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Russian Geology and Geophysics

2018 year, number 10

1.
New data on the geologic structure, magmatism, and mineral resources of the Siberian craton and the Verkhoyansk-Kolyma folded area

N.V. Sobolev1,2, V.Yu. Fridovsky3
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 2, Novosibirsk, 630090, Russia
3Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia



2.
BASITES OF THE VILYUI PALEORIFT: GEOCHEMISTRY AND SEQUENCE OF INTRUSIVE EVENTS

M.D. Tomshin1, A.G. Kopylova1, K.M. Konstantinov2,3, S.S. Gogoleva1
1Diamond and Precious Metals Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
2Research Geological Enterprise ALROSA, Chernyshevskoe Shosse 16, Mirnyi, 678174, Russia
3Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
Keywords: Средний палеозой, Ar/Ar геохронология , палеомагнитные исследования, дайковые пояса, долериты, Middle Paleozoic, 40Ar/39Ar geochronology, paleomagnetic studies, dike swarms, dolerites

Abstract >>
We present results of study of the basites of the Vilyui paleorift. The 40Ar/39Ar isotopic ages were used to establish the sequence of their intrusion, which lasted ~18 Myr. Dolerite sills of the Kontai-Dzherba zone were the first crystallizing phase (378.0-380.7 Ma), which was followed by the intrusion of dikes of the Vilyui-Markha zone (372-373 Ma). Dikes of the Chara-Sinsk zone were the last crystalizing phase (362-364 Ma). The prolonged plume-lithosphere interaction resulted in the successive enrichment of basaltic melt with titanium, phosphorus, REE, HSFE, and LILE. Accumulation of the melt and formation of a magmatic lens at the crust-mantle boundary led to early crystallization of the melt at a depth of 35-40 km from the paleosurface under reducing conditions at a temperature of 1450-1470 °C. We assume that the inception and sequent opening of the Vilyui paleorift were associated with the relative rotation of 22° of the Angara-Anabar block with respect to the Aldan block in Early Famennian time. The Euler pole of rotation was located in the southern part of the paleorift, and a melting zone was directly beneath it.



3.
THE NATURE OF THE HEAT SOURCE OF MAFIC MAGMATISM DURING THE FORMATION OF THE VILYUI RIFT BASED ON THE AGES OF DIKE SWARMS AND RESULTS OF NUMERICAL MODELING

O.P. Polyansky1, A.V. Prokopiev2, O.V. Koroleva2, M.D. Tomshin2, V.V. Reverdatto1, A.V. Babichev1, V.G. Sverdlova1, D.A. Vasiliev2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
Keywords: Дайка, рифтогенез, численное моделирование, Сибирская платформа, Якутско-Вилюйская крупная изверженная провинция, Dike, rifting, numerical modeling, Siberian Platform, Yakutsk-Vilyui Large Igneous Province

Abstract >>
Possible mechanisms of rifting and the thermal regime of the lithosphere beneath the rift zone of the Vilyui sedimentary basin are considered based on the available isotopic ages of dike swarms, rates of sedimentation, and results of numerical modeling. Temporal correlations between the intrusion of mafic magma and a sharp increase in the rate of subsidence and sedimentation in the rift basin prove the contribution of both plate-tectonic and magmatic factors to the formation of the Vilyui rift. The results show a relationship between the rapid extension of the lithosphere and the formation of mafic dike swarms in the Yakutsk-Vilyui Large Igneous Province of the Siberian Platform at the Frasnian-Famennian boundary, with a peak at ~374.1 Ma, and at the end of the Late Devonian, with a peak at ~363.4 Ma. There were two pulses of dike formation during the rapid subsidence of the basin basement in the period 380-360 Ma, with a sedimentation rate of 100-130 m/Myr, at a background rate of 10-20 m/Myr. Analysis of numerical thermomechanical models revealed that the best-fit model is that combining the mechanisms of intraplate extension (passive rifting) and the ascent of a mantle magmatic diapir (active rifting). A conclusion about the nature of the heat source of trap magmatism has been drawn: The plume-driven regime of the lithosphere can better explain the dynamics of extension during rifting than the decompression melting mechanism.



4.
AGE CONSTRAINTS AND TECTONIC SETTINGS OF METALLOGENIC AND MAGMATIC EVENTS IN THE VERKHOYANSK-KOLYMA FOLDED AREA

A.V. Prokopiev1, A.S. Borisenko2,3, G.N. Gamyanin1, V.Yu. Fridovsky1, L.A. Kondrat’eva1, G.S. Anisimova1, V.A. Trunilina1, E.A. Vasyukova2, A.I. Ivanov1, A.V. Travin2, O.V. Koroleva1, D.A. Vasiliev1, A.V. Ponomarchuk2,3
1Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
3Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Металлогения, месторождения, золото, серебро, олово, Ar/Ar и U-Pb геохронология , Верхояно-Колымская складчатая область, Metallogeny, mineral deposit, gold, silver, tin, 40Ar/39Ar and U-Pb geochronology, Verkhoyansk-Kolyma folded area

Abstract >>
The paper presents new isotope geochronological data for several mineral deposits, ore occurrences, and related igneous bodies (plutons and dikes) in the Verkhoyansk-Kolyma folded area, eastern Yakutia. Twenty-one 40Ar/39Ar mica and four U-Pb zircon dates provide the first age constraints on key metallogenic units in the area. The dating results allow correlation between tectonic, magmatic, and metallogenic events. The sampled mineral deposits within the Adycha-Taryn fault zone in the southeastern Verkhoyansk-Chersky orogen apparently formed at the Jurassic-Cretaceous boundary during the final phase of the collision between the Siberian (North Asian) craton and the Kolyma-Omolon microcontinent (Kupol’noe deposit and the early metallogenic pulse of the Malotarynskoe deposit, ~143-144 Ma) and in the latest Early Cretaceous, in the beginning of the orogen collapse (Tallalakh and Dora-Pil’ deposits and the Malotarynskoe late metallogenic pulse, ~126 Ma). According to the suggested new classification of metallogenic units, these deposits belong to the Late Jurassic-Early Cretaceous Yana-Kolyma metallogenic belt. The Kyuchus deposit (~106 Ma), the Deputatsky ore cluster (~106-113 Ma), and the Khotoidokh deposit (~116 Ma) in the northern Verkhoyansk-Kolyma folded area belong to the North Verkhoyansk metallogenic belt. Their origin was associated with accretional and collisional processes that produced the Novosibirsk-Chukchi orogen in the middle Cretaceous. The Mangazeya ore cluster (~100 Ma, Early-Late Cretaceous boundary) in the southwestern end of the North Tirekhtyakh magmatic transverse belt belongs to the West Verkhoyansk metallogenic belt. The Nezhdaninskoe, Zaderzhnoe, Kurum, and Kuta deposits of the South Verkhoyansk area (~125-120 and ~100-95 Ma) can be joined into a single Verkhoyansk-Okhotsk metallogenic belt. The belt resulted from accretion and collision along the East Asian active continental margin and the related formation of the South Verkhoyansk orogen in the Early Cretaceous.



5.
MESOZOIC LITHOSPHERIC MANTLE OF THE NORTHEASTERN SIBERIAN CRATON (evidence from inclusions in kimberlite)

N.S. Tychkov1,2, D.S. Yudin1, E.I. Nikolenko1, E.V. Malygina1, N.V. Sobolev1,2
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 2, Novosibirsk, 630090, Russia
Keywords: Литосферная мантия, кимберлит, мезозой, гранат, клинопироксен, Ar/Ar изотопное датирование , флогопит, Сибирская платформа, Lithospheric mantle, kimberlite, Mesozoic, garnet, clinopyroxene, 40Ar/39Ar dating, phlogopite, Siberian craton

Abstract >>
Several thousand clinopyroxene, garnet, and phlogopite inclusions of mantle rocks from Jurassic and Triassic kimberlites in the northeastern Siberian craton have been analyzed and compared with their counterparts from Paleozoic kimberlites, including those rich in diamond. The new and published mineral chemistry data make a basis for an updated classification of kimberlite-hosted clinopyroxenes according to peridotitic and mafic (eclogite and pyroxenite) parageneses. The obtained results place constraints on the stability field of high-Na lherzolitic clinopyroxenes, which affect the coexisting garnet and decrease its Ca contents. As follows from analyses of the mantle minerals from Mesozoic kimberlites, the cratonic lithosphere contained more pyroxenite and eclogite in the Mesozoic than in the Paleozoic. It virtually lacked ultradepleted harzburgite-dunite lithologies and contained scarce eclogitic diamonds. On the other hand, both inclusions in diamond and individual eclogitic minerals from Mesozoic kimberlites differ from eclogitic inclusions in diamond from Triassic sediments in the northeastern Siberian craton. Xenocrystic phlogopites from the D’yanga pipe have 40Ar/39Ar ages of 384.6, 432.4, and 563.4 Ma, which record several stages of metasomatic impact on the lithosphere. These phlogopites are younger than most of Paleozoic phlogopites from the central part of the craton (Udachnaya kimberlite). Therefore, hydrous mantle metasomatism acted much later on the craton periphery than in the center. Monomineral clinopyroxene thermobarometry shows that Jurassic kimberlites from the northeastern craton part trapped lithospheric material from different maximum depths (170 km in the D’yanga pipe and mostly ≤130 km in other pipes). The inferred thermal thickness of cratonic lithosphere decreased progressively from ~260 km in the Devonian-Carboniferous to ~225 km in the Triassic and to ~200 km in the Jurassic, while the heat flux (Hasterok-Chapman model) was 34.9, 36.7, and 39.0 mW/m2, respectively. Dissimilar PT patterns of samples from closely spaced coeval kimberlites suggest different emplacement scenarios, which influenced both the PT variations across the lithosphere and the diamond potential of kimberlites.



6.
NOBLE-METAL MINERALIZATION OF THE ADYCHA-TARYN METALLOGENIC ZONE: GEOCHEMISTRY OF STABLE ISOTOPES, FLUID REGIME, AND ORE FORMATION CONDITIONS

G.N. Gamyanin1,2, V.Yu. Fridovsky2, O.V. Vikent’eva1
1Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
2Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
Keywords: Адыча-Тарынская металлогеническая зона, благороднометалльная минерализация, стабильные изотопы, флюидные включения, генезис месторождений, Adycha-Taryn metallogenic zone, noble-metal mineralization, stable isotopes, fluid inclusions, genesis of deposits

Abstract >>
The regional geologic setting of the Adycha-Taryn metallogenic zone, one of the areas most productive for noble-metal mineralization in northeastern Russia, is discussed. The intricate metallogenic history of the zone and the prolonged geodynamic activity of its ore-hosting structures are documented. Different types of mineralization, such as hydrothermal-metamorphogenic, gold-bismuth, gold-quartz, gold-antimony, and silver-antimony, are described. New data on the isotopic compositions of oxygen in quartz, sulfur in sulfides, and oxygen and carbon in carbonates from different mineralization types are presented. The early metamorphogenic quartz beyond the ore zones has δ18O = +20.1 ± 2.0 ‰. At the gold-bismuth deposits, the δ18O values of quartz are within the narrow range of +12.5 ± 0.4 ‰. Quartz from the gold-quartz mineralization shows much wider variation in δ18O values, from +14.2 to +19.5 ‰. A similar range (δ18O = +16.5 to +19.8 ‰) is observed for the gold-antimony mineralization. Cryptograined quartz from the gold-antimony mineralization is enriched in light oxygen isotopes (δ18O = -3.2 to +4.7 ‰). The following δ34S values have been established in sulfides of mineralization of different types ( ‰): gold-bismuth, -3.7 to -2.2 (Apy) and -6.7 to -6.8 (Py); gold-quartz, -2.1 to +2.4 (Apy), -6.6 to +5.4 (Py), and -6.1 to +4.2) (Ant); gold-antimony - -2.0 to +1.6 (Apy), -3.5 to +2.1 (Py), and -5.3 to +0.2 (Ant); and silver-antimony, -2.0 to -1.9 (Apy), -2.2 ± 0.1 (Py), and -5.7 to -5.6 (Ant). The δ13C and δ18O values are contrasting in the studied types of mineralization, varying respectively from -6.9 to -5.9 ‰ and from +2.1 to +5.7 ‰, (gold-bismuth), from -9.1 to -6.1 ‰ and from +12.4 to 18.7 ‰ (gold-quartz), from -12.1 to -9.5 ‰ and from +15.0 to +16.3 ‰ (gold-antimony), and from -11.6 to -11.1 ‰ and from +1.5 to +4.7 ‰ (silver-antimony). Metamorphogenic calcites are rich in both heavy C (-1.1 to -1.7 ‰) and heavy O (+20.3 to +20.5 ‰) isotopes. Microthermometric study and crush-leach analysis of fluid inclusions have revealed differences in the composition of ore-forming fluids and formation conditions for different types of mineralization. The isotopic compositions of O, C, and S of mineral-forming fluids suggest a significant input of magmatic fluids to the formation of gold-bismuth and gold-antimony deposits, the contribution of metamorphic fluids increases at gold-quartz deposits, and meteoric water is involved in the formation of silver-antimony deposits.



7.
THE ZADERZHNinskoe GOLD DEPOSIT: MINERAL COMPOSITION, FLUID INCLUSIONS, AND AGE (South Verkhoyansk region)

L.A. Kondrat’eva, G.S. Anisimova, A.I. Zaitsev
Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
Keywords: Гранитоидный магматизм, метаморфизм, Au-Bi (Te), Au-Ag (Sb) оруденение, флюидные включения, Ar/Ar, Rb/Sr возраст, месторождение Задержнинское, Южное Верхоянье, Granitoid magmatism, metamorphism, Au-Bi (Te) and Au-Ag (Sb) mineralization, fluid inclusions, Ar/Ar and Rb-Sr ages, Zaderzhnoe deposit, South Verkhoyansk region

Abstract >>
Based on results of study of the regional position, chemical composition of ores, fluid inclusions, and age relationships between mineralization and igneous rocks, we propose a geological and genetic model for the formation of gold mineralization of the Zaderzhninskoe deposit. Mineralization is located in the tectonic node of the intersection of two regional structures in the supraintrusive zone of a latent granitoid pluton among the terrigenous rocks of the Verkhoyansk complex, which are regionally metamorphosed to the greenschist facies. The sequential deposition of three types of mineralization - Au-quartz (including early low-gold Au-As and late productive Au-Pb-Zn types), Au-rare-metal, and Au-silver - has been established. The Au-Bi (Te) assemblage contains native bismuth, bismuthine, hedleyite, Bi sulfotellurides, gustavite group minerals, and secondary minerals - Bi oxides and Bi tellurites with low-grade gold. Hg-containing electrum and kustelite, Ag-Sb and Ag-Pb-Sb sulfosalts, stutzite, Te-Pb-containing canfieldite, freibergite, and Au and Ag sulfides are indicator minerals of the Au-Ag (Sb) assemblage. Ore formation occurred at temperatures from 90 to 340 ºC, with the participation of lowly and moderately concentrated solutions with CO2 ± CH4 ± N2 gas phase. A decrease in temperature from Au-quartz mineralization (200-220 ºC) to the late epithermal one (160 ºC) and a slight increase in the concentration of solutions (up to 10 wt.% NaCl equiv.) have been established. The deposit resulted from the intricate multistage geodynamic evolution of the South Verkhoyansk region. Ore-forming processes are associated with the evolution of magmatic objects. Dating of igneous rocks yields the following ages: diorites - 130-137 Ma (Rb-Sr), spessartites - 126 ± 3 Ma (Rb-Sr), and kersantites - 115 ± 1.7 Ma (Ar/Ar). Early concordant Au-quartz (Au-As) mineralization of the deposit is comparable with metamorphic-related Au-quartz veins of the Yur-Bular type, and its age is taken as >137 Ma. The time of formation of Au-quartz (Au-Pb-Zn) mineralization is estimated at 123.5 ± 1.6 Ma (Ar/Ar) and is coeval with the time of intrusion of the Early Cretaceous granitoids of the South Verkhoyansk region. The imposed low-temperature mineralization undoubtedly has a younger age. Its formation was followed by the successive deposition of Au-rare-metal mineralization at the final stage of formation of granitoid plutons (~120 Ma) and Au-Ag mineralization in the period 100 ± 5 Ma, i.e., the time of formation of late-stage granodiorite-granite intrusions.



8.
MINERALOGICAL, GEOCHEMICAL, AND AGE CHARACTERISTICS OF THE ROCKS OF THE INAGLI DUNITE-CLINOPYROXENITE-SHONKINITE MASSIF WITH PLATINUM-CHROMITE AND Cr-DIOPSIDE MINERALIZATION (Aldan Shield)

A.V. Okrugin1, A.S. Borisenko2,3, I.R. Prokopiev2, A.I. Zhuravlev1
1Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
3Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Дуниты, шонкиниты, хромиты, диопсиды, платина, дифференциация магмы, Инаглинский массив, Dunites, shonkinites, chromites, diopsides, platinum, magma differentiation, Inagli massif

Abstract >>
We consider the mineralogical and geochemical features of the rocks of the Inagli dunite-clinopyroxenite-shonkinite massif with platinum-chromite and unique jewelry Cr-diopside mineralization, which is a reference object of concentric zonal complexes. The massif rocks, from dunites to pulaskites, including peridotites, clinopyroxenites, shonkinites, and melanocratic alkali syenites, form a single continuous comagmatic series. This is confirmed by a clear dependence of the compositions of olivine, pyroxene, phlogopites, and Cr-spinels on the MgO content of the rocks and on the behavior of trace elements in them. The similar compositions of pyroxenes and trace-element patterns of clinopyroxenite rocks and Cr-diopsidite veins indicate a genetic similarity of these rocks. The age and mineralogical and geochemical compositions of the rocks and the geologic and morphological features of the intrusion prove that the Inagli massif formed from high-K picritoid melts, which underwent gradual decompression solidification during the ascent and formed a cylindrical diapir-like body at the subsurface level in the Early Cretaceous. The new portions of differentiates supplied from the lower horizons of the magma column determined the complex composition of the massif: It has a concentric zonal structure cut by numerous radial-circular vein bodies of pegmatites and pure anchimonomineral rocks (Cr-diopsidites), in places, of jewelry quality.



9.
INDICATIVE FEATURES OF PLACER GOLD FOR THE PREDICTION OF THE FORMATION TYPES OF GOLD DEPOSITS (east of the Siberian Platform)

Z.S. Nikiforova, B.B. Gerasimov, E.G. Glushkova, A.G. Kazhenkina
Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
Keywords: Индикаторные признаки золота, россыпное золото, формационные типы месторождений, прогнозирование, Indicative features of gold, placer gold, formation types of deposits, prediction

Abstract >>
Prediction and search for gold deposits in the east of the Siberian Platform are problematic because the study area is overlain by a thick cover of MZ-KZ deposits. Search for gold deposits by the largest geological institutions using conventional methods have not yielded positive results, because the main attention was focused on the discovery of ancient gold-bearing conglomerates of the Witwatersrand type and on the evaluation of the gold ore potential of basic magmatism. Typomorphism of placer gold bears huge information about the genesis of native gold, both its primary endogenous origin and its exogenous transformation, which makes it possible to identify the formation type of mineralization, increases the reliability of the prediction of gold deposits, and ensures their purposeful search in the platform areas. The revealed indicative features of placer gold made it possible to substantiate the formation of the gold ore sources of Precambrian low-sulfide gold-quartz, gold-iron-quartzite, porphyry gold-copper, and gold-PGE mineralization and Mesozoic gold-silver, gold-rare-metal, and gold-sulfide-quartz mineralization in the east of the Siberian Platform. We have established that high-fineness placer gold with microinclusions of pyrite, arsenopyrite, quartz, and carbonates with recrystallized structures and lines of plastic deformation is specific to the ore sources of low-sulfide gold-quartz mineralization. A high content of Cu (up to 4 %) in flaky high-fineness gold is one of indicators of porphyry gold-copper mineralization. The angular shape of gold grains, the fine fraction and high fineness of gold, its completely recrystallized and regrown internal structure, and the permanent presence of Fe, Bi, and Cu microimpurities and hematite, ilmenite, and corundum microinclusions are typical of gold-iron-quartzite mineralization. Flaky and laminated high-fineness gold particles with steady Pt, Pd, and Ni impurities and Pt-mineral phases and Au-Pt intergrowths in them testify to the ore sources of gold-PGE mineralization. Laminated and cloddy gold fractions of > 0.25-2.0 mm, the medium and low fineness of gold, its single-crystal or, sometimes, porous internal structure, the wide range of microimpurities (Pb, Zn, As, Sb, Cu, Te, etc.), and microinclusions of native Ag, adularia, Sr-barite, and calcite are indicators of gold-silver mineralization. Laminated, dendritic, and cloddy-angular gold grains, wide variation in gold fineness (307-950 ‰), and the presence of microinclusions of native bismuth, maldonite, arsenopyrite, and silver tellurides are indicative of gold-rare-metal mineralization. Laminated and cloddy gold grains, their size varying from dust to >0.25 mm, their mono- and coarse-grained internal structure, wide variation in gold fineness (600-900 ‰), and the presence of Hg microimpurities (up to 6 % and more) and microinclusions of quartz, calcite, pyrite, arsenopyrite, tellurides, selenides, and REE phosphates point to gold-sulfide-quartz mineralization. The established placer gold indicators of the particular formation types of ore sources in the east of the Siberian Platform made it possible to predict Precambrian gold deposits with low-sulfide-gold-quartz mineralization similar to the Kirkland Lake and Porcupine mines and gold deposits with Mesozoic gold-silver mineralization similar to the Cripple Creek mine. The developed criteria for determining the types of mineralization by indicative features of placer gold give an insight into the ore genesis and can be successfully applied to prediction and search for gold deposits and to evaluation of their gold resources.



10.
NODULAR MONAZITE FROM PLACERS IN THE KULAR RIDGE (Arctic Siberia, Russia): COMPOSITION AND AGE

E.V. Lazareva1, S.M. Zhmodik1,2, A.V. Prokopiev3, N.S. Karmanov1, A.I. Sergeenko3
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 2, Novosibirsk, 630090, Russia
3Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
Keywords: Нодулярный монацит (куларит), редкоземельные элементы, Куларский кряж, Nodular monazite (kularite), rare-earth elements, Kular Ridge

Abstract >>
Nodular monazite occurs in metamorphic rocks worldwide and has zonal REE patterns. This paper focuses on the composition of nodular monazite hosted by Permian black shales of the Kular Ridge in the Kular-Nera terrane. This monazite variety (called kularite in the Russian literature) reaches commercial amounts in placers of the area. The contents of Ce, Nd, and La in the analyzed monazite nodules show correlations at Ce/Nd = 14.39La ± 0.0919 (in apfu) and Ce/Nd = 0.2318La ± 0.1135 (in wt.%) and vary regularly from core to rim. All monazite compositions fall on this trend, but specific grains may plot in its different parts. Thermodynamic calculations indicate that monazite forms via an intermediate precursor (LnPO4 · 2H2O). The Ce:La:Nd changes in different grains record Eh-pH variations during nucleation and a gradual temperature increase during subsequent growth. The Ce:La:Nd ratio changes partly in grain rims as a result of oxidative dissolution. Judging by the tectonic setting, REE came to the Kular-Nera rocks from the weathered Tomtor Nb-REE deposit, being transported by the Paleo-Khatanga River with monazite nanoparticles bound to the surface of clay minerals.



11.
Cr-SPINEL ASSEMBLAGE FROM THE UPPER TRIASSIC GRITSTONES OF THE NORTHEASTERN SIBERIAN PLATFORM

E.I. Nikolenko1, A.M. Logvinova1,2, A.E. Izokh1,2, V.P. Afanas’ev1, O.B. Oleynikov3, A.Ya. Biller3
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 2, Novosibirsk, 630090, Russia
3Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
Keywords: Шпинель, карнийский ярус, алмаз, щелочной магматизм, осадочный коллектор, триас, Сибирская платформа, Spinel, Carnian Stage, diamond, alkaline magmatism, sedimentary reservoir, Triassic, Siberian Platform

Abstract >>
An assemblage of Cr-spinels widespread in Carnian (Upper Triassic) diamondiferous deposits in the northeastern Siberian Platform is studied. Analysis of their morphology and chemical composition has revealed two dominant varieties of Cr-spinels and has demonstrated certain regularities in their distribution in the study area. Correlations have been established between the areal distribution of the recognized types of Cr-spinels and diamond varieties typical of kimberlite sources and between the distribution of Cr-spinels and rounded diamond dodecahedrons. The phase and chemical compositions of polyphase inclusions in the Cr-spinels are studied. The spatial arrangement of inclusions along the crystal growth zones indicates their primary genesis and trapping from the melt during crystallization. Compositional features of some minerals in the inclusions-SiO2 impurity in apatite and high CaO contents (0.2-0.8 wt.%) in olivines-point to a nonkimberlite source of these Cr-spinels. The presence of K- and Na-containing phases and calcite in the inclusions indicates saturation of the initial melt with alkalies, Ca, and CO2. The data obtained suggest that the numerous Late Vendian diatremes in K-rich alkaline basites of the Olenek Uplift area are the source of the dominant Cr-spinel variety.



12.
PROSPECTS OF SEARCH FOR DIAMONDiferous KIMBERLITES IN THE NORTHEASTern SIBERIAN PLATFORM

N.V. Sobolev1,2, A.V. Sobolev3, A.A. Tomilenko1, D.V. Kuz’min1,2, S.A. Grakhanov4, V.G. Batanova3, A.M. Logvinova1,2, T.A. Bul’bak1, S.I. Kostrovitskii5, D.A. Yakovlev5, E.N. Fedorova1, G.F. Anastasenko6, E.I. Nikolenko1, A.V. Tolstov7, V.N. Reutskii1
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 2, Novosibirsk, 630090, Russia
3V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russia
4Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
5A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
6St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034, Russia
7AK ALROSA Scientific Research and Geological Exploration Enterprise, ul. Lenina 6, Mirnyi, 678170, Republic of Sakha (Yakutia), Russia
Keywords: Литосферная мантия, гипабиссальный кимберлит, оливин, алмаз, мезозой, U/Pb изотопное датирование, циркон, перовскит, рутил, Сибирская платформа, Литосферная мантия, гипабиссальный кимберлит, оливин, алмаз, мезозой, U/Pb изотопное датирование, циркон, перовскит, рутил, Сибирская платформа, Lithospheric mantle, hypabyssal kimberlite, olivine, diamond, Mesozoic, U/Pb isotope dating, zircon, perovskite, rutile, Siberian Platform

Abstract >>
The objects of study are Triassic hypabyssal diamondiferous kimberlites with an age of 220-245 Ma, containing macrocrysts of unaltered olivine. The latter are close in the time of formation to the main stage of intrusion of the Siberian Trap Province (252 Ma), which lasted less than 1 Myr. A comparative high-precision analytical study of the Ti, Ca, Cr, and Al impurity patterns of about 1000 olivine macrocryst samples with a forsterite content Fo = [100Mg/(Mg + Fe)] of 78 to 93 has demonstrated the effect of traps on the lithospheric composition. A comprehensive comparative study of diamonds from northern placers and Triassic kimberlites, including determination of their carbon isotope composition, was performed. Chromatography-mass-spectroscopic analysis of submicron fluid inclusions in diamonds from northern placers and kimberlites has shown prevailing hydrocarbons of a wide range of compositions and subordinate contents of N2, H2O, and CO2. These findings, together with the results of previous studies of subcalcic Cr-pyropes and diamonds found in the Lower Carboniferous gritstones of the Kyutyungde graben, lead to the conclusion that the Toluopka kimberlite field is promising for Paleozoic kimberlites. The results of comprehensive studies of diamonds and indicator minerals and U/Pb isotope dating of numerous detrital zircon samples from the basal horizon of the Carnian Stage (Upper Triassic) of the Bulkur site in the lower reaches of the Lena River suggest the presence of diamondiferous kimberlites within the northeastern Siberian Platform. The age of the probable primary diamond sources in the study area can be evaluated by an integrated U/Pb isotope dating of zircons, perovskites, and rutiles from the developed diamond placers and from the basal horizon of the Carnian Stage.



13.
PHENANTHRENE BIOMARKERS IN THE ORGANIC MATTER OF PRECAMBRIAN AND PHANEROZOIC DEPOSITS AND IN OILS OF THE SIBERIAN PLATFORM

V.A. Kashirtsev1,2, T.M. Parfenova1,2, A.K. Golovko1, B.L. Nikitenko1,2, I.N. Zueva3, O.N. Chalaya3
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
3Institute of Oil and Gas Problems, ul. Oktyabr’skaya 1, Yakutsk, 677890, Russia
Keywords: Органическая геохимия, фенантрены, биомаркеры, битумоид, осадочные породы, нефть, Сибирская платформа, Organic geochemistry, phenanthrenes, biomarkers, bitumen, sedimentary rocks, oil, Siberian Platform

Abstract >>
The composition and distribution of phenanthrenes (polyaromatic compounds) have been studied in chloroform extracts from dispersed organic matter (OM) of clayey, siliceous, carbonate, and terrigenous rocks of different ages and facies and from some oils of the Siberian Platform. Phenanthrenes have been analyzed by gas chromatography-mass spectrometry. High contents of 1,7,8-trimethylphenanthrene and 1,1,7,8-tetramethyl-1,2,3,4-tetrahydrophenanthrene are present in the OM of Vendian and Cambrian carbonate-shale deposits and in ancient oils of the Nepa-Botuobiya and Anabar anteclises. The OM of Permian continental deposits and oils of the Vilyui syneclise is dominated by 1-methyl-7-isopropylphenanthrene (retene). A triangular diagram for identification of the types of original OM of rocks and classification of genetically related oils has been constructed based on the assessment of phenanthrene biomarker distribution. Putative pathways of the formation of phenanthrene biomarkers are discussed.