Relationship of F-Be mineralization to granites and syenites at the Ermakovka deposit (Western Transbaikalia)

The paper presents the mineralogical and geochemical characteristics of two groups of hydrothermal rocks and their relation with subalkaline granites of the Ermakovskoe deposit. The first group includes fluorite-phenakite-bertrandite ore bodies, occurring outside the granite massif. The second group is presented by silicification bodies with sulfates, phosphates, kaolinite, muscovite and hematite. It bears REE (rare earth elements) mineralization (monazite, florencite, xenotime) and occurs within the massif. Our research included isotopic analyses of Sr, Nd and O, studies of trace, including rare-earth element compositions and age determination (U-Pb) of apatite from F-Be ores. Geochemical and isotopic studies are not according with relation between F-Be ores and granites. This is proven by the absence of Be-mineralization in granites and schlieren pegmatites, and a sharp difference in composition of their fluid phases. A reductive fluid specification forming F-Be ores (containing CH4, H2, N2, CO2 and H2S), contrasts sharply with fluid specification of granites. The granites are characterized by high oxygen fugacity, due to ferrous iron, sulfates and phosphates. Besides isotopic composition of oxygen in quartz (7.4 and 5.1‰ δ18О V-SMOW respectively), initial Sr ratios (0.7056-0.7065 and 0.707-0.709 respectively) and REE compositions are different

COMPOSITIONAL FEATURES AND AGE OF ALKALINE GRANITES OF THE INGUR MASSIF, WESTERN TRANS-BAIKAL AREA

The Ingur alkaline granite massif and the associated Zr-Nb occurrence make up part of the largest Mongolian-Trans-Baikal alkaline granitoid provinces. The massif is composed of arfvedsonite, biotite, and alaskite granites. High content of HREE determines the low La/Ybn (2–7) value and a negative europium anomaly (Eu/Eu*≈0.17). They are depleted in Ba, Sr and enriched in Nb, Ta, Zr, Hf and Y. According to their geochemical properties the rocks of the massif belong to the A-type granites. The rare-metal mineralization of the Ingur granites mainly involves zircon, bastnäsite, monazite, and xenotime. The U-Pb age determined by SHRIMP II with zircon from arfvedsonite granites (272 Ma) indicates the Late Permian formation

Uakitite, VN, a new mononitride mineral from uakit iron meteorite (IIAB)

Uakitite was observed in small troilite–daubréelite (±schreibersite) inclusions (up to 100 µm) and in large troilite–daubréelite nodules (up to 1 cm) in Fe-Ni-metal (kamacite) of the Uakit iron meteorite (IIAB), Republic of Buryatia, Russia. Such associations in the Uakit meteorite seemed to form due to high-temperature (>1000 °C) separation of Fe-Cr-rich sulfide liquid from Fe-metal melt. Most inclusions represent alternation of layers of troilite and daubréelite, which may be a result of solid decay of an initial Fe-Cr-sulfide. These inclusions are partially resorbed and mainly located in fissures of the meteorite, which is now filled with magnetite, and rarely other secondary minerals. Phase relations indicate that uakitite is one of the early minerals in these associations. It forms isometric (cubic) crystals (in daubréelite) or rounded grains (in schreibersite). The size of uakitite grains is usually less than 5 µm. It is associated with sulfides (daubréelite, troilite, grokhovskyite), schreibersite and magnetite. Carlsbergite CrN, a more abundant nitride in the Uakit meteorite, was not found in any assemblages with uakitite. Physical and optical properties of uakitite are quite similar to synthetic VN: yellow and transparent phase with metallic luster; Mohs hardness: 9–10; light gray color with a pinky tint in reflected light; density (calc.) = 6.128 g/cm3. Uakitite is structurally related to the osbornite group minerals: carlsbergite CrN and osbornite TiN. Structural data were obtained for three uakitite crystals using the electron backscatter diffraction (EBSD) technique. Fitting of the EBSD patterns for a synthetic VN model (cubic, Fm-3m, a = 4.1328(3) Å; V = 70.588(9) Å3; Z = 4) resulted in the parameter MAD = 0.14–0.37° (best-good fit). Analytical data for uakitite (n = 54, in wt. %) are: V, 71.33; Cr, 5.58; Fe, 1.56; N, 21.41; Ti, below detection limit (<0.005). The empirical formula (V0.91Cr0.07Fe0.02)1.00N1.00 indicates that chromium incorporates in the structure according to the scheme V3+ → Cr3+ (up to 7 mol. % of the carlsbergite end-member). © 2020 by the authors. Licensee MDPI, Basel, Switzerland.Russian Foundation for Basic Research, RFBR: 17-05-00129, IGM SD 0330-2016-0005Government Council on Grants, Russian FederationMinistry of Science and Higher Education of the Russian FederationFunding: The investigations were partly supported by RFBR (grant 17-05-00129) and the State assignment project (IGM SD 0330-2016-0005). This work was also supported by the Initiative Project of Ministry of Science and Higher Education of the Russian Federation and by Act 211 of the Government of the Russian Federation, agreement no. 02.A03.21.0006

ОСОБЕННОСТИ ВЕЩЕСТВЕННОГО СОСТАВА И ВОЗРАСТ ЩЕЛОЧНЫХ ГРАНИТОВ ИНГУРСКОГО МАССИВА, ЗАПАДНОЕ ЗАБАЙКАЛЬЕ

The Ingur alkaline granite massif and the associated Zr-Nb occurrence make up part of the largest Mongolian-Trans-Baikal alkaline granitoid provinces. The massif is composed of arfvedsonite, biotite, and alaskite granites. High content of HREE determines the low La/Ybn (2–7) value and a negative europium anomaly (Eu/Eu*≈0.17). They are depleted in Ba, Sr and enriched in Nb, Ta, Zr, Hf and Y. According to their geochemical properties the rocks of the massif belong to the A-type granites. The rare-metal mineralization of the Ingur granites mainly involves zircon, bastnäsite, monazite, and xenotime. The U-Pb age determined by SHRIMP II with zircon from arfvedsonite granites (272 Ma) indicates the Late Permian formation.Ингурский массив щелочных гранитов и связанное с ним Zr-Nb проявление входят в состав Монголо-Забайкальской щелочно-гранитоидной провинции. Массив сложен арфведсонитовыми, биотитовыми и аляскитовыми гранитами. Для них характерно высокое содержание тяжелых РЗЭ, что определяет низкую величину La/Ybn (2–7), и отрицательная европиевая аномалия (Eu/Eu*≈0.17). Они обеднены Ba, Sr и обогащены Nb, Ta, Zr, Hf, Y. По своим геохимическим характеристикам породы массива относятся к А-типу гранитов. Редкометалльная минерализация гранитов Ингурского массива представлена в основном цирконом, бастнезитом, монацитом, ксенотимом. U-Pb возраст (SHRIMP II), определенный по циркону из арфведсонитовых гранитов (272 млн лет), указывает на их раннепермский возраст

СОСТАВ, ВОЗРАСТ И ГЕОДИНАМИЧЕСКАЯ ПОЗИЦИЯ ЩЕЛОЧНЫХ ПОРОД БОРГОЙСКОГО И БОЦИНСКОГО МАССИВОВ (ДЖИДИНСКАЯ ЩЕЛОЧНАЯ ПРОВИНЦИЯ)

The Borgoy and Botsy massifs are a part of the Dzhida alkaline province of the Western Transbaikalia. It has been stated that the rocks of the Borgoy massif were formed during the period from 246 to 243 Ma, which coincides with the formation period of the Permian-Triassic alkaline magmatic rocks common in the Vitim province. The age obtained from the zircons in the Botsy massif (121±1.0 Ma) is typical of the final stage of the transformation of the rocks related to rifting and alkali basalt lava flow. The presence of negative Nb-Ta anomaly and a relative enrichment in Rb, Ba, Sr and U imply interaction between the material of the plume and the earlier accretionary complexes of the subduction zones.Боргойский и Боцинский массивы входят в состав Джидинской щелочной провинции Западного Забайкалья. Установлено, что породы Боргойского массива были сформированы в интервале 246–243 млн лет и совпадают с пермско-триасовым этапом формирования щелочных магматических пород, распространенных в Витимской провинции. Полученный возраст по цирконам Боцинского массива (121±1.0 млн лет) характеризует заключительный этап преобразования пород, связанный с рифтогенезом и излиянием щелочных базальтов. Наличие отрицательной Nb-Ta-аномалии и относительное обогащение Rb, Ba, Sr и U свидетельствуют о вероятном взаимодействии вещества плюма с ранее сформированными аккреционными комплексами зон субдукции

МАФИЧЕСКИЕ ВКЛЮЧЕНИЯ И МИНГЛИНГ‐СТРУКТУРЫ В АПЛИТАХ ОШУРКОВСКОГО МАССИВА (ЗАПАДНОЕ ЗАБАЙКАЛЬЕ)

Our study of aplite dykes cross‐cutting the Oshurkov basite massif revealed drop‐shaped inclusions of the monzonite composition. These are crystallized drops of basite melts, which show traces of the interaction with the host acidic melt. The Ar‐Ar method was applied to determine the age of the aplites (114.9 Ma for biotite) and the monzonite inclusions (123.3 Ma for amphibole).Статья посвящена вещественному исследованию даек аплитов, секущих Ошурковский базитовый массив. В нескольких телах аплитов обнаружены каплевидные включения монцонитового состава. Установлено, что они являются закристаллизованными каплями базитового расплава и имеют следы взаимодействия с вмещающим кислым расплавом. Ar‐Ar методом определен возраст аплитов (по биотиту – 114.9 млн лет) и монцонитовых включений (по амфиболу – 123.3 млн лет)

ВОЗРАСТ И ИСТОЧНИКИ РЕДКОЗЕМЕЛЬНО-ФЛЮОРИТОВЫХ ПРОЯВЛЕНИЙ ЮЖНОЕ И УЛАН-УДЭНСКОЕ, СВЯЗАННЫХ С КАРБОНАТИТОВЫМ МАГМАТИЗМОМ (ЗАПАДНОЕ ЗАБАЙКАЛЬЕ, РОССИЯ)

The article presents new data on the age and isotopic (Sr, Nd) characteristics of the Yuzhnoe and Ulan-Ude REE-fluorite occurrences, paragenetically related to alkaline carbonatite magmatism. Age estimates of the fluorite-containing rocks were obtained from bastnaesites using U-Th-Pb (LA-ICP-MS) method and are 130.2±1.1 and 136.6±1.9 Ma for the Yuzhnoe and Ulan-Ude occurrences, respectively. The ƐNd(T) values of the bastnaesites vary from –7.41 to –6.08 for the Yuzhnoe occurrence and from –4.28 to –2.67 for the Ulan-Ude occurrence. The Yuzhnoe carbonatites are characterized by 87Sr/86Sr(I) ratios ranging from 0.705883 to 0.706011, and 87Sr/86Sr(I) ratios obtained for the Ulan-Ude bastnaesite-fluorite rocks are ranging from 0.70683 to 0.70687. The age estimates are consistent with the published geochronological data on alkaline carbonatite magmatism of the Central Asian orogenic belt related to Late Mesozoic intraplate magmatism and rifting. Isotopic Sr-Nd signatures of bastnaesite, as well as of the Yuzhnoe carbonatites and the Ulan-Ude bastnaesite-fluorites, indicate that their source rocks came from the enriched lithospheric mantle.В статье представлены новые данные о возрасте и изотопные (Sr, Nd) характеристики для редкоземельно-флюоритовых проявлений Южное и Улан-Удэнское, парагенетически связанных с щелочным карбонатитовым магматизмом. Возрастные оценки флюоритсодержащих пород были получены U-Th-Pb (LA-ICP-MS) методом по бастнезитам и составляют 130.2±1.1 и 136.6±1.9 млн лет для Южного и Улан-Удэнского проявлений соответственно. Значения ƐNd(T) для бастнезита проявления Южное варьируются в диапазоне от –7.41 до –6.08. Для бастнезитов проявления Улан-Удэнского установлены значения ƐNd(T) от –4.28 до –2.67. Карбонатиты проявления Южное характеризуются 87Sr/86Sr(I) в диапазоне от 0.705883 до 0.706011, а в бастнезит-флюоритовых породах Улан-Удэнского проявления значения 87Sr/86Sr(I) составляют 0.70683–0.70687. Полученные возрастные оценки согласуются с опубликованными геохронологическими данными по щелочному карбонатитовому магматизму Центрально-Азиатского складчатого пояса, связанному с позднемезозойской внутриплитной рифтогенной магматической активностью. Изотопные Sr-Nd характеристики бастнезита, а также карбонатитов проявления Южное и бастнезит-флюоритовых пород проявления Улан-Удэнское свидетельствуют в пользу генерации их источников из обогащенной литосферной мантии

MAFIC INCLUSIONS AND MINGLING STRUCTURES IN APLITES OF THE OSHURKOV MASSIF (WESTERN TRANSBAIKALIA)

Our study of aplite dykes cross‐cutting the Oshurkov basite massif revealed drop‐shaped inclusions of the monzonite composition. These are crystallized drops of basite melts, which show traces of the interaction with the host acidic melt. The Ar‐Ar method was applied to determine the age of the aplites (114.9 Ma for biotite) and the monzonite inclusions (123.3 Ma for amphibole)

Relationship of F-Be mineralization to granites and syenites at the Ermakovka deposit (Western Transbaikalia)

The paper presents the mineralogical and geochemical characteristics of two groups of hydrothermal rocks and their relation with subalkaline granites of the Ermakovskoe deposit. The first group includes fluorite-phenakite-bertrandite ore bodies, occurring outside the granite massif. The second group is presented by silicification bodies with sulfates, phosphates, kaolinite, muscovite and hematite. It bears REE (rare earth elements) mineralization (monazite, florencite, xenotime) and occurs within the massif. Our research included isotopic analyses of Sr, Nd and O, studies of trace, including rare-earth element compositions and age determination (U-Pb) of apatite from F-Be ores. Geochemical and isotopic studies are not according with relation between F-Be ores and granites. This is proven by the absence of Be-mineralization in granites and schlieren pegmatites, and a sharp difference in composition of their fluid phases. A reductive fluid specification forming F-Be ores (containing CH4, H2, N2, CO2 and H2S), contrasts sharply with fluid specification of granites. The granites are characterized by high oxygen fugacity, due to ferrous iron, sulfates and phosphates. Besides isotopic composition of oxygen in quartz (7.4 and 5.1‰ δ18О V-SMOW respectively), initial Sr ratios (0.7056-0.7065 and 0.707-0.709 respectively) and REE compositions are different