Tin–rare-earth element greisens of the Solnechnoe cassiterite–silicate deposit,Russian Far East

The paper considers for the first time the morphology, composition, and conditions of formation of the greisens of the Solnechnoe deposit (Komsomol’sk ore district), a typical cassiterite–silicate assemblage. The greisens are localized in the root parts of the deposit and represent a system of veins and veinlets formed in the contraction fractures of the metasomatically altered roof of the monzogranite intrusion (age of 94–92 Ma). The cassiterite–chlorite–carbonate–muscovite–quartz composition of the greisens with admixture of topaz, fluorite, and apatite reflects the composition of the monzogranites. The greisens are close in age (85.3 Ma on muscovite) to the granitic aplites (80–85 Ma on the whole-rock and biotite) of the final phase of the intrusive magmatism. The fluid regime of their formation differs from that of the economic ores in higher temperature, pressure, and salinity. One distinguishing feature of the greisens is elevated contents of LREE, U, and Th, which are incorporated in the REE fluorcarbonates, thorite, and uranothorite crystallizing together with cassiterite.     

Nature of ore-forming fluids of the Dal’negorsk deposit: Isotopic and geochemical parameters of the altered host rocks

Oxygen isotopic composition was studied in the altered host rocks of the Dal’negorsk borosilicate deposit in order to establish a boron source and the origin of ore-forming fluids responsible for deposition of economic borosilicate ore. The relationships between oxygen isotopic composition and geochemistry of the altered igneous rocks occupying various structural and temporal positions in the ore zone were studied, including premineral high-potassium minor intrusions located in the zones of datolite mineralization; alkali basalt, gabbro, and breccia from the sedimentary framework of the deposit; and postmineral basaltic andesite, basalt, and dolerite dikes. It was suggested that interaction of aqueous fluid with host rocks brought about not only variation in oxygen isotopic composition but also shifts in geochemistry of these rocks, especially as concerns the chemical elements contained in ore-forming fluid. The disturbance of oxygen isotopic system is typical of all studied rocks: δ¹⁸O values sharply decrease indicating interaction with aqueous fluid at elevated temperatures. The lowest δ¹⁸O (from −2.9 to +0.1‰) is characteristic of the premineral high-potassium and ultrapotassium minor intrusions from skarn-datolite zone. Igneous rocks from the sedimentary framework of the deposit have δ¹⁸O of +2 to −0.9‰ The δ¹⁸O of postmineral basaltic andesite, basalt, and dolerite dikes varies from 0 to +7‰ with increasing distance from the ore zone. The oxygen isotopic composition of aqueous fluid evidences its exogenic origin. The geochemical and isotopic characteristics of ore-forming fluid show that it could have been deep-seated subsurface water similar to the contemporary water of the Alpine fold zone, which contain up to 700–1000 mg/l B and is distinguished by high K, Li, Rb, Cs contents and high K/Na ratio. Similar geochemistry is characteristic of the fluid inclusions in quartz from ore zones. It cannot be ruled out that continental evaporites were a source of boron as well. The relationships between δ¹⁸O, K-Ar age, and geochemical parameters of premineral and postmineral altered intrusive bodies allow us to suggest that the subsurface B-bearing water discharged through narrow channels controlled by premineral basaltic bodies. The discharge was probably initiated by emplacement of basalt and dolerite dikes.     

Genesis of the boron potential of the Taukha metallogenic zone,Sikhote Alin,and boron sources during formation of the Dal’negorsk boron deposit

It is shown that the formation of borosilicate skarn in the Taukha metallogenic zone completes a series of successive stages of the formation and transformation of the folded sequences of the Taukha accretionary wedge. The Early Cretaceous sedimentary stage, including accumulation of detrital tourmaline-rich sedimentary rocks, was implemented in the marginal sea of the Paleopacific Sino-Korean segment. In the Turonian–Campanian, the boron-bearing folded sequences of the accretionary wedge were involved in anatexis to generate siliceous S-type boron-bearing melts. The thus-formed magmatic chambers were emptied during catastrophic volcanic eruptions. At the final Middle Campanian volcanic stage, fluid-magmatic differentiation of the melt in the residual chambers generated fluid flow. The infiltration interaction of the fluids, which inherited enrichment in boron, with limestones of the olistostrome sequence resulted in the formation of a giant zone of grossular–wollastonite skarns and danburite lodes. The boron potential of the Taukha boron–lead–zinc metallogenic zone may be considered as a reproduction of the Precambrian boron metallogeny of the eastern Eurasian margin, which was implemented in the Late Mesozoic during recycling of the continental crust.     

Paleogene–Neogene Boundary of Primorye,Russian Far East

Complex geological and paleobotanic analysis of sections of the boundary Oligocene–Miocene sediments of southern Primorye is conducted. The presence of a stratigraphic hiatus is identified in the transitional complexes of the Pushkino and Pavlovka depressions but not in the sections of the Rakovka depression; thus, it is suggested to use one of them (borehole no. 15) to choose the stratotype of the Paleogene–Neogene boundary. The previous conclusion on the presence of economic coal deposits of Primorye within the Paleogene part of the Tertiary complex is supported. It is suggested to use the section which is exposed by the Rakovka brown coal open pit (point 9209) as a stratotype of the upper subformation of the Pavlovka Formation.     

The Dal’negorsk borosilicate skarn deposit,primorye, Russia: Composition of ore-bearing solutions and boron sources

The Dal’negorsk borosilicate skarn deposit (44° 34′ N and 135° 37′ E), located in the center of the ore field bearing the same name, is referred to the category of giant deposits. The currently predominant genetic concept assumes that ore mineralization at this deposit is related to a mantle source and that boron and ore-bearing alkaline fluids are derivatives of a juvenile source as well. The alternative model considered in this paper suggests that sedimentary sequences, probably, evaporites of a local basin, were immediate boron sources and hot subsurface water served as an agent of ore deposition. The authors’ conclusions are based on (1) mineralogical and geochemical features of alteration of premineral dikes as evidence for the composition of percolating ore-bearing fluids, (2) results of fluid inclusion study, and (3) boron and oxygen isotopic compositions of datolite.The latite bodies immediately predating deposition of economic datolite ore do not show mineralogical or geochemical attributes of their belonging to alkaline rock series. According to our data, these bodies are composed of Paleogene premineral basalts that intruded into the future borosilicate deposit close to the central channel of ore-bearing fluid, served as fluid conduits, and were altered to ultrapotassic rocks under the effect of such fluid. It is suggested that hot aqueous ore-bearing fluid was enriched in highly soluble compounds of Ba, K, and B and extremely depleted in poorly soluble compounds of Zr, Nb, Ta, La, and Ce. This suggestion does not contradict the properties and composition of primary and pseudosecondary two-phase fluid inclusions in danburite, datolite, quartz, and fluorite from orebodies. Judging from the boron isotopic composition of datolite (δ¹¹B = ?9 to ?31 ‰), the main amount of boron was extracted from metasedimentary rocks of the Mesozoic basement. The oxygen isotopic composition of datolite from the Dal’negorsk deposit (δ¹⁸O_SMOW = ?1.64 to ?2.97 and less frequently up to ?5‰) indicates a significant contribution of subsurface water to the transport of boron. A model of multistage accumulation of boron in ore of the Dal’negorsk borosilicate skarn deposit is proposed.     

Palynoflora of the Gil’chin and Dim dinosaur localities (the Zeya-Bureya Basin,Russian Far East)

The analysis of the palynological spectra from the Gil’chin and Dim dinosaur localities of the Zeya-Bureya Basin revealed that the first of them is characterized by the high abundance of Filicales spores accompanied (in descending order) by tricolpate, bisaccate conifer pollen, Ginkgocycadophytus, Taxodiaceae, Cupressaceae, Taxaceae (TCT), Ulmoideipites, and “unica”-type pollen. The spectra from the second site are dominated by Filicales spores and (second in significance) pollen of plants characteristic of river valley communities (Platanaceae and Ulmaceae) accompanied by common bisaccate conifer pollen and subordinate TCT and Ginkgocycadophytus pollen. The middle Maastrichtian bone-bearing taphocoenoses of the Gil’chin and Dim localities were formed in spacious swamped river valleys covered by ferns and taxodialeans. The Platanaceae and Ulmaceae pollen implies the development of light forests in river valleys. The Ulmaceae pollen is indicative of highly variable environments in the mid-Maastrichtian, probably, with an intermittent water influx. The low share of bissacate pollen in the palynospectra from these two localities is presumably determined by their remoteness from the slopes of the depression.     

Granitoid massif of the Dal’negorsk borosilicate deposit in the Primorye region of Russia: The role of the intrusion in the formation of the boron mineralization

The granitoids of the Dal’negorsk borosilicate deposit are ascribed mainly to the high-K metaluminous rocks of the calcic and alkali-calcic series. The thermo-baro-geo-chemical studies showed that they originated from melts with low contents of water (H₂O < 3.5% H₂O) and CO₂ at 800–850°C and 65–90 MPa. The data on the average contents of elements in the rock-forming minerals and the estimated initial water content in the magma point to the absence of a genetic relation between the intrusion and boron mineralization. The granitoid magma was responsible for the skarn formation and for the mobilization and remobilization of boron under a favorable environment. The K/Ar dating (51.0 ± 10 Ma), the geochemical typification (signatures of within-plate, subduction, and collisional granitoids), and the low water content in the parental melts of the granitoids, in accordance with the scheme of the geodynamic evolution of the region, indicate their formation in the lithospheric plate sliding environment.     

Shkol’noe gold deposit, the Russian Northeast

The Shkol’noe deposit is localized in a small granitoid stock, the root portion of which is traced using geophysical data to a depth of 5–8 km. The high-grade gold ore (33 gpt Au) is enriched in silver and principally differs in ore composition from the previously studied mesothermal gold-quartz and epithermal gold-silver deposits in the Russian Northeast. The main reserves of the Shkol’noe deposit concentrate in bonanzas (20% of the total volume of orebodies). The internal deformation is related to the rearrangement of matter in freibergite; exsolution structures in fahlore and native gold are related to postmineral metamorphism. It is suggested that the ore of the Shkol’noe deposit occupies a transitional position between porphyrytype and epithermal levels of ore deposition.     

In-bearing potential of tin‒sulfide mineralization in ore deposits of the Russian Far East

The increased demand for indium has made it necessary to revise prospects of In-bearing tin ore deposits in the Russian Far East on the basis of geological data and results of recent analytical methods (X-ray fluorescence with synchrotron radiation, atomic absorption, and ICP-MS). The average In contents in ores of the Tigrinoe and Pravourmiiskoe deposits vary from 55 to 70 ppm, which allows tin ore deposits with Sn?sulfide mineralization to be considered as quite promising with respect to In production from ores of Russian deposits. By their estimated In reserves, the Tigrinoe and Pravourmiiskoe deposits may be attributed to large ore objects.     

Dal’negosrk skarn deposit,Sikhote-Alin: Stages and sources of matter for borosilicate ores

The danburite orebody at the northeastern wall of the open pit of the Dal’negorsk borosilicate deposit is studied. The comparative mineralogical-, isotopic-, and thermobarogeochemical analyses of danburite from the Levoberezhnyi area and datolite of the late skarn stage from the Tsentral’nyi open pit confirms that danburite is a result of the early borosilicate stage of formation of the deposit. Combined with previously published data, it is concluded that marine sedimentary rocks or Early Cretaceous arkose sandstones from the matrix of the Taukhin accretionary prism could be the source of boron.     

Structure,age, and mechanism of emplacement of the Amur and Kiselevka–Manoma accretionary complexes of the lower Amur region,Russian Far East

The Amur and Kiselevka–Manoma accretionary complexes belong to the Cretaceous Khingan–Okhotsk active continental margin, which was formed in the east of Eurasia as a result of the subduction of the Pacific oceanic plates. The Kiselevka–Manoma complex is composed of oceanic pelagic and hemipelagic sedimentary rocks and intraplate oceanic basalts. It is located to the southeast, along the ocean-faced front of the Amur complex, which is predominantly composed of turbidites of the convergent boundary of lithospheric plates. The biostratigraphic study of radiolarians from rocks of the frontal part of the Amur complex allowed us to correlate them with rocks of the Kiselevka–Manoma complex and to define the period of accretion to be from the Late Aptian to the Middle Albian. The tectonostratigraphic interrelations of these two contrasting lithotectonic complexes are established and two possible models of their common emplacement are suggested. Both models suppose a continuous spatiotemporal relation of complexes with the primary paleolocation of the Kiselevka–Manoma complex in front of (on the ocean side) the Amur complex. The frontal part of the Amur complex and the Kiselevka–Manoma complex were emplaced synchronously with the western part of the East Sakhalin accretionary complex. This scenario defines the Early Cretaceous tectonic zonation of the region and the choice of the appropriate paleotectonic model. At the end of the Early Cretaceous, a single convergent boundary of the lithospheric plates is suggested with the position of the Sakhalin island arc system south of the Khingan–Okhotsk active continental margin.     

On the nature of ore-bearing fluids on the Dal’negorskoe borosilicate deposit (Primor’e)

Doklady Earth Sciences -     

Sulfur Isotopic Composition of Sulfides in Skarn and Vein Mineralization of the Dal’negorsk Ore Region (Primorye)

The S isotopic composition in the ore-forming minerals galena and sphalerite was studied in different Ag–Pb–Zn deposits of the region. It was pointed out that the δ³⁴S modal values range from–1.2 to +6.7‰ in the minerals with a positive value for the skarn mineralization. In the flyschoid formation, the vein-type mineralization is characterized by negative and positive values. The narrow range of δ³⁴S values indicates the marginal-continental type of the mineralization and the multiple origins of its sources.     

Yakchi chert–volcanogenic Formation—fragment of the Jurassic accretionary prism in the Central Sikhote-Аlin,Russian Far East

The Yakchi chert–volcanogenic formation is differentiated at the base of the stratigraphic succession in the Khor-Tormasu subzone of the Central Sikhote-clin structural–formational zone or the Samarka terrane of the Jurassic accretionary prism. The paper considers the results of biostratigraphic study of its deposits and petrogeochemical studies of its basalts. A tectonically disrupted sequence of the Yakchi Formation is restored on the basis of fossil conodonts and radiolarians, and its Late cermian–Middle Jurassic age is determined. The authors interpret the resulting stratigraphic succession in terms of changing depositional settings on the moving oceanic plate and recognize events of the ocean history recorded in it. Chert accumulated on the oceanic plate in pelagic canthalassa/caleopacifica from the Late cermian through to the Middle Jurassic. Deposition of siliceous claystone in the Late cermian–Early Triassic reflects the decline in productivity of radiolarians and a long anoxic event in Panthalassa. Chert accumulation resumed in the Triassic and persisted in the Jurassic, and it was interrupted by the eruption of basalts of different nature. Formation of the Middle–Late Triassic oceanic intraplate basalts likely occurred on the thick and old oceanic lithosphere and that of the Jurassic basalts on the thin and newly created lithosphere. In the Middle Jurassic, chert accumulation was replaced by accumulation of tuffaceous siltstone at a subduction zone along the csian continental margin. The middle Bathonian–early Callovian age of this siltstone closely predates accretion of the Yakchi Formation. The materials of the upper layer of the oceanic plate that formed over 100 million years in different parts of the ocean and on the lithospheric fragments of different ages were accreted to the continental margin. The bulk of the accreted material consists of oceanic intraplate basalts, i.e., fragments of volcanic edifices on the oceanic floor. accretion of this western part of the Khor-Tormasu subzone occurred concurrently with accretion of the southeastern part of the Samarka subzone in Primorye, which clarifies the paleotectonic zonation of the Central Sikhote-Alin accretionary prism. The cataclastic gabbroids and granitoids, as well as the clastic rocks with shallow-marine fossils in the Khor-Tormasu subzone, are considered as possible analogues of the Okrainka-Sergeevka allochthonous complex.     

Age stages of metamorphism at the Kitoi Sillimanite schist deposit, southeastern Prisayan’e

The Irkut Block with dominant rocks of the Sharyzhalgai Series and Kitoi Block with prevalence of the Kitoi Series rocks are the main structures of the Presayanian basement elevation of the Siberian Craton. Two stages of metamorphism, Neoarchean (2.6–2.7 Ga) and Paleoproterozoic (1.85–1.87 Ga), were established for the granulitic complexes of these blocks. The rocks of the Kitoi sillimanite schist deposit composed of sillimanite, andalusite-sillimanite, and garnet-sillimanite schists and gneisses underwent by intense ultrametamorphic transformations which led to the formation of sillimanite- and garnet-bearing plagioclase and feldspar migmatites, and also granites, sienites, and granite-pegmatites. The geochronological study of melanocratic schists and leucocratic plagiogneisses-the typical rocks of the Kitoi deposit-showed the manifestation of metamorphism only at the Archean and Proterozoic boundary (2450–2550 Ma).     

Peculiarities of ore formation at the N’yavlenga Au-Ag epithermal deposit,Northeast Russia

Thermobarogeochemical studies have revealed the relatively high-temperature ore-bearing fluid of the N’yavlenga deposit. The dependence between the homogenization temperatures of the fluid inclusions and salinity of the fluid and the bimodal distribution of salinity values indicates mixing of two different fluids in the ore-bearing system. These facts are related to the thermal metamorphism of ores from the N’yavlenga deposit and indicate the complex relations of the early Au-Ag epithermal and late Au-Cu-Mo porphyry mineral complexes in orebodies of the deposit.     

Geology, mineralization, and geochronology of the Qianhe gold deposit, Xiong’ershan area, southern North China Craton

The Qianhe gold deposit in the Xiong’ershan area is located along the southern margin of the Archean-Paleoproterozoic North China Craton. The deposit consists of six orebodies that are hosted in Paleoproterozoic andesites to basaltic andesites and structurally controlled by roughly EW-trending faults. Individual orebodies comprise auriferous quartz veins and disseminated Au-bearing pyrite within hydrothermally altered rocks on both sides of, or close to, the veins. Ore-related hydrothermal alteration has produced various mixtures of K-feldspar, quartz, sericite, chlorite, epidote, carbonate, and sulfides. Pyrite is the most important ore mineral, associated with minor amounts of galena, sphalerite, and chalcopyrite. Other trace minerals include molybdenite, arsenopyrite, scheelite, rutile, xenotime, and parisite. Gold occurs mostly as native gold and electrum enclosed in pyrite or along microfractures of sulfides and quartz. Microthermometric measurements of primary inclusions in auriferous quartz suggest that gold and associated minerals were precipitated in the range of 160–305 °C from aqueous or carbonic-aqueous fluids with salinities of 6–22 wt% NaCl equiv. Samples of molybdenite coexisting with Au-bearing pyrite have Re–Os model ages of 134–135 Ma, whereas ore-related hydrothermal sericite separates yield ⁴⁰Ar/³⁹Ar plateau ages between 127 and 124 Ma. The Re–Os and ⁴⁰Ar/³⁹Ar ages are remarkably consistent with zircon U–Pb ages (134.5?±?1.5 and 127.2?±?1.4 Ma; 1σ) of the biotite monzogranite from the Heyu-intrusive complex and granitic dikes in and close to the Qianhe gold mine, indicating a close temporal and thus possibly genetic relationship between gold mineralization and granitic magmatism in the area. Fluid inclusion waters extracted from auriferous quartz have δD values of ?80 to ?72 ‰, whereas the calculated δ ¹⁸O_H2O values range from 3.1 to 3.8 ‰. The hydrogen and oxygen isotopes from this study and previous work indicate that ore fluids were likely derived from degassing of magmas, with addition of minor amounts of meteoric water. Gold mineralization at Qianhe is temporarily coincident with pervasive bimodal magmatism, widespread fault-basin formation, and well development of metamorphic core complexes in the whole eastern North China Craton that have been interpreted as reflecting reactivation of the craton in the late Mesozoic after prolonged stabilization since its formation in the late Paleoproterozoic. It is therefore concluded that the Qianhe gold deposit formed as a result of this craton reactivation event.     

The Orosirian-Statherian banded iron formation-bearing sequences of the southern border of the Espinhaço Range,Southeast Brazil

The Serra da Serpentina and the Serra de São José groups are two distinct banded iron formation-bearing metasedimentary sequences along the eastern border of the southern Espinhaço Range that were deposited on the boundary between the Orosirian and Statherian periods.The Serra da Serpentina Group (SSG) has an Orosirian maximum depositional age (youngest detrital zircon grain age = 1990 ± 16 Ma) and consists of fine clastic metasediments at the base and chemical sediments, including banded iron formations (BIFs), on the top, corresponding to the Meloso and Serra do Sapo formations, respectively, and correlating with the pre-Espinhaço Costa Sena Group. The SSG represents sedimentary deposition on an epicontinental-epeiric, slow downwarping sag basin with little tectonic activity.The younger Serra de São José Group (SJG) is separated from the older SSG by an erosional unconformity and was deposited in a tectonically active continental rift-basin in the early stages of the opening of the Espinhaço Trough. The Serra do São José sediments stretch along the north-south axis of the rift and comprise a complete cycle of transgressive sedimentary deposits, which were subdivided, from base to top, into the Lapão, Itapanhoacanga, Jacém and Canjica formations. The Itapanhoacanga Formation has a maximum depositional age of 1666 ± 32 Ma (Statherian), which coincides with the maximum depositional age (i.e., 1683 ± 11 Ma) of the São João da Chapada Formation, one of the Espinhaço Supergroup's basal units. The Serra de São José Rift and the Espinhaço Rift likely represent the same system, with basal units that are facies variations of the same sequence.The supracrustal rocks have undergone two stages of deformation during the west-verging Brasiliano orogeny that affected the eastern margin of the São Francisco Craton and generated a regional-scale, foreland N–S trending fold-thrust belt, which partially involved the crystalline basement. Thrust faults have segmented the terrain into a large number of tectonic blocks, where the stratigraphic sequence was nevertheless well preserved.     

Age and depositional conditions of the marine vertebrate concentration Lagerstätte at Gomez Farías,southern Coahuila,Mexico

A 1.5 m thick coquinite discovered in the Upper Jurassic La Casita Formation of the Sierra El Jabalà near Gomez Farías, Coahuila, northeastern Mexico qualifies as a concentration Lagerstâtte owing to its richness in marine vertebrates. Ichthyosaurs, pliosaurs and crocodilians were described to some detail, but other taxa remained unstudied and the precise biostratigraphical age, as well as paleoecological conditions that led to the formation of the fossil deposit, are not known in detail. Here we describe ammonites, aptychi, bivalves and radiolarians, which allow for a stratigraphic assignation of the deposit to the uppermost Kimmeridgian Beckeri Zone. The unit under consideration accumulated in a hemipelagic mud bottom environment during a period of time characterized by low oxygen conditions, while a short term benthic colonization phase near the top of the coquinite corresponds to increased oxygen availability. A combination of upwelling, bottom currents, winnowing, offshore winds, storm events, circulatory nutrient traps, low oxygenated bottom waters, and a transgressional regime with reduced net sedimentation was crucial factors for the subsequent concentration of fossils, as well as for marine phosphate generation and phosphorus migration.