We present the first ID-TIMS U-Pb dating results for cassiterite from the 106 − 76 Ma Okhotsk-Chukotka volcanic belt (OCVB), the major subduction-related igneous province in NE Asia. The three cassiterite samples studied were collected from the Nadezhda prospect and the Khrustalnoe deposit, two key prospects in the Mramornyi mineral district of Central Chukotka area. The cassiterite samples are relatively low in uranium (2.6 to 5.1 ppm) and contain varying amounts of common Pb, with measured 206Pb/204Pb ratios ranging from 48 to 330. The ID-TIMS U-Pb ages obtained are 84.8 ± 0.4 Ma, 83.3 ± 1.0 Ma, and 82.1 ± 1.2 Ma (2σ errors), demonstrating the applicability of ID-TIMS method for dating low-U cassiterite younger than 100 Ma. These ages are consistent with the U-Pb age of zircon from the host rhyolite of the Khrustalnoe deposit (90.7 ± 0.9 Ma). Synthesis of available age data for tin deposits in Central and North Chukotka indicates their formation during at least three magmatic events associated with three distinct igneous provinces: (1) 147–125 Ma in the subduction-related Central Chukotka belt; (2) 110–100 Ma in the extension-related Chaun igneous province; and (3) 96–76 Ma in the subduction-related OCVB. This suggests that tin mineralization in Chukotka was associated with nearly all major episodes of crustal melting in the region during the Jurassic and Cretaceous periods.

Stratigraphy of Campanian deposits in the stratotype of the Kudrinskaya Formation in the Southwestern Crimea is revised. For the first time, integrated sedimentological, biostratigraphic (ichnofossils, cephalopods, inoceramids, foraminifers, dinocysts, nannoplankton, gilianelles), isotope-geochemical, paleo- and petromagnetic characteristics of the section were obtained. The boundary of the lower and upper Campanian is substantiated and confirmed by U–Pb dating of zircons from the well-known bentonite (kil) clay bed in the interval of 77–80 Ma. It is proposed to accept the Campanian Substage boundary of the General Stratigraphic Chart (for bipartite stage subdivision) at the top of the Chron C33r, located near the δ13C isotopic excursion “MCaE” – Mid-Campanian Event, near the first occurrence of the benthic foraminifer Brotzenella monterelensis and a number of other traditional biomarkers.

The Talnikovoye ore field where previous academic research and exploration work revealed porphyry copper mineralization is described. Our data show that mineralization is confined to the intrusions of Turonian granodiorite and quartz diorite (91 Ma, U-Pb metohod), as well as the accompanying hydrothermal-explosive breccias. Biotite-epidote-chlorite propylites are widespread within the ore field; in the southern part, phyllic alteration is superimposed on the halo of K-feldspar alteration. The ore occurs in zones of intense quartz, chlorite-epidote-quartz (with chalcopyrite and molybdenite), sulfide-potassium feldspar-quartz (with chalcopyrite and bornite), and sulfide-quartz-sericite (with chalcopyrite) stockwork veining with copper-molybdenum mineralization. They are characterized by moderate concentrations of Cu (0.1–0.3 %, reaching 1.1 %) and Mo (up to 0.1 %), low concentrations of Au (up to 0.1 g/t) and Ag (up to 2.6 g/t) and have a Cu-Mo-(Au, Ag, Pb, Zn, Sb, As) geochemical signature. Fluid inclusion data suggest the formation of mineralized veinlet quartz during the magmatic-hydrothermal transition (430–150 °С) with solutions at high (50 wt % NaCl equiv.), medium and low concentration (5–18.9 wt % NaCl equiv.) involved under the cooling-dilution scenario. Values of the main geochemical indicators, such as Cu/Mo (30–60) and Cu/Au (> 1 × 105) ratios allowed us to assign the Tal’nikovoye ore field to the porphyry copper-molybdenum type characteristic of continental-margin volcano-plutonic belts formed at the mafic island-arc basement. The geochemical parameters of porphyry granitoids indicate their formation in a setting of subduction-to-transform plate boundary transition.

Across western and northern Chukotka, a region spanning 400 000 km2, we have defined three different tectono-magmatic systems that were active during the Aptian-Albian (123–100 Ma) time span: (1) the Tytylveem post-collisional belt (123–105 Ma); (2) the Chaun province of extension-related magmatism (109–100 Ma); and (3) the earliest eruptive units (106–100 Ma) of the subduction-related Okhotsk-Chukotka volcanic belt (OCVB). The observed tectono-magmatic systems are characterized by their location and by their different chemical and isotopic compositions. The general enrichment of magma sources successively increases from the OCVB to the Tytylveem belt and then to the Chaun province. While the Tytylveem belt was active, the volcanic loci shifted northwest along the strike of the belt, perhaps because of diachronous delamination of the lithosphere of the once present, but extinct, South Anyui ocean. On the scale of the entire region of NE Asia, the tectonic re-arrangement that controlled magmatism in the Early Cretaceous was marked by the extinction of major subduction zones on the periphery of the closing Oimyakon and South Anyui oceanic basins followed by magmatic events likely caused by lithospheric delamination and/or extension. Along the Pacific margin of Asia, subduction-related volcanism was nearly continuous during the entire Cretaceous.

The article presents the first data on rare-earth element-concentrating minerals in the Campanian Pechalny volcanic complex (Magadan Oblast). The volcanic complex is composed of a series of small subvolcanic rhyolite and trachyrhyolite intrusions, their explosive breccias, and basalts lava flow, which, judging by geochemical data, belong to typical intraplate bimodal magmatism. Rhyolites are extremely enriched in rare-earth elements of the lanthanide group (average REE total = 1152 ppm, max. up to 5662 ppm), as well as in Rb, Zr, Y, and Nb. The main rare-elementconcentrating minerals are monazite, allanite (orthite), gel-zircon, as well as Nb-bearing rutile and hematite. All minerals, except allanite, are characterized by a small grain size, from 15 μm to 2 μm and less. Unusual spheroid gel-zircon have been discovered; their genesis is associated with the hydrothermal stage of volcanism, at high oxidation state in a highly concentrated supercritical fluid.

Geological observations and U-Pb dating of zircons from intrusions of the Yana-Kolyma gold province constrain the age of orogenic gold deposits to the time interval between 150 ± 3 Ma and 108 ± 1 Ma. The age of mineralization at Natalka, the largest deposit of key importance in the gold province, is Valanzhinian (136 ± 1 to 132 ± 2 Ma) as we determined by muscovite 40Ar/39Ar dating and Re-Os dating of arsenopyrite and native gold. Since magmatic events of such ages are unknown in the province we conclude that the formation of gold-quartz mineralization is very likely related to metamorphism and metasomatism triggered by regional-scale shear deformation.

The results of study of lacustrine sediments of Northeastern Russia are presented. The reasons for the extremely high values of magnetic susceptibility are considered for the transitional Late Pleistocene to Holocene beds. The magnetic fraction of sediments of Grand Lake includes detrital titanomagnetite and magnetite. The high values of magnetic susceptibility of sediments of Gryazevoe, Sosednee, Vodorazdel’noe, and Sapog lakes are caused by the presence of authigenic Fe sulfides, mostly, greigite. Our data contradict the well-known suggestion on the presence of an impact event at the Pleistocene–Holocene boundary.

This paper reports new data on the geology and stratigraphy of the Upper Jurassic–Lower Cretaceous deposits of the eastern part of the Oloy zone (upper reaches of the Oloy, Ilguveem, Aluchin rivers), including the description of sections, lithological-petrographic and paleontological characteristics of volcaniclastic sediments, the results of petrological-geochemical study of volcanic rocks, and their isotope dating. Two concordant dates were obtained using the zircon U–Pb method: 147 ± 2 Ma (Elom Formation) and 140 ± 2 Ma (Glukhovskaya Formation). The island-arc nature of the studied formations has been substantiated. The facies conditions and geodynamic settings of all stages of the formation of the volcanic-sedimentary complex in the various structural-facies zones have been characterized.

The results of the study of lake sediments in the North-East of Russia are presented. The reasons for the abnormally high values of magnetic susceptibility in the transition layers from the Late Pleistocene to the Holocene are considered. The magnetic fraction of Lake Grand sediments is represented by detrital titanomagnetites and magnetites. In the sediments of the Gryazevoye, Sosednee, Vodorazdelnoye, and Sapog lakes, high values of magnetic susceptibility are due to autigenic iron sulfides, mainly greigite. The data obtained do not confirm the well-known assumption about the presence of an impact event at the boundary of the Pleistocene and Holocene.

The Kupol epithermal Au-Ag vein district is located in the northern part of the Okhotsk-Chukotka volcanic belt, a Late Cretaceous subduction-related continental volcanic arc exposed for >3,000 km along the eastern coast of Russia. High-grade veins are hosted in the Kupol andesite sequence, a 300-to 1,000-m-thick, subhorizontal, layered sequence of andesite flows, sills, and ash tuffs, dated at 97 to 96 Ma (Cenomanian). The Kupol andes-ite sequence is underlain by mixed mafic-felsic volcanic units plus sedimentary rocks ("older volcanics") and overlain by a >1-km-thick "upper felsic" sequence of dacitic-rhyolitic tuffs and associated dikes and flow domes, dated at 95 to 85 Ma, with local sequences of fluvio-lacustrine sedimentary rocks.The epithermal veins occupy N-striking, steeply dipping normal faults that cut thick coherent andesite flows and sills in the central-upper part of the Kupol andesite sequence. The district is dominated by the large Kupol vein (180.7 tonnes (t) Au and 1,986 t Ag produced to 2020), hosted by the 5.5-km-long Kupol fault, which accommodates normal, east-side-down displacement of up to 190 m. The Moroshka and Providence veins, 5 km east-southeast of Kupol, occupy shorter faults (1-to 2-km strike) with smaller vertical displacements (to 70 m). The Moroshka vein is dated at 93.5 +/- 1.5 Ma (Turonian; 40Ar/39Ar method on adularia), and the timing of vein mineralization here and at Kupol overlaps with the early stage of upper felsic sequence magmatism. Veins contain subhorizontal ore shoots, controlled by the intersection of the steep faults with flat-lying Kupol andesite sequence stratigraphy and by steepening of the faults to a more dilational orientation as the inferred paleosurface is approached. Local structural controls are also evident, reflecting a component of oblique slip on the Kupol fault, with the thickest vein segments at steeply pitching jogs and relays. Main-stage veins grew via repeated encrustation by quartz-chalcedony +/- amethyst +/- lattice bladed calcite (replaced by quartz), with Au-Ag-bearing crustiform adularia +/- clays +/- sulfides/sulfosalts/electrum +/- chlorite +/- hematite bands. The main controls on Au grade are inferred to have been boiling, resulting in sharp vertical limits to high metal grades typical of epithermal veins, coupled with optimal dilation of the vein system where the hosting normal fault steepens near surface with decreasing differential stress. Although much of the displacement on the controlling faults is pre-mineralization in timing, lithified cataclastic breccia, coeval with some vein stages, and vein geom-etry patterns indicate that some vein development occurred contemporaneously during late normal displace-ment along the fault system. Waning of the hydrothermal system is marked by late carbonate fill, initially Fe dolomite, then coarse calcite as veins, matrix to vein breccia, and central vein cavity fill. The Kupol district veins have proximal adularia-quartz alteration (haloes meters wide), within an extensive (hundreds of meters in scale) clay alteration halo. Clays are zoned both vertically and laterally with respect to veins, with inner illite-chlorite that was magnetite-destructive (at highest paleotemperature; >220 degrees C), grading outward and upward to illite/interlayered illite-smectite with kaolinite, then to an outer zone (or upper blan-ket) of smectite, at lowest paleo-temperature (<150 degrees C). The boundary between the illite and smectite zones is interpreted to mark the interaction limit of paleo-hydrothermal systems with cooler groundwater. District-scale pathfinder element zonation correlates with clays, with S-Te-Bi-As in the illite-chlorite core and Sb-Cs-Tl(-As-Li) in the smectite blanket. Pathfinder zonation patterns at Kupol point to a magmatic source at depth or, more likely given the scale of the anomalies, multiple magmatic sources, with the surface clay zonation indicating the extent of coalesced paleo-hydrothermal systems associated with upflow plumes. This is the best-defined altera-tion record with geochemical signature for a complete district hosting a large, high-grade vein deposit. Early definition of clay and pathfinder element patterns across an entire epithermal district can be carried out at low cost to provide useful constraints on vein targeting.

The activity of the North-Eastern Shared Research Facilities of the Shilo North-East Interdisciplinary Scientific Research Institute, Far Eastern Branch of the Russian Academy of Sciences (NEISRI FEB RAS) is aimed at conducting analytical studies of rocks, minerals, ores, soils, lake and sea sediments, water bodies using various methods: optical microscopy, X-ray microanalysis, X-ray fluorescence analysis, quantitative emission spectral analysis, atomic absorption spectrometry, isotope geochronology, paleomagnetism and petromagnetism. The results of mineralogical, geochemical, petrophysical, isotope-geochronological (including radiocarbon) and palynological studies have been published in national and international scientific journals.

This study is concerned with the material composition of the ores and the ore-bearing rocks of the Nevenrekan Au–Ag deposit. We provide a petrographic description of the rocks and their metasomatic alterations within the ore field, as well as structural and textural features of the ores. Two hypogenetic phases have been identified in the mineralization. The first, epithermal, volcanogenic phase consisted in the formation of adularia–carbonate–quartz veins and host-rock metasomatites of quartz–hydromica composition, of polysulfide and gold–sulfosalt mineralization, of extensive kaolinization regions, which gives way to chlorization and carbonatization with increasing depth. The contact action of a granitoidal pluton during the second phase gave rise to Te-, Bi-, and Sn-bearing mineral parageneses, silicification, epidotization, and sericite–quartz alterations of the host rocks. We showed the sequence of formation for paragenetic associations of minerals. Our inference is that the deposit is a multiformation feature with no analogues within the Evensky ore region. The age of epithermal mineralization as determined by the 40Ar/39Ar technique using the adularia in ore veins was 79.4 ± 1.0 Ma, which is consistent with the age of several major epithermal gold–silver deposits in the Okhotsk–Chukchi volcano-plutonic belt.

The results of a multidisciplinary study of two Holocene tephras from lacustrine sediments of the Northern Okhotsk area are presented. A comprehensive characterization of the tephra, including magnetic properties, petrochemical and grain-size composition, magnetic–mineralogical data, and radiocarbon dating, is presented for the first time. The distinctive features of two tephra layers and their possible use as regional chronological markers of the Middle and Late Holocene are shown.

The intrusions of Permian monzonites and granitoids exposed in the Koni–Taigonos arc, which composes the basement of the Uda–Murgal magmatic arc, are revealed for the first time in northeastern Asia. On the Taigonos Peninsula, a small Aichan pluton of Early Permian monzonitoids with an age of 297–290 ± 2 Ma (zircon, SHRIMP-II) intrudes the Permian sedimentary rocks, and, on the Koni-P’yagina Peninsula, two intrusions of leucocratic and porphyry granites with ages of 275 and 257 ± 2 Ma (zircon, LA-ICP-MS) are exposed in the basement blocks and are intruded by Early Cretaceous granitoids. The primary Sr and Nd isotope ratios of the Permian granitoids are close to the characteristics of the mantle (87Sr/86Sr = 0.07030‒0.07038, 143Nd/144Nd = 0.51245‒0.51270, εNd of +2 to +7.7). In the geochemical features, the rocks studied belong to type I aluminous granites of volcanic arcs of the shoshonite and high-K calc-alkaline series. These Permian granitoids are compared with those exposed in Japan (Maizuru belt) and Primor’e (Grodekovo batholith in the Khanka Block) and probably reflect the beginning of the most ancient subduction processes on the Pacific continental margin.

This study is concerned with the structure and composition of a sheet of Cenozoic alkaline basaltoids (basanites and trachybasalts) in the upper reaches of the Kedon River, in the Kedon Uplift of the Omolon Massif. Mineralogical and geochemical data provide evidence of an intraplate, poorly differentiated type of magmas. Geochronologic isotope data (40Ar/39Ar and K-Ar methods) indicate a Late Miocene age for the eruptions in the time span between 9 and 7 ± 1 Ma. The magma source contained a considerable percentage of pyroxenites and, judging from the isotopic composition of Sr, Nd, and Pb volcanics, it is similar to the PREMA mantle component that is also characteristic for other Cenozoic alkaline basalt occurrences in Northeast Asia. The potential temperature of the mantle beneath the volcanic area is similar, judging from theoretical calculations, to the mean value of an unexcited mantle, and is consistent with the scenario of lithospheric extension initiated by remote tectonic events.

>Abstract The coastal northwestern part of the Sea of Okhotsk hosts local volcanic fields of olivine–two pyroxene andesites and basaltic andesites of the Kytyima volcanic complex, which were dated at about 48 ± 2 Ma (U–Pb, 40 Ar/ 39 Ar, and K-Ar methods). The age of the eruptions correlates with that of bottom sediments in the Sea of Okhotsk and may reflect local stages of extension on the continental margin of northeast Asia. The geochemistry of the lavas makes it possible to classify them as highly magnesian, calc-alkaline, moderately potassic volcanic series with clearly seen negative Nb, Ta, and Ti anomalies and with positive Sr and Pb ones. The isotopic composition of the rocks [εNd(T) = 2.4–5.5, 87 Sr/ 86 Sr (0) = 0.703415–0.704175] and the relatively “young” Cambrian Nd model ages of the Paleogene volcanic rocks indicate that the melts were derived from a mantle source depleted in radiogenic isotopes (presumably, fragments of the Cretaceous slab under the complexes of the Uda–Murgal ensimatic island arc), which later experienced fluid-assisted metasomatism and enrichment in trace incompatible elements. Variations in isotope composition and in concentrations of major and trace elements in the lavas were controlled by decompressional fractional crystallization without indications of any significant crustal contamination.

The Velitkenay monzonite-granite-migmatite massif is a granite-core gneiss dome on the Arctic coast of Chukotka and a key outcrop for understanding mid-Cretaceous magmatism and metamorphism of the Arctic Alaska–Chukotka terrane. The petrology and geologic history of the complex were investigated using whole rock major and trace element and isotopic analyses (Sr, Nd and Pb), as well as electron microprobe thermobarometry, zircon U-Pb geochronology, trace element geochemistry, and O and Lu-Hf isotopic methods. The massif consists of two distinctive Albian plutonic suites. Deformed 106–103 Ma monzonitoids represent the early phase of plutonism; they were melted from a relatively mature crustal source with the bulk composition εNd(i) from –5.5 to –7.9; T Nd (DM-2st) = 1.4–1.6 Ga, and zircon composition εHf(i) from –11 to –7, δ 18 O from 10 to 8.4; and they evolved via assimilation and fractional crystallization processes. Late phase 102–101 Ma leucogranites (εNd(i) from –3.8 to –6.7, T Nd (DM-2st) = 1.2–1.4 Ga) formed from melting of Neoproterozoic orthogneisses with mantlelike zircon (εHf(i) from +11 to +13, δ 18 O ~ 5.8) and differ from early phase monzonitoids by the systematic presence of inherited Neoproterozoic (660–600 Ma) zircon xenocrysts. Migmatized Neoproterozoic orthogneisses are exposed in the central part of the dome, whereas the country rock on the flanks of the dome are paragenisses and schists with Devonian protolith ages. The intrusion of monzonitoid magmas was syntectonic with early stages of exhumation of the Velitkenay massif, whereas the leucogranite phase of magma intruded after peak metamorphism and does not exhibit ductile deformation. Based on subhorizontal mineral stretching lineations along the flanks of the dome and overall sigmoidal plan view of the massif, structural doming appears related to localized transtension in a more regional dextral strike-slip geodynamic environment. U-Pb isotope-geochronological data make it possible to distinguish seven episodes of granitoid magmatism, of which three major, in terms of volume (Aptian Bilibino, Albian Chaun, and Turonian-Coniacian Okhotsk-Chukotka granitoid magmatism subprovince), reflect the maximum rates of growth and modification of the Chukotka crust. Subordinate, in terms of volume, magmatic events of the Neoproterozoic, Devonian, Permian-Triassic, Late Jurassic, and Valanginian-Hauterivian have also been reconstructed.