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Russian Geology and Geophysics

2007 year, number 12

1.
TOPICAL PROBLEMS OF GOLD METALLOGENY

Yu.G. Safonov, V.V. Popov, A.V. Volkov, T.M. Zlobina, I.V. Chaplygin
Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences,
35 Staromonetny per., Moscow, Russia 119017
Keywords: Metallogeny; gold; deposits; geologic-genetic types; geodynamic regimes; geotectonic settings; activity; specialization
Pages: 977-991

Abstract >>
Siberian geologists in general and Academician V.A. Kuznetsov in particular made a considerable contribution to metallogeny. To follow them, we consider regularities of location and formation of gold deposits. Analysis of topical problems of gold metallogeny reflects general problems of state-of-the-art metallogeny. The analysis is based on concepts of geologic-genetic types of gold deposits and metallogenic specialization of geodynamic-geotectonic regimes and settings. The types of endogenic-polygenic gold ore and gold-bearing deposits restricted to certain settings - among which, in addition to traditional ones, intracratonic basins have been established - are characterized by depressions and heterochronous areas of rift and plume tectonomagmatic activity.



2.
ANTIMONY IN HYDROTHERMAL PROCESSES: SOLUBILITY, CONDITIONS OF TRANSFER, AND METAL-BEARING CAPACITY OF SOLUTIONS

A.A. Obolensky, L.V. Gushchina, A.S. Borisenko, A.A. Borovikov, G.G. Pavlova
Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Antimony; ore-forming systems; antimony species; metal-bearing capacity of solution; thermodynamic modeling
Pages: 992-1001

Abstract >>
Based on data on the composition of ore-bearing hydrothermal solutions and parameters of ore-forming processes at various antimony and antimony-bearing deposits, which were obtained in studies of fluid inclusions in ore minerals, we investigated the behavior of Sb(III) in the system Sb-Cl-H2S-H2O describing the formation of these deposits.
We also performed thermodynamic modeling of native-antimony and stibnite dissolution in sulfide (m HS- = 0.0001-0.1) and chloride ( m Cl- = 0.1 - 5) solutions and the joint dissolution of Sb0(s) and Sb2S 3(s) in sulfide-chloride solution ( m HS- = 0.01; m Cl- = 1) depending on Eh, pH, and temperature. All thermodynamic calculations were carried out using the Chiller computer program. Under the above conditions, stibnite precipitates in acid, weakly acid to neutral, and medium redox solutions, whereas native antimony precipitates before stibnite under more reducing conditions in neutral to alkaline solutions.
The metal-bearing capacity of hydrothermal solutions (200-250



3.
FORMATION OF THE SUPERDEEP SOUTH CASPIAN BASIN: SUBSIDENCE DRIVEN BY PHASE CHANGE IN CONTINENTAL CRUST

E.V. Artyushkov
Institute of the Physics of the Earth, Russian Academy of Sciences, 10 ul. Bol'shaya Gruzinskaya, Moscow, 123810, Russia
Keywords: Crustal structure; crustal subsidence; phase change; lithospheric rheology; seismicity; subduction; South Caspian basin
Pages: 1002-1014

Abstract >>
The large hydrocarbon basin of South Caspian is filled with sediments reaching a thickness of 20-25 km. The sediments overlie a 10-18 km thick high-velocity basement which is often interpreted as oceanic crust. This interpretation is, however, inconsistent with rapid major subsidence in Pliocene-Pleistocene time and deposition of ~ >10 km of sediments because the subsidence of crust produced in spreading ridges normally occurs at decreasing rates. Furthermore, filling a basin upon a 10-18 km thick oceanic crust would require twice less sediments. Subsidence as in the South Caspian, of ≥20 km, can be provided by phase change of gabbro to dense eclogite in a 25-30 km thick lower crust. Eclogites which are denser than the mantle and have nearly mantle P velocities but a chemistry of continental crust may occur beneath the Moho in the South Caspian where consolidated crust totals a thickness of 40-50 km. The high subsidence rates in the Pliocene-Pleistocene may be attributed to the effect of active fluids infiltrated from the asthenosphere to catalyze the gabbro-eclogite transition. Subsidence of this kind is typical of large petroleum provinces. According to some interpretations, historic seismicity with 30-70 km focal depths in a ~100 km wide zone (beneath the Apsheron-Balkhan sill and north of it) has been associated with the initiation of subduction under the Middle Caspian. The consolidated lithosphere of deep continental sedimentary basins being denser than the asthenosphere, can, in principle, subduct into the latter, while the overlying sediments can be delaminated and folded. Yet, subduction in the South Caspian basin is incompatible with the only 5-10 km shortening of sediments in the Apsheron-Balkhan sill and south of it and with the patterns of earthquake foci that show no alignment like in a Benioff zone and have mostly extension mechanisms



4.
NEOPROTEROZOIC CHINGASAN GROUP IN THE YENISEI RIDGE: NEW DATA ON AGE AND DEPOSITION ENVIRONMENTS

A.D. Nozhkina, A.A. Postnikov b , K.E. Nagovitsin b , A.V. Travin a , A.M. Stanevich c , D.S. Yudin a
a Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3, prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
c Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Neoproterozoic; Chingasan Group; geochronology; paleontology; rifting; Yenisei Ridge
Pages: 1015-1025

Abstract >>
Trachybasalt-alkali trachyte volcanism in the Yenisei Ridge was found out to be synchronous with deposition of coarse tilloids and flysch of the Chivida Formation of the Neoproterozoic Chingasan Group. New 703 ± 4 Ma 40Ar/39Ar biotite and titan-augite ages of subalkaline basalts in the Chivida Formation indicated that they erupted in the Late Neoproterozoic. According to microfossil evidence, the Chingasan sediments correlate with Late Neoproterozoic strata in the type sections of the southern Siberian craton. The Chingasan deposition apparently lasted no longer than 30 Myr judging by the isotope ages obtained for the underlying Upper Vorogovka Group and subalkaline basalts in the Chivida Formation. The fault-parallel position of grabens and coarse grain sizes and variable thicknesses of their lithological complexes, as well as syndepositional trachybasalt-alkali trachyte volcanism provided evidence that the volcanosedimentary rocks of the Chingasan Group formed in an environment of active rifting.



5.
THE LATE JURASSIC AGE AND GEOCHEMISTRY OF ULTRAMAFIC-MAFIC MASSIFS OF THE SELENGA-STANOVOY SUPERTERRANE ( southern framing of the North Asian craton )

I.V. Buchkoa, A.A. Sorokin a , E.B. Sal'nikova b , A.B. Kotov b , A.M. Larin b , A.E. Izokh c , S.D. Velikoslavinsky b , S.Z. Yakovleva b
a Institute of Geology and Nature Management, Far Eastern Branch of the RAS, 2 ul. B. Khmel'nitskogo, Blagoveshchensk, 675000, Russia
b Institute of the Precambrian Geology and Geochronology, Russian Academy of Sciences, 2 nab. Makarova, Saint Petersburg,199034, Russia
c Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Ultramafic-mafic massifs, framing of the North Asian craton, petrology, geochemistry, isotope dating
Pages: 1026-1036

Abstract >>
We present new data on the age and geochemistry of the Veselyi and Petropavlovsk ultramafic-mafic massifs of the Selenga-Stanovoy (West Stanovoy) superterrane on the southeastern framing of the North Asian craton. The massifs are composed of rocks of peridotite- websterite-gabbro and peridotite-gabbro-monzodiorite associations, respectively. The latter combine normal, subalkalic, and alkaline rocks and thus are of diverse composition: from ultrabasites and pyroxenites through gabbroids to monzodiorites. The U-Pb zircon age of these massifs is 154±1 and 159±1 Ma, respectively, which permits them to be referred to as the youngest rocks of ultramafic-mafic complexes on the southern framing of the North Asian craton. The rocks of the studied massifs are enriched in LILE (K, Rb, Sr, Ba, LREE) and are depleted in HFSE (Zr, Nb, Hf, Ta). These rocks formed, most likely, in the rear of subduction zone or in the setting of the subducting-slab detachment.



6.
SPECIFIC STRUCTURE OF CONVECTION CURRENTS IN THE SYSTEM LAYERED INTRUSION-FEEDING CONDUIT-PARENTAL MAGMA CHAMBER

L.Sh. Bazarov, V.I. Gordeeva, E.I. Petrushin
Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Experiment; intrusion; melt; modeling; convection
Pages: 1037-1045

Abstract >>
The structure of convection currents was experimentally studied in the model system layered intrusion-feeding conduit-parental magma chamber. Persistent hydrodynamical and thermophysical interaction between interrelated melts of the parental magma and intrusive body occurs through the feeding conduit. Being associated, they control the structure of convection currents and mechanisms of heat and mass transfer in the intrusive, conduit, and magma chamber. The existence of two convection countercurrents in the conduit has experimentally been established: inner central lifting jet and outer annular downward current along the conduit walls. At the top of the conduit, the downward current has the lowest temperature and appears to be quite in equilibrium with the earlier precipitated crystals. Moving downward along the conduit wall, the annular descending current interacts with the lifting jet and, as a result, becomes hotter and undersaturated relative to the crystals that formed before. Thus, there is no possibility for heterogeneous crystallization to occur on the walls of conduit. The experimentally simulated mechanism of melt interaction in a whole natural system rules out the possibility of formation of a zone of immobile melt with stable steady-state temperature stratification anywhere in the chamber's volume.



7.
PETROLEUM POTENTIAL OF BAIKAL DEPOSITS

A.E. Kontorovich a , V.A. Kashirtsev a , V.I. Moskvin a , L.M. Burshtein a , T.I. Zemskaya b , E.A. Kostyreva a , G.V. Kalmychkov c , O.M. Khlystov b
a Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Limnological Institute, Siberian Branch of the RAS, 3 ul. Ulan-Batorskaya, Irkutsk, 664033, Russia
c Institute of Geochemistry, Siberian Branch of the RAS, 1a ul. Favorskogo, Irkutsk, 664033, Russia
Keywords: Oil; gas; biomarker hydrocarbons; biodegradation; resources; Lake Baikal
Pages: 1046-1053

Abstract >>
We analyzed oils, gases, and bitumens of bottom sediments from natural shows on the southeastern shore of Lake Baikal, in the mouth of the Stvolovaya River near Capes Tolstyi and Gorevoi Utes. Based on a set of geological data, we have established that: (1) the lake oils underwent biodegradation to a variable degree:



8.
NANOSECOND ELECTROMAGNETIC SOUNDING OF A FLUID-SATURATED LAYERED FORMATION

M.I. Epova, V.L. Mironov b , S.A. Komarov b , K.V. Muzalevsky c
a Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Institute of Physics, Siberian Branch of the RAS, 50, str. 38, Akademgorodok, Krasnoyarsk, 660036, Russia
c Altai State University, 61 ul. Lenina, Barnaul, 656049, Russia
Keywords: Horizontal well; fluid-saturated formation; complex permittivity; dispersive media; refractive dielectric model; broadband pulse; Green's function; simulation
Pages: 1054-1060

Abstract >>
Mathematical modeling was applied to study attenuation of a nanosecond pulse that propagated in an oil-bearing formation and was reflected from the oil-gas or oil-water interfaces. The problem was formulated and solved for propagation of a short electromagnetic Gaussian pulse in a layered hydrocarbon reservoir in the case of excitation by a long electric line. Complex permittivity of oil-bearing rocks was calculated using a refractive mixing dielectric model for oil, saline water, methane, quartz, and bentonite in each layer. We obtained and analyzed space-time diagrams of wave propagation and reflection and estimated effective attenuation for both cases.



9.
AUTUMN-WINTER ANOMALOUS VARIATIONS IN BOTTOM WATER AND SEDIMENT TEMPERATURES IN LAKE TELETSKOE

A.D. Duchkov, S.A. Kazantsev
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Autonomous temperature recorder; bottom water temperature monitoring; bottom sediment temperature monitoring to different depths; sediment geothermal gradient; Lake Teletskoe
Pages: 1061-1064

Abstract >>
We discuss the results of bottom temperature monitoring run in October through December 2005 in the deepwater basin of Lake Teletskoe at a lake depth of ~320 m using an autonomous recorder. The obtained temperature patterns of water and sediments to a depth of ~1.4 m show sudden large changes. Bottom water temperature fluctuated between 2.9 and 4