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

2009 year, number 7

Specific genesis of gold and silver sulfides at the Yunoe deposit (Magadan Region, Russia)

G.A. Pal'yanova a , N.E. Savva b
a Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Northeastern Interdisciplinary Scientific Research Institute, Far Eastern Branch of the RAS, 16 ul. Portovaya, Magadan, 682000, Russia
Keywords: uytenbogaardtite; parageneses; hypogene formation; ore-bearing hydrothermal solution; thermodynamic modeling
Pages: 579-594

Abstract >>
Hypogene uytenbogaardtite, acanthite, and native gold parageneses have been revealed at the epithermal Yunoe gold-silver deposit, Magadan Region, Russia. Thermodynamic calculations in the system Si-Al-Mg-Ca-Na-K-Fe-Pb-Zn-Cu-Ag-Au-S-C-Cl-H2O were carried out at 25-400 °C and 1-1000 bars to elucidate the role of hydrothermal solutions in the formation of gold and silver sulfides. Several most probable scenarios for ore-forming processes in the deposit are considered: (1) interaction between cold and heated meteoric waters percolating along cracks from surface to depth and reacting with the host rock-rhyolite; (2) evolution of ascending postmagmatic fluid resulting in chloride-carbonic acid solution, which interacts with rhyolite at 100-400 °C; (3) stepwise cooling of hydrothermal ore-bearing solutions; (4) rapid cooling of ore-bearing hydrotherms on their mixing with cold surface waters. Rhyolite with Pb, Zn, Cu, Cl, S, Ag, and Au clarke contents was taken as an initial host rock. Calculations by model 3 showed the possible formation of uytenbogaardtite and petrovskaite at low-temperature stages. Gold and silver sulfides can be deposited during the mixing of ore-bearing acid chloride-carbonic acid hydrothermal solutions with surface alkaline waters.

Thermodynamic modeling of the REE distribution between fluorite and ore-forming fluid in postmagmatic deposits in western Transbaikalia

K.G. Morgunov a , V.G. Bykova b
a Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Novosibirsk State University, 2 ul. Pirogova, Novosibirsk, 630090, Russia
Keywords: computer modeling; REE fractionation; thermodynamic calculations; epithermal fluorite deposits of western Transbaikalia
Pages: 595-601

Abstract >>
The factors determining the REE distribution in natural hydrothermal systems are studied by a numerical experiment. The behavior of REE is examined based on the composition of ore-bearing hydrothermal solutions and the parameters of ore formation processes at different fluorite deposits. These data were obtained in studies of fluid inclusions. Some regularities of the REE behavior during the formation of fluorite deposits have been revealed. It is shown that the REE distribution in fluorites is related mainly to changes in the composition of mineral-producing fluid solution.

Carbon and oxygen isotopes in the Frasnian-Famennian section of the Kuznetsk basin (southern West Siberia)

O.P. Izokh a ,*, N.G. Izokh b , V.A. Ponomarchuk a , D.V. Semenova a
a Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: isotopes; carbon; oxygen; carbonates; Famennian Stage; Upper Devonian; northwestern Kuznetsk Basin
Pages: 602-609

Abstract >>
The first detailed isotope-geochemical study of carbonate deposits has been performed in the Lower Famennian stratotype section of the northwestern Kuznetsk Basin (Kosoy Utyos), which was localized in the middle latitudes of the Northern Hemisphere in the Late Devonian. The δ13 Cкарб, δ13 Cорг and δ18 variation curves were constructed for the section deposits. Geochemical and petrographic studies of carbonates allowed allocation of samples that underwent postsedimentation alteration and exclude them from further interpretation. Compared with coeval sections in the other world's regions, the Kosoy Utyos section is characterized by higher δ13 Ccarb values, up to 5.4 ‰, whereas the maximum value in subequatorial area sections is 4 ‰. The isotope shift amplitude of the studied section reaches 4.6 ‰, which is 1.5 ‰ higher than those in other regions. The δ18O values are 3 ‰ lower than the ones of the world's coeval sections. The results obtained show that δ13C and δ18O variation trends differ from those of coeval subequatorial sections. The high shift amplitude and maximum δ13 Ccarb values in the Kosoy Utyos section are due to the shallow-water carbonate sedimentation environments on the Siberian continental shelf and, probably, the lower temperatures of waters in the middle latitudes as compared with the subequatorial areas.

Neotectonic inversions in the Baikal Rift System

G.F. Ufimtsev, A.A. Shchetnikov, I.A. Filinov
Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: rifting; tectonic inversion; neotectonics; Baikal rift system
Pages: 610-619

Abstract >>
Cenozoic continental rifting in southern East Siberia and northern Mongolia has been associated with subsidence and broadening of rift basins at the account of their mountain borders. This neotectonic trend is, however, superposed with continuous or periodic tectonic inversions in which the basin floor may uplift while marginal fault steps and saddles between basins may subside. Cenozoic geomorphic inversions are expressed in changes of river flow out of Lake Baikal.

On nonlinearity of petroleum formation

L.M. Burshtein
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: petroleum formation; sedimentary basin; accumulation, migration and dissipation of hydrocarbons; petroleum system
Pages: 620-629

Abstract >>
A nonlocal dynamic model of petroleum formation is used to explore possible causes and consequences of the nonlinear behavior of large petroleum systems. As a result of this nonlinearity, migration and accumulation of oil starts only after hydrocarbons in a reservoir reach a threshold amount. Significant differences in the amount of in-place resources in macroscopically similar petroleum systems may be associated with minor random changes in initial conditions.

Kerogen: chemical structure and formation conditions

D.A. Bushnev, N.S. Burdel'naya
Institute of Geology, Komi Research Center, Ural Branch of the RAS, 54 ul. Pervomaiskaya, Syktyvkar, 167982, Russia
Keywords: Mesozoic deposits; carbonaceous strata; kerogen; Russian Plate
Pages: 630-635

Abstract >>
The available data on the composition of the pyrolysis products of kerogen from the Mesozoic carbonaceous strata of the Russian Plate evidence that changes in the contents of total organic carbon (TOC) lead to a regular change of the mechanisms of organic-matter (OM) conservation in sediments. Each mechanism prevails for particular TOC contents. The initial increase in the TOC content of rocks is accounted for by the fact that the higher is the biologic productivity of the basin, the higher is the portion of nonmineralized organic matter. This is due mainly to the mechanism of selective accumulation of the most stable biochemical components such as algaenan. The appearance of H2S first in the pore waters of sediment and then in the water column increases the degree of preservation of initial OM at the expense of its sulfurization. This process runs first in the lipid and then in the carbohydrate fractions of initial OM.

Seismites in Late Pleistocene and Holocene deposits of the northwestern Kola region (northern Baltic Shield)

S.B. Nikolaeva
Geological Institute, Kola Science Center of the Russian Academy of Sciences, 14 ul. Fersmana, Apatity, Murmansk Region, 184200, Russia
Keywords: seismites; paleoseismology; earthquakes; Pleistocene; Holocene; Kola region; Russia
Pages: 636-642

Abstract >>
New data on soft-sediment deformation in Late Pleistocene and Holocene deposits of the northwestern Kola Peninsula (Pechenga River valley) are reported and analyzed in terms of paleoseismicity implications. Soft-sediment deformation is assigned to paleoseismic triggers on the basis of special criteria. One sedimentary section in the Pechenga valley bears signature of several seismic events at the Late Pleistocene-Holocene boundary, constrained by radiocarbon dates. According to the morphology, sizes, and types of seismites, the earthquakes had an MSK-64 intensity at least VI-VII. The observed earthquake-induced deformation may be associated with tectonic subsidence of the Pechenga valley block.

Dielectric loss in ore-forming chromium spinel at temperatures from 20 to 800 °C

V.V. Bakhterev
Institute of Geophysics, Ural Branch of the RAS, 100 ul. Amundsena, Yekaterinburg, 620016, Russia
Keywords: dielectric loss; high temperature; ultramafic rocks; chromite ore; chromium spinel
Pages: 643-647

Abstract >>
Physical, physicochemical, and mineralogical-petrographic methods have been applied to samples of ophiolite-hosted chromite ore from different deposits and occurrences in the Urals. Temperature dependences of dielectric loss obtained for nine chromite ore samples consisting of 95-98% Cr spinel show prominent peaks indicating a relaxation origin of the loss. The analyzed samples have the loss peaks at different temperatures depending mainly on H = (FeO/Fe2O3)*: (FeO/Fe2O3)**, where (FeO/Fe2O3)* and (FeO/Fe2O3)** are, respectively, the ferrous/ferric oxide ratios in the samples before and after heating to 800 °C, and H is thus the heating-induced relative change in the FeO/Fe2O3 ratio. These peak temperatures vary from 550 °C (sample 1, high-Cr chromium spinel with more than 52% Cr2O3) to 750 °C (sample 2, aluminous and magnesian spinel with less than 30% Cr2O3), and H ranges correspondingly from 1.61 to 5.49. The temperature of the loss peaks is related with H as H = 34.30 - 11.52N +? 1.20N2, with an error of σ=0.19 ( N = T · 10-2>, T is temperature in °C).