Petrographic and mineralogical studies have been carried out for major varieties of rocks composing the Burpal & acy; massif: peralkaline (nepheline), alkali, and quartz syenites. The emphasis was put on the major and trace element composition of mafic minerals present in all types of rocks: clinopyroxenes, micas, and amphiboles. The studies have shown that the compositions of mafic minerals fractionate within each group of rocks but do not form a single trend of evolution in the groups of peralkaline, alkali, and quartz syenites. This suggests the formation of the massif under pulsed intrusion of variably differentiated magma, the contamination of the first portion of magma, and the subsequent formation of quartz syenites.

The paper reports the results of petrologic and geochemical study of the Burpala alkaline intrusion composed of quartz syenites, alkaline and nepheline syenites, including ore-bearing varieties, which is a part of the Late Paleozoic North Baikal Alkaline Province. Chemically, the studied rocks belong to foid monzosyenites, foid syenites and syenites, ranging from agpaitic to miascitic varieties. Close Sr-Nd isotopic characteristics and geochemical patterns confirm the syngenetic nature of magmas that produced nepheline, alkaline, and quartz syenites. A negative Eu anomaly in the REE patterns and sufficiently low Mg# of rocks testify in favor of a prolonged fractional crystallization of rocks from an alkaline-basic melt. Sr-Nd-Pb isotopic and geochemical characteristics of rocks of the Burpala intrusion reflect the predominance of metasomatized lithospheric mantle in their source. The formation of the rocks of the intrusion, according to the trace element and isotopic data, was complicated by the upper crustal assimilation, which likely determined the genetic relationship between nepheline and quartz syenites within the intrusion.

The article presents the results of a comprehensive study of fluid inclusions in the fluorite of apatite-fluorite rocks of the Burpala massif, as well as a detailed chemical composition of fluorite. According to the phase composition at room temperature, two types of fluid inclusions are trapped in fluorite of apatite-fluorite rocks: primary multiphase fluid inclusions with 4-5 daughter crystals and secondary fluid inclusions with 1 or 2 crystals. Among the daughter phases of primary multiphase fluid inclusions, halite (NaCl), nahcolite (NaHCO3), burbankite ((Na,Ca)3(Sr,Ba,Ce)3(CO3)5), sidorenkite (Na3Mn(PO4)(CO3)), tenardite (Na2SO4), and villiomite (NaF) are found. The composition of primary multiphase fluid inclusions is alkaline sulfate-chloride- fluoride salt with high concentrations of H2O, CO3-2, and PO4-3. Secondary fluid inclusions are less concentrated and lower temperature compared to primary ones. At the same time, based on the ice melting temperatures, the salinity of fluid inclusions with 1-2 crystalline phases (12,9-15 wt % NaCl-eq.) is higher than in two-phase fluid inclusions (6,5-7,9 wt % NaCl-eq.), i.e. a general trend to decrease the salt concentrations in the initial fluid preserved in inclusions was observed during fluorite crystallization: from primary multiphase fluid inclusions (concentrated)-* secondary fluid inclusions with 1-2 crystalline phases (low-concentrated)-* to secondary two-phase fluid inclusions (the most low-concentrated). In addition, the first data of pyrolysis-free gas chromatography- mass spectrometry analysis of volatiles from primary fluid inclusions in fluorite are presented, showing the presence of a significant content (19,6 rel. %) of hydrocarbons in the fluid phase of the salt melt. Thus, apatite-fluorite rocks were formed at temperatures of about 600 degrees C from an alkaline sulfate-chloride-fluoride salt melt, which also have high concentrations of H2O, CO3-2, and PO4-3. The REE content in fluorites allows us to consider these rocks as the result of crystallization of salt melt, which, apparently, are a product of crystallization differentiation of alkaline melts responsible for the formation of nepheline syenites of the Burpala massif.

The alkaline-ultrabasic carbonatite complex Arbarastakh is located in the southwestern part of the Siberian craton. In addition to ultrabasic rocks such as pyroxenites and ijolites, various types of carbonatite dikes, phoscorites, and aillikites are present in the massif. Based on their modal and compositional characteristics, as well as the chemical composition of minerals, the rocks of the Arbarastakh complex have been divided into three groups: "aillikite," "phoscorite", and "alkaline-silicate and carbonatite" groups. The chemical compositions of olivines, phlogopites and spinellides indicate that aillikites are the least differentiated rocks in the complex. The compositional differences of micas from the "phoscorite" and "alkaline-silicate and carbonatite" groups support the liquation of the aillikite melt into two immiscible silicates and CPIO (carbonate-phosphate/iron-oxide-rich) melts. After liquation, for the "phoscorite" and "alkaline-silicate and carbonatite" groups, evolution follows fractional crystallization. Pyroxene-phlogopite-calcite and calcite carbonatites probably resulted from metasomatic alteration of silicate phases by apatite-dolomite carbonatites, which is confirmed by structural-textural features and the overlapping compositions of phlogopites, apatites and pyroxenes from calcite carbonatites and those from pyroxenites and ijolites.

The Srednyaya Zima alkaline-ultramafic carbonatite complex is located in the Eastern Sayan and is a part of the area of manifestation of Neoproterozoic rare-metal alkaline-carbonatite magmatism along the southern and southeastern margins of the Siberian craton. Mineralogical studies of calciocarbonatites of the Srednyaya Zima complex have shown the presence of primary magmatic mineral phases of calcite, biotite (annite-phlogopite), ilmenite, and fluorapatite. Pyrochlore, zircon, burbankite, magnetite, rutile, titanite, strontianite, and barite were identified of the accessory minerals. The chemical composition of the magmatic minerals of the Srednyaya Zima carbonatites is similar to the mineral composition of the closely aged carbonatite complexes Belaya Zima and Arbarastakh. The rare-element and structural analysis of zircon from carbonatites showed the presence of two zones – a magmatic core and areas of recrystallization. U-Pb dating of igneous zircon showed the age interval of its crystallization – 637±4 Ma, which coincides with the geochronology of the formation of alkali-ultramafic rare-metal complexes along the southern margin of the Siberian craton. The formation of Neoproterozoic alkaline-carbonatite complexes is associated with tectonic events of the breakup of the Rodinia supercontinent.

Late Neoproterozoic Arbarastakh alkaline ultramafic carbonatite-phoscorite complex in the southern margin of the Siberian craton (Aldan-Stanovoy shield), includes carbonatites and phoscorites closely associated with pyroxenites-ijolites and ultramafic lamprophyres. Major and trace elements data, Sr, Nd and Pb isotope com-positions for the Arbarastakh rocks have been obtained to characterize the sources involved in their formation, primary melt composition and to build the petrogenetic model.All rock varieties, excluding nepheline syenites, are characterized by incompatible elements enrichments, including light rare earth elements, and strong fractionation of REEs. The initial isotope ratios of the analyzed samples, calculated at 645 Ma, display limited variations: epsilon Nd from +5.9 to +6.9 and 87Sr/86Sr from 0.70225 to 0.70272, excluding nepheline syenite with epsilon Nd +5.4. The initial Pb isotope ratios for the most studied samples overlap with each other within uncertainties. They yield an age of 642 +/- 5 Ma. The Nd and Sr isotope data of the Arbarastakh rocks generally fit the patterns of the other Neoproterozoic alkaline ultramafic carbonatite com-plexes of the southwestern and southern margins of the Siberian craton. Observed Sr, Nd and Pb isotope vari-ations indicate mixing of the asthenosphere and the depleted mantle components.It is supposed that the primary melts for the Arbarastakh rocks were generated directly by low-degree melting of metasomatic phlogopite-carbonate veins with apatite and Ti-oxides in garnet peridotite, which formed shortly before the onset of melting. Ultramafic lamprophyre (aillikite) is closest to the primary melt composition in terms of high #MgO, Cr and Ni. The aillikite and latter pyroxenite crystallized from primitive melt by fractionating the olivine, phlogopite and clinopyroxene dominated mineral assemblage that was free of feldspar. This fractionation forced Na-enrichment in the magmas resulted in liquid silicate-carbonate immiscibility. Major and trace element and isotope data indicate that the nepheline syenites are unlikely to be related with other alkaline silicate rocks through fractional crystallization and could have been formed through pre-emplacement interaction with the ambient crustal materials. Emplacement of calcite carbonatites resulted in metasomatism of surrounding py-roxenites with formation of clinopyroxene-phlogopite-calcite carbonatites. Subsequent portions of Fe-P-enriched carbonatite magmas crystallized phoscorites and apatite-dolomitic carbonatites.

Geochronological studies have been made on the main types of rocks from the Burpala alkaline massif and two gabbro and gabbro-diorite dikes located nearby. U-Pb LA-SF-ICP-MS zircon geochronology for the Burpala massif yielded a date of 294±2 Ma for gabbro crystallization, 607±4 Ma for diorite crystallization, 298±2 and 296±2 Ma for melanocratic alkaline and nepheline syenite crustallization, 291±2 and 293±3 for quartz and quartz-containing syenite crystallization, and 293±3 Ma for alkaline granite crystallization. The stage of formation of the massif rocks (298–291 Ma) coincides with the formation period of alkaline rocks from the Synnyr pluton and some alkaline complexes of the Vitim segment of Transbaikalia and confirms a widespread occurrence of post-collisional alkaline magmatism in Western Transbaikalia.

The research was focused on the Mara–Kamenka–Uvat interfluve of the Biryusinsky ledge of the Siberian Platform, where more than half a century ago, during prospecting works for manganese, the Marа paleovolcano was identified. However, specific volcanogenic-sedimentary rocks were considered as a part of the Karagas sedimentary series of the Late Riphean. Our mineralogical and petrographic studies have allowed us to establish the wide distribution of high-potassium pyroclastics, ignimbrites, and trachybasalts, indicating a subaerial explosive volcanic nature of the Mara volcano. The age of high-potassium volcanism has been determined based on U–Th–Pb zircon dating as 640 Ma. Lu–Hf isotope systematics of zircon indicate a relation of these volcanic rocks with mantle-derived magmas. The composition and time of formation of the studied rocks do not allow us to correlate them, as previously thought, with sedimentary Late Riphean quartz and quartz-feldspathic sandstones of the Karagas sedimentary series and dolerites of the Nersa intrusive complex. The specific mineralogical and petrographic features of the studied rocks make them suitable as a regional stratigraphic mark.

This work focuses on petrological-and-geochemical features, as well as age of dolerites widespread within the basins of the Mara, Kamenka and Uvat rivers. The isotope geochronological data acquired for baddeleyite allowed referring origination of these rocks to the time interval 1600–1620 Ma, interpreted as the time of their emplacement. It was ascertained, that the age of dolerites represents particular geological event proceeding independently of formation of Neoproterozoic Nersinsk gabbro-dolerite complex. The Sm-Nd isotope signature indicates that parent melt generated from the metasomatic lithosphere mantle.

This paper presents data on the age and trace element composition of perovskites from dykes of ultramafic lamprophyres (aillikites) of the Zima alkaline-ultramafic carbonatite complex (Bolshaya Tagna and Bushkanay) located within the Urik-Iya graben, Eastern Sayan region, southern margin of the Siberian craton. The studied samples exhibit similar textural and structural features but differ slightly in the mineral composition of the groundmass. They have a porphyritic structure, a massive texture, and consist of olivine macrocrystals embedded in a fully crystallized groundmass composed of perovskite, apatite, spinel, phlogopite, garnet, carbonates, clinopyroxene and other minerals. The macrocrystals quantity varies between 40 and 50 vol%. With the exception of a single sample from the Bushkanay dyke, olivine is entirely replaced by serpentine and/or talc. Perovskites from aillikites of the Bolshaya Tagna intrusion exhibit crystals with normal zoning showing a decrease in Na, REE, and Nb contents with center-to-rim increasing Ca content. In contrast, minerals from the aillikites of the Bushkanay dyke demonstrate reverse zoning, with an increase in Na, REE, and Sr and decrease in Ca contents from the center to the rim. We suggest that during crystallization of perovskites, the magma parental to the aillikites of the Bolshaya Tagna intrusion and the Bushkanay dyke had nearly similar trace element composition, but after crystallization of the cores of perovskite crystals each melt portion evolved independently. The samples from the Bushkanay dyke show an increase in f O 2 and the residual magma enrichment in REE, Na, and Sr as evidenced by their elevated contents at the rims of perovskite grains. In the Bolshaya Tagna aillikites after crystallization of perovskite cores, the melt was depleted in REE, Na, and Nb. Based on U-Pb dating of perovskites, the age of aillikites from the Bolshaya Tagna intrusion is 583-654 Ma. Perovskite from aillikites of the Bushkanay dyke is relatively young, with an age of 575 +/- 39 Ma. The obtained ages are consistent with the age of formation of Neoproterozoic alkaline-ultramafic carbonatite complexes of the Siberian craton and other occurrences of aillikites in a response to extension of the Rodinia lithosphere.

The studies are focused in the Mara–Kamenka–Uvat interfluve of the Biryusa Uplift of the basement of the Siberian Platform, where the Mara paleovolcano was recognized during the prospecting works for manganese more than 50 years ago. The specific volcano-sedimentary rocks are considered in the structure of the Late Riphean Karagas Group. Our mineralogical and petrographic studies allowed us to establish abundant high-K pyroclastic rocks, ignimbrites, and trachybasalts, which indicate a subaerial explosive character of the Mara volcano. The age of high-K volcanism of 640 Ma is based on U–Th–Pb dating of zircon. The Lu–Hf isotope systematics of zircon indicates a link of volcanism with mantle magmas. The composition and the period of the formation of rocks prevent their correlation (as was considered before) with sedimentary Late Riphean quartz and quartz–feldspar sandstones of the Karagas Group and dolerites of the Nersa intrusive complex. Specific mineralogical–petrographic features of rocks allow their use as a regional stratigraphic reference.

This paper reports investigation on zircons from quartz syenite, alkaline and foid syenite, as well as metasomatic rock from the fenitization zone hosted by the Burpala massif. It is performed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), cathodoluminescence (CL), laser ablation inductively coupled plasma mass spectrometry (LA ICP MS), and Raman spectroscopy. Generally, all zircons from igneous rocks show rhythmic, crystal growth zoning or sector zoning (type I) except for some zircons from alkaline syenites (type II) showing patchy zoning. They systematically contain pores or cavities. The REE patterns of magmatic zircons share similar features: e.g. depletion of LREE ((Yb/La)N up to 35000), large positive Ce (Ce/Ce* 6–427) and small negative Eu (Eu/Eu* 0.37–0.93) anomalies. Zircons crystallized from quartz syenites at 830±30 °C at the early stage of rock formation, while zircons from alkaline and foid syenites crystallized at the later stage of rock formation (680–750 °C). Meanwhile, crystallization of zircons with rhythmic zoning (type I) occurs at later magmatic stage, while the formation zircons of type II is probably related to the separation of the highly fluorinated aqueous fluid from the residual melt.Zircons from fenites have a bipyramidal habit holding a heterogeneous mosaic core and a homogeneous (or rhythmic zoning) rim. The cores of zircon show flat REE patterns without significant anomalies, while the rims are characterized by noticeable fractionation of REE ((Yb/La)N 85–615) and show a positive Ce anomaly (Ce/Ce* 4–18). The Raman spectra of the cores show a higher degree of crystallinity than the rims, and their flat REE spectra are probably related to the contamination by micro inclusions. The discordant U-Pb age of 295±3 Ma was obtained for zircon rims, which is consistent with the age of formation of igneous rocks of the Burpala massif (298–291 Ma). The latter supports the syngenetic origin of metasomatic ore mineralization with the main stage of massif formation.

The Borgoy and Botsy massifs are a part of the Dzhida alkaline province of the Western Transbaikalia. It has been stated that the rocks of the Borgoy massif were formed during the period from 246 to 243 Ma, which coincides with the formation period of the Permian-Triassic alkaline magmatic rocks common in the Vitim province. The age obtained from the zircons in the Botsy massif (121±1.0 Ma) is typical of the final stage of the transformation of the rocks related to rifting and alkali basalt lava flow. The presence of negative Nb-Ta anomaly and a relative enrichment in Rb, Ba, Sr and U imply interaction between the material of the plume and the earlier accretionary complexes of the subduction zones.

The article presents new data on the age and isotopic (Sr, Nd) characteristics of the Yuzhnoe and Ulan-Ude REE-fluorite occurrences, paragenetically related to alkaline carbonatite magmatism. Age estimates of the fluorite-containing rocks were obtained from bastnaesites using U-Th-Pb (LA-ICP-MS) method and are 130.2±1.1 and 136.6±1.9 Ma for the Yuzhnoe and Ulan-Ude occurrences, respectively. The Ɛ Nd (T) values of the bastnaesites vary from –7.41 to –6.08 for the Yuzhnoe occurrence and from –4.28 to –2.67 for the Ulan-Ude occurrence. The Yuzhnoe carbonatites are characterized by 87 Sr/ 86 Sr (I) ratios ranging from 0.705883 to 0.706011, and 87 Sr/ 86 Sr (I) ratios obtained for the Ulan-Ude bastnaesite-fluorite rocks are ranging from 0.70683 to 0.70687. The age estimates are consistent with the published geochronological data on alkaline carbonatite magmatism of the Central Asian orogenic belt related to Late Mesozoic intraplate magmatism and rifting. Isotopic Sr-Nd signatures of bastnaesite, as well as of the Yuzhnoe carbonatites and the Ulan-Ude bastnaesite-fluorites, indicate that their source rocks came from the enriched lithospheric mantle.

This paper is devoted to a new geochronological data for the main rocks that make up the Arbarastakh alkaline ultramafic carbonatite complex, and includes information on the mineralogical and petrographic features of these rocks. The Arbarastakh complex is located in the Republic of Sakha (Yakutia) in the southeast of Russia, within the basin of the Arbarastakh River, in the Lena River basin. Tectonically, the complex is located in the eastern part of the Aldan shield on the southeastern margin of the Siberian craton. The main structural feature of the Arbarastakh complex is its concentric-zonal structure, expressed in the regular alternation of rocks with different compositions and different occurrence conditions. The main phase of the complex composes a stock-like body of alkaline pyroxenites, which has a rounded-ellipsoid shape in plan view. Between the body of pyroxene rocks and the ring fault there is a continuous zone of fenites - contact-metasomatic rocks. Dikes of alkaline syenites, ijolite-urtites and melteigites, are found in the area of the alkaline complex. Dikes of alkaline syenites are localized in the endocontact zone of the complex. The carbonatites of the Arbarastakh complex are concentrated within the core of pyroxene rocks and occur as a series of incompletely conical dike-like bodies. The most common are calcite varieties of carbonatites with pyrochlore and phlogopite, as well as silicocarbonatites. Veins of dolomitic and ankeritic carbonatites occur much less frequently in pyroxenites. Geochronological studies of alkaline rocks of the Arbarastakh alkaline-ultramafic carbonatite complex reflect a rather long history of the formation of the complex and characterize the multi-stage intrusion of rocks. The results of Ar-Ar dating showed the time of crystallization of the main phase of the complex - pyroxenites - 632.5 +/- 6 Ma; alkaline syenites - 645.9 +/- 6.4 Ma. The emplacement time of silicocarbonatites is 642.6 +/- 6.6 Ma; the formation of carbonatites occurred in the ranges of 651 +/- 6 and 657.8 +/- 6.5 Ma. U-Pb dating of pyroxenites showed an age of 638.2 +/- 3.1 Ma; time of intrusion of carbonatites is 650.3 +/- 9.8 Ma; and the crystallization age of alkaline syenite is 641.7 +/- 5.6 Ma. Thus, a certain age range of formation of rocks of the Arbarastakh complex is similar to 657-636 Ma, which is within the range of values for other alkaline carbonatite complexes, which structurally gravitate towards the marginal parts of the Siberian Craton and are characterized by similar types of rare-metal deposits.