Geology and Geophysics, 2004, V 45, N 10, October.
PETROLOGY, GEOCHEMISTRY, AND MINERALOGY
Gold and silver in ores of volcanogenic hydrothermal and
hydrothermal-sedimentary pyrite- polymetallic deposits of Siberia.
K.R. Kovalev, E.G. Distanov, G.N. Anoshin, I.V. Gas'kov,
V.A. Akimtsev, and M.V. Baulina
1121
Silver and antimony in hydrothermal solutions of Ag-Sb deposits.
G.G. Pavlova, L.V. Gushchina, A.A. Borovikov, A.S. Borisenko,
and A.A. Obolensky
1136
Magnetites from magnesian skarns at dolerite-rock salt contacts.
M.P. Mazurov, S.N. Grishina, and A.T. Titov
1149
Effect of temperature regime on crystallization of leucite from
orendite melt (from experimental data).
E.I. Petrushin, L.Sh. Bazarov, V.V. Sharygin, V.I. Gordeeva,
and N.V. Vladykin
1159
Raman spectroscopic study of the structure and composition of
basaltic glasses.
V.A. Akimtsev, A.M. Pugachev, N.V. Surovtsev, and A.P. Shebanin.
1167
Lithological and geomorphological parameters of distribution of
artificial radionuclides in the Yenisei floodplain landscapes.
V.G. Linnik, V.V. Surkov, V.N. Potapov, A.G. Volosov,
E.M. Korobova, A. Borghuis, and J.E. Brown.
1172
TECTONICS
Fault pattern and stress field in the western Tunka rift
(southwestern flank of the Baikal
rift system). O.V. Lunina and A.S. Gladkov
1188
GEOPHYSICS
Regional isostatic gravity anomalies and
mantle plumes in southern East Siberia (Russia)
and Central Mongolia.
Yu.A. Zorin and E.Kh. Turutanov.
1200
Fast transient electrochemical processes in ore minerals.
A.P. Karasev, V.V. Olenchenko, and E.Yu. Yuditskikh.
1210
GOLD AND SILVER IN ORES OF VOLCANOGENIC
HYDROTHERMAL AND HYDROTHERMAL-SEDIMENTARY
PYRITE-POLYMETALLIC DEPOSITS OF SIBERIA
K.R. Kovalev, E.G. Distanov, G.N. Anoshin, I.V. Gas'kov,
V.A. Akimtsev, and M.V. Baulina
Institute of Geology, Siberian Branch of RAS, 3 prosp. Akad.
Koptyuga, Novosibirsk, 630090, Russia
Volcanogenic hydrothermal and submarine
hydrothermal-sedimentary pyrite-polymetallic deposits
are known from the Asian part of Russia. They form in
island-arc and rifting continental-margin structures and
are related to basaltoid or differentiated basaltoid volcanism.
The sulfide ores of the recognized groups of deposits are
characterized by a sufficiently close composition but differ in
contents of gold and silver. The ores of volcanogenic deposits
contain 1.0-1.5 ppm Au and 15-30 ppm Ag, with gold and
silver distributed rather irregularly. The maximum contents
of gold (up to 7-8 ppm) occur in high-temperature
chalcopyrite-pyrite ores of the root zones and in higher-temperature
barite-polymetallic ores of subsurface deposition. A correlation
between gold and silver has been established. The ores of
large-scale volcanogenic hydrothermal-sedimentary deposits
contain 0.09-0.16 ppm Au on average. The content of silver in them
reaches 80 ppm, averaging 15-35 ppm. There is no principal
difference in levels of gold accumulation in the ores from
tuffaceous-terrigene-carbonate rocks and in the ores from
pyrrhotite-bearing carbon-carbonate-silica schists.
Mineralization systems that form both hydrothermal and
hydrothermal-sedimentary pyrite-polymetallic deposits of
massive sulfide ores of close composition are genetically
related to occurrences of submarine basaltoid volcanism
of different geodynamic settings, and it is unlikely that initially
they had radically different contents of gold and silver.
Significant differences in sulfur isotopic composition of sulfides
are established between volcanogenic hydrothermal and
hydrothermal-sedimentary types of massive sulfide ores.
Sulfur isotopic composition of volcanogenic hydrothermal
deposits is close to the mantle values, whereas sulfur of
volcanogenic hydrothermal-sedimentary deposits is of mixed
mantle-crustal nature because the sulfates of sea water are
involved into hydrothermal system. Low contents of gold in
the ores of hydrothermal-sedimentary deposits can be
explained either by its partial deposition in deep zones
where hydrothermal solutions and sea waters mix or by the
fact that, being dissolved in sea water, gold migrated to more
distal facies of the basin of ore deposition. Contents of silver
in ores of both groups of deposits are kept approximately at
the same level, though in some hydrothermal-sedimentary
deposits the ores are enriched in silver. The volcanogenic
hydrothermal deposits show close patterns of distribution
of gold and silver in ores of ancient and recent sulfide
mineralization systems.
Massive sulfide polymetallic ores, volcanogenic hydrothermal
and hydrothermal-sedimentary deposits, gold, silver
SILVER AND ANTIMONY IN HYDROTHERMAL
SOLUTIONS OF Ag-Sb DEPOSITS
G.G. Pavlova, L.V. Gushchina, A.A. Borovikov, A.S. Borisenko, and
A.A. Obolensky
Institute of Geology, Siberian Branch of the RAS, 3 prosp. Akad.
Koptyuga, Novosibirsk, 630090, Russia
Thermodynamic computer modeling of the Ag and Sb behavior in
hydrothermal process at Ag-Sb deposits has been performed.
Parameters of ore-forming fluids, obtained by studying fluid
inclusions in minerals of igneous rocks and ores of Sn and Ag
deposits, were used as original data for the modeling. Calculations
intimate that Ag and Sb occur in concentrated high-temperature acid
chloride solutions mainly as chloride species. Computer modeling
showed high metal-bearing capacity of natural chloride solutions and
their capability for transport of large amounts of Ag and Sb.
Temperature regime is the most important factor for ore formation,
which controls the deposition of various parageneses at different
levels of hydrothermal ore-forming system as temperature decreases.
Ag and Sb deposits, Ag and Sb species, fluid inclusions,
thermodynamic modeling, ore-forming systems, mineral composition
MAGNETITES FROM MAGNESIAN SKARNS AT
DOLERITE-ROCK SALT CONTACTS
M.P. Mazurov, S.N. Grishina, and A.T. Titov
United Institute of Geology, Geophysics and Mineralogy, Siberian
Branch of RAS, 3 prosp. Akad. Koptyuga,
Novosibirsk, 630090, Russia
Methods of scanning and transmission electron microscopy and
electron microprobe analysis were used to study magnetites from
dolerite-rock salt contacts. It has been established that the first
generation of magnetite was formed in the interval 750-800 °C with
participation of supersaline brines (salt melts) and is closely
associated with magnesian skarns of postmagmatic stage. This
magnetite was an iron oxide solid solution, which concentrated Ti,
Mg, Al, Mn, Zn, and V impurities coextracted with iron from
dolerites. Succession and mechanism of exsolution and phase
composition of products of stage-by-stage decomposition of
first-generation magnetite are close to those of magnetites from the
magnesian skarns at dolerite-dolomite contacts. A significant
difference is abundance and structural diversity of ilmenite
lamellae. The impurities extracted by the decomposition of solid
solutions formed inter- and intragranular particles of ilmenite and
spinel, and were also components of titanite, phlogopite, and other
silicates. The second generation of magnetite contains no
isomorphous impurities and is associated with mineral
assemblages of altered magnesian skarns, sulfides,
and hydrothermal rock salt. The revealed characteristics
of composition and microstructure of magnetites are indicative
of the development of mineralization and ore-element extraction;
they show that one of the typical features
of dolerite-rock-salt interaction is abnormally high mobility of Ti.
Magnetite, dolerite, rock salt, extraction, partitioning
EFFECT OF TEMPERATURE REGIME ON CRYSTALLIZATION
OF LEUCITE FROM ORENDITE MELT (from experimental data)
E.I. Petrushin, L.Sh. Bazarov, V.V. Sharygin, V.I. Gordeeva, and
N.V. Vladykin*
Institute of Mineralogy and Petrography, Siberian Branch of the RAS,
3 prosp. Koptyuga, Novosibirsk,
630090, Russia
* Vinogradov Institute of Geochemistry, Siberian Branch of the RAS,
1a ul. Favorskogo, Irkutsk, 664033, Russia
A series of experiments on melting and crystallization of
orendite from the Leucite Hills province (Wyoming, USA) was carried
out at atmospheric pressure in air. The liquidus temperature of the
melt has been determined, 1300 ± 10 °C; leucite is the first phase
to crystallize. Most leucite forms in the temperature range
1250-1150 °C. At 1150 ± 10 °C, clinopyroxene of diopside composition
cocrystallizes with leucite. Study was also given to the dependence
of leucite crystal morphology on the melt supercooling and to the
trapping of melt inclusions during the crystal growth.
Experimental petrography, leucite, crystallization, lamproite,
Leucite Hills
RAMAN SPECTROSCOPIC STUDY OF THE STRUCTURE
AND COMPOSITION OF BASALTIC GLASSES
V.A. Akimtsev, A.M. Pugachev*, N.V. Surovtsev*, and A.P. Shebanin
United Institute of Geology, Geophysics and Mineralogy, Siberian
Branch of the RAS, 3 prosp. Koptyuga,
Novosibirsk, 630090, Russia
* Institute of Automatics and Electrometry, Siberian Branch of the
RAS, 1 prosp. Koptyuga, Novosibirsk, 630090,
Russia
Using Raman spectroscopy, quenching crusts from mid-ocean
ridges have been studied. This experimental method permits
identification of the crystalline or amorphous state of a substance.
It has been revealed that a decrease in the efficient rate of
quenching of matter from periphery to core of a sample leads to the
appearance of a disseminated crystalline phase. The characteristic
size of the glass structural inhomogeneities, ~2 nm, has been
estimated by low-frequency Raman scattering.
Basaltic glass, Raman scattering
LITHOLOGICAL AND GEOMORPHOLOGICAL PARAMETERS
OF DISTRIBUTION OF ARTIFICIAL RADIONUCLIDES IN THE
YENISEI FLOODPLAIN LANDSCAPES
V.G. Linnik, V.V. Surkov*, V.N. Potapov**, A.G. Volosov, E.M.
Korobova,
A. Borghuis***, and J.E. Brown***
Vernadsky Institute of Geochemistry and Analytical Chemistry of RAS,
19 ul. Kosygina, Moscow, 117975, Russia
* Lomonosov Moscow State University, Geography Department, Moscow,
119992, Russia
** Russian Scientific Center «Kurchatov's Insitute», 1 pl.
Kurchatova, Moscow, 123182, Russia
*** Norway Agency on Radiation Protection, POB 55, N-1332, Osteres,
Norway
In August 2000, an internatonal expedition participating in the
COPERNICUS project «STREAM» explored two floodplain localities on
the Yenisei River (Balchug and Kazachinskoe stations) to estimate
the contribution of the Krasnoyarsk Mining Chemical Plant to the
radioactive contamination of the floodplain. It has revealed zones
of maximum 137Cs contamination (up to 1000 kBq/m2) in the low-level
floodplain made up of fine- and very fine-grained sands with loam
partings, in the bottom of breachways overlain by thin beds of peat,
and in depressions at the back of the medium-level floodplain with
sandy silt deposition. The densities of 60Co and 152,154Eu
contamination reach their maximum (up to 188 kBq/m2) in silty,
peaty, and sandy loam parts of the low-level floodplain. Traces of
60Co and 152,154Eu radionuclides were also found in the medium-level
floodplain (Balchug station). The high-level floodplain, up to 5.5 m
above low-water line, composed of medium- and fine-grained sands is
subject to 16-fold 137Cs contamination against the background. The
medium-level floodplain near the Kazachinskoe station, made up of
fine-grained sands, is contaminated by 137Cs at 250-280 kBq/m2, with
the maximum value, 504 kBq/m2, detected on the barrier beach.
Landscape, floodplain lithology, field radiometry,
radionuclides, Yenisei River
FAULT PATTERN AND STRESS FIELD IN THE WESTERN
TUNKA RIFT (southwestern flank of the Baikal rift system)
O.V. Lunina and A.S. Gladkov
Institute of the Earth's Crust, Siberian Branch of the RAS, 128, ul.
Lermontova, Irkutsk, 664033, Russia
New structural and tectonophysical data provide more details on
the fault pattern and the stress field of the western Tunka rift in
the southwestern flank of the Baikal rift system. The rift valley is
controlled mostly by W-E and NE faults, and the rift ridges and
basin links are dominated by NW and N-S faults. The fault pattern
shows good correlation with the distribution of M; 3.3 earthquakes.
Stress fields reconstructed from fracture measurements and
correlated to the available earthquake mechanisms show that the rift
currently evolves in a transtension environment.
Faults, fractures, stress field, earthquakes, earthquake
mechanisms, Tunka rift
REGIONAL ISOSTATIC GRAVITY ANOMALIES AND
MANTLE PLUMES IN SOUTHERN EAST SIBERIA (Russia)
AND CENTRAL MONGOLIA
Yu.A. Zorin and E.Kh. Turutanov
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul.
Lermontova, Irkutsk, 664033, Russia
Isostatic gravity anomalies were inverted under the assumption
that compensation of topographic loads is only partly provided by
Moho depth variations but is to a large extent due to the geometry
of the lithosphere/asthenosphere boundary. This approach allowed us
to reveal regional (long-wavelength) gravity lows possibly
associated with Late Cenozoic mantle plumes beneath the Baikal rift
and mountains in Central Mongolia. The plume tails were simulated in
several 3D gravity versions. The position of plumes predicted from
gravity inversion is consistent with zones of low seismic velocities
in the mantle and with azimuthal anisotropy as the plumes control
mantle flow above their tails. The position of most plumes does not
contradict the pattern of Late Cenozoic flood volcanism known from
geological evidence.
Distribution of compensating mass, isostatic gravity anomalies,
mantle plumes, seismic velocities, seismic anisotropy, volcanics
FAST TRANSIENT ELECTROCHEMICAL
PROCESSES IN ORE MINERALS
A.P. Karasev, V.V. Olenchenko*, and E.Yu. Yuditskikh**
Chita Institute of Natural Resources, Siberian Branch of the RAS, 26
ul. Butina, Chita, 672090, Russia
* Chita Laboratory of Engineering Geocryology, Institute of
Permafrost, Siberian Branch of the RAS, 54 ul. Lenina,
Chita, 672010, Russia
** Chita State Technological University, 30 ul. Alekzavodskaya,
Chita, 672039, Russia
Laboratory experiments on transient electrochemical processes
in synthetic and natural ore minerals revealed correlation of their
potential response with electrochemistry. The shapes of potential
curves correlate with electrochemistry in metals and with
stoichiometry and contents of isomorphic impurities in synthetic
galena. The geometric diversity of anode and cathode curves for
natural minerals is controlled by their composition and
physicochemical conditions of formation. Time-dependent
polarizability functions record the compositional and
electrochemical homogeneity of laboratory samples and in situ
orebodies. The transient response of impurity-bearing polarizable
conductors contains delays in potential or voltage buildup which
produce peaks in polarization curves.
Transient electrochemical process, potential, potential
response, relaxation time, polarizability, electrical prospecting
setup