Publishing House SB RAS:

Publishing House SB RAS:

Address of the Publishing House SB RAS:
Morskoy pr. 2, 630090 Novosibirsk, Russia



Advanced Search

Russian Geology and Geophysics

2010 year, number 10

1.
THE STAGES AND DURATION OF FORMATION OF GOLD MINERALIZATION AT COPPER-SKARN DEPOSITS ( Altai-Sayan folded area )

I.V. Gas'kov, A.S. Borisenko, V.V. Babich, and E.A. Naumov
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, prosp. Akad. Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Gold mineralization, skarns, copper-skarn deposits, hydrothermal-metasomatic formations
Pages: 1091-1101

Abstract >>
Gold mineralization at copper-skarn deposits (Tardanskoe, Murzinskoe, Sinyukhinskoe, Choiskoe) in the Altai-Sayan folded area is related to different hydrothermal-metasomatic formations. It was produced at 400-150 °C in several stages spanning 5-6 Myr, which determined the diversity of its mineral assemblages. Gold mineralization associated with magnetite bodies is spatially correlated with magnesian and calcareous skarns, whereas gold mineralization in crushing zones and along fault sutures in moderate- and low-temperature hydrothermal-metasomatic rocks (propylites, beresites, serpentinites, and argillizites) is of post-skarn formation. Different stages were manifested with different intensities at gold deposits. For example, the Sinyukhinskoe deposit abounds in early high-temperature mineral assemblages; the Choiskoe deposit, in low-temperature ones; and the Tardanskoe and Murzinskoe deposits are rich in both early and late gold minerals.
Formation of commercial gold mineralization at different copper-skarn deposits is due to the combination of gold mineralization produced at different stages as a result of formation of intricate igneous complexes (Tannu-Ola, Ust'-Belaya, and Yugala) composed of differentiated rocks from gabbros to granites.
																								



2.
THE FLUID REGIME OF ORE FORMATION IN THE BALEI GOLD-BEARING ORE-MAGMATIC SYSTEM ( eastern Transbaikalia )

A.M. Spiridonova, L.D. Zorinaa, S.P. Letunovb, and V.Yu. Prokof'evc
a V.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
b Irkutsk State University, ul. Karla Marksa 1, Irkutsk, 664003, Russia
Institute of Mineral Geology, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
Keywords: Gold deposit, gold-bearing ore-magmatic system, epithermal mineralization, gold-silver formation, fluid regime
Pages: 1102-1109

Abstract >>
Based on comprehensive studies of fluid inclusions in quartz formed at different stages of hydrothermal process, we consider the physicochemical conditions of formation of epithermal ores (K1) in the Balei ore field. The limiting parameters of hydrothermal process have been established: 353-131 °C, 150-30 bars, and salt concentrations of 7.6-0.5 wt.%-equiv. NaCl. A specific feature of the ore-forming process at the Balei deposits is a rapid drop in temperature and pressure, which is typical of open hydrothermal systems. The temperature increase at the beginning of each stage evidences pulse-like ore formation. The productive stage coincides with the initiation of a drastic decrease in temperature (<225 °C) and salt concentration in the solution. The deposits resulted from the functioning of the common Balei ore-magmatic system at shallow depths with a high permeability of the host rocks. High-K calc-alkalic magmas might have been sources of gold mineralization. The ore formation zone is localized above intrusive bodies near their roof. It is not ruled out that the Balei gold was partly borrowed from the products of the early cycles (J2-3) of gold mineralization and from the host rocks.
																								



3.
FLUID AND MAGMATIC PROCESSES IN THE FORMATION OF THE ARY-BULAK ONGONITE MASSIF ( eastern Transbaikalia )

I.S. Peretyazhko and E.A. Savina
A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Porphyritic ongonite, aphyric rocks, melt and fluid inclusions, brine, P-Q solution, immiscible ongonite and calcium fluoride melts, melt convection
Pages: 1110-1125

Abstract >>
The paper discusses the formation conditions of the Ary-Bulak ongonite massif (eastern Transbaikalia). Studies of melt and fluid inclusions have shown that, along with crystalline phases and a silicate melt, ongonitic magma contained aqueous-saline fluids of different types, fluoride melts compositionally similar to fluorite, sellaite, cryolite, chiolite, and more complex aluminum fluorides as well as silicate melts with abnormal Cs and As contents. The ongonitic melt crystallized with the participation of P-Q fluids as vapor solutions, presumably NaF-containing and slightly admixed with chlorides. We studied the properties and composition of brine inclusions from Ca- and F-rich rocks on the margin of the massif. Depending on the thermophysical properties of the host rocks and ongonitic melt, the duration of its crystallization has been estimated for a magma chamber with the size and shape of the Ary-Bulak massif. Magma chamber cooling has been modeled, and the density, viscosity, and the Rayleigh criterion have been estimated from the composition of silicate glasses in melt inclusions. These data strongly suggest intense convection in the residual magma chamber lasting for centuries. We have calculated possible fluid overpressure during the crystallization and degassing of the ongonitic melt in a closed magma chamber.
Calcium- and fluorine-rich aphyric and porphyritic rocks on the southwestern margin of the massif might have formed by the following mechanism. Local decompression in the magma chamber quenched an oxygen-containing calcium fluoride melt accumulated at the crystallization front, and these rocks altered during the interaction with fluids. When penetrating the marginal zone, a P-Q magmatic fluid which coexisted with the melt in the residual magma chamber cooled and changed its composition and properties. This caused the fluid to boil and segregate into immiscible phases: a vapor solution and a brine extremely rich in Cl, F, K, Cs, Mn, Fe, and Al. The fluoride and silicate liquids were immiscible; silicate melts had abnormal Cs and As contents; changes in the composition and properties of the magmatic fluids caused them to boil and produce brines. All this is evidence for complex fluid-magma interaction and heterogeneous ongonitic magma during the crystallization of the Ary-Bulak rocks. These processes were favored by the low viscosity and high mobility of the F- and water-rich ongonitic melt, intense melt convection in the residual magma chamber, and rising fluid pressure during its degassing.
																								



4.
ELEMENTAL COMPOSITION OF SUSPENDED PARTICLES FROM THE SURFACE WATERS OF LAKE BAIKAL IN THE ZONE AFFECTED BY THE SELENGA RIVER

E.P. Chebykina, E.L. Goldbergb, and N.S. Kulikovaa
a Limnological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Ulan-Batorskaya 3, Irkutsk, 664033, Russia
b Institute of Archeology and Ethnography, pr. Akad. Lavrent'eva 17, Novosibirsk, 630090, Russia
Keywords: Suspended matter, ICP MS, Lake Baikal
Pages: 1126-1132

Abstract >>
The elemental composition of suspended particles in surface waters of Lake Baikal has been studied by ICP MS along a transect of the zone affected by the Selenga River. The amount of terrigenous suspension in water was estimated fr om Al content, which decreases in a saltatory manner along the transect: 6.5-8.3 km offshore it decreases by an order of magnitude; 11-14 km offshore, by other 20 times; in the pelagic zone it remains almost unchanged. During the study period (late June 2001), the distribution lim it of suspension from the Selenga River in the lake's surface waters lays 11-14 km offshore.
It has been found that pelagic suspension is more than 20 times richer in Ca, P, Zn, Cu, Ni, Sn, Mo, Bi, S, and Cd than littoral one (6.5 km offshore) in the zone affected by the Selenga River. This is mainly due to fine suspension (<1.2 ?m), which was considerably richer in Ca, P, Zn, Cu, Ni, Sn, Mo, Sb, and Cd than coarser ones in the river.
Fine suspension in Lake Baikal, both in the zone affected by the river and in the pelagic zone, is considerably (2-35 times) richer in most elements, except for typical terrigenous ones, than river one. This suggests that element enrichment takes place in the lake, probably owing to bioaccumulation and chemisorption. These processes may be affected by additional factors, because fine suspension from the zone affected by the river differs significantly from pelagic one in elemental composition.
																								



5.
FIFTY YEARS OF SEISMIC-ANISOTROPY STUDIES IN RUSSIA

I.R. Obolentsevaa and T.I. Chichininab
a A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, prosp. Akad. Koptyuga 3, Novosibirsk, 630090, Russia
b Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas 152, 07730, Mexico D.F., Mexico
Keywords: Multicomponent seismic surveys, polarization, anisotropy, azimuthal anisotropy
Pages: 1133-1146

Abstract >>
This is a historic overview of seismic-anisotropy studies in Russia run as part of seismic exploration work in the 1940s through the 1980s, with a focus on main research lines. At the early stage in the 1940s through 1950s, most important contributions belonged to A.G. Tarkhov, Yu.V. Risnichenko, and S.M. Rytov (averaging the parameters of stratified media), I.I. Gurvich (processing reflection and refraction traveltime curves in media with elliptical anisotropy), and N.I. Berdennikova (shear-wave velocity anisotropy). In the 1960s-1980s, there were two basic schools of thought: one of G.I. Petrashen', with a more theoretical approach, and the other of N.N. Puzyrev dealing more with experimental work. Most of experiments addressed a newly discovered phenomenon of azimuthal anisotropy. This anisotropy appearing as "anomalous" polarization of shear and converted waves was found out to result from vertical fractures in rocks. The unusual polarization became understood owing to Klem-Musatov's model of a subsurface with a system of aligned cracks. The problem was fully resolved after field data had been processed with an algorithm by I.R. Obolentseva and S.B. Gorshkalev, for separating the total field of interfering shear waves of two types into fast and slow phases polarized in crack-parallel and crack-orthogonal directions, respectively.
																								



6.
RESTORATION OF SEISMIC DATA USING THE TWO-DIMENSIONAL DMO EQUATION

V.A. Pozdnyakov and E.V. Mezentsev
Krasnoyarskgeofizika, ul. Partizana Zheleznyaka 24v, Krasnoyarsk, 660022, Russia
Keywords: DMO, finite element method, Goursat problem
Pages: 1147-1152

Abstract >>
This paper presents a method for restoring missing seismic traces by using the two-dimensional dip moveout (DMO) equation. A fundamentally new formulation of the initial-boundary-value problem based on the Goursat problem is proposed. A modified finite element method is used for numerical solution. The method is tested on model examples and actual seismic data.
																								



7.
A QUADRUPOLE SYSTEM FOR INDUCTION SOUNDINGS

B.M. Chistoserdov
Institute of Geophysics, Ural Branch of the Russian Academy of Sciences, ul. Amundsena 100, Yekaterinburg, 620016, Russia
Keywords: Quadrupole system, field focusing, frequency sounding
Pages: 1153-1156

Abstract >>
It is shown that vertical focusing of the normal magnetic field can be performed using a quadrupole induction system. The frequency dependence of apparent resistivity calculated fr om the real part of the measured magnetic field allows effective detection of anomalously conducting objects, even in the cases wh ere the investigated object is overlapped by a thick layer with high electrical conductivity.