Age and geochemistry of the Early Mesozoic granitoid massifs of the southern Bureya terrane of the Russian Far East

A massif of porhyritic microcline biotite granites located in the southern part of the Bureya (Turan) terrane has an age of 185 ± 1 Ma. The granites are characterized by (K₂O + Na₂O) > 8%, a K₂O predominance over Na₂O, and a moderately differentiated REE distribution pattern ((La/Yb)_n = 14.7–28.5). The obtained age indicates that at least one stage of the Early Mesozoic granitoid magmatism in the Bureya terrane occurred in the Early Jurassic. The formation of early Mesozoic granitoids was presumably related to collision between North Asian and Sino-Korean cratons, and the intervening Amur superterrane, although a subduction origin also cannot be completely ruled out.     

Late Jurassic-Early Cretaceous coal-forming plants of the Bureya Basin,Russian Far East

The analysis of the composition of fossil palynomorphs from coals and clastic rocks of the Talyndzhan, Dublikan, Soloni, Chagdamyn, and Chemchuko formations of the Bureya coaliferous Basin revealed that the main coal-forming plants during the Talyndzhan and Dublikan time were represented by cyatheaceous ferns, plants similar to Pinaceae, and plants produced Ginkgocycadophytus pollen. In the Soloni time, the boggy plant communities were composed of dominant Cyatheaceae, subordinate Pinaceae, rare Gleichenaceae representatives, and Ginkgocycadophytus-producing plants. During the Chagdamyn time, the main coal-forming role belonged to gleicheniaceous ferns, bryophytes, and lycopsids, while the Chemchuko time was marked by the dominant contribution of Gleicheniaceae, Cyatheaceae, Ginkgocycadophytus, and plants close to Taxodiaceae to the coal formation.     

Noble metal-bearing ferromanganese deposits in the Kimkan basin,Russian Far East

It has been established that large ferromanganese deposits enriched in noble metals, Co, U, V, and REE in the Kimkan sedimentary basin are confined to Vendian–Cambrian black shales. Lithostratigraphy plays an important role in the localization of such deposits and promising ore-bearing fields. Deposits and occurrences of complex iron and ferromanganese ores are polygenous and polychronous, because they underwent intense hydrothermal alterations with the superposition of noble metal and uranium mineralization in the Cretaceous. Efficient utilization of complex iron ores in the Kimkan open pit needs the construction of a metallurgical plant.     

Deep structure,genesis, and seismic activation of the Bureya orogen,Russian Far East

The Bureya orogen is a special object among the geodynamic factors determining the high seismicity of the Lower Amur region. Its location and deep structure are studied on the basis of comprehensive geophysical and tectonic data. This orogen is a low-density lithospheric domain expressed by an intensive negative gravity anomaly and Moho sunken down to 40 km depth. Within the limits of this lithospheric structure, contemporary uplifting takes place to form a meridional dome peaking at more than 2000 m altitude. The position of the orogen in the regional structure gives us grounds to think that the Bureya orogen formed in the Paleogene, at the finishing stage of tectonic block movement along the Pacific margin represented by the NE-trending strike-slip faults of the Tang Lu Fault Zone. Compression was concentrated at the triple junction between the Central Asian, Mongolian–Okhotian, and Sikhote Alin tectonic belts. The meridional orientation of the Bureya orogen is associated with the parallel elongated Cenozoic depressions in the region. The united morphotectonic system may have formed resulting from lithospheric folding under horizontal shortening in the Paleocene–Eocene. The wavelength of the Lower Amurian fold system is 250 km, which is consistent with the theoretical estimates and examples of lithospheric folds in other regions. The contemporary activation of the Bureya orogen began in the Miocene, under the effect of the Amurian Plate front moving in the northeastern direction. As a result of shortening, the meridional cluster of weak (M ≥ 2.0) earthquakes formed along the western boundary of the orogenic dome. The most intensive deformations caused another type of seismicity associated with the activation-related uplift of the mentioned orogen. As a result, the so-called Bureya seismic zone formed above the apex of the dome, and it is here that the strongest regional earthquakes (M ≥ 4.5) occur.     

Palynological evidence for dating Jurassic-Cretaceous boundary sediments in the Bureya basin, Russian Far East

Palynological complexes from the coaliferous Talyndzhan and Dublikan formations of the Bureya sedimentary basin are analyzed. The palynological assemblage from the upper part of the Talyndzhan Formation is characterized by dominant gymnosperms largely close to Pinaceae and Ginkgocycadophytus. The content of ferns is insignificant against the background of their relatively high taxonomic diversity. The assemblage is marked by the last occurrence of Staplinisporites pocockii, Camptotriletes cerebriformis, C. nitida, and Cingulatisporites sanguinolentus spores typical of the Late Jurassic palynofloras. The palynological assemblage from the Dublikan Formation is dominated by Pteridophyts representing mainly by Cyathidites and Duplexisporites. In addition to the conifer, the role of Classopollis increased among the gymnosperms in this assemblage. It also includes the first-appearing Stereisporites bujargiensis, Neoraistrickia rotundiformis, Contignisporites dorsostriatus, Duplexisporites pseudotuberculatus, D. rotundatus, Appendicisporites tricostatus, and Concavissimisporites asper. These sporomorphs are characteristic of the Berriasian palynofloras. Thus, the Jurassic-Cretaceous boundary is most likely located between the Talyndzhan and Dublikan formations.     

Carbonization and geochemical characteristics of graphite-bearing rocks in the northern Khanka terrane,primorie, Russian Far East

Regional carbonization was examined in Riphean metamorphic complexes in the northern part of the Khanka terrane. The results obtained by various techniques of physicochemical analysis indicate that all petrographic rock varieties of this complex bear elevated concentrations (from 10⁻⁴ to 10⁻⁶ wt %) of Au and PGE. XRF data were used to describe a wide spectrum of trace elements: Ti, V, Ni, Cr, Pt, Pd, Re, Rh, Os, Ir, Cu, Hg, Au, Ag, Ta, Nb, Sr, Rb, Zr, La, W, Sn, Pb, and Zn. The Rb/Sr-Ba diagram shows the fields of anatectic granite-gneisses, biotite granites, lamprophyres, graphitized crystalline schists, black shales, skarns, and quartz-graphite metasomatic rocks. The C isotopic composition in graphite from the metaigneous rocks (lamprophyres and crystalline schists of the amphibolite facies) corresponds to δ¹³C from −8.5 to −8.7‰, which suggests that the carbon could be of endogenic provenance. The carbon isotopic composition of the greenschist-facies black shales corresponds to δ¹³C from −19.9 to −26.6‰, as is typical of organogenic carbon. The concentrations of precious metals in the rocks are, on average, one order of magnitude lower than in the graphitized crystalline schists. The origin of the precious-metal ore mineralization was likely genetically related to the regional carbonization process.     

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.     

Geochronology and geochemistry of early Paleozoic intrusive rocks from the Khanka Massif of the Russian Far East

The Russian Far East and Northeast(NE)China are located in the eastern part of the Central Asian Orogenic Belt(CAOB),which consists of a series of micro-continental massifs including the Erguna,Xing’an,Songnen–Zhangguangcai Range,Bureya,Jiamusi,and Khanka massifs.The Khanka Massif is located in the easternmost part of the CAOB,mainly cropping out in the territory of Russia,with a small segment in NE China.To the north and west of the Khanka Massif are the Jiamusi and Songnen–Zhangguangcai Range massifs,respectively.The boundary between these massifs is marked by the Dunhua–Mishan Fault.To the south lies the North China Craton,and to the east is the Sikhote–Alin Orogenic Belt separated by the Arsenyev Fault.However,the early Paleozoic evolution and tectonic attributes of the Khanka Massif are debated.These conflicting ideas result from the lack of systematic research on early Paleozoic igneous rocks from the Russian part of the Khanka Massif.It is generally accepted that the CAOB represents the largest known Phanerozoic accretionary orogenic belt.However,questions remain concerning the nature of the deep crust beneath the Khanka Massif,and whether Precambrian crust exists within the massif itself. In this paper,we report new zircon U–Pb ages,Hf isotopic data,and major-and trace-element compositions of the early Paleozoic intrusive rocks from the Khanka Massif of the Russian Far East,with the aim of elucidating the early Paleozoic evolution and the tectonic attributes of the Khanka Massif,as well as the nature of the underlying deep crust. New U–Pb zircon data indicate that early Paleozoic magmatism within the Khanka Massif can be subdivided into at least four stages:~502 Ma,~492 Ma,462–445 Ma,and~430 Ma. The~502 Ma pyroxene diorites show negative Eu anomalies,and the~492 Ma syenogranites,intruding the~502 Ma diorites,show positive Eu anomalies.These observations indicate that the primary parental magmas of these rocks were derived from different origins. The 462–445 Ma magmatism is made up of syenogranites and tonalites.The~445 Ma Na-rich tonalites contain low REE concentrations,and are enriched in Eu and Sr.These observations,together with the positiveεHf(t)values,indicate that they were derived from magmas generated by partial melting of cumulate gabbros. The~430 Ma I-type granodiorites and monzogranites from the northern Khanka Massif,and the A-type monzogranites from the central Khanka Massif display zirconεHf(t)values ranging from–5.4 to+5.8.This suggests that they formed from magmas generated by partial melting of heterogeneous lower crustal material. Zircon Hf isotopic data reveal the existence of Precambrian crustal material within the Khanka Massif.The geochemistry of the Middle Cambrian intrusive rocks is indicative of formation in an extensional setting,while Late Cambrian–middle Silurian magmatism was generated in an active continental margin setting associated with the subduction of a paleo-oceanic plate beneath the Khanka Massif.Regional comparisons of the magmatic events indicate that the Khanka Massif has a tectonic affinity to the Songnen–Zhangguangcai Range Massif rather than the Jiamusi Massif.     

Complex mineralization at large ore deposits in the Russian Far East

Genetic and mineralogical features of large deposits with complex Sn, W, and Mo mineralization in the Sikhote-Alin and Amur-Khingan metallogenic provinces are considered, as well as those of raremetal, rare earth, and uranium deposits in the Aldan-Stanovoi province. The spatiotemporal, geological, and mineralogical attributes of large deposits are set forth, and their geodynamic settings are determined. These attributes are exemplified in the large Tigriny Sn-W greisen-type deposit. The variation of regional tectonic settings and their spatial superposition are the main factor controlling formation of large deposits. Such a variation gives rise to multiple reactivation of the ore-magmatic system and long-term, multistage formation of deposits. Pulsatory mineralogical zoning with telescoped mineral assemblages related to different stages results in the formation of complex ores. The highest-grade zones of mass discharge of hydrothermal solutions are formed at the deposits. The promising greisen-type mineralization with complex Sn-W-Mo ore is suggested to be an additional source of tungsten and molybdenum. The Tigriny, Pravourminsky, and Arsen’evsky deposits, as well as deposits of the Komsomol’sk and Khingan-Olonoi ore districts are examples. Large and superlarge U, Ta, Nb, Be, and REE deposits are localized in the southeastern Aldan-Stanovoi Shield. The Ulkan and Arbarastakh ore districts attract special attention. The confirmed prospects of new large deposits with Sn, W, Mo, Ta, Nb, Be, REE, and U mineralization in the south of the Russian Far East assure expediency of further geological exploration in this territory.     

Catagenesis of Jurassic-Cretaceous coals and rocks of the Bureya basin in the Russian Far East with respect to hydrocarbon generation

The catagenesis of the Jurassic-Cretaceous deposits and coals has been comprehensively examined based on a complex of features including the reflectance (R _o and R _a), the qualitative properties, and the petrochemical characteristics (the density and saturation porosity) of the host rocks. The catagenesis of the Jurassic-Cretaceous deposits was studied based on the structural zones in which the coal-bearing deposits occur at different depths ranging from ～ 10 to 300 m, down to 700m, and from 5 to 3460 m in the Western, Central, and Kyndal zones, accordingly. The following regularities of the changing of the coal’s catagenesis have been established: from group 3B to 1G, 2G, and GFL; from gradation PC₃ to MC₁-MC₂; and from MC₂ to MC₃-MC₄ with the changing of the composition of the coals from long-flame coal to gas and gasfat-lean coal. In the intrusive bodies distribution areas breaking through the coal-bearing deposits, the coal seams are metamorphosed to the marks of lean caking and lean coals. The data obtained have made possible the assessment of the hydrocarbon generation in the Jurassic-Lower Cretaceous deposits of the basin.     

Mesozoic Metallogeny of the Russian Far East

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Ancient mantle lithosphere beneath the Khanka massif in the Russian Far East: in situ Re–Os evidence

The Os‐isotope compositions of sulphides in mantle xenoliths hosted by Late Miocene alkali basalts from the Sviyaginsky volcano, Russian Far East, reveal the presence of Archaean–Proterozoic subcontinental lithospheric mantle beneath the Khanka massif. Their T_MA and T_RD model ages reveal similar peaks at 1.1 and 0.8 Ga suggesting later thermotectonic events in the subcontinental lithospheric mantle, whereas T_RD model ages range back to 2.8 ± 0.5 (2σ) Ga. The events recognized in the subcontinental lithospheric mantle are consistent with those recorded in the crust of the Khanka massif. The sulphide Os‐isotope data show that the subcontinental lithospheric mantle beneath the Khanka massif had formed at least by the Mesoproterozoic, and was subsequently metasomatized by juvenile crustal‐growth events related to the evolution of the Altaids. The Khanka massif is further proposed to have tectonic affinity to the Siberia Craton and should originate from it accordingly.     

Noble metal mineralization in carbonaceous rocks: A synthesis of data on the Russian Far East

The relationship between noble metal mineralization and carbonaceous rocks (black shales and brown coals) is considered. We have confirmed the previous conclusions of multistage syn- and epimetamorphic formation of gold-bearing deposits in black shales and syn- and epigenetic accumulation of noble metals in brown coals. The gold and PGE in the brown coals of the Verkhnii Amur region and Primorye were presumably derived by disintegration of adjacent ore sources in the Cenozoic. Addition studies and sampling are required at the coal and graphite objects of the Russian Far East to solve this problem.     

A new concept of pedogenic nodule formation in landscapes of the Russian Far East

The typification of ferromanganese nodules (FMN) formed in subaqueous and subaerial settings and in residual materials, as well as FMN localization in various sediments and soils, is discussed. The genetic diversity of morphologically similar FMN and the transformation of FMN-bearing complexes with changes in landscapes have been established.     

Paleogeography of the Bureya Foredeep (in the Far East) in the Jurassic

Using the standard methods of paleogeographic analysis, small-scale paleogeographic sketch maps of the Verkhnyaya Bureya and Gudzhik depressions of the Bureya Foredeep are compiled for the Pliensbachian, Bajocian-Bathonian, Callovian, and Tithonian ages of the Jurassic. Marine sedimentation settings that existed during the Late Triassic and the major part of the Jurassic are characterized.     

Noble metal-graphite mineralization: A comparative study of the carbonaceous granite-gneiss complex and shales of the Russian Far East

A new noble metal-graphite mineralization has been revealed in the Ruzhino amphibolite-facies rocks of the northern Khanka block. It is characterized by Au and PGE (platinum group elements) contents (up to tens g/t, Pt > Au) as high as those in world-class deposits hosted by sedimentary and magmatic rocks, but is distinguished from them by isotopic composition of carbon, hydrogen and oxygen, all suggesting a distinct mantle contribution (δ¹³С_VPDB from − 8.5 to − 10.5‰ in graphite, δD_VSMOW from − 82.5 to − 106.7‰ and δ¹⁸O_VSMOW from 8.2 to 10.1‰ in biotite). The Ruzhino-type mineralization is highly resistant to common chemical treatments, so that detection of their metals requires that some special methods be developed. Atomic Absorption Spectrophotometry and Inductively Coupled Plasma Mass Spectrometry following severe chemical treatments and ignition at 600–650 °C, as well as Ion Mass Spectrometry allowing a direct detection of elements in solid materials were employed in this study. These methods increased noble-metal contents of the graphitized rocks compared to standard analyses including a conventional fire assay. In addition, electron microscopy surveys discovered extremely diverse native-metal and intermetallic complexes with C, O, Cl, F, REE and other elements. The microinclusions, however, represent a minor part of the mineralization. Major constituents seem to form carbonaceous nanocompounds invisible under a microscope. These graphite-based nanocomplexes, which are especially developed in the case of Pt, seem to be responsible for the highly resistant character of the Ruzhino mineralization. They also may be present in the latent form among the common Au ± PGE ores hosted by carbonaceous shales like those we studied in the close vicinity of the Ruzhino amphibolite-facies rocks and in the northeastern Bureya–Jiamusi terrane.     

Formation particularities of hypergene ferromanganese nodules: Far East Russia and Vietnam

Ferromanganese nodules (pisolites) form accumulations in basal layers of Pliocene-Quaternary clayey sections of Far East Russia and Vietnam. They are composed of minerals that are in common for both these regions (authigenic vernadite, feroxyhyte, goethite, halloysite, and terrigenous quartz) and minerals that are characteristic of either the northern (authigenic hollandite, lithiophorite, and bernessite) or southern (authigenic alumophorite, lepidocrocite, ferrihydrite, gibbsite, and terrigenous ilmenite) regions. Pisolites are considered to be microbial colonies with Mn and Fe oxides frequently forming biomorphs. The growth of the colonies was accompanied by dying off and mineralization of microorganisms successively from the central toward the peripheral parts of the nodules. The formation of metalliferous pisolites was linked to the oxidizing geochemical barrier developed at the interface between compact sedimentary clays and the underlying porous readily permeable weathered products of basalts.