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Russian Geology and Geophysics

2018 year, number 1

1.
COMPARISON AMONG THE OORTSOG, DULAAN, AND NOMGON MAFIC-ULTRAMAFIC INTRUSIONS IN CENTRAL MONGOLIA AND Ni-Cu DEPOSITS IN NW CHINA: IMPLICATIONS FOR ECONOMIC Ni-Cu-PGE ORE EXPLORATION IN CENTRAL MONGOLIA

Y.-J. Mao1, D. Bat-Ulzii2, K.-Z. Qin1,3, B. Bujinlkham2, D.-M. Tang1
1Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
2Department of Geology and Mineralogy, Mongolian University of Science and Technology, Ulaanbaatar-46/520, Mongolia
3University of Chinese Academy of Sciences, Beijing 100049, China
Keywords: Ni-Cu deposit, platinum group elements, exploration, mafic-ultramafic intrusion, Central Asian Orogenic Belt, central Mongolia

Abstract >>
Although there are many mafic-ultramafic intrusions in the western and central regions of Mongolia, Central Asian Orogenic Belt (CAOB), no economic-grade Ni-Cu deposits have yet been discovered. To understand the economic Ni-Cu deposit potential of the intrusions in central Mongolia, the parental magma affinity and sulfide saturation of the Oortsog, Dulaan, and Nomgon Ni-Cu mineralized mafic-ultramafic intrusions are studied. These three intrusions are predominantly gabbroic in composition, while the Oortsog and Dulaan intrusions additionally contain small proportions of peridotites. The parental magmas of the Oortsog and Dulaan intrusions are tholeiitic, as indicated by their Cr-spinel and clinopyroxene compositions, whereas the parental magma of the Nomgon intrusions is likely calc-alkaline. The compositions of Cr-spinel and clinopyroxene, combined with significant Nb-Ta depletion, indicate that these rocks were most likely derived from modified mantle sources. Both the Oortsog and Nomgon intrusions form two clusters in terms of their olivine composition, suggesting that multiple magma surges were involved during their emplacement. The relatively low Fo values and Ni contents in olivine from the three intrusions compared to those from Ni-Cu deposits in NW China, as well as those in the Voiseys Bay deposit in Canada, indicate that the three intrusions crystallized from relatively evolved magmas. The Cu/Zr ratios of rocks of the Oortsog, Dulaan, and Nomgon intrusions are higher than 1, suggesting that these rocks contain cumulus sulfide. This, coupled with the presence of rounded sulfide inclusions in olivine of the Oortsog and Dulaan intrusions, suggests that sulfide saturation occurred before or during olivine crystallization. The distribution patterns of platinum group elements (PGEs) of the Dulaan and Oortsog intrusions record slight Rh, Pt, and Pd (PPGE) enrichment relative to Os, Ir, and Rh (IPGE). Furthermore, the Ni/Cu ratios of sulfide-bearing rocks from the Oortsog intrusion vary from 1.8 to 3.8 and are consistent with those of the Ni-Cu sulfide deposits in NW China. In contrast, the Ni/Cu ratios of sulfide-bearing rocks from the Nomgon intrusion are extremely low (0.03 to 0.07). This, together with the significant enrichment in PPGE relative to IPGE, suggests that these sulfides of the Nomgon intrusion were segregated from a magma that was extremely enriched in Cu and PPGE but depleted in Ni and IPGE. The characteristics of the chalcophile elements in these intrusions are attributed to the fact that the derivation of the Nomgon magma was significantly different from that of the Dulaan and Oortsog parental magmas. Overall, although the parental magmas of the intrusions in central Mongolia are more evolved than those in NW China, they are comparable in the sizes of their intrusions, constituent minerals, and mineral chemistry. These similarities suggest that the intrusions in central Mongolia have an economic Ni-Cu sulfide potential. Furthermore, intrusions similar to the Nomgon intrusion may feature a PGE mineralization potential.



2.
PETROGENESIS OF COMposite DIKES IN GRANITOIDS OF WESTERN TRANSBAIKALIA

G.N. Burmakina1, A.A. Tsygankov1,2, V.B. Khubanov1,2
1Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakhyanovoi 6a, Ulan Ude, 670047, Russia
2Buryatian State University, ul. Smolina 24a, Ulan Ude, 670000, Russia
Keywords: Composite dikes, granitoids, mixing, sources of magmas, U-Pb isotopic age, formation conditions, western Transbaikalia

Abstract >>
The performed studies have revealed two varieties of composite dikes differing in morphology and internal structure depending on (1) the proportions of salic and basic components and (2) the rheologic state of the host environment. The latter can be both a solid substrate with open fractures and a melt at different stages of crystallization. The evaluated isotopic age of dikes in the Shaluta massif, 290.8 2.7 Ma and 283.4 3.4 Ma, is correlated with the time of the pluton formation. The age of the composite dike breaking through the metamorphic deposits on the eastern shore of Lake Baikal is 284.10 0.96 Ma. The mass formation of composite dikes in western Transbaikalia is correlated with the Late Paleozoic magmatism, which resulted in one of the Earths largest granitoid provinces. The intrusion of dikes was not a single-stage event; it lasted at least 10-12 Myr and was apparently related to the repeated intrusion of large volumes of salic magmas and the formation of granitoid plutons. Early Mesozoic composite dikes associated with alkali-granitoid plutons of the Late Kunalei igneous complex (230-210 Ma) are much scarcer. Basic magmas of the composite dikes were generated at depths greater than 75 km as a result of the melting of a modified (enriched in crustal components) mantle source. Salic components of the dikes, independently of their geologic position, are generally similar in composition to the granitoids of the plutonic facies, and the differences are apparently due to hybridization proceeding at great depths.



3.
PETROGENESIS OF THE LATE CENOZOIC COLLISION VOLCANISM IN THE CENTRAL PART OF THE LESSER CAUCASUS (Azerbaijan)

N.A. Imamverdiyev1, M.Ya. Gasangulieva2, G.D. Babaeva2, Sh.F. Abdullaeva1, A.A. Veliev3
1Baku State University, Azerbaijan, Academic Zahid Khalilov str. 23, Baku, AZ-1073/1, AZ 1148, Republic of Azerbaijan
2Institute of Geology and Geophysics, Azerbaijan National Academy of Sciences, H. Javid Av. 119, Baku, AZ 1143, Azerbaijan
3Azerbaijan International Mining Company, Hanifa Aleskerov str. 16, Nasimi, Baku, AZ 1022, Azerbaijan
Keywords: Petrogenesis, collision volcanism, Lesser Caucasus

Abstract >>
The Late Cenozoic volcanic deposits of the Lesser Caucasus have similar trace-element and REE patterns with negative anomalies of Nb, Ta, Hf, and Zr. They are highly enriched in Rb, Ba, Th, and La and depleted in Ti, Yb, and Y with respect to N-MORB, which indicates their formation from the subduction-metasomatized lithospheric mantle. Partial melting of the subcontinental mantle lithosphere and crustal assimilation and fractional crystallization controlled the magma evolution in the collisional magmatic belts.



4.
RECONSTRUCTION OF BRACKISH-WATER SYSTEMS USING AN ICHNOLOGICAL FRAMEWORK

A.V. Shchepetkina, M.K. Gingras, S.G. Pemberton
Ichnology Research Group, Department of Earth Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
Keywords: Ichnology, trace fossils, sedimentology, brackish-water systems, estuaries

Abstract >>
This paper provides an overview of the history of ichnology from both Russian and international perspectives. However, the main purpose of the paper is to review how trace fossils can be used to discern the brackish-water sedimentary environments from their open-marine counterparts. A number of modern studies are presented, including: (1) Kouchibouguac Bay, New Brunswick, Canada; (2) Willapa Bay, Washington, USA; (3) Ogeechee River Estuary, Georgia, USA; and (4) Petitcodiac River estuary, New Brunswick, Canada. Cretaceous examples from the Western Canada Sedimentary Basin (i.e., McMurray Formation, AB, Canada and Gething Formation, British Columbia, Canada) are provided to test the models derived from the modern estuaries.



5.
THE UPPER ORDOVICIAN OF NORTHEASTERN GORNY ALTAI: STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS

N.V. Sennikov1,2, O.T. Obut1,2, T.Yu. Tolmacheva3, E.V. Lykova1, R.A. Khabibulina1
1A.A. Trofimuk 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 2, Novosibirsk, 630090, Russia
3Karpinsky Russian Geological Research Institute (VSEGEI), Federal Agency of Mineral Resources, Srednii pr. 74, St. Petersburg, 199106, Russia
Keywords: Ordovician, facies, depositional environment, conodonts, Gorny Altai

Abstract >>
Comprehensive lithofacies and biofacies analysis provided constraints on the origin of Upper Ordovician clastic and carbonate deposits in northeastern Gorny Altai, which form large low-elevated flat carbonate banks located relatively close to the shore. The sediments were deposited during the Sandbian and early-middle Katian stages, according to new conodont data. Upper Ordovician sections in northeastern Gorny Altai store record of two global regressions: the early Sandbian (Vollen Lowstand) and early Katian (Frognerkilen Lowstand) events.



6.
SHALE STRATA DEVELOPMENT PROBLEMS AND Origin OF THE BAZHENOV FORMATION FRACTURES IN THE SOUTHEAST OF THE WEST SIBERIAN PLATE

V.B. Belozerov, L.A. Krasnoshchekova, V.P. Merkulov
National Research Tomsk Polytechnic University, pr. Lenina 30, Tomsk, 634050, Russia
Keywords: Fractures, palaeomagnetic orientation, Bazhenov Formation, pore pressure, hydraulic fracturing

Abstract >>
Shale strata development is one of the most promising trends for the hydrocarbon production increase within the West Siberian petroliferous province. The lack of understanding of fracturing mechanism, which is crucial for steady well production during hydraulic fracturing or drilling of horizontal wells, substantially restricts the choice of process capabilities for effective development of such horizons. This paper considers the Bazhenov Formation fractures based on the core data. The role of open and mineralized fractures (their slope angles, density, and specific surface) in the structure of bituminous shales is considered. Paleomagnetic orientation of the core samples with open fractures is implemented, and litho-petrographical description of the strata is made. The obtained results indicate that the planetary paleotension system of rocks controls the origin of open fractures in the Bazhenov Formation. Therefore, their spatial orientation and autogeneration capability can be used during the development of the bituminous shale strata.



7.
RESULTS OF MAGNETOTELLURIC SURVEY ON REFERENCE GEOPHYSICAL PROFILES OF THE KARATON-SARKAMYS BLOCK IN KAZAKHSTAN

G.K. Umirova1, S.A. Istekova1, I.N. Modin2
1K.I. Satpaev Kazakh National Technical University, ul. Satpaeva 22, Almaty, 050013, Kazakhstan
2Faculty of Geology, Lomonosov Moscow State University, Leniniskie Gory 1, Moscow, 119991, Russia
Keywords: Magnetotelluric (MT) sounding, petroleum potential, seismic prospecting, integrated interpretation, Caspian Depression, oil and gas

Abstract >>
A digital geoelectric model of the Karaton-Sarkamys block located in the southern (Kazakhstan) part of the Caspian Depression has been elaborated on the basis of processing and interpretation of magnetotelluric-sounding data. Geoelectric sections and structural maps of geoelectric layers have been constructed. It has been shown that magnetotelluric sounding combined with seismic and GIS data can be efficiently used to obtain additional information about the lithologic and reservoir properties of petroleum plays.



8.
DIAGNOSTICS OF THE SHAPE AND ORIENTATION OF A ROCK FAILURE ZONE BASED ON ELECTRICAL MEASUREMENTS AS AN INVERSE PROBLEM OF GEOPHYSICS

D.Yu. Sirota, V.V. Ivanov
T.F. Gorbachev Kuzbass State Technical University, ul. Vesennyaya 28, Kemerovo, 650000, Russia
Keywords: Exploration geophysics, diagnostic problem, interpretation of geophysical data, rock burst, integral equation of the first kind, inverse ill-posed problem, Tikhonov regularization method

Abstract >>
Exploration geophysics is concerned with the development of methods and techniques for remote search for mineral deposits, solution of various engineering and geological problems, mining monitoring, and diagnostics of zones of rock bursts and natural and technogenic tectonic earthquakes. In this paper we consider the diagnostic problem of exploration geophysics related to the determination of the shape and inclination angle of a plane source of the natural geoelectric field, which, under certain conditions, simulates a rock failure zone, e.g., during the preparation of rock bursts at the sites of developed mineral deposits. This approach may also be useful in determining the shape and size of ore shoots by electrical measurements on the ground surface. Evaluation of the parameters of a rock failure zone is required in the case of accumulation of multiple fractures having charges of the same sign before a catastrophic failure. This problem is formulated as a Fredholm-Urysohn integral equation of the first kind. The solution of the integral equation is sought using the Tikhonov regularization method of the second order.