Mineralogy and PT formation conditions of lead-zinc ore at the Dzhimidon deposit, north Ossetia     

E. O. Groznova  M. G. Dobrovol’skaya  V. A. Kovalenker  K. V. Davydov  V. T. Bitarov  M. V. Razin 《Geology of Ore Deposits》2006,48(2):108-133

The mineralogy and PT formation conditions of the Dzhimidon Pb-Zn deposit in the Sadon ore district are considered. The deposit is localized in metamorphic rocks of the Buron Formation, which pertain to the pre-Jurassic basement (lower structural stage) and are cut through by Upper Paleozoic granitoids, and in the Lower Jurassic terrigenous sequence (upper structural stage). Orebodies as quartz-sulfide veins are mainly hosted in the metamorphic rocks. Galena, sphalerite, chalcopyrite, pyrite, pyrrhotite, and arsenopyrite are the most abundant sulfides, while quartz, carbonates, chlorite, sericite, and feldspar are gangue minerals. The bismuth mineralization identified at this deposit for the first time is represented by diverse phases of the Ag-Pb-Bi-S system. Five stages of the ore deposit formation are recognized: a premineral stage (quartz-feldspar), three ore-bearing stages (pyrite-arsenopyrite, pyrrhotite-chalcopyrite-sphalerite, and arsenopyrite-sphalerite-galena), and a postmineral stage (quartz-calcite); each stage comprises one or several mineral assemblages. The study of fluid inclusions in quartz, calcite, and sphalerite of the premineral, ore-forming, and postmineral stages has shown that the ore was deposited mainly from Na chloride solution with a salinity varying from >22 to <1.0 wt % NaCl equiv at a temperature from 460 to ～120°C and 430–290 bars pressure. The third stage was characterized by an abrupt increase in temperature and by the appearance of Mg(Fe,Ca) chloride solutions equally with Na chloride fluids, presumably owing to the emplacement of granite porphyry.  相似文献   

Radio and optical spectra of objects from three complete samples of radio sources     

V. L. Afanas’ev  S. N. Dodonov  A. V. Moiseev  A. G. Gorshkov  V. K. Konnikova  M. G. Mingaliev 《Astronomy Reports》2006,50(4):255-272

We present classifications, optical identifications, and radio spectra for 19 radio sources from three complete samples, with declinations 4°–6° (B1950, S _{3.9 GHz} > 200 mJy), 10°–12°30′ (J2000, S _{4.85 GHz} > 200 mJy), and 74°–75° (J2000, S _{4.85 GHz} > 100 mJy). We also present corresponding information for the radio source J0527+0331. The right ascensions are 0–24^h and the Galactic latitudes |b| > 15° for all the samples. Our observations were obtained with the 6 m telescope from the Special Astrophysical Observatory in the range 4000–9000 Å or 4000–7500 Å and the RATAN-600 radio telescope at frequencies in the range 0.97–21.7 GHz. We obtained flux densities for the radio sources and optical spectra for their optical counterparts. Nine objects were classified as quasars with redshifts from z = 1.029 to 3.212; nine objects are emission-line galaxies with redshifts from 0.172 to 0.546, and one is a galaxy with burstlike star formation at z = 0.156, and one is a BL Lac object with z = 0.509. The spectra of five radio sources were decomposed into extended and compact components. The radio source J0527+0331, identified with a BL Lac object, displays significant variations of time scales from several days to several years. Data on flux variations are presented for 11 radio sources, as well as their spectra at several epochs.  相似文献   

New data on Upper Kimmeridgian-Tithonian biostratigraphy and ammonites of the eastern Crimea     

V. V. Arkad’ev  M. A. Rogov 《Stratigraphy and Geological Correlation》2006,14(2):185-199

Based on ammonites, Upper Kimmeridgian sediments are first established in the Crimean Mountains. The Kimmeridgian-Tithonian boundary recognizable in a continuous section is placed inside the Dvuyakomaya Formation of uniform largely clayey sediments. Assemblages of Kimmeridgian ammonites Lingulaticeras cf. procurvum (Ziegler), Pseudowaagenia gemmellariana Oloriz, Euvirgalithacoceras cf. tantalus (Herbich), Subplanites sp.) and Tithonian forms (?Lingulaticeras efimovi (Rogov), Phylloceras consaguineum Gemmellaro, Oloriziceras cf. schneidi Tavera, and Paraulacosphinctes cf. transitorius (Oppel) are described. A new biostratigraphic scheme proposed for the upper Tithonian-Berriasian of the Crimean Mountains includes the following new biostratigraphic units: the Euvirgalithacoceras cf. tantalus Beds of the upper Kimmeridgian, ?Lingulaticeras efimovi Beds of the lower Tithonian, and Oloriziceras cf. schneidi and Paraulacosphinctes cf. transitorius beds of the upper Tithonian. The middle Tithonian is proposed to consist of the fallauxi and semiforme (presumably) zones. The ammonities found determine the early Kimmeridgian-Berriasian age of the Dvuyakornaya Formation that is most likely in tectonic contact with the underlying Khutoran Formation.  相似文献   

Computer microtomography of zircon: A new approach to the selection of targets for U-Pb geochronologic studies     

Yu. V. Plotkina  E. B. Sal’nikova  A. B. Kotov  M. D. Tolkachev  M. R. Pavlov 《Petrology》2006,14(2):201-208

The paper reports results obtained by the complex studying of zircon crystals from rocks of various genesis. Zircon is one of the minerals most often used as geochronometers. It also provides genetic information on superimposed processes that is “recorded” in the external and internal morphology of its crystals. This mineral is thoroughly examined to select its unaltered crystals for U-Pb dating by the single-grain method. Zircon grains are selected with the use of optical and electron microscopy and cathodoluminescence. This publication presents the first results obtained by examining zircon by computer microtomography (μCT) and the results of the studying of the external and internal structure by conventional techniques ([optical microscopy and SEM (SE and CL)]. The paper demonstrates the advantages of the application of the μCT techniques to the selection of targets for U-Pb zircon dating: there is no need for the special preparation of the samples and no material is destructed. However, this technique may be not informative enough if the zircon contains inherited core whose density does not differ from the density of the surrounding mineral.  相似文献   

Hydrothermal sulfide deposits of the Lucky Strike vent field, Mid-Atlantic Ridge     

Yu. A. Bogdanov  A. Yu. Lein  A. M. Sagalevich  A. A. Ul’yanov  S. A. Dorofeev  N. V. Ul’yanova 《Geochemistry International》2006,44(4):403-418

Several hydrothermal sulfide structures were sampled using Mir manned submersibles in the relatively shallow Lucky Strike vent field, Mid-Atlantic Ridge; the bathymetric position of these structures varies by approximately 100 m. The investigation of the chemical and mineral compositions of hydrothermal ore occurrences led to the conclusion that the initial high-temperature ore-bearing solution ascending toward the surface became unstable and experienced phase separation beneath the ocean floor. The phase separation was responsible for the bathymetric control of hydrothermal ore formation in the ocean.  相似文献   

Early Proterozoic syn-and postcollision granites in the northern part of the Baikal fold area     

A. M. Larin  E. B. Sal’nikova  A. B. Kotov  L. B. Makar’ev  S. Z. Yakovleva  V. P. Kovach 《Stratigraphy and Geological Correlation》2006,14(5):463-474

Early Proterozoic granitoids are of a limited occurrence in the Baikal fold area being confined here exclusively to an arcuate belt delineating the outer contour of Baikalides, where rocks of the Early Precambrian basement are exposed. Geochronological and geochemical study of the Kevakta granite massif and Nichatka complex showed that their origin was related with different stages of geological evolution of the Baikal fold area that progressed in diverse geodynamic environments. The Nichatka complex of syncollision granites was emplaced 1908 ± 5 Ma ago, when the Aldan-Olekma microplate collided with the Nechera terrane. Granites of the Kevakta massif (1846 ± 8 Ma) belong to the South Siberian postcollision magmatic belt that developed since ～1.9 Ga during successive accretion of microplates, continental blocks and island arcs to the Siberian craton. In age and other characteristics, these granites sharply differ from granitoids of the Chuya complex they have been formerly attributed to. Accordingly, it is suggested to divide the former association of granitoids into the Chuya complex proper of diorite-granodiorite association ～2.02 Ga old (Neymark et al., 1998) with geochemical characteristics of island-arc granitoids and the Chuya-Kodar complex of postcollision S-type granitoids 1.85 Ga old. The Early Proterozoic evolution of the Baikal fold area and junction zone with Aldan shield lasted about 170 m.y. that is comparable with development periods of analogous structures in other regions of the world.  相似文献   

青藏高原近地面层微气象学特征   总被引：12，自引：3，他引：12  

Liu Huizhi  Zhang Hongsheng  Bian Lin＇gen  Chen Jiayi  Zhou Mingyu  Xu Xiangde  Li Shiming  Zhao Yijun 《大气科学进展》2002,19(1):73-88

利用1998年5月-7月在改则、当雄和昌都三测站获得的近地面层气象要素变化的观测资料，分析了青藏高原近地面层风速、温度和湿度日变化特征及廓线规律，发现高原近地面层微气象学特征具有自己的特点；同时还讨论了高原近地面层白天出现的逆湿现象。  相似文献   

Variability of the photospheric radiation of active K-M dwarfs and their X-ray luminosities     

N. I. Bondar’ 《Astronomy Reports》2002,46(6):489-496

Variability of the photospheric radiation of 40 (dKe-dMe) dwarfs in the solar neighborhood due to variations in the spottedness of their surfaces is analyzed based on the behavior of their mean annual brightnesses over long time intervals. The amplitudes and characteristic time scales of the variations of the mean annual brightness are taken to be indicators of photospheric activity and were used to infer the levels of photospheric activity in the stars studied. The influence of axial rotation on the development of cyclic activity in young red dwarfs and F-M main-sequence stars is analyzed. The durations and amplitudes of the photospheric variability of rapidly rotating (dK0e-dK5e) stars testifies to a higher level of photospheric activity among red dwarfs and solar-type stars. The X-ray luminosities of these stars grow with the amplitude of the variations of the mean annual brightness. However, this is not typical of rapidly rotating M dwarfs, for which the X-ray emission varies by more than two orders of magnitude, although their degrees of spottedness are all virtually the same. A linear relationship between the X-ray and bolometric luminosities is observed for young (dKe-dMe) stars, with their ratios log(L _x/L _bol) being about ?3. These properties can be used to determine whether a red dwarf is a young star or is already on the main sequence.  相似文献   

Al hematites prepared by homogeneous precipitation of oxinates: material characterization and determination of the Morin transition     

G. M. da Costa  E. Van San  E. De Grave  R. E. Vandenberghe  V. Barrón  L. Datas 《Physics and Chemistry of Minerals》2002,29(2):122-131

A novel method for synthesis of aluminium hematites, based upon the homogeneous precipitation of Fe and Al oxinates in various proportions, is presented. The precursor precipitates are heated in air at 700?°C. X-ray diffraction, thermal analyses, BET, FTIR, optical reflection analysis, TEM and Mössbauer spectroscopy at room temperature and 80?K of the resulting products indicate that single-phase hematites are formed with structural Al substitution of up to 10 at%. Interestingly, the particle size (>100?nm) is not substantially reduced by the Al content. Although it remains difficult to obtain a homogeneously distributed Al substitution in the final hematite, this processing line offers a unique opportunity to separate the effects of grain size and Al substitution on the Morin transition temperature (T _M) of Al hematite. From the comparison between the present hematites and a series of Al-substituted hematites with lepidocrocite as precursor, it could be shown that the effect on T _M, associated with a change of a factor 10 in grain size, is about 1/3 of the effect caused by a change of 10 in the degree of substitution. Finally, it is suggested that proper thermal treatments under different conditions of the same precursors are likely to produce spinel phases.  相似文献   

Anhydrite-bearing rocks from the Rožná district (Moldanubian zone,Czech Republic): high-grade metamorphosed exhalites?     

Bohdan Kříbek  Jana Hladíková  Daniel Holeczy 《Mineralium Deposita》2002,37(5):465-479

Several types of anhydrite-bearing rocks have been found in the amphibolite-facies metamorphosed rocks at the north-eastern margin of the Moldanubian Zone. Anhydrite either forms monomineralic bands up to 40 cm thick, or occurs in the form of disseminated grains in surrounding calc-silicate gneiss together with feldspar, scapolite, amphibole, pyroxene, epidote and pyrite. The isotopic composition of sulphur ('³⁴S=30.6 to 32.3‰) and strontium (⁸⁷Sr/⁸⁶Sr=0.70797 to 0.70781) in anhydrite may indicate a marine source of sulphate. The isotopic ratio of strontium is in the same range as that of metamorphosed strata-bound barite-sulphide ores, which have been previously described in the same area. The '³⁴S values of coexisting pyrite range from 21.4 to 22.5‰, the (³⁴S_{anhydrite-pyrite} corresponding to the metamorphic temperature of 600 to 660 °C. In contrast to many submarine-exhalative deposits, the oxygen isotopic compositions of anhydrite ('¹⁸O=9.3 to 10.2‰) are lighter than that of barite ('¹⁸O=10.4 to 13.8‰). This indicates that the both minerals are not in isotopic equilibrium. Therefore, it is probable that anhydrite and barite from the Ro—ná district were deposited from fluids that contained different proportions of seawater and hydrothermal fluids or from hydrothermal fluids that underwent variable extent of oxygen isotope exchange with seafloor rocks. The '¹³C values in calcite ('¹³C=-17.2 to -18.7‰) from anhydrite-bearing rock are lower than those in distant marbles. As graphite is absent in anhydrite- and calcite-bearing rocks, impoverishment in the ¹³C isotope cannot be attributed to the graphite-carbonate isotopic exchange during metamorphism. It is proposed that low '¹³C values in carbonates are caused by pre-metamorphic oxidation of organic matter in course of hydrothermal processes. Anhydrite and anhydrite-bearing calc-silicate gneiss from the north-eastern part of the Moldanubian Zone are interpreted to be the high-grade metamorphosed analogue of anhydrite-rich exhalites commonly found in submarine-exhalative hydrothermal deposits.  相似文献