Fomina, E.; Sidorov, M.; Shilovskikh, V. Ti-Nb Mineralization of Late Carbonatites and Role of Fluids in its Formation: Petyayan-Vara Rare-Earth Carbonatites (Vuoriyarvi Intrusion, Russia). Geosciences 2018, 8, 281. [Google Scholar] [CrossRef]
  56. Geisler, T.; Schaltegger, U.; Tomaschek, F. Re-equilibration of Zircon in Aqueous Fluids and Melts. Elements 2007, 3, 43–50. [Google Scholar] [CrossRef]
  57. Corfu, F.; Hanchar, J.; Hoskin, P.W.O.; Kinny, P. Atlas of Zircon Textures. Rev. Miner. Geochem. 2003, 53, 469–500. [Google Scholar] [CrossRef]
  58. Geisler, T.; Pidgeon, R.T.; Bronswijk, W.; Kurtz, R. Transport of Uranium, Thorium, and Lead in Metamict Zircon under Low-Temperature Hydrothermal Conditions. Chem. Geol. 2002, 191, 141–154. [Google Scholar] [CrossRef]
  59. Hoskin, P.W.O. Trace-Element Compositions of Hydrothermal Zircon and the Alteration of Hadean Zircon from the Jack Hills. Geochim. Cosmochim. Acta 2005, 69, 637–648. [Google Scholar] [CrossRef]
  60. Förster, H.J. Composition and Origin of Intermediate Solid Solutions in the System Thorite–Xenotime–Zircon–Coffinite. Lithos 2006, 88, 35–55. [Google Scholar] [CrossRef]
  61. Xie, L.; Wang, R.; Chen, X.; Wang, D. Th-Rich Zircon from Peralkaline A-Type Granite: Mineralogical Features and Petrological Implications. Chin. Sci. Bull. 2005, 50, 809–817. [Google Scholar]
  62. Yin, R.; Sun, X.-M.; Wang, S.-W.; Ru-Cheng, W.; Ran, M.-L.; Wu, B.; Huang, X.-L. Zircons in NYF-Type Pegmatites in the Emeishan Large Igneous Province, SW China: A Record of Nb and REE Mineralization Processes. Ore Geol. Rev. 2023, 162, 105700. [Google Scholar] [CrossRef]
  63. Mumpton, F.A.; Roy, R. Hydrothermal Stability Studies of the Zircon-Thorite Group. Geochim. Cosmochim. Acta 1961, 21, 217–238. [Google Scholar] [CrossRef]
  64. Burnham, A.D.; Berry, A.J. An Experimental Study of Trace Element Partitioning Between Zircon and Melt as a Function of Oxygen Fugacity. Geochim. Cosmochim. Acta 2012, 95, 196–212. [Google Scholar] [CrossRef]
  65. Trail, D.; Bruce, E.; Tailby, N.D. Ce and Eu Anomalies in Zircon as Proxies for the Oxidation State of Magmas. Geochim. Cosmochim. Acta 2012, 97, 70–87. [Google Scholar] [CrossRef]
  66. Markl, G.; Marks, M.A.W.; Frost, B.R. On the Controls of Oxygen Fugacity in the Generation and Crystallization of Peralkaline Melts. J. Petrol. 2010, 51, 1831–1847. [Google Scholar] [CrossRef]
  67. Skublov, S.G. Geochemistry of Rare Earth Elements in Rock-Forming Minerals of Metamorphic Rocks; Nauka: St. Petersburg, Russia, 2005; p. 147. [Google Scholar]
  68. Bouvier, A.-S.; Ushikubo, T.; Kita, N.T.; Cavosie, A.J.; Kozdon, R.; Valley, J.W. Li Isotopes and Trace Elements as a Petrogenetic Tracer in Zircon: Insights from Archean TTGs and Sanukitoids. Contrib. Miner. Petrol. 2012, 163, 745–768. [Google Scholar] [CrossRef]
  69. De Hoog, J.C.M.; Lissenberg, C.J.; Brooker, R.A.; Hinton, R.W.; Trail, D.; Hellebrand, E. Hydrogen Incorporation and Charge Balance in Natural Zircon. Geochim. Cosmochim. Acta 2014, 141, 472–486. [Google Scholar] [CrossRef]
  70. Hay, D.C.; Dempster, T.J. Zircon Alteration, Formation and Preservation in Sandstones. Sedimentology 2009, 56, 2175–2191. [Google Scholar] [CrossRef]
  71. Hoshino, M.; Watanabe, Y.; Murakami, H.; Kon, Y.; Tsunematsu, M. Formation Process of Zircon Associated with REE-Fluorocarbonate and Niobium Minerals in the Nechalacho REE Deposit, Thor Lake, Canada. Resour. Geol. 2012, 63, 1–26. [Google Scholar] [CrossRef]
  72. Breiter, K.; Förster, H.-J.; Škoda, R. Extreme P-, Bi-, Nb-, Sc-, U- and F-Rich Zircon from Fractionated Perphosphorous Granites: The Peraluminous Podlesí Granite System, Czech Republic. Lithos 2006, 88, 15–34. [Google Scholar] [CrossRef]
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Figure 1. (a). Schematic geologic map of the Burpala alkaline intrusion [36]. The inset shows the alkaline intrusions of the Synnyr complex: G—Goujekit, B—Burpala, A—Akit, S—Synnyr, and M—Monyukan. (b). Scheme of the geological structure of the northern part of the Burpala ore manifestation [9,36].
Figure 1. (a). Schematic geologic map of the Burpala alkaline intrusion [36]. The inset shows the alkaline intrusions of the Synnyr complex: G—Goujekit, B—Burpala, A—Akit, S—Synnyr, and M—Monyukan. (b). Scheme of the geological structure of the northern part of the Burpala ore manifestation [9,36].
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Figure 2. Photographs of samples (a,b) and thin sections (c,d) of albite–aegirine rocks: (a)—sinuous contact of aegirine–albite rocks enriched in “metaloparite” with quartz syenites; (b)—sample fragment of essentially aegirine rocks with aggregates of “metaloparite” (m-Lop) and Th-bearing zircon (Th-Zrc); (c,d) transmitted-light microphotographs of zircon in aegirine grains (Cpx), polarized light sound (thin section k8-1). Ab—albite and Bsn—bastnäsite.
Figure 2. Photographs of samples (a,b) and thin sections (c,d) of albite–aegirine rocks: (a)—sinuous contact of aegirine–albite rocks enriched in “metaloparite” with quartz syenites; (b)—sample fragment of essentially aegirine rocks with aggregates of “metaloparite” (m-Lop) and Th-bearing zircon (Th-Zrc); (c,d) transmitted-light microphotographs of zircon in aegirine grains (Cpx), polarized light sound (thin section k8-1). Ab—albite and Bsn—bastnäsite.
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Figure 3. Back-scattered electron (BSE) images show the morphology and internal structure of “metaloparite” and titanium oxides: (a)—fragment of a “metaloparite” grain partially replaced by bastnäsite-(Ce) (Bsn-(Ce)), a phase compositionally similar to “metaloparite” (x-Lop), and associated Ti-oxides (rutile (Rt) and anatase (Ant)) with marked analytical points, for which Raman spectra were obtained (Nb2O5 content in wt% is given in brackets); (b–d)—grains of “metaloparite” completely replaced by aggregate of bastnäsite and rutile; Th-bearing zircon and mineral aggregate of Th-REE-Si-Ti-Zr composition are developed at the edges. Aeg—aegirine, Mnz-(Ce)—monazite-(Ce) and Fap—fluorapatite. Sample k8-1.
Figure 3. Back-scattered electron (BSE) images show the morphology and internal structure of “metaloparite” and titanium oxides: (a)—fragment of a “metaloparite” grain partially replaced by bastnäsite-(Ce) (Bsn-(Ce)), a phase compositionally similar to “metaloparite” (x-Lop), and associated Ti-oxides (rutile (Rt) and anatase (Ant)) with marked analytical points, for which Raman spectra were obtained (Nb2O5 content in wt% is given in brackets); (b–d)—grains of “metaloparite” completely replaced by aggregate of bastnäsite and rutile; Th-bearing zircon and mineral aggregate of Th-REE-Si-Ti-Zr composition are developed at the edges. Aeg—aegirine, Mnz-(Ce)—monazite-(Ce) and Fap—fluorapatite. Sample k8-1.
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Figure 4. Raman spectra of titanium oxides. 1, 2—rutile (point 172 in Figure 3a and point 106 in Figure 5, respectively) and 3—anatase (point 168 in Figure 3a).
Figure 4. Raman spectra of titanium oxides. 1, 2—rutile (point 172 in Figure 3a and point 106 in Figure 5, respectively) and 3—anatase (point 168 in Figure 3a).
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Figure 5. The occurrence of different types of zircon in albite–aegirine rocks of the Burpala alkaline intrusion. (a) Finely disseminated zircon (Zrn) in aegirine and interstitial high-Th zircon (Th-Zrn); (b) zoomed-in fragment of high-Th zircon, where points indicate areas for which the Raman spectra were obtained. ThO2 and Nb2O5 contents (in wt%) of zircon and rutile, respectively, are given in parentheses. (a,b)—BSE images; (c) high-Th zircon elemental maps based on the energy-dispersive analysis (EDS) technique; (d) the 2D Raman map for a high-Th zircon grain obtained using a filter of 440 ± 70 cm−1.
Figure 5. The occurrence of different types of zircon in albite–aegirine rocks of the Burpala alkaline intrusion. (a) Finely disseminated zircon (Zrn) in aegirine and interstitial high-Th zircon (Th-Zrn); (b) zoomed-in fragment of high-Th zircon, where points indicate areas for which the Raman spectra were obtained. ThO2 and Nb2O5 contents (in wt%) of zircon and rutile, respectively, are given in parentheses. (a,b)—BSE images; (c) high-Th zircon elemental maps based on the energy-dispersive analysis (EDS) technique; (d) the 2D Raman map for a high-Th zircon grain obtained using a filter of 440 ± 70 cm−1.
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Figure 6. Compositional diagrams of Th-free zircon of the first type (blue squares) and high-Th zircon of the second type (orange circles), based on EPMA determinations. Data are from albite–aegirine rocks of the Burpala alkaline intrusion: (a) Si content (apfu) versus non-formula element totals (apfu); (b) Zr + Hf content (apfu) versus non-formula element totals (apfu); (c) Triangular diagram showing the distribution of (Y + REE), (U + Th), and (Zr + Hf) in zircon grains (apfu). Th, U, REEs, Y, Nb, Ca, Na, Fe, Mn, and Ti are referred to as non-formular elements.
Figure 6. Compositional diagrams of Th-free zircon of the first type (blue squares) and high-Th zircon of the second type (orange circles), based on EPMA determinations. Data are from albite–aegirine rocks of the Burpala alkaline intrusion: (a) Si content (apfu) versus non-formula element totals (apfu); (b) Zr + Hf content (apfu) versus non-formula element totals (apfu); (c) Triangular diagram showing the distribution of (Y + REE), (U + Th), and (Zr + Hf) in zircon grains (apfu). Th, U, REEs, Y, Nb, Ca, Na, Fe, Mn, and Ti are referred to as non-formular elements.
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Figure 7. The chondrite-normalized [46] REE patterns for high-Th zircon of the second type as compared to zircon from the Burpala alkaline intrusion rocks. Zircon fields are shown according to [39].
Figure 7. The chondrite-normalized [46] REE patterns for high-Th zircon of the second type as compared to zircon from the Burpala alkaline intrusion rocks. Zircon fields are shown according to [39].
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Figure 8. Raman spectra of zircon from aegirine–albite rocks (sample k8-1). (a,b) Raman spectra at the points corresponding to the electron microscope analysis in Figure 5 and Figure 8c, respectively. (c) Raman spectrum and luminescence of moderately metamict zircon (points 87 and 90 in Figure 8b (ThO2 content in wt% is given in brackets).
Figure 8. Raman spectra of zircon from aegirine–albite rocks (sample k8-1). (a,b) Raman spectra at the points corresponding to the electron microscope analysis in Figure 5 and Figure 8c, respectively. (c) Raman spectrum and luminescence of moderately metamict zircon (points 87 and 90 in Figure 8b (ThO2 content in wt% is given in brackets).
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Figure 9. Discrimination diagrams for zircon from aegirine–albite rocks. (a) La vs. (Sm/La)n, and (b) (Sm/La)n vs. Ce/Ce* fields after [59,68].
Figure 9. Discrimination diagrams for zircon from aegirine–albite rocks. (a) La vs. (Sm/La)n, and (b) (Sm/La)n vs. Ce/Ce* fields after [59,68].
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Table 1. List of ore minerals in the mineralization zones of the Burpala alkaline intrusion.
Table 1. List of ore minerals in the mineralization zones of the Burpala alkaline intrusion.
Ore ZoneType of RocksOre Minerals Associated SizeAge, Ma (References)
№5Nepheline syenitesZircon, thorite, loparite-(Ce), chevkinite-(Ce), bastnäsite-(Ce), and apatite-(Ce),The total thickness of the zone is more than 100 m, with a length of more than 2 km.296 ± 2 [38]
№4Dyke-like fluorite-apatite body, fluoritized, and albitized syenitesApatite-(Ce), fluorite, and leucophaniteThe thickness is 4–5 m, with a length of up to 150 m and eluvial landfills on an area of 150 × 40 m
№3Pegmatoid alkaline syenites and pegmatitesEudialyte, lamprophyllite, catapleite, lovenite, vlasovite, ramsite, astrophyllite, tainiolite, ilmenite, pyrophanite, magnetite, chalcopyrite, chalcosine, pyrite, wolframite, apatite-(Ce), britholite-(Ce), and titaniteThe thickness is 1–2 m, up to 30 m, and the length is 100–200 m283 ± 8 [37]
№2Fenites AND albite–aegirine rocksZircon, thorite, catapleiite, lovenite, astrophyllite, aeschynite, calcium seidoserite, ilmenite, rutile, loparite-(Ce), “metaloparite”, melanocerite-(Ce), chevkinite-(Ce), bastnäsite-(Ce), monazite-(Ce), apatite-(Ce), perrierite, leucophanite, burpalite, landauite, U-pyrochlore, and fluoriteThe thickness of the fenitization zone is 10–30 m, with albite–aegirine metasomatites 1–5 m, extending up to 4 km295 ± 3 [39]
№1Albite–aegirine and aegirine–microcline rocksZircon, thorite, catapleiite, lovenite, astrophyllite, aeschynite, calcium seidoserite, ilmenite, rutile, loparite-(Ce), “metaloparite”, melanocerite-(Ce), chevkinite-(Ce), bastnäsite-(Ce), monazite-(Ce), apatite-(Ce), perrierite, leucophanite, burpalite, landauite, U-pyrochlore, and fluoriteThe thickness is 1–5 m in length with interruptions up to 4 km
Table 2. The representative analyses of newly formed phases and “metaloparite” from albite–aegirine rocks (sample k8-1 of the Burpala alkaline intrusion (wt%).
Table 2. The representative analyses of newly formed phases and “metaloparite” from albite–aegirine rocks (sample k8-1 of the Burpala alkaline intrusion (wt%).
№1234567891011
Samplek8-1k8-1k8-1ak8-2k8-1k8-1ak8-1k8-1k8-1k8-1k8-1
SiO2b.d.b.d.b.d.b.d.b.d.b.d.0.609.698.328.909.65
CaO0.921.040.740.150.130.140.322.141.372.142.01
SrO1.470.430.78b.d.b.d.b.d.b.d.b.d.b.d.b.d.0.69
BaOb.d.b.d.b.d.b.d.b.d.b.d.b.d.2.492.13b.d.b.d.
La2O312.6513.9014.0514.7313.7412.2913.744.448.47b.d.2.54
Ce2O320.2221.0720.8723.1221.8921.4622.0312.0416.496.448.48
Pr2O31.161.431.401.191.581.491.640.941.29b.d.1.04
Nd2O33.563.673.383.324.154.303.783.182.902.693.23
ThO24.894.164.563.805.137.035.877.174.7519.6719.08
UO2b.d.b.d.b.d.b.d.b.d.b.d.b.d.b.d.b.d.b.d.1.17
PbOb.d.b.d.b.d.b.d.b.d.b.d.b.d.b.d.b.d.8.814.19
MnOb.d.b.d.b.d.b.d.b.d.b.d.b.d.2.001.301.981.61
TiO245.7044.6544.2743.8043.4943.2442.9035.3534.2523.6224.07
Fe2O3b.d.b.d.b.d.b.d.b.d.b.d.b.d.0.510.45b.d.b.d.
Nb2O52.534.383.734.714.664.083.965.114.467.307.85
Total93.1094.7393.7894.8294.7794.0394.8485.0686.1884.3785.61
The formula is calculated on the basis of two cations at the B site
Si0.000.000.000.000.000.000.04
Ca0.060.060.050.010.010.010.02
Sr0.050.010.030.000.000.000.00
Ba0.000.000.000.000.000.000.00
La0.260.290.300.310.290.260.30
Ce0.420.430.440.480.460.460.47
Pb0.000.000.000.000.000.000.00
Pr0.020.030.030.030.030.030.04
Nd0.070.070.070.070.090.090.08
Th0.060.050.060.050.070.090.08
U0.000.000.000.000.000.000.00
Mn0.000.000.000.000.000.000.00
∑0.940.960.960.940.950.941.02
Ti1.941.891.901.881.881.891.90
Fe3+0.000.000.000.000.000.000.00
Nb0.070.110.100.120.120.110.11
∑2.002.002.002.002.002.002.00
Note. Here and in other tables, b.d. = below detection limit. 1–7—“metaloparite” (m-Lop); 8–11—mineral phases developed over “metaloparite” (x-Lop).
Table 3. The chemical composition of bastnäsite-(Ce) from albite–aegirine rocks (sample k8-1) in the Burpala alkaline intrusion (wt%).
Table 3. The chemical composition of bastnäsite-(Ce) from albite–aegirine rocks (sample k8-1) in the Burpala alkaline intrusion (wt%).
1234567891011
CaO1.250.15b.d.b.d.b.d.0.20b.d.b.d.0.35b.d.b.d.
TiO2b.d.b.d.b.d.b.d.0.820.72b.d.0.730.57b.d.b.d.
SrOb.d.b.d.b.d.0.72b.d.b.d.b.d.0.48b.d.b.d.b.d.
ThO21.351.631.133.031.410.530.831.66b.d.b.d.b.d.
La2O328.1721.8826.2225.0325.7325.9521.7224.3127.2323.9721.98
Ce2O330.5534.8735.1436.1136.7236.7336.7436.7537.1237.1637.46
Pr2O32.132.121.951.991.952.502.291.941.722.212.48
Nd2O36.147.224.984.914.985.167.075.184.115.775.61
F8.607.908.748.868.969.208.748.877.928.558.59
Total78.1975.7778.1680.6580.5780.9977.3979.9279.0277.6676.12
–O=F23.613.323.673.723.763.873.673.733.333.593.61
Total74.5872.4574.4976.9376.8177.1273.7276.1975.6974.0772.51
Note. b.d. = below detection limit.
Table 4. Representative analyses of zircon from albite–aegirine rocks of the Burpala alkaline intrusion (wt%).
Table 4. Representative analyses of zircon from albite–aegirine rocks of the Burpala alkaline intrusion (wt%).
№1234567891011
Samplek8-1k8-1ak8-2k8-1ak8-2k8-1k8-1k8-1k8-1k8-1ak8-1
SiO233.7533.1633.7330.4430.7425.6528.1323.9423.4729.0328.35
ZrO265.7364.9763.7659.3857.6941.8151.0229.6629.1849.943.06
HfO21.011.891.760.81.2b.d.1.360.87b.d.1.060.99
ThO2b.d.b.d.b.d.1.832.002.573.215.5417.694.049.02
UO2b.d.b.d.b.d.b.d.b.d.0.59b.d.b.d.b.d.b.d.b.d.
TiO2b.d.b.d.b.d.b.d.0.380.870.431.031.020.530.95
Al2O3b.d.b.d.b.d.b.d.b.d.0.420.21b.d.b.d.b.d.0.28
Ce2O3b.d.b.d.b.d.b.d.b.d.1.17b.d.1.041.190.490.8
Nd2O3b.d.b.d.b.d.b.d.b.d.b.d.b.d.0.790.790.580.78
Y2O3b.d.b.d.b.d.b.d.b.d.b.d.b.d.b.d.b.d.1.841.93
FeOb.d.b.d.b.d.b.d.1.040.901.072.501.831.811.83
Fe2O3b.d.b.d.b.d.b.d.1.161.001.192.782.032.012.03
MnOb.d.b.d.b.d.b.d.0.430.560.340.71.010.50.74
CaOb.d.b.d.b.d.b.d.0.240.670.321.051.120.620.83
Na2Ob.d.b.d.b.d.0.630.361.240.42b.d.b.d.0.350.42
Nb2O5b.d.b.d.b.d.b.d.b.d.2.031.321.391.86b.d.1.30
Total100.49100.0299.2593.0895.2479.4889.0181.2981.1992.7693.31
Cation proportions on the basis of 16 oxygen atoms
Si3.953.913.954.024.034.023.984.104.064.014.00
Zr3.873.893.873.823.683.203.522.482.463.362.96
Hf0.040.070.060.030.040.000.050.040.000.040.04
Th0.000.000.000.050.060.090.100.610.700.130.29
U0.000.000.000.000.000.020.000.000.000.000.00
Ti0.000.000.000.000.040.100.050.130.130.060.10
Al0.000.000.000.000.000.080.030.000.000.000.05
Ce0.000.000.000.000.000.070.000.070.080.020.04
Nd0.000.000.000.000.000.000.000.050.050.030.04
Y0.000.000.000.000.000.000.000.000.000.140.14
Fe0.000.000.000.050.110.120.130.360.260.210.22
Mn0.000.000.000.000.050.070.040.100.150.060.09
Ca0.000.000.000.000.030.110.050.190.210.090.13
Na0.000.000.000.160.090.380.120.000.000.090.11
Nb0.000.000.000.000.000.140.080.110.150.000.08
Note. b.d. = below detection limit. 1–3 Th-free zircon of the first type; 4–11—high-Th zircon of the second type.
Table 5. The trace element composition (ppm) of high-Th zircon of the second type (sample k8-1).
Table 5. The trace element composition (ppm) of high-Th zircon of the second type (sample k8-1).
Component123456789
P155159168230428390268204120
Ca15311225113762530201235999553352
Ti238333356139135792829214036
Rb5.31102442172866501.5
Sr1421031043926273643716
Y10,11064288150683283796950681564915201
Nb8601227131945824371503745489118
Ba186156175742832101306921
La4691926212590865016
Ce71116919771285752283888965174
Pr762261181481434312113815
Nd66813656481177832235849975109
Sm374338226337418133284299130
Eu11587718611142817959
Gd495325311308445219302293412
Tb12675847511974737196
Dy11136748507031070809715669828
Ho304184264214292244207188217
Er1226809116395912131026939864752
Tm278189292238280243226204143
Yb21781520237119532209188918131646906
Lu346248389326361311299273136
Hf719780906870818574027610727077834901
Ta33425517463321161.7
Th572228512523497465135407400230493368
U47410429437902004132710758972930
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Izbrodin, I.A.; Doroshkevich, A.G.; Starikova, A.E.; Malyutina, A.V.; Moroz, T.N.; Sharygin, I.S. Zr-Th-REE Mineralization Associated with Albite–Aegirine-Bearing Rocks of the Burpala Alkaline Intrusion (North Baikal Region, South Margin of the Siberian Craton). Minerals 2025, 15, 742. https://doi.org/10.3390/min15070742

AMA Style

Izbrodin IA, Doroshkevich AG, Starikova AE, Malyutina AV, Moroz TN, Sharygin IS. Zr-Th-REE Mineralization Associated with Albite–Aegirine-Bearing Rocks of the Burpala Alkaline Intrusion (North Baikal Region, South Margin of the Siberian Craton). Minerals. 2025; 15(7):742. https://doi.org/10.3390/min15070742

Chicago/Turabian Style

Izbrodin, Ivan Aleksandrovich, Anna Gennadievna Doroshkevich, Anastasia Evgenyevna Starikova, Alexandra Vladislavovna Malyutina, Tatyana Nikolaevna Moroz, and Igor Sergeevich Sharygin. 2025. "Zr-Th-REE Mineralization Associated with Albite–Aegirine-Bearing Rocks of the Burpala Alkaline Intrusion (North Baikal Region, South Margin of the Siberian Craton)" Minerals 15, no. 7: 742. https://doi.org/10.3390/min15070742

APA Style

Izbrodin, I. A., Doroshkevich, A. G., Starikova, A. E., Malyutina, A. V., Moroz, T. N., & Sharygin, I. S. (2025). Zr-Th-REE Mineralization Associated with Albite–Aegirine-Bearing Rocks of the Burpala Alkaline Intrusion (North Baikal Region, South Margin of the Siberian Craton). Minerals, 15(7), 742. https://doi.org/10.3390/min15070742

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