Geologiya i Geofizika, 2004, V 45, N 8

STRATIGRAPHY AND PALEONTOLOGY

Silurian stratigraphy of East Siberia . Yu.I. Tesakov.......................................................................887

Specific geographic differentiation of Boreal cephalopods of Carnian age. A.G. Konstantinov

and E.S. Sobolev.......................................................................................................................905

PETROLOGY, GEOCHEMISTRY, AND MINERALOGY

Evolution of sulfur isotopes in porphyry Cu-Mo ore-magmatic systems of Siberia

and Mongolia . V.I. Sotnikov, V.A. Ponomarchuk, A.P. Pertseva, A.P. Berzina, A.N. Berzina,

and V.O. Gimon.........................................................................................................................913

The Sm-Nd age of wollastonite skarns in the southern Baikal region. S.I. Shkol'nik,

V.P. Kovach, L.Z. Reznitsky, and N.Yu. Zagornaya.......................................................................924

Peculiarities of the formation of diverse veinlet beryllium mineralization at the Ermakovskoe

deposit (western Transbaikalia). L.B. Damdinova and F.G. Reyf......................................................928

Specific structure of the lowermost Earth's crust at the Zagadochnaya kimberlite pipe, Yakutia.

L.V. Buzlukova, V.S. Shatsky, and N.V. Sobolev..........................................................................942

OIL AND GAS GEOLOGY

The nature of vertical hydrogeochemical zoning of petroleum deposits (exemplified by the

Nadym-Taz interfluve, West Siberia ). S.L. Shvartsev and D.A. Novikov...........................................960

Prediction of in-field oil and gas reserves in underexplored petroleum provinces.

V.R. Livshits..............................................................................................................................973

GEOPHYSICS

Evolution of invaded zone inferred from electromagnetic logging and hydrodynamic modeling.

M.I. Epov, I.N. Yeltsov, A.A. Kashevarov, A.Yu. Sobolev, and V.N. Ul'yanov.....................................985

Phase-amplitude modulation of a seismoacoustic wave under diurnal tides. B.N. Bogolyubov,

V.N. Lobanov, V.E. Nazarov, V.I. Rylov, A.A. Stromkov, and V.I. Talanov........................................996

BRIEF COMMUNICATIONS

Assessment of mineral resources in terms of the estimation theory. Yu.A. Voronin........................1001

SILURIAN STRATIGRAPHY OF EAST SIBERIA

Yu.I. Tesakov

Institute of Petroleum Geology , Siberian Branch of the RAS,3 prosp. Akad. Koptyuga, Novosibirsk , 630090, Russia

Fauna-based formation units distinguished for the first time in the Silurian stratigraphy of East Siberia (Siberian Platform, Taimyr peninsula ) have been correlated to the chronostratigraphic units. The Silurian section includes eleven formations (deep shelf mudstone, lower shallow shelf marl, shallow shelf limestone, half-restricted shelf dolostone, inner half-restricted shelf and restricted shelf marl dolostone, restricted shelf siltstone, tidal sandstone, tidal and trough conglomerate, tidal and trough brachiopod-coral marl, and shelly sapropel of coastal troughs) and thirty one subformations. The correlation of diachronic (formations and subformations) and isochronic (stages, horizons, and subhorizons) stratigraphic units is shown in five transects along and across the Silurian East Siberian sedimentary basin.

Formations, sedimentary basin, Silurian, East Siberia

SPECIFIC GEOGRAPHIC DIFFERENTIATION OF BOREAL CEPHALOPODS

OF CARNIAN AGE

A.G. Konstantinov and E.S. Sobolev

Institute of Petroleum Geology , Siberian Branch of RAS,3 prosp. Akad. Koptyuga, Novosibirsk , 630090, Russia

Comparative analysis of complexes of Boreal nautiloids and ammonoids has been made for the first time for some phases of the Carnian Age, and the rules that control their geographic differentiation have been unraveled. The distinctions between Carnian cephalopods of the western (Svalbard, Arctic Canada) and eastern (northeastern Asia) Boreal Realm allowed us to distinguish the Canadian and Siberian Provinces . Ammonoid-based provinces are possible for the late Early Carnian and Late Carnian, when ammonoid fauna in the Boreal Realm was distinguished by genera and families. The best-pronounced distinctions between these provinces by nautiloids (presence of specific genera) have been found in the Early Carnian (tenuis phase).

Paleobiogeography, ammonoids, nautiloids, Late Triassic, Carnian Age, Boreal Realm

EVOLUTION OF SULFUR ISOTOPES IN PORPHYRY Cu-MoORE-MAGMATIC SYSTEMS

OF SIBERIA AND MONGOLIA

V.I. Sotnikov, V.A. Ponomarchuk, A.P. Pertseva, A.P. Berzina, A.N. Berzina,

and V.O. Gimon

United Institute of Geology , Geophysics and Mineralogy, Siberian Branch of the RAS,3 prosp. Akad. Koptyuga,

Novosibirsk , 630090, Russia

Paleozoic-Mesozoic (D-J₃) porphyry Cu-Mo deposits in Siberia and Mongolia are characterized by a narrow range of δ₃₄S values of sulfides (pyrite, chalcopyrite, molybdenite), -2.0...10.2‰. Sulfides of essentially copper deposits, whose ore-bearing porphyry complexes have (⁸⁷Sr/⁸⁶Sr)₀ = 0.7039-0.7046, show the least δ₃₄S values, -2.0...3.8‰, close to those in the meteoritic standard. Deep-seated horizons of essentially copper deposits (Erdenetuin-Obo, Aksug) abound in anhydrite with δ₃₄S = 10-16‰. Sulfides of essentially molybdenum deposits with ⁸⁷Sr/⁸⁶Sr)₀ = 0.7046-0.7078 are enriched in ³⁴S. Elevated δ₃₄S values might be due to a partial borrowing of sulfur from sulfur-carbon compounds and syngenetic pyrite of sedimentary strata that host intrusions in porphyry Cu-Mo ore regions. At some deposits, the ores show a rather uniform isotopic composition of sulfur, which is probably due to its perfect homogenization in high-temperature magma chamber. Such favorable conditions might have appeared first of all in large ore-magmatic systems producing large deposits. The revealed minor variations in δ₃₄S in sulfides, as well as the isotopic fractionation of sulfur in the system sulfide-sulfate, might have been due to the interaction of fluids with the host rocks, which resulted in fluctuations in pH and/or f_O2.

Porphyry Cu-Mo deposits, S and Sr isotopes, sulfide-sulfate system, sources of matter, Siberia , Mongolia

THE Sm-Nd AGE OF WOLLASTONITE SKARNS IN THE SOUTHERN BAIKAL REGION

S.I. Shkol'nik, V.P. Kovach*, L.Z. Reznitsky, and N.Yu. Zagornaya*

Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia* Institute

of Geology and Geochronology of the Precambrian, 2 nab. Makarova, St. Petersburg , 199034, Russia

The age of wollastonite skarns from the Andreevskoe deposit (Slyudyanka crystalline complex, southern Baikal region) has been determined by the Sm-Nd method. A Sm-Nd isochron was constructed by five points: garnet, clinopyroxene, wollastonite, K-feldspar, and bulk rock (T = 419 ± 19 Ma, MSWD = 1.8, ε_Nd = -6.5). Formation of wollastonite skarns marks the final stage of orogeny and rise of the complex to a hypabyssal level.

Wollastonite, skarns, Sm-Nd age, southern Baikal region

PECULIARITIES OF THE FORMATION OF DIVERSE VEINLET BERYLLIUM

MINERALIZATION AT THE ERMAKOVSKOE DEPOSIT(western Transbaikalia)

L.B. Damdinova and F.G. Reyf

Geological Institute, Siberian Branch of the RAS, 6a ul. Sakh'yanovoi, Ulan Ude, 670047, Russia

Based on geological, mineralogical, and petrographic data and results of thermometric and microanalytical (electron probe microanalysis and atomic-emission spectroscopy) studies of fluid inclusions (FI), the major factors have been established which determined the composition and Be content of various types of veinlet mineralization at the Ermakovskoe F-Be deposit. Despite a great difference in the composition of vein filling (ores of types I and II), the parageneses in all near-fracture metasomatites are the same. In limestones, they form diffusion-metasomatic fringes composed of predominant fluorite, subordinate K-feldspar, calcite, quartz, apatite, spodiophyllite, and phenakite (up to 4%). In aluminosilicate schists, the veinlet fringes are <= 0.6 cm thick; they are dominated by K-feldspar, albite, and, to a lesser extent, dolomite and calcite, bear minor fluorite, and lack phenakite. These schists bear nearly barren veinlet mineralization of type II, which is due to the effect of the wallrock lithology on the composition of near-fracture metasomatites. Beryllium mineralization of type II occurs only in carbonates, though it is also poorer in Be than the ores of type I because of the low content of phenakite in the vein filling.As the composition of veinlets does not depend on the lithology of the host rocks (in contrast to the composition of near-fracture metasomatites), the minerals seem to have deposited in fractures as a result of cooling of hydrothermal solutions. But the ores of types I and II are characterized by close temperature ranges of formation ( ~ 300-150 and 360-90 °C , respectively), which indicates that temperature was not responsible for their compositional difference.The composition of products of the interaction between limestone and fracture solution evidences that both types of mineralization were formed by nearly neutral F-rich fluids (L1 (type I) and L2 (type II)), which also contained K, Na, Al, Si, P, and Be. Study of FI showed that they are enriched in CaCO₃ ( ~ 3%) but differ slightly in salt composition (T_eut = -21.5...-27 and -35.6...- 36.6 °C for L1 and L2, respectively) and concentration (4.7-10.8 and 10.7-11.1 % equiv. NaCl). Moreover, L1 are richer in Be and CO₂ than L2 (up to 3.8 g/kg against <= 0.1 g/kg and 4.1-181.1 wt.% against <<3.6 wt.%, respectively).As the stability of Be compounds depends on temperature and F^- and CO₃^2- activities, a conclusion is drawn that it is the high content of CO₂ in L1 solutions that is responsible for their enrichment in Be relative to L2: At high activity of CO₃^2-, Be exists in fluoride solutions not only as BeF₃^- and BeF₄^2- but also as BeCO₃F^-; the solubility of this complex at 300 °C is nearly two orders of magnitude higher than those of the former two complexes. This is consistent with the great (more than 10 times) difference in Be contents between the two types of veinlet mineralization but leaves unexplained the cause of their opposite fluorite/K-feldspar ratios.

Mineralization, beryllium, fluid inclusions, thermometry, microanalysis, role of CO₂, Ermakovskoe deposit

SPECIFIC STRUCTURE OF THE LOWERMOST EARTH'S CRUSTAT

THE ZAGADOCHNAYA KIMBERLITE PIPE, YAKUTIA

L.V. Buzlukova, V.S. Shatsky, and N.V. Sobolev

Institute of Mineralogy and Petrography, Siberian Branch of RAS,3 prosp. Akad. Koptyuga, Novosibirsk ,

630090, Russia

Study has addressed xenoliths of the crustal rocks from the Zagadochnaya kimberlite pipe, in the Daldyn-Alakit diamondiferous district of the Yakutian kimberlite province. Most xenoliths are represented by garnet granulites (60% of the bulk of xenoliths, of which paraganeses with amphibole amount to 20%), by plagiogneisses (30%) and garnet-biotite schists (10%).P-T conditions of metamorphism for garnet granulites are 700- 780 °C and 8-11 kbar. The temperatures obtained for plagiogneisses are within 660-770 °C , and for garnet-biotite schists, 500-600 °C .Densities and compressional wave velocities (V_P) were calculated for the studied garnet granulites and plagiogneisses. Values of V_P for garnet granulites, which, according to P-T, occur in the lower Earth's crust, are 7.7-8.0 km/s, i.e. much higher than the velocities recorded by geophysical methods (6.7-6.9 km/s). At the same time, the velocities for plagiogneisses, 6.7-6.8 km/s, are close to experimentally measured velocities. This discrepancy in values of V_P may indicate that the medium between the boundaries of K₂ and Moho is not homogeneous. Given the composition of the lower crust has not changed since the time of intrusion of kimberlite pipes, we must admit that the lower crust is made up of plagiogneisses with lenses of garnet granulites.The section of the Earth's crust in the Zagadochnaya pipe is as follows: The lowermost crust is made up of plagiogneisses with interbeds (lenses) of garnet granulites, and upsection garnet-biotite schists occur.

Lower crustal xenoliths, garnet granulites, compressional wave velocities

THE NATURE OF VERTICAL HYDROGEOCHEMICAL ZONING OF PETROLEUM DEPOSITS

(exemplified by the Nadym-Taz interfluve, West Siberia )

S.L. Shvartsev and D.A. Novikov

Tomsk Affiliate of Institute of Petroleum Geology, Siberian Branch of RAS,3 prosp. Akademichesky, Tomsk ,

634021, Russia

Geochemistry of underground waters of petroliferous deposits was studied in a vast region with different types of vertical hydrogeochemical zoning. It has been shown that the zoning nature is governed by two main factors: the genetic type of underground waters and character of water interaction with rocks and organic matter, which are, in turn, the products of the geologic history of the region. According to genesis, the groundwaters are divided into four types: (1) connate Jurassic, (2) connate from the Paleozoic basement, (3) ancient infiltrated, and (4) condensation-related. The chemical composition of each of these types of water is considerably modified by water interaction with rocks, gases, and organic matter, as well as by mixing with waters of other genetic types. Different successions of genetic types of waters subjected to different grade metamorphism and mixing at depth are responsible for the character of direct, inverse, or more intricate hydrogeochemical zoning in the region.

Underground waters, chemical composition, oil hydrogeology, vertical hydrogeochemical zoning, water genesis, composition formation, hydrogeochemistry

PREDICTION OF IN-FIELD OIL AND GAS RESERVES

IN UNDEREXPLORED PETROLEUM PROVINCES

V.R. Livshits

Institute of Petroleum Geology , Siberian Branch of RAS, 3 prosp. Akad. Koptyuga, Novosibirsk , 630090, Russia

A new algorithm is suggested to assess in-field oil and gas reserves based on the size distribution of discoveries. The statistical performances of the estimators are tested through the Monte-Carlo imitation.

Petroleum province, hydrocarbon reserves, in-field reserves, Bayesian estimator, Monte-Carlo imitation, statistical performances

EVOLUTION OF INVADED ZONE INFERRED FROM ELECTROMAGNETIC LOGGING

AND HYDRODYNAMIC MODELING

M.I. Epov, I.N. Yeltsov, A.A. Kashevarov*, A.Yu. Sobolev, and V.N. Ul'yanov

Institute of Geophysics , Siberian Branch of the RAS,3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia* Lavrentiev

Institute of Hydrodynamics, Siberian Branch of the RAS,15 prosp. Akad. Lavrentieva, Novosibirsk , 630090, Russia

The geoelectrical and hydrodynamic parameters of the near-hole space bear much useful information on the physical properties of hydrocarbon reservoirs. Time-dependent changes in the zone where wellbore fluids leak off into permeable formation make it difficult to estimate the electrical resistivity of the undisturbed portion of the reservoir. However, the invaded zone itself can be a target of studies.The available advanced multiprobe logging tools yield high-resolution images of resistivity near a well. These data, integrated with the available advanced theoretical background and computing facilities for hydrodynamic modeling of porous media with a two-component fluid fill, provide a clue to reliable interpretation of electromagnetic logs.The suggested 2D models of drilling mud circulation near the bore face take into account the real size of drill, growth and erosion of mud cake, filtration of water and oil (two immiscible fluids), salt transport, rock compressibility, and fluid viscosity.Results of 2D simulation of the process in which drilling mud displaces oil and formation water from the invaded zone are reported for different drilling conditions and hydrophysical parameters of reservoirs. The parameters of the invaded zone show different distributions classified on the basis of numerical experiments and porosity and water content dependences of resistivity.Problems related to inversion of EM logs in vertical and horizontal wells are discussed for specific field examples.

Electromagnetic soundings, hydrodynamic modeling, reservoirs

PHASE-AMPLITUDE MODULATION OF A SEISMOACOUSTIC WAVE

UNDER DIURNAL TIDES

B.N. Bogolyubov, V.N. Lobanov, V.E. Nazarov, V.I. Rylov, A.A. Stromkov, and V.I. Talanov

Institute of Applied Physics , Russian Academy of Sciences ,46 ul. Ul'yanova, Nizhniy Novgorod, 603600, Russia

The effect of diurnal tides observed during a field experiment investigating the phase-amplitude modulation of a seismoacoustic P wave that propagated in porous oil- and gas-saturated sandstone is explained in terms of dissipative and reactive nonlinearity of rocks. The parameters of this nonlinearity at the observation site are predicted from comparison of theoretical and field estimates.

Rocks, dissipative and reactive nonlinearity, diurnal tide, phase-amplitude modulation

ASSESSMENT OF MINERAL RESOURCES IN TERMS OF THE ESTIMATION THEORY

Yu.A. Voronin

Institute of Computing Mathematics and Mathematical Geophysics, Siberian Branch of RAS,6 prosp. Akad. Lavrentieva,

Novosibirsk , 630090, Russia

The assessment of mineral resources is a formula expertise, and its results are applicable only to plausible arguments. A new approach is suggested to update the method using the theory of estimation and pattern recognition.

Theory of estimation and pattern recognition, mineral resources, calculation, formula expertise, normative recovery


Founded in January 1960	Monthly	Vol. 45, № 8	August 2004


CONTENTS

CONTENTS

STRATIGRAPHY AND PALEONTOLOGY