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Russian Geology and Geophysics

2020 year, number 12

1.
SOLUBILITY OF GOLD IN COMMON GOLD-CONCENTRATING MINERALS

V.L. Tauson and S.V. Lipko
A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences
ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Gold, solubility, pyrite, arsenopyrite, pyrrhotite, chalcopyrite, bornite, galena, sphalerite, magnetite

Abstract >>
The paper is a summary of the authors and published data on the occurrence of Au in common gold-concentrating minerals (pyrite, arsenopyrite, pyrrhotite, chalcopyrite, bornite, galena, sphalerite, and magnetite). The solubility of gold in minerals is evaluated through identification of the limiting element incorporation into the real crystal. The distribution of gold between coexisting minerals is considered. Obtaining reliable data on the gold solubility involves discrimination of the structural form of the element and correct separation of Au forms between the surface and the volume, which is not always possible because of the small size and low quality of crystals (defects and highly developed internal surfaces). It is also necessary to have a phase (individual or nonautonomous) limiting the incorporation of Au or to compare the mineral under study (within the framework of the principle of phase composition correlation) with a reference mineral with a reliably established structural form of Au. The most reliable and consistent estimates for the hydrothermal parameters (450500 ºC, 1 kbar) are as follows (g/g): sphalerite 0.7, highly ferrous sphalerite 5, magnetite 1, pyrite 3, manganese and copper-containing pyrite 10, pyrrhotite 21, chalcopyrite 110, bornite 140, and galena 240. The highest solubility of gold (up to 30,000 g/g) is established in arsenopyrite, but it is likely to be a metastable miscibility caused by the nonstationary conditions of crystal growth or by the crystal growth at the expense of the surficial nonau-tonomous phase. The same factors can cause supersaturation of pyrite with Au admixture at low tem-peratures. The dual behavior of Au in pyrrhotite and magnetite is for a different reason: Under reducing conditions, these minerals can contain a submicroscopic elemental form of Au indistinguishable from the structural one. We consider the forms of Au occurrence and the relationship between the solubility of gold and metallicity of chemical bond in minerals.

DOI: 10.15372/RGG2020165
																				  																		



2.
PHASE RELATIONS OF IRON CARBIDES Fe2C, Fe3C, AND Fe7C3 AT THE EARTHS CORE PRESSURES AND TEMPERATURES

N.E. Sagatov1,2, P.N. Gavryushkin1,2, I.V. Medrish3,4, T.M. Inerbaev1,5, K.D. Litasov6,7
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090, Russia
3International Research Center for Theoretical Materials Science, Samara State Technical University, ul. Molodogvardeiskaya 244, Samara, 443100, Russia
4Samara Center for Theoretical Materials Science, Samara National Research University, ul. Akademika Pavlova 1, Samara, 443011, Russia
5L.N. Gumilyov Eurasian National University, ul. Satbaeva 2, Astana, 010008, Kazakhstan
6Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, Kaluzhskoe sh. 14, Troitsk, Moscow, 108840, Russia
7Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskii pr. 18/2, Moscow, 119071, Russia
Keywords: Iron carbides, USPEX, AIRSS, crystal structure prediction, quasi-harmonic approximation

Abstract >>
Based on first-principle calculations in the framework of the density functional theory and structure prediction algorithms, we have determined iron carbide phases stable at the Earths core pressures and temperatures. It is shown that Fe7C3 is unstable and decomposes into the mixture Fe2C + Fe3C over the entire range of pressures and temperatures specific to the Earths inner core. Subsequent decomposition of Fe3C into the mixture Fe + Fe2C is unfavorable. We also predict a new low-temperature modification Fe3C-C2/m-II dynamically and thermodynamically stable over the pressure range 290-305 GPa.

DOI: 10.15372/RGG2019146
																				  																		



3.
THE ROLE OF BLACK-SHALE STRATA IN THE FORMATION OF THE NATALKA AND PAVLIK GOLD DEPOSITS (Yana-Kolyma orogenic belt)

T.I. Mikhalitsyna1,2, O.T. Sotskaya1
1N.A. Shilo Northeastern Interdisciplinary Scientific Research Institute, Far Eastern Branch of the Russian Academy of Sciences, ul. Portovaya 16, Magadan, 685000, Russia
2Northeastern State University, ul. Portovaya 13, Magadan, 685000, Russia
Keywords: Late Permian, black-shale strata, Natalka and Pavlik gold deposits, rare-earth elements (REE), ore minerals, precious metals, microinclusions, micromineralogy

Abstract >>
Data on geochemistry, distribution of ore and rare-earth elements and precious metals, and micromineralogy are presented. The objects of study are late Permian sedimentary and volcanosedimentary deposits of the Tikhonya Brook (Atkan (P3at) and Omchak (P3om) formations) and hydrothermally metamorphosed rocks of the Natalka and Pavlik gold deposits of the Omchak ore-placer cluster. Analysis of the deposit ores showed enrichment in chalcophile trace elements Au, Ag, As, W, and Sb relative to their average contents in the upper crust and the host Permian rocks. The high contents of W and Bi in the ores suggest the participation of a magmatic fluid. The absence of abnormal contents of Ni, Co, Sb, Mo, Cr, and Se indicates the redeposition of these elements from ore-bearing rocks, without their input by ore-forming fluids, which is confirmed by the isotopic composition of sulfide sulfur and the characteristics of carbonaceous ore material. The formation of deposits proceeded with a change in REE contents. All objects show similar trace-element patterns: The rocks are enriched in LREE and lack a Ce anomaly. The identical REE patterns of ores reflect their inheritance from unaltered late Permian deposits. It has been established that the ores formed under different redox conditions, mainly with the participation of a relatively oxidized fluid enriched in LREE of the hydrothermal system NaCl-H2O, with domination of Cl over F. The studies have shown that the host carbonaceous sedimentary complexes, which served as additional sources of precious and associated metals, played a crucial role in the formation of the Natalka and Pavlik gold deposits. Some of the ore elements in the unaltered deposits form their own minerals.

DOI: 10.15372/RGG2020149
																				  																		



4.
THE TOLOGOI KEY SECTION (upper Cenozoic, Transbaikalia): RECONSTRUCTION OF THE PECULIARITIES AND DEPOSITIONAL ENVIRONMENT

V.V. Ivanova1,2,3, M.A. Erbaeva4, A.A. Shchetnikov5,2,6,7, A.Yu. Kazansky8,3, G.G. Matasova3,9, N.V. Alekseeva4, I.A. Filinov5,7,3, M.I. Kuzmin2
1I.S. Gramberg All-Russia Scientific Research Institute for Geology and Mineral Resources of the Ocean, Angliiskii pr. 1, St. Petersburg, 190121, Russia
2Vinogradov Institute of Geochemistry, ul. Favorskogo 1a, Irkutsk, 664033, Russia
3Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017, Russia
4Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakhyanovoi 61, Ulan-Ude, 670047, Russia
5Institute of the Earths Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
6Irkutsk Scientific Center, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 134, Irkutsk, 664033, Russia
7Irkutsk State University, ul. Karla Marksa 1, Irkutsk, 664003, Russia
8Lomonosov Moscow State University, Leninskie Gory 1, Moscow, 119991, Russia
9Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Pleistocene, Pliocene, geochemical composition of loose deposits, environmental changes, lithology, Tologoi key section, Transbaikalia

Abstract >>
This paper presents new data on the structure and lithologic, geochemical, and granulometric features of the Quaternary deposits of the Tologoi key section (upper Cenozoic, Transbaikalia). These data made it possible to determine the location of paleosol horizons throughout the section and their thicknesses. Four main sedimentation cycles have been identified; each of them terminated with the formation of soil horizons. It is shown that the climate during the formation of the deposits had a cyclic nature: Wet periods were changed by dry epochs of different durations. During warming and the formation of soil horizons, distant and medium-range provenance areas prevailed. In situ biochemical postsedimentary transformations of the deposits dominated in the periods of the most intense pedogenesis, as reflected in the changes in their chemical composition. It is shown that the warmest climate and the activation of weathering and leaching processes during the Pleistocene were in the period of the accumulation of a paleosol horizon in the section interval 16.4-15.0 m. It was a period of pedogenic and biologic activity and reduced salinization and carbonation. Stages with prevailing cryogenic environments are clearly recorded in the studied geochemical profile as involutions, pseudomorphs after ice wedges, and thick carbonate lenses. The deposits formed at these stages are characterized by minimum salinization, high calcification, and low leaching (hydrolysis) and oxidation indices as well as a positive Eu anomaly and high ΣCe/ΣY and low La/Sm values.

DOI: 10.15372/RGG2020141
																				  																		



5.
THE BASAL UNIT OF THE VERKHOYANSK SEDIMENTARY COMPLEX, NORTHERN KHARAULAKH: LITHOSTRATIGRAPHY, BIOSTRATIGRAPHY, AND DEPOSITION ENVIRONMENTS

N.V. Sennikov1,2, R.A. Khabibulina1, T.V. Gonta1,2, O.T. Obut1,2
1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090. Russia
2Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090. Russia
Keywords: Carboniferous, Visean, stratigraphy, lithology, Northern Kharaulakh

Abstract >>
The origin and biostratigraphic constraints of the Krestyakh conglomerate remain among most controversial issues in the Late Paleozoic history of the North Kharaulakh basin. The Krestyakh conglomerate is a sequence of coarse sand to pebble-size sediments at the base of the Late Paleozoic Verkhoyansk clastic complex. According to geological, lithological, and sedimentation data, the Krestyakh conglomerate in the Atyrdakh Formation is composed of debrites: deposits carried by debris flows that fill submarine canyons. The Verkhoyansk clastic deposition began in the middle Visean stage of the Early Carboniferous.

DOI: 10.15372/RGG2020138
																				  																		



6.
ORGANIC GEOCHEMISTRY AND MICROFOSSILS OF THE UPPER JURASSIC AND LOWER CRETACEOUS STRATA IN THE LOWER REACHES OF THE OLENEK RIVER (northeastern framing of the Siberian Platform, Arctic Siberia)

V.A. Kashirtsev1,2, B.L. Nikitenko1,2, E.B. Pestchevitskaya1, E.A. Fursenko1,2, N.P. Shevchenko1
1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090, Russia
Keywords: Jurassic and Cretaceous, organic geochemistry, biomarkers, microfauna, terrestrial and marine palynomorphs, Arctic Siberia, Lena-Anabar basin

Abstract >>
The organic-geochemistry data reveal two levels in the reference Upper Jurassic-Lower Cretaceous section of the lower reaches of the Olenek River: lower (Volgian-lower Boreal Berriasian (diasterene)) and upper (Boreal Berriasian-Valanginian (hopane)). The Volgian beds are composed of clays with abundant prasinophytes Leiosphaeridia and Tasmanites and various dinocyst associations and have the highest content of organic carbon (Corg), up to 9 %. Isoprenoids, in particular, pristane and phytane, are highly predominant among aliphatic hydrocarbons; their content is more than three times higher than that of coeluting n-alkanes, which is typical of buried chlorophyll-containing plankton (dinocysts and prasinophytes). Sedimentological, biofacies, and paleoecological analyses show that the highly carbonaceous beds of the Buolkalakh Formation formed under oxygen deficit conditions. An integrated analysis demonstrated that the pristane/phytane ratio not always reliably reflects the reducing or oxidizing conditions of organic-matter accumulation and diagenesis. The discrepancy between the geochemical identification of organic matter according to the pristane/phytane ratio and the biofacies and sedimentological data is due to the low catagenetic maturity of OM. The Volgian was marked by a significant transgression of the Anabar-Lena sea, which was gradually changed by a successive regression of its basin at the end of this stage and in the Boreal Berriasian. The Corg contents in the coastal and subcontinental sediments decreased. Diasterenes and 4-methyldiasterenes disappeared from the balance of biomarker molecules, and the portion of hopanoids increased. Aerobic environments prevailed in the subbottom waters. Earlier, three biomarker horizons were identified according to geochemical criteria in the synchronous sections of Anabar Bay (Laptev Sea coast): terpane, diasterene, and hopane ones. In the section of the Olenek basin, the upper two horizons are well identified by specific biomarkers, and the lower one is absent because of the sedimentation break. Stratigraphic analysis of the location of these geochemical levels in different parts (and bathymetric zones) of the Anabar-Lena basin shows their diachronous formation. According to all geological and geochemical criteria, the Volgian Stage and the lower beds of the Boreal Berriasian Stage of this basin have a high petroleum potential. In the axial zone of the basin and, especially, on the Laptev Sea shelf, there were probably favorable conditions for the generation and accumulation of hydrocarbons genetically related to the Upper Jurassic highly carbonaceous rocks.

DOI: 10.15372/RGG2020131
																				  																		



7.
A MODEL OF THE GEOLOGIC STRUCTURE AND THE OIL AND GAS PROSPECTS OF NEOCOMIAN (Berriasian-lower Aptian) SEDIMENTS OF THE WEST SIBERIAN ARCTIC REGIONS AND THE KARA SEA SHELF

V.A. Kontorovich1,2
1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090. Russia
Keywords: Shelf, seismic cross section, reflecting horizon, megacomplex, complex, clinoform, Achim member, shelf formations, structure, oil- and gas-promising object, Arctic regions of West Siberia, Kara Sea

Abstract >>
The paper presents a model of the geologic structure of Neocomian (Berriasian-lower Aptian) sediments in the Arctic regions of West Siberia and on the shelf of the Kara Sea. The southern part of the Kara Sea is the northern end of the West Siberian sedimentary basin and is identified as the South Kara regional depression of the West Siberian oil and gas province (OGP). Structural and tectonic analysis was performed, and 97 oil- and gas-promising anticlinal objects (structures of ranks III-IV) were identified in the Neocomian megacomplex relief, including 61 on the continent and 36 on the shelf. In the Yamal and Gydan oil and gas areas (OGA), the Neocomian complex of sediments has a structure typical of West Siberia. The megacomplex includes clinoform and shelf complexes. Clinoforms resulted from the ablation of terrigenous material from the eastern and southeastern edges of the plate and are tilted in the northwestern direction; the depocenter within which the eastern and western clinoforms converge is located in the Urals zone, west of the Nurmin megaswell. In the South Kara regional depression, the Berriasian-lower Aptian megacomplex is also represented by clinoform and shelf complexes. On the Kara Sea shelf, Neocomian clinoforms are tilted in the southern, western, and eastern directions; they resulted from the ablation of sediments from the Novaya Zemlya Archipelago and the Siberian Sill. Throughout most of the South Kara regional depression, clinoforms have a typical structure and contain shelf and Achim sandstones that can concentrate significant volumes of hydrocarbons; in the northeast, in the pre-sill zone, clinoform deposits will be represented by poorly sorted «dump sandstones.

DOI: 10.15372/RGG2020154
																				  																		



8.
RESULTS OF MAGNETIC-VARIATION SOUNDING OF THE TATAR STRAIT AT TWO POINTS ON ITS OPPOSITE SHORES

S.S. Starzhinskii, V.M. Nikiforov
V.I. Ilichev Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, 690041, Vladivostok, ul. Baltiiskaya, 43, Russia
Keywords: Magnetic-variation sounding, 3D inversion, ModEM, geoelectric section, Tatar Strait

Abstract >>
Results of magnetic-variation sounding on the opposite shores of the Tatar Strait are presented. The resulting frequency dependences of tippers serve as a basis for 3D inversion carried out using the ModEM software. The inversion yields horizontal and vertical sections of the Tatar Strait in a 400×400×400 km area along the x , y , and z axes, respectively. A conductive zone is revealed near the continental shore, and its central part has an electric resistivity of 0.5 Ohmm at a depth of 5-7 km. The zone reaches 20-40 km across and vanishes in the lower crust. Along the shore, an anomaly begins north of the Datta Village and extends to the area south of the town of Sovetskaya Gavan. There is a similar anomaly that is isometric in the horizontal plane and less contrasting, which exists near Sakhalin Island at depths of 8-12 km, where the crust resistivity is 15 Ohmm. The position of the anomaly matches the nearby zone of local = 4-6 earthquakes in the upper crust. At depths greater than 10 km beneath the strait, these anomalies merge and the electrical resistivity increases. In the lower crust and in the upper mantle beneath the strait, the section is characterized by a resistivity of 30-60 Ohmm. At depths greater than 100 km, there is a conductive layer submerging beneath the Tatar Strait from the Sea of Okhotsk, with conductive branches running from it beneath the Tatar Strait south and north of the Datta Village. The possible causes of near-shore conductive anomalies are discussed.

DOI: 10.15372/RGG2020101
																				  																		



9.
Obituary: Coleman Robert Griffin