Complex Characteristic of Zircon from Granitoids of the Verkhneurmiysky Massif (Amur Region)

: The study presents a complex characteristic of zircon from the Verkhneurmiysky intrusive series with Li-F granites. A wide range of morphological and chemical properties of zircon allowed us to obtain new information on the formation and alteration of zircon from biotite and zinnwaldite granitoids and to determine its features, which contribute to the correct deﬁnition of Li-F granites formed directly before the tin mineralization. The reviled trends of zircon morphology and composition evolution in the Verkhneurmiysky granites series are: the high-temperature morphotypes are followed by low-temperature ones with more complicated internal structure with secondary alteration zones, mineral inclusions, pores, and cracks; the increasing concentration of volatile (H 2 O, F), large ion lithophile (Cs, Sr), high ﬁeld strength (Hf, Nb) and rare-earth elements with decreasing crystallization temperatures and the determining role of the ﬂuid phase (predominantly, F) in the trace element accumulation. The composition of zircon cores in biotite and zinnwaldite granites is very similar. However, the zircon rims from zinnwaldite granites are much more enriched in trace elements compared to those from biotite granites. The ﬁrst study of zircon from the Verkhneurmiysky granitoids provides new data on the formation and alteration conditions of granitoids, including zinnwaldite ones. increase in the gradient of uranium concentration; b ) abrupt increase in the concentration of volatile and rare alkalis at the stage of Li-F granites formation, which had a direct impact on the alteration of zircon from biotite leucogranites. The Raman spectra of Zrn-Bt and Zrn-Znw show zircon crystallinity reduction through the formation of Verkhneurmiysky granitoid series. The reduction of zircon crystallinity is also veriﬁed by an increase in uranium accumulation gradient and resulting in an extension of the isomorphic capacity of zircon lattice with naturally determined accumulation of rare-earth (REE, Y) elements and abrupt increase in the concentration of volatiles (F) and rare alkalis (Li) at the stage of lithium–ﬂuorine granites formation.


Introduction
Granitoid plutons are widespread in the Badzhal and Myao-Chan ridges of the Amur Region and play an important role in the localization of the Badzhal-Komsomolsky tin ore district. At the same time, rare metal Li-F granites formed shortly before tin mineralization were found only in [1987][1988][1989][1990], when an expedition of the Leningrad Mining Institute conducted a special mapping of the territory of the Verkhneurmiysky ore cluster.
In recent years, rare-metal granites were determined only by their chemical composition, without taking into account their geological, mineralogical, and petrographic features. Due to the statistically insignificant differences in the composition of biotite and zinnwaldite granites, this approach leads to errors in geological mapping and mineral prospecting and exploration.

Mineral and Chemical Composition of Granitoids of the Verkhneurmiysky Massif
Here we give a brief geological, petrographic, and geochemical characteristics of biotite granites of the Badzhal complex and zinwalditic granites of the Pravourmiysky complex.
Leucogranites of the Badzhal complex form middle-sized hypabyssal intrusive bodies, which stretch along with the magma-controlling faults. Crystallization of granites of the Badzhal complex lasted several billion years (crystallization started 94-95 billion years ago and completed~92-93 billion years ago) and ended with the intrusion of porphyraceous granite dikes within the Verkhneurmiysky ore cluster.
Leucogranites are characterized by high concentrations of SiO 2 (70-75%), increased alkalinity (Σ(K 2 O + Na 2 O)) = 8-9%, K > Na, and alumina, but do not contain minerals with high alumina content. These granites belong to the type of leucogranite-alaskaite formation of tin provinces and are characterized by elevated concentrations of Li, Rb, Cs, Y, Yb, W, Mo, Sn, and lower concentrations of Ba and Sr. At the same time, the concentrations of Rb, Cs, W, Nb, Y, Yb, and Sc in the granites of later phases increase successively, while the Ba and Sr concentrations decrease. Consequently, the fractionation degree of granitoid systems (Rb/K, Rb/Ba, Rb/Sr, Cs/K, and K/Ba) increases too. We also revealed an increase in the Li, Sn, and F content and a decrease in the Mo concentration [2].
Post-magmatic alterations are widespread in the Badzhal leucogranites, including those acquired under the influence of late zinwalditic rare-metal granites. These alterations make leucogranites and zinwalditic granites quite similar in mineralogical and geochemical composition [2,11].
Li-F granites of the Verkhneurmiysky massif are the youngest intrusive complexes completing the Late Cretaceous rare-metal granite intrusive series [2,12]. According to the tectonic, geological, and structural conditions, as well as petrographic, mineralogical, and geochemical features-these granites belong to the Li-F type of subalkaline leucogranite formation of rare-metal granites. Li-F granites of Verkhneurmiysky massif are zinwalditic tantalum-tungsten-niobium-bearing granites with Nb-wolframite, W-ixiolite, and samarskite, specific for the in post-magmatic tungsten-tin deposits [13,14].
Li-F granites of the Verkhneurmiysk massif are characterized by a massive or eutaxitic texture, light gray or white color, and the same crystallinity as the host medium-grained leucogranite. Macroscopically, leucogranites are characterized by a lighter color, absence of porphyraceous phenocrysts, and chain aggregation of quartz. Rock-forming minerals are K-feldspar (33-43 vol.%), albite (27-38 vol.%), quartz (32-36 vol.%), and zinnwaldite (3-5 vol.%). Characteristic features of the Verkhneurmiysky Li-F granites are zinnwaldite nodules (up to 0.6 mm) with inclusions of fluorite and plagioclase with incorporated topaz crystals. The rounded pea-shaped quartz forms chains and snowball structures. Mica of the zinnwaldite series was defined as a Li-bearing siderophyllite that differs from the biotite of leucogranites by the increased content of Al, Li, Mn, and lower concentrations of Mg, Fe, and Ti [2].
The composition of the main accessory minerals of zinnwaldite granites differs significantly from biotite ones. The zinnwaldite granites contain topaz, fluorite, fluocerite, ixiolite-(W), fergusonite-(Y), ferberite, while apatite, allanite-(Ce), and anatase are absent. In addition, zinnwaldite granites have higher contents of zircon, monazite-(Ce), xenotime-(Y), thorite and decreased fraction of ilmenite and rutile [15]. One of the main typomorphic features of zinnwaldite granites is the presence of rare-earth and rare-metal-bearing minerals. They are characterized by the stable presence of W (fergusonite-(Y), calciosamarskite, samarskite-(Yb), eschinite-(Y), strüverite, ilmenite, liandratite), the predominance of Nb over Ta, a significant role of As, Bi, Th, and U, and low content of Sn. Thus, the feature of Li-F granites is the presence of W and Y-rare-earth elements (REE)-Nb-bearing mineralization [10].
Thus, we can conclude that the detection of ore-bearing granites within the Verkhneurmiysky massif is a promising task for modern geological exploration. The exploration for rare-metal mineralization in this region should consider not only the spatial and genetic relationship of Li-F granites with plutons of leucogranites and small intrusions of mon- zonites, but also all identified mineralogical and petrographic features of Li-F granites, including the detailed characteristics of the accessory minerals and, first of all-zircon. The comprehensive study of granitoids of the Verkhneurmiysky massif, described in the works of V.A. Alekseev, Yu.B. Marin, et al. [2,12], allow identifying the initial and final members of the Verkhneurmiyskaya granitoid series: biotite leucogranites of the Badzhal complex and zinnwaldite granites of the Pravourmiysky complex [2].
To clarify the geochemical types of biotite and zinnwaldite granite samples under study ( Figure 2) and to compare them with the other granites of a similar genesis-we performed a bulk chemical analysis (XRF for petrogenic elements, ICP-MS for an extended set of elements). nificant role of As, Bi, Th, and U, and low content of Sn. Thus, the feature of Li-F granites is the presence of W and Y-rare-earth elements (REE)-Nb-bearing mineralization [10].
Thus, we can conclude that the detection of ore-bearing granites within the Verkhneurmiysky massif is a promising task for modern geological exploration. The exploration for rare-metal mineralization in this region should consider not only the spatial and genetic relationship of Li-F granites with plutons of leucogranites and small intrusions of monzonites, but also all identified mineralogical and petrographic features of Li-F granites, including the detailed characteristics of the accessory minerals and, first of all-zircon. The comprehensive study of granitoids of the Verkhneurmiysky massif, described in the works of V.A. Alekseev, Yu.B. Marin, et al. [2,12], allow identifying the initial and final members of the Verkhneurmiyskaya granitoid series: biotite leucogranites of the Badzhal complex and zinnwaldite granites of the Pravourmiysky complex [2].
To clarify the geochemical types of biotite and zinnwaldite granite samples under study ( Figure 2) and to compare them with the other granites of a similar genesis-we performed a bulk chemical analysis (XRF for petrogenic elements, ICP-MS for an extended set of elements). The table of contents of granites from the Verkhneurmiysky massif, Severny massif (Chukotka), as well as zinnwaldite and protolithionitic granites from Erzgebirge (Germany) ( Table 1) and their position on the Frost diagram [16] (Figure 3a) demonstrate that studied Verkhneurmiysky's granites are subalkaline and all of the compared rocks are rather similar in terms of the ratio of major oxides. Moreover, not only biotite and zinnwaldite granites compositions are close, but also the compositions of granites of the Far East, Chukotka, and the Erzgebirge in general. The table of contents of granites from the Verkhneurmiysky massif, Severny massif (Chukotka), as well as zinnwaldite and protolithionitic granites from Erzgebirge (Germany) ( Table 1) and their position on the Frost diagram [16] (Figure 3a) demonstrate that studied Verkhneurmiysky's granites are subalkaline and all of the compared rocks are rather similar in terms of the ratio of major oxides. Moreover, not only biotite and zinnwaldite granites compositions are close, but also the compositions of granites of the Far East, Chukotka, and the Erzgebirge in general.
The content of trace elements (Figure 3b) in biotite leucogranites reflects a rare metal melt nature, however, less contrasting than in the zinnwaldite Li-F granites of both Far Eastern massifs. Elevated concentrations of Li, F, Rb, Cs, Sn, W, Nb, Ta, Y, REE, Th, and other granitophile elements were also observed [2,10], with the accumulation of volatile (F), rare alkaline (Li, Rb) and some high field strength elements (Nb, Ta) in the zinnwaldite granites of the Erzgebirge. Some elements (Ba, Sr, Zr) in biotite granites have concentrations below the relative abundance of the elements and predictably increase in Li-F granites.
(a) The content of trace elements (Figure 3b) in biotite leucogranites reflects a rare metal melt nature, however, less contrasting than in the zinnwaldite Li-F granites of both Far Eastern massifs. Elevated concentrations of Li, F, Rb, Cs, Sn, W, Nb, Ta, Y, REE, Th, and other granitophile elements were also observed [2,10], with the accumulation of volatile (F), rare alkaline (Li, Rb) and some high field strength elements (Nb, Ta) in the zinnwaldite granites of the Erzgebirge. Some elements (Ba, Sr, Zr) in biotite granites have concentrations below the relative abundance of the elements and predictably increase in Li-F granites.
Comparison of the elemental composition of the studied granitoids is consistent with the geochemical evolution of the Far Eastern granitoid complexes [2], expressed in an increase in alumina content, accumulation of rare elements, reducing the values of K/Rb (Bt-Gr-0.67, Znw-Gr-0.64), Nb/Ta (Bt-Gr-7.7, Znw-Gr-5.1), a sharp increase in Rb/Sr (Bt-Gr-15.3, Znw-Gr-22.4), and a deepening of Eu anomaly on the course from biotite to zinnwaldite granites.

Materials and Methods
This work is based on the samples collected by the staff of the Mineralogical Department (Saint Petersburg Mining University) during the fieldwork from 1987 to 1990, headed by Yu.B. Marin and focused on the special mapping of the Verkhneurmiysky ore cluster. We studied 13 bulk samples and the corresponding thin sections, zircon single fraction from 8 samples of biotite granites (more than 555 grains), and 5 samples of zinnwaldite Li-F granites (460 grains). The studies were conducted in the laboratories of the Mining University [18][19][20], the Russian Geological Research Institute (VSEGEI), the Institute of Precambrian Geology and Geochronology, the Russian Academy of Sciences (Saint Petersburg, Russia), and the Institute of Mineralogy, TU Bergakademie Freiberg (Freiberg, Germany) ( Table 2).

Materials and Methods
This work is based on the samples collected by the staff of the Mineralogical Department (Saint Petersburg Mining University) during the fieldwork from 1987 to 1990, headed by Yu.B. Marin and focused on the special mapping of the Verkhneurmiysky ore cluster. We studied 13 bulk samples and the corresponding thin sections, zircon single fraction from 8 samples of biotite granites (more than 555 grains), and 5 samples of zinnwaldite Li-F granites (460 grains). The studies were conducted in the laboratories of the Mining University [18][19][20], the Russian Geological Research Institute (VSEGEI), the Institute of Precambrian Geology and Geochronology, the Russian Academy of Sciences (Saint Petersburg, Russia), and the Institute of Mineralogy, TU Bergakademie Freiberg (Freiberg, Germany) ( Table 2).
To study the morphology and surfaces of zircon faces, 118 grains were applied to electrically conductive tape with subsequent conductive film deposition. They were studied in the laboratory of the Geological Institute of the TU Bergakademie Freiberg on a scanning electron microscope JEOL JSM-7001F. The SE images were obtained with the following parameters: accelerating voltage-15 kV, probe current-20 pA, resolution-3.0 nm; BSE imaging was carried out under accelerating voltage of 20 kV and probe current of 14 pA. The analyzed crystals were cleaned, impregnated into epoxy resin, and polished to study grain inner structure in BSE and CL. Table 2. The list of analyzed granite samples and extracted zircons, indicating the methods used and the corresponding number of measurements: OM-optical microscopy of granites in thin sections and extracted zircon grains, SEM-scanning electron microscopy (JSM-6460LV, Saint Petersburg, Russia) includes BSE imaging, WDX analysis of zircon and neighboring minerals in thin sections; SEM *-scanning electron microscopy (JEOL JSM-7001F, Freiberg, Germany) includes SE imaging of extracted zircon grains, applied to electrically conductive tape, to study the surface of crystal faces and BSE imaging of zircon grains, impregnated into epoxy resin and polished, to study the inner structure; SIMS-secondary ion mass spectrometry (Cameca IMS-4f, Yaroslavl, Russia) of zircon grains, impregnated into epoxy resin, to measure the trace element content (accompanied with BSE and cathodoluminescence (CL) imaging of zircon inner structure); Raman spectroscopy was applied to measure the degree of zircon crystallinity (Renishaw InVia Raman spectrometer, Saint Petersburg, Russia); XRF analysis of granite samples to determine the content of petrogenic elements and ICP-MS analysis for the petrogenic elements, as well as for a wide range of trace elements (Actlabs, Ancaster, ON, Canada). The analysis of the trace elements content in zircon (67 analytical points/41 grains) was carried out on the Cameca IMS-4f ion microprobe (Valiev Institute of Physics and Technology of RAS, Yaroslavl, Russia) using standard methods [21,22]. The ion beam diameter was not more than 15-20 µm, the relative error for the majority of elements did not exceed 15%, and the detection limit is 10 ppb on average. We obtained data on the content of 11 lanthanides, Li, P, Ca, Ti, Sr, Y, Nb, Cs, Ba, Hf, Th U, F, and H 2 O, and calculated the most important geochemical parameters, including Th/U ratio, Eu-and Ceanomalies, ΣREE, ΣLREE, ΣHREE, and chondrite-normalized [23] LuN/LaN, LuN/GdN, and SmN/LaN ratios.
A non-destructive Raman spectroscopy technique was applied to measure the degree of crystallinity of zircon. Raman spectra were collected by means of the Renishaw InVia Raman spectrometer installed in the Department of Mineralogy, Saint Petersburg Mining University, using an excitation wavelength of 785 nm (diode NIR laser) and a thermoelectrically cooled charge-coupled device (CCD) detector equipped with a 1200 L/mm grating. The laser output power of 300 mW was reduced to 0.1% of the standard value, which is non-destructive to samples of interest. In each experiment, five scans were collected and averaged. The typical acquisition time was 20 s. The theoretical diffraction-limited confocal-spot diameter of the laser beam at the sample surface was approximately 1.5 mm with a Leica 50× long-working-distance objective and a 10× ocular. Repeated acquisitions of the crystals using the highest magnification (50×) were accumulated to improve the signal-to-noise ratio in the spectra. The Raman spectra of zircon from biotite granite (20 spectra/10 grains) and zinnwaldite granite (16 spectra/8 grains) were obtained from the analytical points of the preceding ion microprobe analysis of trace elements content. The spectra were recorded in a narrow range from 950 to 1050 cm −1 , containing ν 1 (975 cm −1 ) and ν 3 (1008 cm −1 ) bands, which are responsible for symmetric and anti-symmetric stretching of the SiO 4 group, respectively [24,25]. Spectra were calibrated using the 520.5 cm −1 line of a silicon wafer. Spectral manipulations such as smoothing (without baseline correction) and peak parameters recording were performed using the software package Wire 2.0.
No indications of surface damage and change of color by the laser radiation were observed during the sample checking after Raman measurements.

Zircon Mineral Associations
The set of Li-F granite accessory minerals and their determining role in the prospecting works are briefly discussed in Section 2.2. The geochemical evolution of the granitoid series of the Far East can also be traced in the evolution of the composition of typomorphic accessory minerals: zircon, ixiolite-(W), ferberite-(Nb), allanite-(Y), and chernovite-(Y) [2]. An example of an indicator accessory mineral coexisting with zircon is allanite, which changes from Ce and alumina-bearing type in the complex of early biotite leucogranites to Y-bearing ferriferous allanites in zinnwaldite granites ( Figure 4) [2,26].    Mica shows plastic deformations (Figure 6f), which are consistent with the concept of early syngenetic protoclase of rock-forming and accessory minerals of rare-metal granites associated with increased fluid pressure [10,27]. Zircon and xenotime occur together, both as the intergrowth of weakly altered grains of both minerals and as xenotime microinclusions in strongly altered zircon grains formed in the recrystallization and/or dissolution-precipitation processes (Figure 7a,b).
Xenotime crystals included in zircon show partial substitution with chernovite that forms an almost continuous xenotime-chernovite isomorphic series (Figure 7c). The chernovite formation is associated with the autometasomatic alterations in rare-metal granites which took place under the As-bearing fluids, characteristic to the rare-metal magma, enriched with both lithophile (W, Nb, Y, REE, Th, etc.) and chalcophile elements (As, S, Sn, Cu, Bi, etc.) [14,28]. The appearance of the As-phases in Zrn-Znw is consistent with the sharply increased content of As in zinnwaldite granites.  (e) (f)

Zircon Morphology
Zircon morphology can record genetic information about changes in the crystallization parameters, which makes it reasonable to study morphological and anatomical features of both microcrystals and intergrowth of zircon.
Primary microscopic study of 13 samples (60-200 grains/samples) allowed identifying at least two types of zircon grains in all samples:


The first type is represented by the relatively short prisms, brown and honey-colored, semi-transparent idiomorphic crystals. Some grains have rims, which are cleaner, lighter, and have a lower refractive index. Such rims may indicate postmagmatic changes or at least a significant interruption in zircon growth and a change in physical and chemical growth conditions. Almost all grains have metamict cores and partial amorphization in the near-core regions (Figure 8a,b);


The second type includes virtually colorless, long-prismatic grains without metamict cores; however, mineral and melt inclusions are present in considerable quantities (Figure 8c,d).

Zircon Morphology
Zircon morphology can record genetic information about changes in the crystallization parameters, which makes it reasonable to study morphological and anatomical features of both microcrystals and intergrowth of zircon.
Primary microscopic study of 13 samples (60-200 grains/samples) allowed identifying at least two types of zircon grains in all samples:

•
The first type is represented by the relatively short prisms, brown and honey-colored, semi-transparent idiomorphic crystals. Some grains have rims, which are cleaner, lighter, and have a lower refractive index. Such rims may indicate postmagmatic changes or at least a significant interruption in zircon growth and a change in physical and chemical growth conditions. Almost all grains have metamict cores and partial amorphization in the near-core regions (Figure 8a,b); • The second type includes virtually colorless, long-prismatic grains without metamict cores; however, mineral and melt inclusions are present in considerable quantities (Figure 8c,d).
Primary microscopic study of 13 samples (60-200 grains/samples) allowed identifying at least two types of zircon grains in all samples:


The first type is represented by the relatively short prisms, brown and honey-colored, semi-transparent idiomorphic crystals. Some grains have rims, which are cleaner, lighter, and have a lower refractive index. Such rims may indicate postmagmatic changes or at least a significant interruption in zircon growth and a change in physical and chemical growth conditions. Almost all grains have metamict cores and partial amorphization in the near-core regions (Figure 8a,b);


The second type includes virtually colorless, long-prismatic grains without metamict cores; however, mineral and melt inclusions are present in considerable quantities (Figure 8c,d). The division into long-and short-prismatic zircon varieties is based on the median elongation value of 1.92 for biotite granites, and a median elongation value of 1.55 for zinnwaldite granites.
This approach partially solves the question of adequate interpretation of morphotype distribution in the Pupin diagram [29], since the entire zircon population, can record only the general trend of all morphotypes predominance, while the division into varieties records the stages of zircon evolution even within a single sample. The result of a statistically valid division of the zircon sample into short-and long-prismatic varieties is the presence of two different evolutionary trends. The trend of the long-prismatic zircon coincides with the general trend of the entire sample, while the evolution curve of the short-prismatic variety is directed towards the lower lines of the Pupin diagrams (Figure 9). The division into long-and short-prismatic zircon varieties is based on the median elongation value of 1.92 for biotite granites, and a median elongation value of 1.55 for zinnwaldite granites.
This approach partially solves the question of adequate interpretation of morphotype distribution in the Pupin diagram [29], since the entire zircon population, can record only the general trend of all morphotypes predominance, while the division into varieties records the stages of zircon evolution even within a single sample. The result of a statistically valid division of the zircon sample into short-and long-prismatic varieties is the presence of two different evolutionary trends. The trend of the long-prismatic zircon coincides with the general trend of the entire sample, while the evolution curve of the short-prismatic variety is directed towards the lower lines of the Pupin diagrams (Figure 9). distribution in the Pupin diagram [29], since the entire zircon population, can record only the general trend of all morphotypes predominance, while the division into varieties records the stages of zircon evolution even within a single sample. The result of a statistically valid division of the zircon sample into short-and long-prismatic varieties is the presence of two different evolutionary trends. The trend of the long-prismatic zircon coincides with the general trend of the entire sample, while the evolution curve of the short-prismatic variety is directed towards the lower lines of the Pupin diagrams (Figure 9).  The two distinct zircon morphotypes are taken as evidence of the fluid phase evaporation from the melt [30], the formation of two zircon varieties within a single sample may be related to the F-containing fluids, which separated during emanation differentiation and affected already crystallized rocks. The scattering of the Zrn-Bt morphotypes along the horizontal axis demonstrates breaking points in its evolution and characterizes the heterogeneity of the melt. The relatively low intended temperature of Zrn-Znw formation indicates the fluid saturation of the melt and indirectly confirms the transfer of lithium and tin in the composition of F-complexes. Thus, the most abundant Zrn-Bt and Zrn-Znw morphotypes are P4 and P1/P3, respectively ( Figure 9).

SE and BSE Zircon Images
The electron microscopy study of zircon confirmed the presence of short-and longprismatic varieties in both studied granitoids and allowed the tracing of some genetic features of the formation processes.
Zircon from biotite granites (Zrn-Bt) is enriched with impurities, shows partially or completely altered cores of short-prismatic crystals with preserved oscillatory zoning, saturated with micropores and microinclusions of coffinite-thorite, monazite-cheralite phases and dark (in BSE) rims around the central zones (Figure 10a,b).
The formation of such a spongy texture with an abundance of mineral inclusions is a consequence of the dissolution-precipitation of zircon enriched with impurities under the influence of fluids, seeping through the numerous fissures formed during crystal growth [31][32][33][34][35]. In contrast, in the long-prismatic zircon Zrn-Bt, the cores have less impurities and have an elongated habit with reduced dipyramids and weak zoning (Figure 10c,d). Both types of Zrn-Bt have similar corrosion of the grain edges, presence of thin zones with wavy edges, and concentric heterometry-induced cracks that intersect the primary growth zoning.
influence of fluids, seeping through the numerous fissures formed during crystal gro [31][32][33][34][35]. In contrast, in the long-prismatic zircon Zrn-Bt, the cores have less impurities have an elongated habit with reduced dipyramids and weak zoning (Figure 10c,d). types of Zrn-Bt have similar corrosion of the grain edges, presence of thin zones wavy edges, and concentric heterometry-induced cracks that intersect the primary gro zoning. Morphological and inner texture features of zircon in biotite granites allowed assuming some stages of mineral formation and transformation, namely: alkalinity increase in the crystallization medium (dipyramid facets growth) at the rims growth and active influence of the fluid phase at the final magmatic stages of the massif formation (similar nature of secondary alterations in the short and long-prismatic variety of zircon Zrn-Bt). Zircon Zrn-Znw from Li-F zinnwaldite granites does not form parallel intergrowth but is characterized by a complex internal structure and intergrowth with micro-spherulitic aggregates of the chernovite Y[AsO 4 ]-xenotime Y[PO 4 ] series ( Figure 11).
It should be noted that the formation of similar chernovite aggregates in Li-F granites of Zinnwald is connected with the arsenic supply at the oxidation stage [36], and in A-type granites (Zinnowitz-Rejkovo) post-magmatic fluids are considered as a unique source of arsenic [37]. Thus, the nature of such intergrowth is a strong argument for autometasomatic alterations in rare-metal Li-F granites [10,28].
Morphological and inner texture features of zircon in biotite granites allowed assuming some stages of mineral formation and transformation, namely: alkalinity increase in the crystallization medium (dipyramid facets growth) at the rims growth and active influence of the fluid phase at the final magmatic stages of the massif formation (similar nature of secondary alterations in the short and long-prismatic variety of zircon Zrn-Bt). Zircon Zrn-Znw from Li-F zinnwaldite granites does not form parallel intergrowth but is characterized by a complex internal structure and intergrowth with micro-spherulitic aggregates of the chernovite Y[AsO4]-xenotime Y[PO4] series ( Figure 11). It should be noted that the formation of similar chernovite aggregates in Li-F granites of Zinnwald is connected with the arsenic supply at the oxidation stage [36], and in Atype granites (Zinnowitz-Rejkovo) post-magmatic fluids are considered as a unique source of arsenic [37]. Thus, the nature of such intergrowth is a strong argument for autometasomatic alterations in rare-metal Li-F granites [10,28].
Crystals of the long-prismatic Zrn-Znw variety are characterized by spotty zoning (Figure 12b) with rare remains of the primary oscillatory one, obscured by an uneven distribution of secondary blocks of trace elements concentration/depletion [2,38]; increased rims brightness in BSE images, indicating enrichment with heavy elements; increased amount and irregular distribution of cracks. Postmagmatic alterations of long-prismatic Zrn-Znw under the influence of the fluid phase are evidenced by superimposed wavy zoning and chains, formed after gas-liquid inclusions decrepitation, and crossing the primary growth zoning (Figure 12a). Crystals of the long-prismatic Zrn-Znw variety are characterized by spotty zoning (Figure 12b) with rare remains of the primary oscillatory one, obscured by an uneven distribution of secondary blocks of trace elements concentration/depletion [2,38]; increased rims brightness in BSE images, indicating enrichment with heavy elements; increased amount and irregular distribution of cracks. Postmagmatic alterations of long-prismatic Zrn-Znw under the influence of the fluid phase are evidenced by superimposed wavy zoning and chains, formed after gas-liquid inclusions decrepitation, and crossing the primary growth zoning (Figure 12a). Short-prismatic Zrn-Znw variety shows the most complex inner structure: the core/rim boundaries and the primary growth zoning are obscured and give way to the secondary wavy zones and homogeneous blocks with soft edges; pores of different sizes are widespread and concentrate numerous inclusions of thorite, xenotime, chernovite, and monazite.
Distinctive features of the short-prismatic Zrn-Znw are the maximum content of heavy trace elements (relatively bright BSE images), as well as the secondary wavy zoning, porosity, and abundance of inclusions, which occupy a significantly larger grain area Short-prismatic Zrn-Znw variety shows the most complex inner structure: the core/rim boundaries and the primary growth zoning are obscured and give way to the secondary wavy zones and homogeneous blocks with soft edges; pores of different sizes are widespread and concentrate numerous inclusions of thorite, xenotime, chernovite, and monazite.
Distinctive features of the short-prismatic Zrn-Znw are the maximum content of heavy trace elements (relatively bright BSE images), as well as the secondary wavy zoning, porosity, and abundance of inclusions, which occupy a significantly larger grain area (in the section) than similar alteration zones in zircon from biotite granites. Secondary alterations can be seen on the surface of Zrn-Znw faces as the abundance of caverns and dissolution relief.
Thus, the contrast of morphological features of both zircon types from the initial (Zrn-Bt) and final (Zrn-Znw) granite series is an important additional tool to reveal rare-metal Li-F granites within the Verkhneurmiysky massif. The oscillatory zoning of Zrn-Bt reflects the long path of water-poor magma evolution, which is able to travel long distances; the spotty zoning and increased porosity of Zrn-Znw indicate less stable growth conditions, increased activity of the fluid phase, and lattice defects due to secondary alterations and formation of mineral inclusions ( Figure 13).

Trace-Element Composition of Zircon
Before proceeding to the discussion of the elemental composition of the studied zircon, it is necessary to make a brief comparison with zircon from granites of similar genesis from different geographical regions, for example: biotite and Li-F granites of the Severny massif (Chukotka) [2], Li-F granites of Zinnwald deposit (Germany) [39,40] and zinnwaldite granites of Mole massif (Australia) [41] (Tables 3 and 4).

Trace-Element Composition of Zircon
Before proceeding to the discussion of the elemental composition of the studied zircon, it is necessary to make a brief comparison with zircon from granites of similar genesis from different geographical regions, for example: biotite and Li-F granites of the Severny massif (Chukotka) [2], Li-F granites of Zinnwald deposit (Germany) [39,40] and zinnwaldite granites of Mole massif (Australia) [41] (Tables 3 and 4). Table 3. Composition of zircon (ppm) from biotite leucogranites of the Verkhneurmisky massif, Amur region (median and quartiles calculated from ion probe data), and the Severny massif, Chukotka [2].  Table 4. Composition of zircon (ppm) from Li-F granites of the Verkhneurmisky massif, Amur region (median and quartiles calculated from ion probe data), and the Severny massif, Chukotka [2], Mole massif (Australia) [41] and Zinnwald Massif (Germany) [40].  Analyzing the published data, we can say that, in general, the level of trace elements content in zircon from granitoids is relatively low: Hf (0.39-3.98%), Y (0.1-0.5%), REE, P, U, Th (up to 0.5%), and~0.0 n% for the rest [42]. An exception is a zircon from the Li-F granites from Europe (Bohemia; Carpathians), Australia (New England batholith), Asia (Transbaikalia), Africa (Arabian desert), and North America (Guadalupe Mountains), with concentrations of rare elements reaching 10 wt.% or more [2,43].
The distinctive feature of zircon from Verkhneurmiysky granites is the increased content of Hf, reaching the level of zircon from the granite of the Erzgebirge (Germany) and Mole massif (Australia). Hf content is significantly increased in the altered rims of the studied zircon, reflecting the process of the melt differentiation and hydrothermal alterations, and almost reach the anomalous values typical of zircon from Zinnwald granite (Figure 14a). Compared to zircon of the Severny Massif, the Verkhneurmiysky zircon shows approximately equal levels of actinoids (Th, U) and high-field-strength (HFS) elements (Ti, Nb) and sharply increased levels of both groups of elements in the altered zircon rims in Zrn-Znw (Figure 14b). Analyzing the published data, we can say that, in general, the level of trace elements content in zircon from granitoids is relatively low: Hf (0.39-3.98%), Y (0.1-0.5%), REE, P, U, Th (up to 0.5%), and ~0.0 n% for the rest [42]. An exception is a zircon from the Li-F granites from Europe (Bohemia; Carpathians), Australia (New England batholith), Asia (Transbaikalia), Africa (Arabian desert), and North America (Guadalupe Mountains), with concentrations of rare elements reaching 10 wt.% or more [2,43].
The distinctive feature of zircon from Verkhneurmiysky granites is the increased content of Hf, reaching the level of zircon from the granite of the Erzgebirge (Germany) and Mole massif (Australia). Hf content is significantly increased in the altered rims of the studied zircon, reflecting the process of the melt differentiation and hydrothermal alterations, and almost reach the anomalous values typical of zircon from Zinnwald granite (Figure 14a). Compared to zircon of the Severny Massif, the Verkhneurmiysky zircon shows approximately equal levels of actinoids (Th, U) and high-field-strength (HFS) elements (Ti, Nb) and sharply increased levels of both groups of elements in the altered zircon rims in Zrn-Znw (Figure 14b). The electron-microscopic studies have already shown that all zircon types from Verkhneurmiysky granites show anomalously high concentrations of U, Th, REE, and Y. According to many researchers [46][47][48], the probability of finding these elements in the structure of zircon as an isomorphic impurity is small; whereas they rather form their own minerals enclosed in the zircon matrix. From this point of view, anomalous U, Th, REE, and Y concentrations associated with their own minerals (uraninite, coffinite, thorite, monazite, allanite, etc.), either captured during crystal growth or formed in the process of zircon secondary alterations, are quite understandable. Such anomalous values were not considered in the composition analysis of zircon under study. The electron-microscopic studies have already shown that all zircon types from Verkhneurmiysky granites show anomalously high concentrations of U, Th, REE, and Y. According to many researchers [46][47][48], the probability of finding these elements in the structure of zircon as an isomorphic impurity is small; whereas they rather form their own minerals enclosed in the zircon matrix. From this point of view, anomalous U, Th, REE, and Y concentrations associated with their own minerals (uraninite, coffinite, thorite, monazite, allanite, etc.), either captured during crystal growth or formed in the process of zircon secondary alterations, are quite understandable. Such anomalous values were not considered in the composition analysis of zircon under study.
The ion microprobe analysis of zircon also allows limiting the samples by the grain alteration degree and titanium content for the correct application of the Ti-in-zircon ther-mometer [49][50][51]. Thus, the median values of Ti-in-zircon temperatures, calculated for the unaltered zircons with a Ti content not exceeding 30 ppm, are 831 • C and 710 • C for the Zrn-Bt and Zrn-Znw, respectively. Zircon saturation thermometry [52][53][54], based on the granite's composition (Table 1) and calculated with M = (Na + K + 2·Ca)/(Al·Si), provides the values of 761 • C and 685 • C for the Zrn-Bt and Zrn-Znw, respectively. Despite the discrepancy between the absolute temperature values, obtained by different methods, the fact that the temperature of zircon formation decreases with time seems to be reliable.
Even in the case of pronounced contrast of morphology, microtexture, and zoning of zircon, the convergence of these features complicates the ambiguity of zircon typing. The relative reliability of Zrn-Znw type definition is achieved only when we consider the element composition. According to the results of the study on the zircon internal structure, the dataset of zircons in situ analysis was divided into the "core" and "rim" groups. The need for such separation was confirmed on the factor score diagrams for each sample, where the points corresponding to cores and rims are clearly split up ( Figure 15). The ion microprobe analysis of zircon also allows limiting the samples by the grain alteration degree and titanium content for the correct application of the Ti-in-zircon thermometer [49][50][51]. Thus, the median values of Ti-in-zircon temperatures, calculated for the unaltered zircons with a Ti content not exceeding 30 ppm, are 831 °C and 710 °C for the Zrn-Bt and Zrn-Znw, respectively. Zircon saturation thermometry [52][53][54], based on the granite's composition (Table 1) and calculated with M = (Na + K + 2·Ca)/(Al·Si), provides the values of 761 °C and 685 °C for the Zrn-Bt and Zrn-Znw, respectively. Despite the discrepancy between the absolute temperature values, obtained by different methods, the fact that the temperature of zircon formation decreases with time seems to be reliable.
Even in the case of pronounced contrast of morphology, microtexture, and zoning of zircon, the convergence of these features complicates the ambiguity of zircon typing. The relative reliability of Zrn-Znw type definition is achieved only when we consider the element composition. According to the results of the study on the zircon internal structure, the dataset of zircons in situ analysis was divided into the "core" and "rim" groups. The need for such separation was confirmed on the factor score diagrams for each sample, where the points corresponding to cores and rims are clearly split up (Figure 15). Thus, it is reasonable to consider the relationships between cores and rims within each zircon type, assuming that the magmatic history of zircon formation should be reflected in compositional and structural changes of the unaltered central domains of grains, while the intensity of the secondary alterations affects the composition of rims. The accumulation of U, Th, Nb, HREE, Cs, P, Y, Li, Sr, H2O, and Hf (in descending order of accumulation intensity) and decrease in LREE, F, Ba, Ca, and Ti concentrations (Figure 16a,c) are observed in the rims of zircon from biotite granite. Zircon from zinnwaldite granite demonstrates a general increase in the concentrations of all trace elements (Figure 16a,c). Thus, it is reasonable to consider the relationships between cores and rims within each zircon type, assuming that the magmatic history of zircon formation should be reflected in compositional and structural changes of the unaltered central domains of grains, while the intensity of the secondary alterations affects the composition of rims. The accumulation of U, Th, Nb, HREE, Cs, P, Y, Li, Sr, H 2 O, and Hf (in descending order of accumulation intensity) and decrease in LREE, F, Ba, Ca, and Ti concentrations (Figure 16a,c) are observed in the rims of zircon from biotite granite. Zircon from zinnwaldite granite demonstrates a general increase in the concentrations of all trace elements (Figure 16a,c).
It is interesting to note that there are no significant variations in the composition of the central unaltered domains in zircon from different granites, which suggests similar physical and chemical parameters of zircon crystallization during the formation of the Verkhneurmiysky granitoid series (Figure 16a). Zircon from zinnwaldite granites has only initially slightly increased content of F, Cs, and Nb, emphasized by increasing zircon/melt distribution coefficients in the transition from biotite to zinnwaldite granites, which is likely a reflection of the increased degree of emanation differentiation in the final stages of granite magmatism. Additionally, cores are characterized by the REE spectra typical for magmatic zircon-the smooth growth of chondrite-normalized REE concentrations with an increase in atomic number, disturbed by Ce-and Eu-anomalies. Zircon from zinnwaldite granite differs in a slightly lower content of LREE and a bit weaker Ce-anomaly ( Figure 16c,d). Positive Ce-anomaly is controlled by oxygen fugacity and is explained by the fact that Ce 4+ is incorporated in the structure of zircon according to the isovalent isomorphism. Moreover, the radius of Ce 4+ ion is close to HREE ones, so the calculated value of zircon/melt distribution coefficient for Ce 4+ is several orders of magnitude higher than for Ce 3+ . The depth of the Eu-anomaly depends on the Eu 2+ /Eu 3+ ratio, and its manifestation in zircon REE spectra is caused by early processes of acid melts appearance as a result of crystallization differentiation. However, in this case, it seems more likely to associate the variations of Eu-anomaly in the melt not only with the participation of feldspars in the crystallization process but also with the fluid differentiation. It is interesting to note that there are no significant variations in the composition of the central unaltered domains in zircon from different granites, which suggests similar physical and chemical parameters of zircon crystallization during the formation of the Verkhneurmiysky granitoid series (Figure 16a). Zircon from zinnwaldite granites has only initially slightly increased content of F, Cs, and Nb, emphasized by increasing zircon/melt distribution coefficients in the transition from biotite to zinnwaldite granites, which is likely a reflection of the increased degree of emanation differentiation in the final stages of granite magmatism. Additionally, cores are characterized by the REE spectra typical for magmatic zircon-the smooth growth of chondrite-normalized REE concentrations with an increase in atomic number, disturbed by Ce-and Eu-anomalies. Zircon from zinnwaldite granite differs in a slightly lower content of LREE and a bit weaker Ce-anomaly (Figure 16c,d). Positive Ce-anomaly is controlled by oxygen fugacity and is explained by the fact that Ce 4+ is incorporated in the structure of zircon according to the isovalent isomorphism. Moreover, the radius of Ce 4+ ion is close to HREE ones, so the calculated value of zircon/melt distribution coefficient for Ce 4+ is several orders of magnitude higher than for Ce 3+ . The depth of the Eu-anomaly depends on the Eu 2+ /Eu 3+ ratio, and its manifestation in zircon REE spectra is caused by early processes of acid melts appearance as a result of crystallization differentiation. However, in this case, it seems more likely to associate the variations of Eu-anomaly in the melt not only with the participation of feldspars in the crystallization process but also with the fluid differentiation. Against the similar composition of cores in zircon of different types, the content of trace elements in the altered crystals domains experiences a sharp jump in the transition from Zrn-Bt to Zrn-Znw, which can be caused by the active influence of fluid phase accompanying the intrusion of the zinnwaldite granites. This assumption is also supported by the widespread secondary alterations in zircon Zrn-Znw, such as a decrease in the degree of grains crystallinity and the development of spongy texture, saturated with pores and inclusions. It should be noted that the set of elements (P, Y, Th, and U) corresponding to the composition of common mineral inclusions (xenotime, coffinite, and thorite) has an approximately equal level of concentrations in the rims of all zircons under study. This suggests that the evolution of zircon composition is regulated not only and not so much by the parameters of the crystallization medium as by the isomorphic capacity of the mineral lattice. REE spectra illustrate sharp enrichment of altered Zrn-Znw domains with rare earth elements, with the flattering on the left side of the spectrum (LREE), reduction of Ce-anomaly, and decrease in the ΣHREE/ΣLREE ratio. This may be the result of a destructive fluid effect on the zircon lattice that facilitates the isomorphism of LREE [55] ( Figure 16d).
The SmN/LaN ratio together with the Ce-anomaly (Ce/Ce*) value allows tracing the distribution of points corresponding to zircon from biotite leucogranites and zinnwaldite granites between the fields of magmatic and hydrothermal zircon [56]. The density of Zrn-Znw sampling points distribution shows maximum near the field of hydrothermal zircon. Consequently, a relative enrichment of Ce 3+ is observed for Zrn-Znw, which is typical for secondary altered zircons [57]. The separation of Zrn-Bt and Zrn-Znw on the diagram in SmN/LaN-Ce/Ce* coordinates illustrates the full post-magmatic processing of magmatic zircon from zinnwaldite granites and serves as its additional characteristic.
Statistical analysis of zircon composition data included the results of preliminary correlation analysis of SIMS data, which revealed a strong correlation between such groups of elements as Cs, Sr, and P; Ca, Ba, and Li in zircon from biotite granites, and the absence of such correlations, along with the shift of the negative correlation between Ca and Sr, on the strong positive one in zircon from zinnwaldite granites. Zrn-Znw is characterized by a strong positive correlation between halogens (F), LIL (Ba, Cs), LREE, and H 2 O, which is explained by the formation of late magmatic Zrn-Znw grains with active gas evaporation from the fluid-saturated melt and imperfection of Zrn-Znw structure caused by fluid action and facilitating the entrance of incompatible elements into the zircon structure. Similar dependencies in zircon Zrn-Bt are very weak and are due to the contribution of rare-metal rims, which formed around the early magmatic zircon during the intrusion of the Li-F granites. The principal component analysis allowed interpreting two significant factors overlapping 73% of the total dispersion (Figure 17a): the first factor is the formation of rims enriched with impurities under the temperature decrease; the second factor reflects the process of REE fractionation, and the formation of mineral inclusions (xenotime, thorite, coffinite) in the altered zircon domains. The reliability of interpretation of the first factor is confirmed by the factor score diagrams, where the points corresponding to cores and rims are clearly split up (Figure 17b).
approximately equal level of concentrations in the rims of all zircons under study. This suggests that the evolution of zircon composition is regulated not only and not so much by the parameters of the crystallization medium as by the isomorphic capacity of the mineral lattice. REE spectra illustrate sharp enrichment of altered Zrn-Znw domains with rare earth elements, with the flattering on the left side of the spectrum (LREE), reduction of Ce-anomaly, and decrease in the ΣHREE/ΣLREE ratio. This may be the result of a destructive fluid effect on the zircon lattice that facilitates the isomorphism of LREE [55] (Figure 16d).
The SmN/LaN ratio together with the Ce-anomaly (Ce/Ce*) value allows tracing the distribution of points corresponding to zircon from biotite leucogranites and zinnwaldite granites between the fields of magmatic and hydrothermal zircon [56]. The density of Zrn-Znw sampling points distribution shows maximum near the field of hydrothermal zircon. Consequently, a relative enrichment of Ce 3+ is observed for Zrn-Znw, which is typical for secondary altered zircons [57]. The separation of Zrn-Bt and Zrn-Znw on the diagram in SmN/LaN-Ce/Ce* coordinates illustrates the full post-magmatic processing of magmatic zircon from zinnwaldite granites and serves as its additional characteristic.
Statistical analysis of zircon composition data included the results of preliminary correlation analysis of SIMS data, which revealed a strong correlation between such groups of elements as Cs, Sr, and P; Ca, Ba, and Li in zircon from biotite granites, and the absence of such correlations, along with the shift of the negative correlation between Ca and Sr, on the strong positive one in zircon from zinnwaldite granites. Zrn-Znw is characterized by a strong positive correlation between halogens (F), LIL (Ba, Cs), LREE, and H2O, which is explained by the formation of late magmatic Zrn-Znw grains with active gas evaporation from the fluid-saturated melt and imperfection of Zrn-Znw structure caused by fluid action and facilitating the entrance of incompatible elements into the zircon structure. Similar dependencies in zircon Zrn-Bt are very weak and are due to the contribution of rare-metal rims, which formed around the early magmatic zircon during the intrusion of the Li-F granites. The principal component analysis allowed interpreting two significant factors overlapping 73% of the total dispersion (Figure 17a): the first factor is the formation of rims enriched with impurities under the temperature decrease; the second factor reflects the process of REE fractionation, and the formation of mineral inclusions (xenotime, thorite, coffinite) in the altered zircon domains. The reliability of interpretation of the first factor is confirmed by the factor score diagrams, where the points corresponding to cores and rims are clearly split up (Figure 17b). Thus, we identified the main trends in the composition evolution of zircon from the Verkhneurmiysky intrusive series with Li-F granites, which are determined by both the degree of melt differentiation and the intensity of post-magmatic processes, as well as the special features of the zircon lattice: accumulation of HFS (Hf, Nb) and rare-earth (REE, Y) elements at a decrease in the Th/U ratio, which sensitively records the degree of zircon recrystallization and positively correlates with Eu-anomaly ( Figure 18a); an abrupt increase in the concentration of volatile (H 2 O, F) and rare alkalis (Li, Cs) at the formation of Li-F granites, which directly affected the alteration of zircon from biotite leucogranites (Figure 18b).
Thus, we identified the main trends in the composition evolution of zircon from the Verkhneurmiysky intrusive series with Li-F granites, which are determined by both the degree of melt differentiation and the intensity of post-magmatic processes, as well as the special features of the zircon lattice: accumulation of HFS (Hf, Nb) and rare-earth (REE, Y) elements at a decrease in the Th/U ratio, which sensitively records the degree of zircon recrystallization and positively correlates with Eu-anomaly ( Figure 18a); an abrupt increase in the concentration of volatile (H2O, F) and rare alkalis (Li, Cs) at the formation of Li-F granites, which directly affected the alteration of zircon from biotite leucogranites (Figure 18b).

Raman Spectroscopy of Zircon
The set of rather conformal spectra and wavenumbers of Raman modes for both zircon types under study agree with other studies [24,25,58,59] and characterized by the left side wave-shaped curves elevation with the extremum value in the range of 200-350 cm −1 , overlapping an external translational (202, 225, 355 cm −1 ) modes of SiO4 tetrahedra ( Figure 19).

Raman Spectroscopy of Zircon
The set of rather conformal spectra and wavenumbers of Raman modes for both zircon types under study agree with other studies [24,25,58,59] and characterized by the left side wave-shaped curves elevation with the extremum value in the range of 200-350 cm −1 , overlapping an external translational (202, 225, 355 cm −1 ) modes of SiO 4 tetrahedra ( Figure 19). special features of the zircon lattice: accumulation of HFS (Hf, Nb) and rare-earth (REE, Y) elements at a decrease in the Th/U ratio, which sensitively records the degree of zircon recrystallization and positively correlates with Eu-anomaly ( Figure 18a); an abrupt increase in the concentration of volatile (H2O, F) and rare alkalis (Li, Cs) at the formation of Li-F granites, which directly affected the alteration of zircon from biotite leucogranites (Figure 18b).

Raman Spectroscopy of Zircon
The set of rather conformal spectra and wavenumbers of Raman modes for both zircon types under study agree with other studies [24,25,58,59] and characterized by the left side wave-shaped curves elevation with the extremum value in the range of 200-350 cm −1 , overlapping an external translational (202, 225, 355 cm −1 ) modes of SiO4 tetrahedra ( Figure 19). The spectra of the Zrn-Znw without distinction of core/rim crystal zones are characterized by whole peaks reduction grading into the wave-shaped curves. Whereas in passing from core to rim in the vast majority of Zrn-Bt grains, there is a gradual shift in the red region for the ν 1 (SiO 4 ) and ν 3 (SiO 4 ) peaks, accompanied by peak tailing up to complete disappearance of the peaks and the emergence of so-called amorphous halo, typical for zircon enriched in REE and resulting from laser-induced fluorescence emissions of the luminophor impurities [58]. In some cases, Raman spectra of the Zrn-Bt rims are similar to Zrn-Znw spectra along the whole grain, which could indicate the same alteration processes. In the light CL-zones (principally corresponding with core zones) of the Zrn-Bt crystals, FWHM of the ν 3 (SiO 4 ) band ranges from 8.7 to 18.4 cm −1 , which suggests only a partial amorphization of the crystal structure (so-called transit state). The peak reduction in the spectra of the zircon rim gives evidence of significant structural radiation damage (FWHM minimum value is 29.1 cm −1 ), leading to an increase in the zircon reactive capacity and dramatic accumulation of trace elements [59].
The coincidence of Raman and ion microprobe analytical points make it possible to trace the relationship between the characteristics of the ν 3 (SiO 4 ) peak with the composition of zircon, expressing them through appropriate correlations. As consequence, it was revealed that the peak broadening and the value of the Raman shift expectedly decrease with the increase in LREE, Li, F content and Th/U ratio. However, the increasing Ceanomaly value is accompanied by an increase in Raman shift magnitude of ν 3 (SiO 4 ) peak. Shown correlation is regular from the standpoint of Ce 4+ incorporating into the zircon crystal structure according to the isovalent substitution model: due to the proximity of Ce 4+ (0.097 nm) and Zr 4+ (0.084 nm) ionic radius, isomorphic occurrence of Ce 4+ in Zr 4+ position does not lead to significant distortions of the zircon crystal lattice. The reduction of zircon crystallinity accompanied by the broadening and redshift of the ν 3 (SiO 4 ) peak is also confirmed by the decrease in the degree of REE fractionation (LuN/LaN) specific to altered zircon.

Conclusions
The result of this study is a complex characteristic of zircon from the Verkhneurmiysky intrusive series with Li-F granites. A wide range of morphological and chemical features of zircon allowed to obtain new information on the formation and alteration of zircon from granitoids of different types and to determine a set of zircon characteristic features, which contribute to the correct identification of Li-F granites formed directly before the tin mineralization within the Verkhneurmiysky massif.
The division into varieties by the coefficient of crystal elongation contributed to an adequate interpretation of the morphotype distribution and facilitated the establishment of zircon stages of evolution even within a single sample.
We also found that the change in the trace elements content level on the way from zircon cores to its rims are quite different in zircon from biotite (Zrn-Bt) and zinwalditic (Zrn-Znw) granites with the maximum impurities' accumulation level in the rims of zircon from zinwalditic ones. Active fluid evaporation and their transporting role is the reason for the secondary alterations affected not only zircon from the rare-metal granites but also from the early biotite granites, which led to the accumulation of a wide range of trace elements (Ca, Ti, Ba, F, Cs, Eu, La, Li, Pr, P, Nb, Lu, Yb, Nd, and Hf) in the altered zircon rims. The main trend in the evolution of zircon composition is the progressive accumulation of volatile (H 2 O, F), LIL (Cs, Sr), HFS (Hf, Nb), and rare-earth elements. The evolution of zircon morphology is not only the fact, that the low-temperature zircon morphotypes expectedly followed the high-temperature ones, but also the complication of the zircon structure in time-the formation of rare metal rims, the spread of secondary alteration zones with the crystal lattice disturbance, mineral inclusions, pores, and cracks. The Raman spectra of Zrn-Bt and Zrn-Znw show zircon crystallinity reduction through the formation of Verkhneurmiysky granitoid series. The reduction of zircon crystallinity is also verified by an increase in uranium accumulation gradient and resulting in an extension of the isomorphic capacity of zircon lattice with naturally determined accumulation of rare-earth (REE, Y) elements and abrupt increase in the concentration of volatiles (F) and rare alkalis (Li) at the stage of lithium-fluorine granites formation.
The composition and morphology of the studied zircon from zinnwaldite granites are similar to zircon from the Li-F granite of Severny Massif (Chukotka), the Mole Massif (Australia), the Erzgebirge (Germany, Czech Republic), which allows the possibility of using the identified complex of zircon features for the correct revealing of the Li-F granites.