The composition and structure of aktashite from the Aktash deposit, Gorny Altai, Russia, have been studied by electron microprobe and X-ray structural analysis. On the basis of close compositions and crystal structures, the identity of aktashite from the Gal-Khaya and Aktash deposits has been demonstrated. Crystals of aktashite are of trigonal symmetry; the unit-cell dimensions are: a = 13.7500(4), c = 9.3600(3) Å, V = 532.54(8) Å3, space group R3, Z = 3 for the composition of Cu6Hg3As4S12, R = 0.043. The structure of aktashite as a framework of vertex-shared HgS4? and CuS4? tetrahedrons of the same orientation is intimately related to the sphalerite-type structure. The earlier identified uncommon cluster group [As4] has been verified and its parameters have been refined. It is shown that the structure may be represented as construction blocks (As4S12)12? packed according to the law of the distorted cubic I-cell. 相似文献
Seismoacoustic investigations with a high-resolution parametric echo-sounder “SES 2000 deep” carried out on cruises 33, 35, and 37 of the R/V Akademik Ioffe revealed several erosional-depositional contourite systems on the São Paulo Plateau escarpment and its toe in the South Atlantic. Two contourite terraces related to interfaces between different water masses are observable on the escarpment. These terraces presumably reflect the activity of internal waves and turbulent eddies. The São Paulo contourite channel and genetically related drift are traceable along the escarpment toe. Changes in planktonic foraminiferal assemblages in Core AI-2563 retrieved from the summit of the São Paulo contourite drift suggest a shallowing of the Weddell Sea Deep Water mass during glacial times. It is established that the contour current of the Weddell Sea Deep Water and Lower Circumpolar Water considerably affect the formation of contourite depositional systems on the escarpment and its toe. 相似文献
Temporal distributions of the isotopic composition in arid rain storms and in the associated runoff were investigated in
a small arid rocky basin in Israel. Customized rain and runoff samplers provided sequential water samples hermetically sealed
in high-density PVC bags. In several storms where the runoff was isotopically depleted, compared with the rainfall, the difference
could not be explained by fractionation effects occurring during overland flow. A water-balance study relating the runoff
discharge to rainfall over a rocky watershed showed that the entire discharge is produced by a very small segment (1–2 mm)
of the rain storm. The major objective, therefore, was to provide quantitative relations between segments of rainfall (rain
showers and rain spells) and runoff. The time distribution of the composition of stable isotopes (oxygen and hydrogen) was
used to quantify the correlation between the rain spell's amount and the consequent runoff. The aim of this work was to (a)
utilize the dynamic variations in the isotopic composition in rainfall and runoff and model the magnitude of surface-storage
capacity associated with runoff processes of overland flow, and (b) characterize the isotopic composition of the percolating
water with respect to the isotopic distribution in rainfall and runoff events. The conceptual model postulates an isotopic
mixing of overland flow with water within the depression storage. A transport model was then formulated in order to estimate
the physical watershed parameters that control the development of overland flow from a certain rainfall period. Part I (this
paper) presents the results and the assessment of the relative depression storage obtained from oxygen-18 and deuterium analyses
that lead to the physical and mathematical formulation of a double-component model of kinematic-wave flow and transport, which
is presented in Part II (accompanying paper).
Received, February 1997 · Revised, September 1997 · Accepted, September 1997 相似文献
The highly siderophile elements (HSE's: Ru, Rh, Pd, Re, Os, Ir, Pt and Au) and those elements with distribution coefficients between Fe-rich metal and silicate phases which exceed 104. The large magnitude of these distribution coefficients makes them exceedingly difficult to measure experimentally. We describe a new experimental campaign aimed at obtaining reliable values of DMmets/sil melt for selected HSE's indirectly, by measuring the solubilities of the pure metals (or simple HSE alloys) in haplobasaltic melts as a function of oxygen fugacity.
Preliminary results for Pd, Au, Ir and Re indicate that the HSE's may dissolve in silicate melts in unusually low valence states, e.g., 2+ for Ir and 1+ for the others. These unusual valence states may be important in understanding the geochemical properties of the HSE's. Inferred values of DMmet/sil melt from the solubility data at 1400°C and IW −1 are 107 for Pd and Au, and 109−1012 for Ir. Metal/silicate partition coefficients are thus confirmed to be very large, and are also different for the different HSE's.
A review of the abundance of the HSE's in the Earth's upper mantle shows that they are all present at 0.8% of chondritic, i.e. they have the same relative abundance, and the ratios of their concentrations are chondritic (e.g., Re/Os). Both the low degree of depletion (compared to the high values of DMmet/sil melt) and the chondritic relative abundances support the idea that the mantle's HSE's were added in a “late veneer” after the cessation of core formation. Sulfur is even more depleted in the mantle relative to CI chondrites than the HSE's: this implies a late veneer which was depleted in volatile elements, and which was added to a mantle stripped of S. Since considerable S dissolves in silicate melt, this further implies that core formation in the Earth either occurred under P−T conditions below the solicate solidus, or, if the process occurred over a range of temperatures in a cooling Earth, then the process continued down to conditions below the silicate solidus.
The chondritic relative abundances of the HSE's in the upper mantle argue for a chemically unstratified primitive mantle, unless the late veneer was mixed only into the upper mantle. 相似文献
The analysis of the bulk samples of ore veins from the Dzhimidon base-metal deposit in Northern Ossetia, Russia, has revealed
the vertical zoning of Cd and Zn distribution: the average (Cd/Zn) × 1000 ratio is 1.64 ± 0.17 at the lower level (1520 m,
adit no. 49), 4.23 ± 0.16, at the intermediate level (1640 m, adit no. 47), and 7.0 ± 0.3, at the upper level (1680 m, adit
no. 3). The average value of the (Cd/Zn) × 1000 ratio in the total sampling is 4.1 ± 0.2. The decrease in temperature up the
dip of ore veins is a possible cause of the established zoning. 相似文献
Data on the Ruza and Mozhaisk reservoirs are used to analyze the applicability of different sampling methods and bioindication systems for rapid water quality assessment. The collected data were analyzed with the use of twelve biotic indices and their modifications. The mean water quality estimate in the coastal zones of both reservoirs varied from “moderate” to “good” and corresponded to α-mesosaprobic zone. The best performance in saprobity assessment was demonstrated by Pantle–Buck index modified by M.V. Chertoprud in the coastal zone and Balushkina index in soft soils in the central zones of the reservoirs. It is proposed to extend the number of indicator taxa in Pantle–Buck index modified by M.V. Chertoprud by incorporating taxa typical of soft soils, in particular, Chironomid larvae from Chironomus plumosus group. Recommendations are given for carrying out express-monitoring of the state of reservoirs. 相似文献
This paper presents the results of the studies performed from aboard the R/V Akademik Boris Petrov of the Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, in 2002–2004 aimed at surveying
the sites of dumping of potentially dangerous objects in Stepovoy, Abrosimov, and Tsivol’ka bays of the Kara Sea. These studies
coupled the instrumental facilities of acoustic survey with the visual examination of the objects recovered and also included
sampling of the bottom sediments and near-bottom water in the vicinity of the objects and away from them. Subsequently, the
samples collected were analyzed using direct gamma spectrometry and radiochemical concentrating selected radionuclides. This
allowed us to obtain a statistically reliable database on the specific concentrations of radionuclides (cesium, strontium,
cobalt, and plutonium) in the water column and in the bottom sediments. In selected parts of Stepovoy and Abrosimov bays,
at the sites where containers were located, local areas with contaminated bottom sediments were registered in the immediate
vicinity of the objects, in which significant concentrations of Cs-137 were detected. We also carried out experiments with
the samples of the collected bottom sediments on the determination of the kinetic parameters of sorption in the sediment-solution
system using the method of radioactive indicators. Taking into account the hydrological conditions, the results obtained allow
one to explain particular features of radioactivity distribution in selected aquatic areas. Based on a comparison between
the results of the studies performed in 1992–1994 and 2002–2004, we estimated the dynamics of the changes in the mean level
of specific concentrations of radionuclides in the regions of the location of sunken objects in shallow-water bays of the
Novaya Zemlya Archipelago. The registration of elevated concentrations of corrosive elements in the surface layers of the
bottom sediments in these zones suggests a necessity of a multidisciplinary study consisting of regular repeated measurements
at reference points in different areas aimed at before-the-fact prevention of possible leakages of radioactive substances
from the sunken objects, which might result in a significant contamination of the environment.
Original Russian Text ? O.V. Stepanets, L.A. Kodina, A.N. Ligaev, A.P. Borisov. G.Yu. Solov’eva, 2006, published in Geokhimiya,
2006, No. 12, pp. 1315–1324. 相似文献
The aim of this study was to determine at which parameters hydrothermal systems generate rich veins with bulk sphalerite contents
of 30% and local concentrations in vein cross sections up to 60–70% and more. Such contents were found in the vein bodies
of the Dzhimi deposit in the Sadon ore district, North Osetiya. For this purpose, we examined the thermodynamic models of
the formation of base-metal filling veins. Ore-bearing fluids are formed in the root part of the hydrothermal system by the
interaction of barren solutions with the host rocks (granites), which contain background contents of ore elements. The thermodynamic
simulations were conducted for the system H-O-K-Na-Ca-Mg-Al-Si-Fe-C-Cl-S-Zn-Pb-Cu, which is described by 54 minerals of constant
and variable composition and 78 aqueous species. The calculations for the mobilization zone were carried out for the temperature
range of 360–440°C (through 10°C) and pressures of 600–1200 bar (with a 100 bar step). At each of the indicated temperature
and pressure values, 100 waves (portions) of primary barren solution were subsequently passed through the granites. More than
20 complete models of the formation of filling veins (each model involving from 1000 to 1300 calculations) were constructed
for individual T-P points in the mobilization zone, which was modeled by a sequence of multiwave step flowing reactors with a step of 10°C from
350–420 to 100°C at a constant pressure within the range of 600–1100 bar. We studied the effect of different background contents
of Zn and Pb in granites on the efficiency of mobilization and ore formation and compared the relations in the naturally occurring
distribution of ore elements along the continuous cross sections through Pb-Zb veins with the results of thermodynamic simulation.
It was established that ore bodies with indicated bulk and local cross sectional contents of sphalerite could be formed in
a narrow range of conditions in the mobilization zone (410–440°C and 900–1200 bar) and elevated background contents of Zn
(more than 0.007 wt %) in the host granite. The maximum sphalerite contents (bulk and local in vein cross sections) are achieved
updip the model veins within the temperature range of 150–200°C.
Original Russian Text ? M.V. Borisov, D.A. Bychkov, Yu.V. Shvarov, 2006, published in Geokhimiya, 2006, No. 11, pp. 1218–1239. 相似文献
The solubility of Ni in silicate melts with variable SiO2 content was studied at a total pressure of 1 atm within a wide range of temperature and oxygen fugacity. The maximum solubility of Ni (minimum activity coefficient of NiO) was observed in melts with ~55–57 wt % SiO2, regardless of temperature and oxygen fugacity. Melts beyond this range showed significantly lower Ni solubility and, correspondingly, higher NiO activity coefficients. The analysis of our results and literature data led us to the conclusion that the NBO/T (number of nonbridging oxygen atoms per tetrahedrally coordinated atom) is inadequate to describe the effect of melt composition on Ni solubility. 相似文献