Geology and Geophysics, 2002, V 43, N 12, December.

PETROLOGY, GEOCHEMISTRY, AND MINERALOGY

PHYSICOCHEMICAL CONDITIONS OF FORMATION OF EPITHERMAL GOLD-MERCURY
DEPOSITS 
E. A. Naumov, A. A. Borovikov, A. S. Borisenko, M. V. Zadorozhnyi,
and V. V. Murzin
1055

     Fluid inclusions in minerals from more than 22 Au-Hg deposits (Central 
Asia, Urals, East Sayan, Gorny Altai, northeastern Russia, Mongolia, etc.) have 
been examined by thermobarogeochemical methods (thermo- and cryometry, Raman 
spectroscopy of gas phase). It has been established that Au-Hg deposits are low-
temperature (280-50 °C) hydrothermal objects which formed in subsurface 
(volcanogenic-hydrothermal) or shallow-depth (plutonogenic-hydrothermal) 
conditions, under pressures lower than 500-600 bars. The volcanogenic-
hydrothermal Au-Hg deposits were formed with participation of weakly 
concentrated (10-0.5, less frequently to 14<|>wt.%) chloride or chloride-
bicarbonate-sodium hydrothermal fluids with low-density N2-CO2 (<$E+->CH2) gas 
phase. The ore-forming fluids of plutonogenic-hydrothermal deposits are 
characterized by wider variations in concentration (from 0.2 to 25 wt.%), 
complex salt composition (NaCl, CaCl2, FeCl2, KCl, etc.), and dense highly CO2 
gas phase (CO2 >> N2 >> CH2); in salt composition and reduced character they 
similar to magmatic fluids. The characteristic feature of the fluid regime of 
ore-forming systems of volcanogenic- and plutonogenic-hydrothermal Au-Hg 
deposits is the heterogenous state of ore-forming fluids. In particular ore 
districts, the physicochemical parameters of formation of volcanogenic- and 
plutonogenic-hydrothermal Au-Hg deposits are generally close to the parameters 
of formation of similar Au-Sb, Sb and Sb-Hg deposits. The results obtained from 
the thermobarogeochemical study stress the polygene nature of Au-Hg deposits.
     Gold, mercury, Au-Hg ore deposits, fluid inclusions, composition and 
concentration of ore-forming fluid, hydrothermal ore deposition 

MANTLE SOURCES OF LATE CENOZOIC VOLCANICS (EAST SAYAN), AS INFERRED 
FROM Pb, Sr, AND Nd ISOTOPES 
S. V. Rasskazov, E. V. Saranina, and E. I. Demonterova
1065

     Mantle sources of Late Cenozoic alkali-basalt lavas in the vast territory 
of East Sayan have been investigated based on space and time variations of Pb, 
Sr, and Nd isotopic ratios. The evolution of volcanism is interpreted in the 
context of interaction of a plume-like mantle thermal anomaly and a moving 
lithospheric plate. Volcanism initiated 22-20 myr ago in the northeastern part 
of the Riphean Tuva-Mongolia massif (Urik segment), propagated westward through 
its northwestern part, and focussed within the Caledonian East Tuva zone in the 
past 2 Ma. Between 22 and 12 Ma, basaltic lavas contained a predominant common 
component of a deep convecting mantle material (probably, rising from greater 
depths) with high Pb and Nd and low Sr isotopic ratios. The interaction of this 
material with the lithosphere produced a shallower lens with lower Pb and Nd and 
higher Sr ratios. This component first appeared at 12-9.5 myr and became part of 
all later volcanic products. The role of lithospheric material varied in space 
and time: <$EDELTA>8/4Pb<|>=<|>60-93 were in the range of the DUPAL anomaly in 
the Tuva-Mongolian basalts, below this range (20-54) in the East Tuva lavas, and 
intermediate (50-63) on the periphery of the basaltic massif.
     Late Cenozoic, alkali basalts, Pb, Nd, Sr isotopes, East Sayan.

LANDSCAPE-GEOCHEMICAL PATTERNS OF DISTRIBUTION OF HEAVY METALS
IN BIOLOGICAL OBJECTS AND BOTTOM SEDIMENTS OF THE ALTAI LAKES 
G. A. Leonova, G. N. Anoshin, V. A. Bychinskii, B. L. Shcherbov, 
and V. D. Strakhovenko
1080

     Biogeochemical studies have been carried out on seven lakes of the Altai 
Territory, situated in different landscape-geochemical zones. The basic contents 
of heavy metals in the biological objects determining the biogeochemical 
background have been estimated. These contents serve as references in monitoring 
of increasing element concentrations during the man-induced pollution of lakes. 
The method of cluster analysis was used to carry out a computer-aided 
classification of correlations between chemical compositions of biological 
objects, bottom sediments, and regional soils. It has been established that the 
accumulation of trace elements in the living matter differs considerably from 
their accumulation in bottom sediments. The bottom sediments accumulate chiefly 
Cr, Ni, and Co, whereas the living matter accumulates Hg, Zn, Cd, and Mn. There 
are zones of local pollution in Lake Bol'shoe Yarovoe with elevated 
concentrations of mercury in biological objects and bottom sediments, resulting 
from industrial waste of a chemical plant in the town of Yarovoe.
     Biogeochemical background, pollution, heavy metals, cluster analysis, 
biological objects, plankton, water plants, bottom sediments, Altai Territory

TECTONICS

THE MID-TIEN-SHAN OPHIOLITES: STRUCTURAL POSITION AND AGE 
K. S. Ivanov, A. V. Mikolaichuk, V. N. Puchkov, Yu. V. Erokhin,
and E. V. Khristov
1093
     The Mid-Tien-Shan ophiolites make up several blocks in the Chatkal Ridge, 
tectonically related to the type sections of the region. The study was carried 
out at the most representative, Karaterek, ophiolite complex, which forms a 
nappe lying on the Silurian volcanogenic-terrigenous deposits and Middle 
Carbonaceous olistostrome. The Karaterek Massif is tectonically layered and is 
in inverse setting. It contains (1) a complex of the melanocratic basement 
represented by pyroxenites, antigorite serpentinites, gabbro-amphibolites, and 
actinolite schists and (2) volcanogenic-sedimentary cover, whose bottom is made 
up of apovolcanic chlorite-epidote and other schists with members of quartz-
sericite and siliceous schists. Above lie phyllites, tuff sandstones, and 
cherts. A complex of the conodonts Drepanoistodus sp., Paracordylodus sp., and 
Periodon cf. aculeatus have been documented in the cherts from the Arenigian-
lower Middle Ordovician, which is the first reliable dating of the ophiolites of 
the region. In age and composition, the Karaterek ophiolites may, probably, be 
compared with the Ordovician ophiolites from the eastern Urals.
     Ophiolites, conodonts, Ordovician, Tien Shan

NEOTECTONIC ANALYSIS OF NORTHERN LAKE TELETSKOYE USING DIGITAL 
ELEVATION MODELING 
E. M. Vysotsky, E. A. Vishnevskaya, and A. V. Elobogoev
1099
     A digital elevation model (DEM) is applied to morphotectonic analysis of 
the northern mountain surroundings of Lake Telestkoye. The investigation into 
the neotectonic structure of the region and vertical offset of block movements 
implies detection of peneplain remnants, digital elevation modeling, and 
interpretation of aerial and satellite imagery. Lineaments expressed in the 
surface topography and/or distinguished on aerial and satellite images were 
divided into three groups. Those of the first two groups are different kinds of 
normal faults, and the third-group lineaments without geomorphically expressed 
vertical component have been interpreted as eroded structures of the pre-
Cenozoic basement. Structures of the three types often belong to single 
lineament, which may indicate reactivated and stable neotectonic segments of the 
old basement faults. The revealed neotectonic blocks are rarely larger than a 
few kilometers across. Most of normal faults occur on the sides of the Teletsk 
and the adjacent Kamga and Koldor grabens, where vertical offset of recent block 
movements reach their maximum of 400-1200 m; in other grabens, the offset is 
mostly under 100-300 m. The surface topography of the region is strongly 
controlled by tectonics, evident from long V-shaped river valleys along zones of 
weakness. Some valleys are up to 600-800 m deep, and the total topographic 
gradient is 1600 m. In addition to tectonic factors, intense erosion is caused 
by recent lowering of the Lake Teletskoye level which is the regional base level 
of erosion.
     Morphotectonics, digital elevation model, Lake Teletskoye.

OIL AND GAS GEOLOGY

DEEPLY SUBSIDED LOWER JURASSIC UNITS IN THE NORTH OF THE WEST SIBERIAN 
OIL AND GAS PROVINCE: CRITERIA AND EVALUATION OF PETROLEUM POTENTIAL 
G. G. Shemin, A. Yu. Nekhaev, V. O. Krasavchikov, L. V. Ryabkova, A. N. Fomin,
G. F. Bukreeva, L. G. Vakulenko, S. V. Zinov'ev, D. V. Kosyakov, P. S. Lapin,
A. M. Brekhuntsov, V. S. Bochkarev, N. P. Deshchenya, and B. L. Urasinov
1107

     To predict the petroleum potential, we used stratigraphic, tectonic, 
lithologo-facies, and geochemical criteria. We have considered their 
significance and estimated the petroleum potential from a total of criteria. The 
structures of the Toarcian, Pliensbachian, and Hettangian-Sinemurian regional 
reservoirs of the Lower Jurassic have been characterized. The low petroleum 
potential of the reservoirs is due to the following factors: intricate 
structure, low and very low values of capacity-filtration parameters of 
reservoir rocks, widespread sealing beds of poor and very poor quality, low oil-
generating potential of oil source rocks, and a high degree of catagenetic 
transformation of OM, as well as nearly ubiquitous saturation of reservoirs with 
formational waters.
     Reservoir, sealing bed, permeable complex, catagenesis, oil source rocks, 
reservoir rocks, porosity, permeability, oil potential

GEOPHYSICS

INDUCED POLARIZATION EFFECTS AS INDICATORS OF HYDROCARBON POLLUTION 
OF GROUNDWATER 
V. Yu. Zadorozhnaya and A. D. Bessonov
1124

     Time-domain electromagnetic (TEM) soundings were performed in the vicinity 
of a plant in Saratov town, Russia, to detect hydrocarbon pollution of 
groundwater and to trace possible pollution flows in drainage zones. The 
presence of hydrocarbons in rocks is indicated by high electrical resistance and 
induced polarization (IP) effects found in many TEM curves. Calculations show 
that the polarizability <$Eeta> is the ratio of the excess electrical 
conductance to the electrical conductance in pores. Relaxation time <$Etau> was 
found to be controlled mainly by the radius of pores in water-saturated 
sediments. IP effects can be recorded by TEM soundings in wet sediments with 
imperfect phase relationships if the pore radius is the in the range of <$E10 
sup -4> to <$E5 cdot 10 sup -6> m. The interpretation of the TEM data based on 
the "floating plane version" (<$ES sub tau> version) and mathematical modeling 
allowed us to identify hydrocarbon-bearing layers. The layers containing 
hydrocarbon compounds were indentified by their higher resistivity of 12 to 17 
<$EOMEGA cdot roman m>. The polarizability of the anomalous zones was found to 
vary between 20 and 30 % with a time constant of <$E1.8 cdot 10 sup {-4}> s. The 
surface of the polluted groundwater plume roughly follows the topography of the 
underlying Cretaceous sediments. The plume is located below the groundwater 
table in the region of the thickest Quaternary sands. The zones of subsided 
surfaces of Albian clays were found to act as temporal traps of hydrocarbons 
from surface industrial wastes drained with groundwater.
     Groundwater pollution, TEM soundings, induced polarization, resistance, 
polarizability, S sub ... version, mathematical modeling.

APPLICATION OF DIFFERENTIAL-NORMALIZED ELECTRICAL MEASUREMENTS IN
PETROLEUM PROSPECTING: THE STATE OF THE ART AND PROSPECTS FOR FUTURE 
M. M. Mandelbaum, P. Yu. Legueido, N. I. Ryklinskii, E. B. Ageenkov,
and I. Yu. Pesterev
1137

     Differential-normalized electrical measurements (DNEM) have shown their 
efficiency in petroleum prospecting. The method implies detection of oil and gas 
deposits from polarization anomalies in haloes around rocks altered under the 
effect of the hydrocarbon pool. Polarization in the geoelectric section is 
determined layer-by-layer using space and time derivatives of the TEM process 
and differential-normalized parameters. 
     Electrical prospecting, polarizability, Cole-Cole, inversion of TEM data, 
hydrocarbons.