Bureya Massif Research Articles

МЕТАЛЛОГЕНИЯ И РЕДОКС-УСЛОВИЯ КРИСТАЛЛИЗАЦИИ МАГМАТИЧЕСКИХ ПОРОД БУРЕИНСКОГО МАССИВА (ЕВРЕЙСКАЯ АВТОНОМНАЯ ОБЛАСТЬ): ПРЕДВАРИТЕЛЬНЫЕ МАТЕРИАЛЫ

The Bureya massif is part of the Central Asian fold belt. According to the redox zoning scheme of the Sikhote-Alin orogenic belt, part of it is located in the ilmenite Okhotsk-Sungari block. This work shows the relation between the Bureinsky massif redox conditions of rocks formation in the Jewish Autonomous region and its ore specialization.

ГЕОХИМИЧЕСКИЕ ОСОБЕННОСТИ ГАББРОИДОВ И ГРАНИТОИДОВ НЯТЫГРАНСКОГО КОМПЛЕКСА (БУРЕИНСКИЙ МАССИВ)

Gneissic gabbros, gabbrodiorites, granodiorites, and granites of the Late Proterozoic Nyatygransky Complex, exposed by erosion in the eastern part of the Bureya massif, form small intrusive bodies within the boundaries of the Melgin metalliferous trough, as well as around it. Analysis of chemical and trace-element compositions of rocks from the Nyatygransky Complex revealed their geochemical features. The calculated agpaitic index values for gabbroids are very low and range from 0.11 to 0.33. Granodiorites have slightly higher index values ranging from 0.5 to 0.38, and only gneiss-granites are plumasitic with agpaitic index values between 0.45 and 0.75. Both gabbroids and granitoids are assigned to calc-alkaline rocks by their agpaitic index. Gneissic gabbros, dominated by dark-colored minerals (labradorite, hornblende), show enhanced alkalinity not common to gabbros (4%); in them, the magnesium content prevails over the iron content. They are characterized by high alumina content (15–18%), reaching 20.38%. Geochemically, they are interpreted as I-type igneous rocks. Gneissic granitoids with a slight predominance of the iron content over the magnesium content are less aluminous (Al2O3 12–15%). They are interpreted as S-type (sedimentary) and I-type (igneous) granitoids, formed in sedimentary and granitic layers of the earth’s crust. According to petrochemical diagrams, the gabbroids and granitoids of the Nyatigransky Complex belong to the volcanic arcs of the active continental margin.

Late Paleozoic and early Mesozoic granitoids in the northwestern Bureya Massif, Central Asian Orogenic Belt: Timing and tectonic significance

ABSTRACT The Bureya Massif is an important massif in the eastern Central Asian Orogenic Belt (CAOB), and contains voluminous late Palaeozoic–early Mesozoic granitoids that are ideal for investigating the tectonic evolution of the eastern CAOB. Here we report whole-rock geochemical, and zircon U–Pb geochronological and Lu–Hf isotope data for several granite intrusions in the northwestern Bureya Massif, with the aim of constraining the timing of magmatism and late Palaeozoic–early Mesozoic tectonism in the eastern CAOB. The zircon U–Pb dating results indicate that granitoids with ages of 306 ± 4, 243 ± 3, 191 ± 2, and 189 ± 4 Ma occur in the Bureya Massif. These, and previously published data, reveal that at least four stages of magmatism occurred in the northwestern part of the massif: ~306 Ma, ~243 Ma, 219–212 Ma, and ~201-189 Ma. The late Carboniferous (306 ± 4 Ma) gneissic monzogranites have an S and A-type granite affinity, and were derived with significant contribution of the mantle component in a syn- to post-collisional setting between the Bureya and Xing’an massifs. The Middle Triassic (243 ± 3 Ma) porphyritic I-type monzogranites, Early Jurassic (191 ± 2 Ma) porphyritic S-type syenogranites, and Early Jurassic (189 ± 4 Ma) gneissic S-type monzogranites have a supra-subduction zone geochemical signature. These granitoids formed in an active continental margin setting associated with southward subduction of the Mongol–Okhotsk oceanic plate.

ПЕРСПЕКТИВЫ ФЛЮОРИТОНОСНОСТИ ХАБАРОВСКОГО КРАЯ, ЕАО И АМУРСКОЙ ОБЛАСТИ

The available data on the presence of fluorites in the Khabarovsky Krai, the Jewish Autonomous Oblast and Amur Oblast have been synthesized. Fluorite deposits and occurrences are classified as rare-earth-fluorite, beryllium-fluorite, fluorite-tin-ore, polymetallic-fluorite, and fluorite. Also, fluorite occurs in ore deposits and phosphorite deposits. The features of their localization in different tectono-stratigraphic areas of the region are shown. Fluorite-bearing regions were identified and their potential for development was assessed. Fluorite occurrences that are economically attractive targets for exploration are located along the periphery of the Siberian platform and in the southern part of the Bureya massif. Forecast resources of fluorite were calculated and the prospects for their industrial development were assessed.

Udurchukan formation and ayakit complex (Bureya massif, Sikhote-Alin): location, age and geochemistry

Neogene basalts in the eastern of the Bureya massif and the adjacent Kursk-Komsomolskaya zone of the Sikhote-Alin fold system occur in the seismically and tectonically active area along the Khingan, Amgun and Tanlu-Kharpi deep faults. Analysis of age constraints on the timing of basaltoid magmatism in the Miocene suggests three phases of magmatism in the study areas: Early Miocene (Udurchukan Formation: 22,6–18,6 Ma); Middle Miocene (Ayakit Complex: 14,8–13,0 Ma), and Late Miocene (Ayakit Complex: 10,0–9,3 Ma). Rock studies have found that basalts (Ayakit plateau), basaltic andesites (Udurchukan plateau), and leucitites (Yadasen Island) are enriched in sodium oxides, potassium, titanium, iron, magnesium, and phosphorus. Two samples of alkaline olivine basalts from the Ayakit plateau yielded high KkTe (578,0) and Ag (172,7); elevated Kk in high field-strength Nb (6,2), Ta (3,4) and radioactive Th (2,7), U (2,4). The contents of Co, Ni, Zr, Mo, W, Zn, Sr, Ba, Hg, light and middle REE are 1,1–1,5 times or even higher than the clarke values for mafic rocks. There is a slight deficit of Sb, Cs, Bi, Cu, Li, Sc, Rb, Tm, Yb, Lu (Kk < 0,7). A similar chemical composition of the SASS basalts (Solnechny settlement and Yadasen Island) suggests that they have a common magma source.

ПОЗДНЕКАЙНОЗОЙСКИЕ БАЗАЛЬТОИДЫ ВОСТОКА БУРЕИНСКОГО МАССИВА И ПРИГРАНИЧНЫХ РАЙОНОВ СИХОТЭ-АЛИНЯ

The author has made a comparative analysis between Miocene basaltoids of the eastern Bureya Massif (Udurchukan Formation, Ayakit Complex) and the adjacent areas of the Sikhote-Alin fold system (Ostrogorsk Complex).

Early Paleozoic magmatic events in the Bureya Continental Massif, Central Asian Orogenic Belt: Timing and tectonic significance

The Bureya Massif is one of the largest continental massifs in the eastern Central Asian Orogenic Belt. The reconstructions of tectonic scenarios for the evolution of this belt are mainly based on geochronological and geochemical data. However, relevant data from the Bureya Massif are scarce. Here, we report whole-rock geochemistry, zircon U-Pb geochronology, and Lu-Hf isotope data for Early Paleozoic granite intrusions to constrain the timing of the magmatic and tectonic processes in the Bureya Massif. Geochronological data yielded ages of 495 ± 5, 486 ± 8, 471 ± 6, 453 ± 2, and 426 ± 6 Ma for the granitoids in the Bureya Massif. The chemical composition of the Early Paleozoic granitoids mostly showed affinities to A-type (A2-subtype) granites. Furthermore, they have zircon εHf(t) values of −5.3 to +5.7, and two-stage model ages tHf(C) of 1.52–0.95 Ga. These results suggest that the parental magmas of the Early Paleozoic granitoids were derived either from melting of a dominantly Neo- and Mesoproterozoic crustal source. Early Paleozoic magmatism in the Bureya and Songnen–Zhangguangcai Range massifs was characterized by similar timing and identical Hf-in zircon isotope compositions. Additionally, both arrays contain early Neoproterozoic granitic intrusions and Early Cambrian and Ordovician sedimentary units, suggesting that they were part of a single continental massif at the beginning of the Cambrian or even in the Neoproterozoic. In this case, the tectonic nature of the Early Paleozoic magmatism in these two massifs should be the same and was probably related to the docking of the Jiamusi Massif.

The Iorokhan Complex of Minor Intrusions in the Eastern Part of the Bureya Massif: Geology, Age, and Gold Mineralization

We analyze and generalize new data inferred from the geological, geochronological, and metallogenic studies performed in recent decades on igneous rocks of the Iorokhan gold-bearing complex in the eastern Bureya Massif. It is shown that four phases are determinative of the structure of the Iorokhan complex of minor intrusions whose rocks are referred to hypabyssal and subvolcanic intrusive facies. Specific features of their rock composition and structural tectonic conditions of localization are described and geological and geochronological (103 ± 1.0-97.4 ± 6.5 Ma) data on their Late Albian–Early Cenomanian age are presented. Based on the alumina, calcium, and alkali ratio, the major part of their compositions corresponds to the I-type (A/CNK < 1.1) high-alumina magnesia and magnesia–ferruginous varieties with decreased HFSE concentrations, including HREE. Melts formed due to amphibolite source melting might have been the deep sources of the Iorokhan diorites. The Noni deposit is briefly described and the main localization factors of the gold-ore mineralization are considered. The Iorokhan magmatite areals of the East Bureya Volcano–Plutonic Zone may be considered as one of the fragments of the structure bordering between the continental margin of the Bureya Massif and the accretionary prisms of the Sikhote Alin Orogenic Belt. The Iorokhan complex of minor intrusions is assumed to be a small fragment of an extensive band of Late Albian–Early Cenomanian magmatites developed in southern Far East Russia that originated under the transform continental marginal setting, and a combination of synstrike–slip compression and extension zones typical of such margins with further development of the pull-apart depressions.

ИОРОХАНСКИЙ КОМПЛЕКС МАЛЫХ ИНТРУЗИЙ ВОСТОЧНОЙ ЧАСТИ БУРЕИНСКОГО МАССИВА: ГЕОЛОГИЯ, ВОЗРАСТ, ЗОЛОТОНОСНОСТЬ

In this paper we analyze and summarize some recently acquired data coupled with the findings of previous geological, geochronological and metallogenic studies on igneous rocks of the Iorokhan gold-bearing complex in the eastern part of the Bureya massif. Four phases, whose rocks are of hypabyssal and subvolcanic intrusive facies, are shown to define the structure of the Iorokhan complex of minor intrusions; characteristic features of their composition and structural and tectonic settings of localization are given; geological and geochronological data are reported on their age (103 ± 1.0–97.4 ± 6.5 Ma), i.e. late Albian–early Cenomanian. By the ratio of alumina, calcium and alkalis, most of their compositions correspond to I-type high-alumina magnesia and magnesia-ferruginous varieties (A/CNK &lt; 1.1) with low concentrations of HFSE, including HREE. Melting of an amphibolitic source rock produced a melt that could be a deep source of the Iorokhan diorites. A brief description of the Noni deposit is given and the main factors contributing to the localization of gold mineralization are considered. The ranges of the Iorokhan magmatites in the East Bureya volcano-plutonic zone can be considered as one of the fragments of the boundary structure between the continental margin of the eastern part of the Bureya massif and the accretionary wedges of the Sikhote-Alin orogenic belt. The Iorokhan complex of minor intrusions is assumed to be a small fragment of the wide belt of Late Albian–Early Cenomanian magmatite occurrence in the southern Far East of Russia, which formed in a setting of transform continental margin and zones of compression associated with extension resulting in the development of pull-apart basins typical of such margins.

Late Permian–Triassic tectonic nature of the eastern Central Asian Orogenic Belt: Constraints from the geochronology and geochemistry of igneous rocks in the Bureya Massif

The late Paleozoic–early Mesozoic tectonic nature of the eastern Central Asian Orogenic Belt (CAOB) has been subject to debate, and the late Paleozoic–early Mesozoic magmatism in the Bureya Massif provides an opportunity to address this issue. We report new zircon UPb ages, Hf isotope data, and whole-rock major and trace element data for late Paleozoic–early Mesozoic igneous rocks from the south of the Bureya Massif. These data provide insight into the petrogenesis of the igneous rocks, and constrain the late Paleozoic–early Mesozoic tectonic nature of the eastern CAOB. Zircon UPb ages indicate that the late Permian (ca. 255 Ma) and Middle–Late Triassic (ca. 216 Ma) magmatic events are identified in the south of the Bureya Massif. The late Permian igneous rocks consist mainly of bimodal rock suites, which include quartz monzodiorites, gneissic monzogranites, and A-type gneissic syenogranites. The Middle–Late Triassic igneous rocks are dominated by porphyritic syenogranites, and A-type granite porphyries, syenogranites, and gneissic macroporphyritic quartz syenites. The quartz monzodiorites have low SiO2 contents (53.9–56.1 wt%), high Mg# (56–57), and Cr (160–175 ppm), Co (25.2–27.8 ppm), and Ni (61.2–72.3 ppm) contents, and are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE; e.g., K, Rb, Sr, and Ba). These characteristics, along with enriched zircon Hf compositions [εHf(t) = −8.31 to −0.44], suggest that their primary magma was derived from the partial melting of lithospheric mantle that had been metasomatized by fluids released from a fossil subducted slab. The granitoids have high SiO2, and low MgO contents, and are enriched in LILE, depleted in high field strength elements (HFSE), and yield εHf(t) values of −11.5 to +2.87 and two-stage model ages (TDM2) ages of 1968–1024 Ma. These characteristics suggest that they were derived from the partial melting of Paleoproterozoic–Mesoproterozoic accreted crustal material; however, these granitoids have distinct, heterogeneous geochemical compositions, precluding simple fractional crystallization of a single parental melt, and strongly suggesting that they were originated from distinct petrogenetic processes. The late Permian–Triassic bimodal igneous rock suites and A-type granites imply an extensional environment in the eastern CAOB.

The First Evidence of Cambrian Granitoid Magmatism during the Formation History of the Bureya Continental Massif of the Central Asian Fold Belt

The results of U–Pb geochronological studies of Early Paleozoic granitoids from the northern part of the Bureya continental massif are presented. It has been established that porphyroblastic hornblende–biotite granites of the Kivili massif referring to the complex of the same name are of 502+6 Ma in age, while weakly gneissic biotite granites of the Kivity massif, Sularin complex, are of 492+6 Ma in age. Thus, granitoids of both complexes are of Cambrian rather than Ordovician age, as was previously assumed. In combination with materials already obtained, these data indicate that intensive granitoid magmatism manifested itself in the Middle Cambrian–Early Ordovician within the Bureya continental massif. It is noteworthy that, in the structure of the Jiamusi–Khanka continental massif, which is adjacent to the Bureya one, Early Paleozoic magmatism manifested itself in a broader range, which is from the Early Cambrian to the Silurian. This may indicate both differences in the formation history of these continental massifs and insufficient knowledge of the Bureya massif.

Granitoids of the Khara Complex in the Eastern Bureya Continental Massif of the Central Asian Orogenic Belt: Age and Geodynamic Settings of Formation

Petrogeochemical and geochronological studies were conducted on the main varieties of granitoids from the Sedelga and Berezovsky batholiths in the eastern Bureya continental Massif of the Central Asian Fold Belt. SHRIMP-II U–Pb zircon dating of granitoids constrained the time of formation to the Late Triassic and Early Jurassic between 208 to 193 Ma. Our studies revealed that the batholiths contain peraluminous granitoids of high K calc-alkaline series clearly enriched in Rb, K, Th, U, and Pb and relatively depleted in Nb, Ta, Y, HREE, Sr, Ba, Ti, and P and belong to I-type granites. Synthesis of the U–Pb geochronological data indicates that magmatism of tectonic blocks constituting the Bureya Massif at 213–183 Ma was accompanied by the emplacement of granitoid rocks of the Khara Complex. Strike-slip tectonics as a reflection of oblique collision of continental blocks and transform movement might have been an important mechanism of granitoid derivation in the Bureya Massif. Strike-slip faults were likely to penetrate deep into the crust initiating the ascent of an asthenospheric diapir and its fluids into the higher crustal levels thus transferring the heat and triggering melting with appreciable concentrations of Th, U, Rb, Pb and losses of Sr, P, Ba, and Ti. The depletion in Nb, Ta, Ti, and P and the enrichment in Pb make these granitoids similar to those of subduction zones. Granitoids of the Khara Complex display subduction-related (associated with the preceding subduction) and within-plate (associated with an asthenospheric diapir and its fluids) geochemical features, which is characteristic of transform margin environments. The most likely settings for granitoid magmatism to occur throughout the eastern margin of the Bureya Massif in the Late Triassic and Early Jurassic were transform settings associated with asthenospheric diapirism following the cessation of subduction.

CHARACTERISTICS OF SELF‐SIMILARITY OF SEISMICITY AND THE FAULT NETWORK OF THE SIKHOTE ALIN OROGENIC BELT AND THE ADJACENT AREAS

We performed a comprehensive analysis of the characteristics of self‐similarity of seismicity and the fault network within the Sikhote Alin orogenic belt and the adjacent areas. It has been established that the main features of seismicity are controlled by the crustal earthquakes. Differentiation of the study area according to the density of earthquake epicenters and the fractal dimension of the epicentral field of earthquakes (De) shows that the most active crustal areas are linked to the Kharpi‐Kur‐Priamurye zone, the northern Bureya massif and the Mongol‐Okhotsk folded system. The analysis of the earthquake recurrence plot slope values reveals that the highest b‐values correlate with the areas of the highest seismic activity of the northern part of the Bureya massif and, to a less extent, of the Mongol‐Okhotsk folded system. The increased fractal dimension values for the fault network (Df) correlate with the folded systems (Sikhote Alin and Mongol‐Okhotsk), while the decreased values conform to the depressions and troughs (Middle Amur, Uda and Torom). A comparison of the fractal analysis results for the fault network with the recent stress‐strain data gives evidence of their general confineness to the contemporary areas of intense compression. The correspondence between the field of the parameter b‐value for the upper crustal earthquakes and the fractal dimension value for the fault network (Df) suggests a general consistency between the self‐similar earthquake magnitude (energy) distribution and the fractal distribution of the fault sizes. The analysis results demonstrate that the selfsimilarity parameters provide an important quantitative characteristic in seismotectonics and can be used for the neotectonic and geodynamic analyses.

Ages and nature of the protolith of the Tulovchikha metamorphic complex in the Bureya Massif, Central Asian Orogenic Belt, Russia: Evidence from U–Th–Pb, Lu–Hf, Sm–Nd, and 40Ar/39Ar data

The Bureya Massif is located in the eastern segment of the Central Asian Orogenic Belt (CAOB) and its tectonic affinity and Precambrian evolution is highly controversial. Here we present mineralogical, whole-rock geochemical (major and trace elements and Sm–Nd isotopes) and zircon Hf isotopic data, together with zircon geochronological and mica 40Ar/39Ar dating of the biotite and amphibole gneisses from the Tulovchikha metamorphic complex (previously considered as Archean or Paleoproterozoic basement) in the Bureya Massif, in order to investigate their protolith, metamorphic and deformation ages, petrogenesis, and tectonic implications. LA-ICP-MS U–Pb dating of magmatic zircons from the biotite gneiss, the amphibole–biotite gneiss, and the amphibolite yields single zircon age populations cluster at ~950 Ma, ~920 Ma and ~940 Ma, respectively. The narrow zircon age ranges, together with the morphological features of the zircon crystals and the geochemical data, indicate that the studied metamorphic rocks have a magmatic origin and their protoliths were formed in the early Neoproterozoic (i.e., 950–920 Ma). The consistent formation ages further suggest that the Neoproterozoic gabbro–granitic rocks within the Nyatygran Complex in the Bureya Massif probably represent the protolith of the studied metamorphic rocks. The biotite and amphibole-biotite gneisses of the Tulovchikha metamorphic complex yield whole-rock Nd model ages (tNd(DM)) of 2.4–1.5 Ga and Hf zircon crustal model ages (tHf(C)) of 1.7–1.2 Ga, indicating that the precursors of the Tulovchikha Complex gneisses formed from the reworking of Meso–Paleoproterozoic rocks or mixed Neoproterozoic juvenile and Meso–Paleoproterozoic crustal sources. Considering that the Bureya and Jiamusi massifs experienced similar Neoproterozoic magmatic events, we suggest that these massifs form a contiguous crustal unit and share a common geological history. The rocks of Tulovchikha metamorphic complex in the studied area experienced epidote-amphibolite to amphibolite facies metamorphism probably in the early Paleozoic, as evidenced by the 471 ± 19 Ma age of a metamorphic zircon with a low Th/U ratio (<0.1). According to 40Ar/39Ar biotite dating of the biotite gneiss, the Tulovchikha Complex experienced a youngest thermal event at 227 ± 3 Ma. This event may be related to the final closure of the Paleo-Asian Ocean, or may have been caused by the deformation of the blocks of East Asia in connection with the initial stages of the closure of the Mongol–Okhotsk Ocean.

Provenance and tectonic implications of Cambrian sedimentary rocks in the Bureya Massif, Central Asian Orogenic Belt, Russia

In this paper we present new detrital zircon U–Pb ages and Lu–Hf isotopic data as well as whole-rock geochemical data for siltstones of the Cambrian Chergilen and Allin formations in the Mel’gin Trough of the Bureya Massif, Russia. Our aim is to constrain the provenance and tectonic settings of these strata. The detrital zircons in these rocks are dominantly Neoproterozoic in age (∼80% of all zircons), along with some Mesoproterozoic and Paleoproterozoic zircons, and the main age peaks are at ca. 1.78, 1.64, 1.45, 1.18, 0.94, and 0.82 Ga. The zircon Hf and whole-rock Sm–Nd isotopic compositions, together with geochronological data, show that the main sources of the Cambrian sediments were Neoproterozoic and Mesoproterozoic igneous complexes formed by the reworking of Paleoproterozoic rocks. The main age populations of detrital zircons from the Cambrian siltstones in the Bureya Massif are similar to those of detrital zircons from the Neoproterozoic and early Paleozoic deposits within the Jiamusi Massif, suggesting that they share a common history. However, the crustal basements of the Bureya and Jiamusi massifs are different from those of other massifs in the eastern part of the CAOB, such as the Erguna, Khanka, Khingan, and Songnen–Zhangguangcai Range massifs. The wide Neoproterozoic magmatic events suggest that the Bureya and Jiamusi massifs have an affinity to the Tarim Craton or the northern Tian Shan block, different from the North Asian and North China cratons.

Structure of the Northwestern Boundary of the Middle Amur Sedimentary Basin (Russian Far East) from Audiomagnetotelluric Sounding Data

This paper reports the data on the structure of the northwestern boundary of the Middle Amur sedimentary basin which were obtained after resumption of audiomagnetotelluric soundings. The geoelectric sections for two profiles across the basin strike are constructed, the sedimentary cover and basement structures are studied, and their electrical properties are determined. The compared data of the earlier and present studies show low-resistivity zones of 50–150 Ohm m beneath high-resistivity rocks of 500–1000 Ohm m in the northwestern part of the Ul’dura–Churki uplift at a 2–4 km depth, which are absent in the southwestern part of the uplift. This fact is related to strike-slip–overthrust processes due to graben formation in the area of junction with the Jiamusi–Bureya Massif in the Kur fault zone (YYilan–Yitong branch of the Tan-Lu fault zone) and also to global left-lateral strike-slip displacements and volcanic activity.

Dynamics of geophysical medium from power spectral density of microseisms before and after earthquakes: case study of Bureya massif, Amur region

The time–frequency parameters of weak earthquakes and microseisms are studied. The qualitative and quantitative relationships of the power spectral density of seismic waves are established; these relationships vary in terms of frequency spectrum for the areas of the northeastern framing of the Tan Lu fault system and Bureya massif. The reason for these differences could be the influence of the crustal geological structure near the observations points. Resulting from the time–frequency analysis of weak earthquakes, two sites located in the Tan Lu fault zone show an increase in the power spectrum at frequencies of 1 to 5 Hz and the resonant excitation of the medium at high frequencies (12.5–35 Hz) for the area of the Bureya hydroelectric power station during the travelling of seismic waves from weak earthquakes. A longer attenuation of the power spectral density of seismic waves at high frequencies is noted, and this may occur due to resonant excitation of the medium and the influence of the dam on the geological medium. On the contrary, this effect was not observed at the second site located near Lake Udyl. It is shown that the increase in power can be attributed to the interaction between seismic waves and spatial inhomogeneities in the Earth’s crust.

Formation conditions and rare-earth mineralization of Riphean carbonaceous shales of the Upper Nyatygran Subformation, Russian Far East

Graphitic and graphite varieties are distinguished in the carbonaceous shales of the Riphean Upper Nyatygran Subformation in the Melgin fragment of the Turan block, eastern Bureya Massif. The protolith of the graphitic shales had a terrigenous source related to island-arc volcanism. Pelagic sedimentation played a great role in the formation of the protolith of the graphite shale. These rocks were juxtaposed during the formation of an accretionary wedge on an active continental margin. The carbonaceous shales are characterized by high (>600 ppm) REE + Y contents, especially in the zones of brecciation and hydrothermal reworking. Detrial monazite enriched in LREE and MREE is the main carrier of REE mineralization in the graphitic shales. The main REE carrier in the graphite shales is REE phosphate (xenotime) formed during lithogenesis of sediments. Preliminary experimental treatment of the graphite shales of the Upper Nyatygran Subformation by ammonium hydrofluoride shows their potential for economic extraction of REE and Y.

Sources and formation conditions of ferromanganese mineralization of the Bureya and Khanka massifs, Russian Far East

The geochemical features of typical representatives of ferromanganese deposits are studied in the eastern Bureya and Khanka massifs (Russian Far East). Based on the major-, trace-, and rare-earth element distribution, the hydrothermal–sedimentary (with hydrogenic component) nature of their mineralization is established and the geodynamic setting and depth of ore formation are estimated. The differences in the depth and redox conditions of ore formation resulted in the metallogenic zonation of the Khingan block (Bureya Massif), which is expressed in a westward change in ore composition from the magnetite ores of the Kosten’ga–Kimkan zone to the hematite–magnetite and iron–manganese ores of the South Khingan zone. The conclusions about the participation of hydrothermal sources in the formation of ore mineralization of the studied deposits and the specifics of their localization require revision of the strategy of exploration and evaluation of ferromanganese ores in the southern Far East.

New data on chemical composition of Jurassic–Lower Cretaceous sedimentary rocks of the Bureya basin (Far East of Russia)

The first data on the whole-rock chemical composition of Jurassic–Lower Cretaceous sedimentary rocks cropping out in the Soloni–Umal’ta river interfluve (Bureya sedimentary basin) are used for revealing the distribution of their rock-forming elements. It is shown that the clastic material originated mostly from acid igneous rocks, while their intermediate varieties, as well as quartz-rich sedimentary and metamorphic rocks, played a subordinate role. It is assumed that the bulk of the clastic material was transported from the west and southwest (Bureya massif) and a smaller share from the east. The most significant differences between the Lower–Middle Jurassic and Upper Jurassic–Lower Cretaceous rocks mark a break in sedimentation.