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Prokofiev V.,Moscow State University | Baksheev I.,Moscow State University | Zorina L.,Vinogradov Institute of Geochemistry | Belyatsky B.,Russian Academy of Sciences | And 2 more authors.
Geoscience Frontiers | Year: 2012

Zoned tourmaline (schorl-dravite) in the matrix of hydrothermal explosive breccia and ore veins in gold deposits, Chita region, Eastern Transbaikalia, Russia, are associated with Na- and K-rich porphyry-type subvolcanic intrusives. δ 18O values of tourmaline from three gold deposits (Darasun, Talatui, Teremkinskoye) are +8.3‰, +7.6‰, and +6.0‰ and calculated δ 18O values of fluids responsible for the tourmalinization are +7.3‰, +7.7‰, and +4.2‰, respectively. These data imply an igneous fluid source, except at the Teremkin deposit where mixing with meteoric water is indicated. Wide ranges of Fe 3+/Fe tot and the presence of vacancies characterize the Darasun deposit tourmaline indicating wide ranges of (O 2) and pH of mineralizing fluids. Initial stage tourmalines from the gold deposits of the Darasun ore district are dravite or high mg schorl. Second stage tourmaline is characterized by oscillatory zoning but with Fe generally increasing towards crystal rims indicating decreasing temperature. Third stage tourmaline formed unzoned crystals with x Mg (mole fraction of Mg) close to that of the first stage tourmaline, due to a close association with pyrite and arsenopyrite. From Fe 3+/Fe tot values, chemical composition and crystallization temperatures, logf(O 2) of mineralizing fluids ranged from ca. -25 to -20, much higher than for the gold-bearing beresite-listvenite association, indicating that tourmalinization was not related to gold mineralization. © 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved. Source


Sizova T.,Vinogradov Institute of Geochemistry | Radzhabov E.,Irkutsk State University
IEEE Transactions on Nuclear Science | Year: 2012

This paper reports the absorption spectra of photochromic centers in CaF 2 and SrF 2 crystals doped with Ce 3+ and Gd 3+ impurities and thermal decay of the centers in temperature range 80-500 K. The ionized photochromic color centers are generated in crystals under low-temperature X-rays irradiation. These centers are transformed into photochromic color centers upon heating of crystals. All color centers decay at temperature about 500 K. © 2012 IEEE. Source


Bindeman I.N.,University of Oregon | Leonov V.L.,Institute of Volcanology and Seismology | Izbekov P.E.,University of Alaska Fairbanks | Ponomareva V.V.,Institute of Volcanology and Seismology | And 9 more authors.
Journal of Volcanology and Geothermal Research | Year: 2010

The Kamchatka Peninsula in far eastern Russia represents the most volcanically active arc in the world in terms of magma production and the number of explosive eruptions. We investigate large-scale silicic volcanism in the past several million years and present new geochronologic results from major ignimbrite sheets exposed in Kamchatka. These ignimbrites are found in the vicinity of morphologically-preserved rims of partially eroded source calderas with diameters from ∼ 2 to ∼ 30 km and with estimated volumes of eruptions ranging from 10 to several hundred cubic kilometers of magma. We also identify and date two of the largest ignimbrites: Golygin Ignimbrite in southern Kamchatka (0.45 Ma), and Karymshina River Ignimbrites (1.78 Ma) in south-central Kamchatka. We present whole-rock geochemical analyses that can be used to correlate ignimbrites laterally. These large-volume ignimbrites sample a significant proportion of remelted Kamchatkan crust as constrained by the oxygen isotopes. Oxygen isotope analyses of minerals and matrix span a 3‰ range with a significant proportion of moderately low-δ18O values. This suggests that the source for these ignimbrites involved a hydrothermally-altered shallow crust, while participation of the Cretaceous siliceous basement is also evidenced by moderately elevated δ18O and Sr isotopes and xenocryst contamination in two volcanoes. The majority of dates obtained for caldera-forming eruptions coincide with glacial stages in accordance with the sediment record in the NW Pacific, suggesting an increase in explosive volcanic activity since the onset of the last glaciation 2.6 Ma. Rapid changes in ice volume during glacial times and the resulting fluctuation of glacial loading/unloading could have caused volatile saturation in shallow magma chambers and, in combination with availability of low-δ18O glacial meltwaters, increased the proportion of explosive vs effusive eruptions. The presented results provide new constraints on Pliocene-Pleistocene volcanic activity in Kamchatka, and thus constrain an important component of the Pacific Ring of Fire. © 2009 Elsevier B.V. All rights reserved. Source


Pechersky D.M.,Russian Academy of Sciences | Gil'manova D.M.,Kazan Federal University | Ivanov E.V.,Vinogradov Institute of Geochemistry | Kuz'min M.I.,Vinogradov Institute of Geochemistry | And 3 more authors.
Russian Geology and Geophysics | Year: 2013

We performed a thermomagnetic analysis of 91 samples and a probe microanalysis of five samples of sedimentary rocks from the lower zone of the borehole BDP-98 drilled at the bottom of Lake Baikal. The results show the scarcity of native iron: It was found only in five samples. Its concentration varies from ~10-5 to 7 × 10-4%. The distribution of native iron by content is bimodal, with a distinct "zero" mode. This scarcity of native iron in the Baikal sediments distinguishes them from continental (Eurasia) and oceanic (Atlantic) sediments of different ages. It is due to the high rate of sedimentation in the studied interval of BDP-98. © 2013. Source


Antipin V.,Vinogradov Institute of Geochemistry | Gerel O.,Mongolian University of Science and Technology | Perepelov A.,Vinogradov Institute of Geochemistry | Odgerel D.,Mongolian Academy of science | Zolboo T.,Vinogradov Institute of Geochemistry
Journal of Geosciences (Czech Republic) | Year: 2016

The Central Asian Orogenic Belt (CAOB) was a scene of intense granitoid magmatism during the Phanerozoic with formation of vast batholiths: Angara-Vitim and Daurian-Khentei. In the Late Paleozoic and Early Mesozoic times, the peripheral zones of batholiths underwent granitic magmatism associated with rare-metal mineralization. Petrological and geochemical studies show that the rare-metal Li–F granites formed, with a gap about 100 My, large igneous provinces of the Mongol-Okhotsk Belt. Late Paleozoic rare-metal granites build a series of multiphase plutons in the Baikal region (e.g. Kharagul 318 ± 7 Ma, Bitu-Dzhida 311 ± 10 Ma and Urugudei 321 ± 5 Ma). The early medium-grained biotite granites and leucogranites were followed by topaz-bearing microcline- and amazonite–albite granites and a series of dikes. The Early Mesozoic epoch was marked by the formation of the Daurian-Khentei Batholith (230–190 Ma) in the center of area and rifting zones with alkaline and rare-metal granite plutons on the peripheries. In contrast to the Late Paleozoic, small Early Mesozoic intrusions (e.g., Avdar Pluton ~10 km2, 212–209 Ma) of rare-metal Li–F granites within the Avdar-Khoshutul series of granitoids coexisted with sizable plutons (e.g., Janchivlan Pluton ~70 km2, 227–195.3 Ma). Rare-metal Li–F granites of the Janchivlan Pluton produced small domal intrusions composed of microcline–albite, amazonite–albite and albite– lepidolite granites. The Sn–Ta–Nb mineralization is associated with albite–lepidolite granites. The rare-metal granites of the Baikal region and Central Mongolia of contrasting ages show an identical geochemical signature of Li–F granites. It is expressed by increase in F, Li, Rb, Cs, Sn, Be, Ta and Pb and decrease in Sr, Ba, Zn, Zr, Th and U contents in course of multiphase intrusions formation. The geochemical data confirm the magmatic model for genesis of the studied rare-metal Li–F granites. However, this process of magma differentiation was terminated with formation of albitites, microclinites and muscovite greisens. The whole-rock geochemistry and isotopic composition of the granites points to the Precambrian crust of the Baikal region (T2DМ = 1.0–1.3 Ga) as the most likely source. We propose the formation of the initial granitic melts due to anatexis of the higher levels of the continental crust, with fluids released during granulite-facies metamorphism in the lower crust. The rare-metal Li–F granites of the studied provinces are intraplate formations geochemically different from the Early Paleozoic collisional granitoids. This could be caused by the influence of deep-seated source on the occurrence of rare-metal magmatism. © 2016, Czech Geological Survey. All rights reserved. Source

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