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.     

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.     

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.     

Lithological composition of island-arc complexes in the Russian Far East

The results of study of geochemistry of terrigenous rocks from the contrast (in structure) Cretaceous-Paleogene complexes of Sikhote Alin and Kamchatka are summarized. The data obtained were interpreted based on comparison with the geochemical composition of recent and ancient sediments accumulated in the well-known geodynamic settings. It is shown that the chemical composition of terrigenous rocks and some petrochemical ratios can serve as reliable indicators of various island-arc settings. These indicators make it possible to discriminate sufficiently reliably these settings in paleobasins of orogenic zones.     

Fahlores of the Prasolovka Au-Ag volcanogenic deposit, Kunashir Island, Russian Far East

The chemical study shows that fahlores from the Prasolovka deposit are complex compounds with significant variations in their composition and the proportions of their constituent elements. Based on their major-element composition, they are subdivided into 3 species and 11 inter-and intra-species varieties. The chemical composition of the fahlores in different mineral assemblages from different ore types indicates that As fahlores subsequently replaced by Sb, Te-Sb, and Te fahlores during ore precipitation. The revealed evolution of the ore solutions from the early to late stages testifies that different ores at the Prasolovka deposit were formed under different physicochemical conditions.     

俄罗斯远东金属矿床形成条件的古地球动力学分析

根据本区地质构造的新资料,提出了区域板块构造模型。研究了从俯冲到加利福尼亚型转换和由后者又到俯冲的古地球动力学环境更替的意义。这种更替发生在对本区最重要的中—新生代历史时期,对区域成矿带整体乃至一些金属矿床的形成具有重要影响。论证了一些地体性质,尤其是俯冲-增生杂岩对矿床形成的重要意义。     

Tungsten accessory minerals in lithium-fluoric granites of the Russian Far East

By means of the technique of local analysis, the presence of a wide variety of tungsten and tungsten-containing accessories was first revealed in the composition of lithium-fluoric granites of the Far East, which represents a substantial similarity and regional peculiarity of these rocks. It was concluded that the tungsten accessory mineralization might be considered as an indication of the genetic relationship of the mineralization of the East Asian tin-tungsten zone to the Pacific rare-metal granites.     

Unique Marine Olenekian-Anisian Boundary Section from South Primorye, Russian Far East

INTRODUCTION LateOlenekianandAnisianmarinedepositsin SouthPrimoryewerefirststudiedbyD.L.Ivanov,thechiefofageologicalteammakingreconnaissance workfortheconstructionofthetrans Siberianrail road.HecollectedEarlyandMiddleTriassicam monoidsonRussianIsland.Arep…     

Mesocyclicity of Upper Triassic-Jurassic rocks in the Bureya Basin in the Far East of Russia: Their tectonics, eustasy, and sequence stratigraphy

The mesocyclicity of Upper Triassic-Jurassic rocks in the Bureya Basin located at that time at the paleocontinent margin was examined. The rock sections of this basin distinctly reflect the chronology of the eustatic sea-level fluctuations, which enabled us for the first time to construct a sequence stratigraphic model for this basin. Based on all the factors affecting the cyclicity, cycles of six orders (ranks) were recognized in the Bureya Basin for the Jurassic stage of its evolution. The tectonic factor predominates in the identification of the first three orders: the first-order cycle (the Alpian), the second-order cycles (the Indo-Sinian and Yanshanian), and the third-order cycles (the Late Indo-Sinian, Early Yanshanian, and Middle Yanshanian subcycles). The formation of the fourth-to sixth-order cycles was affected by not only the tectonic processes but also the eustatic sea-level fluctuations, the sediment supply??s volume, the sedimentary environment, and the climatic changes. Since the oil source rocks are formed during the maximal transgressions, the aleuropelitic strata of the fifth-order cycles (the Chagany, El??ga, Epikan, and Sinkal??tu formations along with the Khavagda Sequence) accumulated in the deepest parts of the basin are believed to be the most prospective objects.