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Russian Geology and Geophysics

2019 year, number 5

1.
MANTLE–CRUSTAL NATURE OF EARLY PALEOZOIC ALKALINE INTRUSIONS IN CENTRAL SANGILEN, TUVA (from Nd, Sr, Pb, C, and O isotope data)

V.V. Vrublevskii1, A.V. Nikiforov2, A.M. Sugorakova3, and T.V. Kozulina1
1 Tomsk State University, pr. Lenina 36, Tomsk, 634050, Russia
2 Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
3 Tuva Institute for Exploration of Natural Resources, Siberian Branch of the Russian Academy of Sciences, ul. Internatsional’naya 117a, Kyzyl, Tyva Republic, 667010, Russia
Keywords: Alkaline magmatism, isotope geochemistry and geochronology, plume–lithosphere interaction, Sangilen upland, Central Asian Orogenic Belt

Abstract >>
The Paleozoic foidolite–foyaite plutons of the Sangilen upland (Bayan-Kol, Dakhu-Nur, Chik, and Kharly ones) might have formed in the Late Cambrian–Early Ordovician (~490–500 Ma, Sm–Nd and U–Pb); they are the result of the oldest alkaline magmatism in southeastern Tuva. The intrusion was accompanied by the formation of high-temperature (up to ~600–900 ºC) endogenous carbonate rocks containing calcite, alkali pyroxene, Na–Ca amphibole, biotite, fluorapatite, microcline, and nepheline. Silicate and carbonate derivates were produced, most likely, from genetically related heterogeneous sources with εNd(T) varying from 3.0 to 6.3 and from –0.5 to 6.5, respectively, which might be due to the mixing of the depleted (PREMA) and enriched (EM) mantle materials. Initial ratios 207Pb/206Pb ≈ 0.89 and 208Pb/206Pb ≈ 2.15 in K-feldspar from calcitic rocks are close to those of EM 1. The correlation between the stable-isotope ratios (δ18O ~ 7.2–19.5, δ13C from –6.0 to –1.4 ‰) and the high 87Sr/86Sr(T) ratio (0.7057–0.7076) indicates a significant crustal contamination of magma in the upper horizons of the lithosphere and a minor impact of a meteoric fluid. The assumed synchronous formation of the studied plutons and other alkaline rock complexes of the Early Paleozoic Large Igneous Province in the west of the Central Asian Orogenic Belt as well as their isotope similarity do not rule out that the intrusion took place in the plume–lithosphere interaction setting.

DOI: 10.15372/RGG2019032



2.
DIAMONDS IN THE KAMCHATKA PENINSULA (Tolbachik and Avacha Volcanoes): NATURAL ORIGIN OR CONTAMINATION?

N.P. Pokhilenko1,2, T.G. Shumilova3, V.P. Afanasiev1, and K.D. Litasov1,2

1 V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia

2 Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia

3 Institute of Geology, Komi Science Center, Ural Branch of the Russian Academy of Sciences, ul. Pervomaiskaya 54, Syktyvkar, 167982, Russia
Keywords: Natural diamond, synthetic diamond, carbonado, volcano, ophiolite, contamination
Abstract >>
Lavas of the Kamchatka volcanoes store cubic-octahedral diamonds identical in morphology and structure to synthetic crystals, and their natural origin is doubted. Judging by published data, the diamonds discovered in the Tolbachik lavas are similar to synthetic diamonds made by different producers, and the analyzed samples ra-ther result from contamination with synthetic material. Ophiolite-hosted diamonds reported from Europe, China, Mongolia, and Polar Urals look like the Tolbachik diamonds and are of the same type. The similarity between crystals coming from geologically dissimilar objects indicates that contamination may occur in those cases as well. Thus, diamonds found in unusual hosts or geologic settings require careful checking. These findings have to be reproduced repeatedly in other in situ samples and approved by independent experts; with all respect to the priority of the first finders, the sampling sites should be open to many researchers, especially the respective spe-cialists. The inevitable disproval of false diamond findings is discouraging and discredits the true discoveries. Possible contamination with synthetic or natural material from cutting tools has to be excluded in all newly found diamonds before claiming their natural origin.

DOI: 10.15372/RGG2019024



3.
GEOCHEMISTRY AND ISOTOPIC AGE OF ZIRCONS FROM ROCKS OF ULTRAMAFIC MASSIFS IN THE SOUTHERN FOLDED FRAMING OF THE SAO FRANCISCO CRATON (southeastern Brazil)

F.P. Lesnov1, M.A.P. Pinheiro2, S.A. Sergeev3,5, and N.S. Medvedev4

1 V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences,
pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia

2 Serviço Geológico do Brasil, Av. Brasil 1731, Funcionários, Belo Horizonte, MG 30140-002, Brasil

3 Center of Isotopic Research, A.P. Karpinsky Russian Geological Research Institute, Srednii pr. 74, St. Petersburg, 1999106, Russia

4 A.V. Nikolaev Institute of Inorganic Chemistry, pr. Akademika Lavrent’eva 3, Novosibirsk, 630090, Russia

5 Institute of Earth Sciences, St. Petersburg State University, 10-ya Liniya Vasil’evskogo Ostrova, St. Petersburg, 199034, Russia
Keywords: Ultramafic rocks, zircons, geochemistry, LA–ICP-MS method, isotopic age, U–Pb method, SIMS SHRIMP II, São Francisco Craton, Brazil
Abstract >>
We present the first data on the geochemistry and isotopic age of zircons from rocks of the Roseta (lher-zolite and olivine orthopyroxenite) and Córrego da Areia (olivine orthopyroxenite) ultramafic massifs localized among Archean–Proterozoic metamorphic strata in the southern folded framing of the São Francisco Craton. The examined zircons differ in crystal morphology, the intensity and type of cathodoluminescence, oscillatory zoning, the distribution of trace elements, and U–Pb isotopic age. Zircon crystals from the Roseta lherzolite have an age of 800–728 Ma and show negligible cathodoluminescence. Some of them have reaction rims with an age of 663–619 Ma. The crystal cores are enriched in REE but are often depleted in U as compared with the reaction rims. The age of zircons from the Roseta olivine orthopyroxenite showing moderate cathodoluminescence is within 622.6–596.9 Ma. Zircons from the Córrego da Areia olivine orthopyroxenite show moderate to intense cathodo-luminescence and often have a rhythmic oscillatory zoning. They are characterized by an uneven distribution of REE and other trace elements and have high contents of U and Th. Most of these zircons have an ancient isotopic age (2558–2100 Ma). The examined zircons are of several types: relict, inherited (xenogenic), syngenetic, and epigenetic. The Roseta and Córrego da Areia massifs are considered to be protrusive outliers of a deep-seated Precambrian mafic–ultramafic complex, which were tectonically transferred along faults into the intensely meta-morphosed Archean–Proterozoic strata in the southern folded framing of the São Francisco Craton.

DOI: 10.15372/RGG2019025



4.
EARLY PALEOZOIC GRANITOID MAGMATISM IN THE EAST TANNU-OLA SECTOR OF THE TUVINIAN MAGMATIC BELT: GEODYNAMIC SETTING, AGE, AND METALLOGENY

E.V. Vetrov1,2, A.I. Chernykh3, and G.A. Babin1,4

1 Siberian Research Institute of Geology, Geophysics and Mineral Resources, Krasnyi pr. 67, Novosibirsk, 630091, Russia

2 V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences,
pr. Koptyuga 3, Novosibirsk, 630090, Russia

3 Central Research Institute of Geological Prospecting for Base and Precious Metals, Varshavskoe shosse 129, korp. 1, Moscow, 117545, Russia

4 A.P. Karpinsky Russian Geological Research Institute, Srednii pr. 7, St. Petersburg, 199026, Russia
Keywords: Granitoid magmatism, U/Pb (SHRIMP-II) zircon dating, petrogeochemical and isotope-geochemical (Sm/Nd and Rb/Sr) studies, gold, copper, lead, zinc, metallogeny, Republic of Tyva, East Tannu-Ola sector, Tuvinian magmatic belt
Abstract >>
The East Tannu-Ola sector of the Tuvinian magmatic belt is composed of Early Cambrian volcanosedi-mentary rocks of an island-arc association (Kadvoi, Serlig, and Irbitei Formations), which are intruded by granit-oid massifs of different ages (from Cambrian to Devonian) of the Tannu-Ola areal pluton. We analyzed the structural and geologic position, chemical composition, metallogenic signatures, and ge-ochronological (U/Pb) and isotope-geochemical (Sm/Nd and Rb/Sr) characteristics of Early Paleozoic granitoids of the Ungesh pluton (western part of the Tannu-Ola areal pluton). The available and our new data made it possi-ble to establish the specific chemical parameters, age sequence, duration, intensity, and metallogeny of granitoid magmatism in the East Tannu-Ola sector of the Tuvinian magmatic belt. An early Cambrian (534–518 Ma) gabbro–plagiogranite complex similar to the Maina complex in West Sayan has been recognized in the Ungesh pluton. The age and metallogeny of the middle–late Cambrian (508–492 Ma) Tannu-Ola diorite–granodiorite–plagiogranite and Late Ordovician (451–447 Ma) Argolik granite–leucogranite complexes have been refined. Granitoids of the early Cambrian complex formed probably at the initial stage of formation of an island arc, in association with the Kadvoi–Serlig basalt–andesite–rhyolite complex. It is in these granitoids that early low-productivity gold–sulfide–quartz veins and veinlets originated. Granitoids of the Tannu-Ola complex formed at the initial stage of evolution of the accretion–collision system. Magnetite-containing skarns and numerous vein–veinlet zones of late high-productivity gold-sulfide-quartz mineralization evolved in these granitoids. Granitoid massifs of the Argolik complex formed at the final stage of evolution of the accretion–collision system and probably played a crucial role in the regeneration of ore mineralization in some areas.

DOI: 10.15372/RGG2019047



5.
GOLD-BEARING PYRRHOTITE ORES IN EAST SAYAN: COMPOSITION AND FORMATION CONDITIONS (by the example of the Ol’ginskoe ore occurrence)

B.B. Damdinov, L.B. Damdinova, S.M. Zhmodik*, and A.G. Mironov

Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh’yanovoi 6a, Ulan Ude, 670047, Russia

*V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences,
pr. Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Gold, pyrrhotite ores, composition, formation conditions, genesis, East Sayan
Abstract >>
We present results of study of the chemical composition, formation conditions, and genesis of gold-bearing pyrite–pyrrhotite ores widespread within the ophiolite belts in the southeast of East Sayan. The study was performed at the Ol’ginskoe ore occurrence localized in the Ol’gino gold ore zone. Sulfide mineraliza-tion zones are composed of lenticular interbeds and bodies subconformable with the bedding of the enclosing schist strata. The ores are carbonaceous siliceous garnet–biotite schists variably enriched in sulfide minerals, mainly pyrrhotite, with impurities of other silicate minerals: tremolite, chlorite, albite, plagioclase, diopside, and epidote. In addition, sphalerite, chalcopyrite, pyrite, and arsenopyrite are present in small amounts in the ores. The established Ð–Ò conditions of ore metamorphism (T = 430–540 °Ñ, P ~ 5 kbar) correspond to the lower boundary of the epidote–amphibolite facies. Thermobarogeochemical studies of fluid inclusions in vein quartz showed close temperatures (536–340 °Ñ) but lower pressures, 200–800 bars, which indicates that the quartz vein formation was related to a pressure drop. The predominant salts of the fluid inclusions are Fe and Mg chlorides with Na and K impurities. The geologic location, structures, textures, and mineral, geochemical, and isotope compositions of the studied sulfide ores indicate their formation in submarine deep-water environments as a re-sult of the activity of hydrothermal systems, analogues of «black smokers», later subjected to metamorphism. During metamorphism, primary ores underwent mineral and chemical transformations: pyrrhotitization of pyrite, appearance and coarsening of native gold particles, and redistribution of components (Mn, As, etc). The low contents of gold and some ore-forming elements (Zn, Cu, and Pb) in pyrrhotite ores testify to the removal of these elements with a metamorphogenic fluid. The removed ore-forming components might have been a source of material for later gold–sulfide–quartz deposits of the Urik–Kitoi zone in East Sayan.

DOI: 10.15372/RGG2019028



6.
THE EQUILIBRIUM OF CLAY MINERALS WITH AQUEOUS SOLUTIONS IN SOILS

V.N. Shoba and K.V. Chudnenko*

Siberian Research Institute of Soil Management and Chemicalization of Agriculture, Siberian Federal AgroBioTech Scientific Center,
Russian Academy of Sciences, Krasnoobsk, 630501, Russia

*A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1A, Irkutsk, 664033, Russia


Keywords: Physicochemical modeling, soils, fine colloids, clay minerals, humic acids, end-members, chemical po-tentials, activity coefficients
Abstract >>
We studied the total chemical and mineralogical compositions of fine colloids (fraction <0.08 μm) in the upper horizons of contrasting soil compositions and properties. Based on the analytical data, the crystallochemi-cal formulas of clay minerals with a 2:1 structure are calculated, and the chemical potentials of independent com-ponents and the activity coefficients of the main end-members are determined. Using the Selector software, the equilibrium phase–multicomponent composition of soils is calculated, and the similarity and difference in the crystal chemistry of 2:1 clay minerals produced by two different methods are shown. The calculated Gibbs ener-gy values of these minerals are close to the calorimetric data for smectites. It is shown that the contents of typical elements in 2:1 clay minerals reflect the genetic properties of soils. In soils of alkaline series (Solonetz), such minerals are relatively enriched in sodium and magnesium; in soils of acidic series (Podzoluvisols and Cambi-sols), in hydrogen and iron; and in soils of the neutral series (Chernozems, Arenosols, and Umbric Gleysols), in calcium.

DOI: 10.15372/RGG2019035



7.
DISTURBED STRATIFICATION IN LATE PLEISTOCENE SEDIMENTS OF THE KHIBINY PLUTON (Kola Peninsula)

Å.S. Gorbatov, S.F. Kolesnikov*, and À.À. Sorokin

Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, ul. Bol’shaya Grusinskaya 10-1, Moscow, 123242, Russia

* Moscow State University of Geodesy and Cartography, per. Gorokhovskii 4, 105064, Moscow, Russia
Keywords: Deformation structures, wavy stratification, seismic liquefaction, mudflow, glaciolacustrine deposits, Khibiny, Kola Peninsula
Abstract >>
The paper presents a description of three Late Pleistocene sections within the Khibiny pluton, outcropping on the proximal slope of the Kukisvum morainic ridge, a fluvioglacial terrain in the valley of the Kukisiok River, and a glacial complex in the valley of the Vuonnemiok River. Various small disturbances of the primary stratifi-cation were found in the first two sections. These structures do not form horizons sustained along the strike and are associated with the top of sand–silt sediments with horizontal or wavy bedding of shallow lacustrine genesis. They form small wavy bends, ‘tongues”, ovoids, and flexural microfolds that could not be preserved at the bot-tom of the basin and, consequently, formed after overlapping deposits accumulation. Analysis of the cross bed-ding of the coarse clastic deposits of the fluvioglacial terrace has allowed us to relate its formation to north-to-south glacial water discharge along the trough valley of the Kukisiok River. In the glaciolacustrine varve clays of the third section (the Koashva open pit), extended horizons of plicative disturbances 0.5–2 m in thick-ness and 300 m in length were studied. The soft-sediment deformations are covered with an unstructured horizon composed of coarse grains dispersed in sand–silt matrix, which means that the deformation was caused by either a glacial flood or a mudflow. The study has revealed no signs of seismic liquefaction during the formation of the folded structures. The relevance of the performed study is determined by the fact that it has become possible not only to clarify the formation conditions of the Quaternary Khibiny deposits but also to develop the objective criteria for determination of the soft-sediment deformation structures associated with thixotropic effects in weakly consoli-dated sediments. Similar structures are sometimes regarded as seismic convolutions, which can lead to unjustified overestimation of the regional seismic hazard level.

DOI: 10.15372/RGG2019022



8.
GEOCHEMISTRY OF SODA WATERS OF THE CHULYM–YENISEI ARTESIAN BASIN (West Siberia)

O.E. Lepokurova1,2 and S.L. Shvartsev1,2

1 Tomsk Division of the A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences,
pr. Akademicheskii 4, Tomsk, 634055, Russia

2 Tomsk Polytechnic University, pr. Lenina 30, Tomsk, 634050, Russia
Keywords: Soda waters, conditions of water spread, chemical and isotope compositions, water–rock system, for-mation mechanisms, equilibrium, Chulym–Yenisei basin
Abstract >>
Results of studies of soda waters of the Chulym–Yenisei artesian basin are presented. It is shown that these waters are ubiquitous within Cretaceous or Jurassic sediments at depths of ~100–300 m to 1.5–2.3 km. According to the formation conditions, mineralization, and pH, they are divided into three groups: Type I waters spread to a depth of 600 m and have pH = 7.4–8.4 and TDS  0.5 g/L, type II soda waters occur at depths of 0.6–2.3 km and are characterized by pH = 8.0–8.9 and TDS = 0.7–4.1 g/L, and type III waters («Omega») form a local segment among type II waters and have a unique composition: high alkalinity (pH = 9.0–10.3) and low mineralization (TSD = 0.2–0.6 g/L). We focus special attention on type III waters and present results of studies of their microcomponent, gas, and isotope compositions. The cause of their low salinity and high pH is explained for the first time. Taking into account the isotope data (δD, δ18O, and δ13C), we have established the infiltration origin of soda waters of the three types and the biogenic source of their carbon dioxide. Calculations of equilibria in the water–host-mineral system have shown that all soda waters are in disequilibrium with many primary alu-minosilicate minerals but are in equilibrium with a wide range of carbonates and clays. In passing from type I to type III waters, the number of minerals in equilibrium with water continuously increases (albite, microcline, muscovite, and biotite). Taking into account the data obtained, we present schemes of formation of different types of soda waters in the studied basin at different stages of the evolution of the water–rock–gas–organic-matter sys-tem and estimate the time of each system.

DOI: 10.15372/RGG2019044



9.
SEISMOGEOLOGICAL CRITERIA FOR THE GAS POTENTIAL OF APTIAN–CENOMANIAN SEDIMENTS IN THE NORTH OF WEST SIBERIA (by the example of the Yubileinoe field)

V.A. Kontorovich1,2, E.S. Surikova1, and D.V. Ayunova1,2

1 A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences,
pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia

2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia


Keywords: Seismic exploration, petroleum prediction, gas pool, «bright spot», dynamic parameters of a seismic record, West Siberia
Abstract >>
Seismogeological criteria for the gas potential of the Aptian–Cenomanian sediments of West Siberia are substantiated. The research was carried out by the method of integrated interpretation of seismic materials, well logs, well test results, and petrophysical studies. As a reference object we used the Yubileinoe oil and gas con-densate field located in the Nadym–Pur interfluve, in which a unique gas deposit is concentrated in the Cenoma-nian reservoir PK1 and the Albian sand bed PK18. Based on the research results, seismogeologic criteria for gas prediction have been formulated. Massive Cenomanian gas pools are displayed in wave seismic fields by: (1) the presence of reflectors formed at the gas–water contacts in time sections and a decrease in the amplitude parameters of the reflector G confined to the roof of Cenomanian sequence; (2) an increase in the time thickness (Δt), a decrease in the interval velocities (vint), and a decrease in the amplitude–energy parameters of a seismic record in the Aptian–Cenomanian sequence. Aptian–Albian sheet gas pools are displayed in the wave fields by a drastic increase in the amplitudes of a seismic record, forming «bright spot» anomalies in the time sections.

DOI: 10.15372/RGG2019077