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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. [ABSTRACT FROM AUTHOR]

High-grade epithermal Au–Ag veins of the Vodorazdelnaya district in far eastern Russia are hosted by Early Cretaceous volcanic rocks of the Tytylveem belt. The largest deposit is Zone 37, a 1-km long, northeast-striking vein that is up to 35-m wide, containing at least 32 t Au. The main shoot consists of crustiform—colloform banded quartz-chalcedony-adularia-sulfide veins, of low-sulfidation style. The vein is cut by late-mineral rhyolite sills and dikes. Zone 37 vein is dated at 117 ± 2 Ma, overlapping within error with the cross-cutting rhyolites (121–119 Ma) and with intrusions of the nearby Ilirney granitic pluton (119–117 Ma). The volcanic host rocks are dated at 121–115 Ma. At September Northeast, 15 km west-northwest of Zone 37, mineralisation consists of veins up to 4 m wide, with crustiform banded quartz ± chalcedony ± adularia ± chlorite, and Zn-Pb-Cu sulfides, of intermediate sulfidation style, in a 1-km-long, north-northeast striking trend. High grades are associated with gold dendrites in fine-grained quartz bands and with minor late-stage tellurides. The veins were disrupted by intrusion of rhyolite dikes and associated phreatic breccias. Some breccias host mineralisation as vein clasts and minor matrix sulfides. The Tytylveem belt is preserved below a regional unconformity that forms the base to the overlying Late Cretaceous (106–77 Ma) Okhotsk-Chukotka Volcanic Belt (OCVB). Intrusive rocks attributed to OCVB magmatism were emplaced at about 96 Ma and are associated with overprinting hydrothermal alteration, sub-economic veins and thermal resetting of some vein adularia ages at Zone 37, to 91–97 Ma. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Neogene alkaline intraplate volcanic rocks from the Viliga Volcanic Field (NE-Russia) were studied both to precisely characterize their geochemical composition and to unravel their petrogenetic history. The sampled volcanic rocks crop out within the voluminous calc-alkaline sequences of the Cretaceous Okhostk–Chukokta Volcanic Belt, an Andean-type arc formed during subduction of the Paleo-Pacific Plate beneath modern far-east Asia. The mantle xenolith- and xenocryst-bearing basanites and nephelinites have intraplate ocean island basalt-type geochemical features. Sr and Nd isotopes combined with major and trace element systematics and rare-earth element modeling suggest polybaric melt generation of these alkaline magmatic rocks from a homogeneous garnet peridotite facies source with minor involvement of spinel peridotite facies partial melts. The basanite samples indicate segregation PT conditions around 1500°C at 33–38kbar whilst the nephelinites reflect smaller melt fractions segregated at over 40kbar. During ascent, olivine (up to 7%) was the main fractionating phase in the basanites; whereas in the nephelinites, both olivine and minor clinopyroxene fractionation occurred. Crustal contamination during ascent was insignificant. We argue that the melt generation of these alkaline magmas from the Viliga Volcanic Field was triggered by an extending lithosphere resulting in upwelling asthenosphere and decompression melting, analogous to geodynamic models of the coeval alkaline volcanic rocks along the adjacent North Pacific continental margins, rather than by subduction- or plume-related processes. [ABSTRACT FROM AUTHOR]

The article presents a study that uses Uranium (U)-Lead (Pb) and Argon (Ar)-Ar dating to examine Enmyvaam and Amguema-Kanchalan volcanic fields development in the Okhotsk-Chukotka volcanic belt (OCHVB) of the Central and East Chukotka segments in Russia. The study performs the Uranium (U)-Lead (Pb) and Argon (Ar)-Ar dating and extracts the zircon crystals collected into six age volcanic complexes including rhyolite, pykarvaam, and voron'ya, that represents the different early and late development stages of OCHVB. Result shows Amguema-Kanchalan volcanic field to be 80.6±1.3 Megaanum (Ma); while 88.2±1.5 Ma was noted for Enmyvaam field. It concludes that continental-marginal volcanism in Amguema-Kanchalan field is 4 to 8 mega year (myr) younger than Enmyvaam volcanic field.

The article reports on the study that summarizes the field observations and structural data on the relative timing of deformational events in the Bilibino region of the Russian Arctic. It presents new geochronologic and thermochronologic data that help place more reliable age brackets on both deformation and magmatism across the region. It indicates that deformation began in the Late Jurassic, based on fossil ages of synorogenic clastic strata.

Discusses the pollutions from blasting operations at quarries in Russia. Evolution of the amount of pollutants formed in the explosion of the above-described explosives; Composition of explosion of products of mixed explosives.

Abstract: The Chersky seismic belt (NE-Russia) forms the modern plate boundary of the Eurasian−North American continental plate. The geodynamic evolution of this continent−continent setting is highly complex and remains a matter of debate, as the extent and influence of the Mid-Arctic Ocean spreading center on the North Asian continent since the Eocene remains unclear. The progression from a tensional stress regime to a modern day transpressional one in the Chersky seismic belt, makes the understanding even more complicated. The alkaline volcanism that has erupted along the Chersky range from Eocene through to the Recent can provide constraints on the geodynamic evolution of this continental boundary, however, the source and petrogenetic evolution of these volcanic rocks and their initiating mechanisms are poorly understood. We studied basanites of the central Chersky belt, which are thought to represent the first alkaline volcanic activity in the area, after initial opening of the Arctic Ocean basin. We present mineral and bulk rock geochemical data as well as Sr–Nd–Pb–Hf isotopes of the alkaline suite of rocks combined with new precise K–Ar and 40Ar/39Ar dating, and discuss an integrated tectono-magmatic model for the Chersky belt. Our findings show that the basanites were generated from a homogeneous asthenospheric mantle reservoir with an EM-1 isotopic flavor, under relatively ‘dry’ conditions at segregation depths around 110km and temperatures of ~1500°C. Trace element and isotope systematics combined with mantle potential temperature estimates offer no confirmation of magmatism related to subduction or plume activity. Mineral geochemical and petrographical observations together with bulk geochemical evidence indicate a rapid ascent of melts and high cooling rates after emplacement in the continental crust. Our preferred model is that volcanism was triggered by extension and thinning of the lithosphere combined with adiabatic upwelling of the underlying mantle at 37Ma. This suggests that at that time, rift tectonics in the Mid-Arctic Ocean most likely had also affected the North-Asian continent, causing volcanic activity in the Chersky belt, before the regional geodynamic regime changed from a tensional to compressional. Our conclusions contribute not only to the understanding of volcanism in the Chersky seismic belt (NE-Russia) but also to general aspects of plate dynamics between the Eurasian and North American continent. [Copyright &y& Elsevier]