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21.
A two-stage evolution model for the Amantaytau orogenic-type gold deposit in Uzbekistan 总被引：4，自引：0，他引：4
Jan Pasava Hartwig Frimmel Anna Vymazalová Petr Dobes Alexandr V. Jukov Rustam I. Koneev 《Mineralium Deposita》2013,48(7):825-840
A lithogeochemical, mineral chemical, isotopic, and fluid inclusion study of barren, low-, and high-grade Au-mineralized samples from the shear zone-hosted Amantaytau gold deposit, Uzbekistan, shows that the local host rocks, Late Ordovician–Earlz Silurian carbonacous shales, are likely to have been an important source of Au, As, Ni, and S in the formation of the deposit. Syn-depositional pyrite in these shales contains on average 0.23 ppm Au, 1,083 ppm As, and 861 ppm Ni. The distribution of rare earth elements (REE) indicates a homogeneous source of light REE, whereas the heavy REE distribution reflects most likely primary variations in the sediments. The mineralized zone is marked by a positive Eu anomaly, which supports reducing conditions during the mineralization. A hydrothermal overprint by an aqueous–carbonic fluid is reflected in a high-grade Au-mineralized sample by δ13C values of ?13.0?‰ (V-PDB). The δ 34S values in pyrite (?0.13 to +7.30?‰ CDT) from barren and mineralized samples are consistent with marine sulfate being the principal source of the ore sulfur. Assuming a formation temperature of between 300 and 400 °C for the main stage of mineralization, as indicated by the alteration mineral assemblage, the calculated δ 18Ofluid is between 9.5 and 13.4?‰ V-SMOW, which points at a metamorphic origin of the ore fluid. 相似文献
22.
Sergey Alexandrovich Gorbarenko Evgenia L’vovich Goldberg Michaele Kashgarian Tat’yana Alekseevna Velivetskaya Sergey Petrovich Zakharkov Vladimir Stepanovich Pechnikov Alexandr Anatol’evich Bosin Olga Yur’evna Psheneva Elena Diamilevna Ivanova 《Journal of Oceanography》2007,63(4):609-623
The paper presents the records of several paleoproductivity proxies (PP) (biogenic opal and Ba (Si_bio, Ba_bio), organic carbon
(C_org) and carbonate Ca_carb, chlorin and benthic foraminifera abundance (BFA)) in sediments of the Okhotsk Sea for the last
80 kyr with a resolution of ∼100–300 years. The sediment age model was based on the AMS 14C data, records of benthic foraminifera δ18O, paleointensity of the Earth’s geomagnetic field and magnetic susceptibility. PP values demonstrate series of severe prolonged
productivity drops in the Okhotsk Sea followed by a sharp increase during the last glaciation. On the basis of quantitative
estimations of the paleoproductivity in the Okhotsk Sea during the cold MIS 2 and warm Holocene (Gorbarenko and Goldberg,
2005), it is suggested that the millennium scale relationship in productivity-climate changes of this basin was similar: an
increase in the sea’s productivity was related with regional climate warming and vice-versa. The PP records of productivity/climate
oscillations in the Okhotsk Sea during MIS 2–4 occurred contemporaneously with the North Atlantic cold Heinrich events (HE)
and Greenland Dansgaard-Oyeshger interstadial (DOI). Observed successions of prolonged climate cooling events followed by
rapid, abrupt warming are similar to climate and environmental oscillations in the N. Atlantic and Greenland, that confirms
the millennium-scale climate changes synchronicities in the Northern Hemisphere including the far NW Pacific, the hydrology
and climate conditions of which are close to those of the Okhotsk Sea. Synchronism of the N. Hemisphere severe cooling (including
the Okhotsk Sea) with the Antarctic warming suggests that mechanisms of the “seesaw” effect (Blunier and Brook, 2001) in the
low latitude heat redistribution between high latitudes of both hemispheres were more complicated than direct NADW formation
forcing and encompasses the global atmospheric reorganization. Within the PP used a closer connection in the Okhotsk Sea millennium
oscillations was observed for the C_org, BFA and chlorin; Ba_bio increases more closely to DOI. Si_bio variability does not
show any evident correlation with productivity changes. 相似文献
23.
24.
Disappointment with the results of forced amalgamation programs across almost all Australian local government jurisdictions has created great interest in shared service models as an alternative method of improving the operational efficiency of local councils, while at the same time preserving local democracy and local autonomy. While an embryonic literature on shared service provision in the Australian municipal milieu does exist, much remains to be done. This paper seeks to contribute to this nascent literature in two main ways: (a) to locate shared services in local government within broader global trends and theoretical disputations on devolution and local economic development, highlighting the importance of political geography in these debates; and (b) in the light of this complexity and ambiguity, develop a new typology of local government shared service provision to inform public policy making on real-world problems in Australian local government. 相似文献
25.
Recent dedicated Hinode polar region campaigns revealed the presence of concentrated kilogauss patches of the magnetic field in the polar regions of the Sun, which are also shown to be correlated with facular bright points at the photospheric level. In this work, we demonstrate that this spatial intermittency of the magnetic field persists even up to the chromospheric heights. The small-scale bright elements visible in the bright network lanes of the solar network structure as seen in the Ca ii H images are termed network bright points. We use special Hinode campaigns devoted to the observation of polar regions of the Sun to study the polar network bright points during the phase of the last extended solar minimum. We use Ca ii H images of chromosphere observed by the Solar Optical Telescope. For magnetic field information, level-2 data of the spectro-polarimeter is used. We observe a considerable association between the polar network bright points and magnetic field concentrations. The intensity of such bright points is found to be correlated well with the photospheric magnetic field strength underneath with a linear relation existing between them.
相似文献26.
Nadezhda Alexandrovna Krivolutskaya Alexandr Vladimirovich Sobolev Sergey Grigor’evich Snisar Bronislav Iosiphovich Gongalskiy Dmitry Vladimirovich Kuzmin Folkmar Hauff Irina Nikolaevna Tushentsova Natalya Mikhailovna Svirskaya Natalya Nikolaevna Kononkova Tatyana B. Schlychkova 《Mineralium Deposita》2012,47(1-2):69-88
We report new data on the stratigraphy, mineralogy and geochemistry of the rocks and ores of the Maslovsky Pt–Cu–Ni sulfide deposit which is thought to be the southwestern extension of the Noril’sk 1 intrusion. Variations in the Ta/Nb ratio of the gabbro-dolerites hosting the sulfide mineralization and the compositions of their pyroxene and olivine indicate that these rocks were produced by two discrete magmatic pulses, which gave rise to the Northern and Southern Maslovsky intrusions that together host the Maslovsky deposit. The Northern intrusion is located inside the Tungusska sandstones and basalt of the Ivakinsky Formation. The Southern intrusion cuts through all of the lower units of the Siberian Trap tuff-lavas, including the Lower Nadezhdinsky Formation; demonstrating that the ore-bearing intrusions of the Noril’sk Complex post-date that unit. Rocks in both intrusions have low TiO2 and elevated MgO contents (average mean TiO2 <1 and MgO?=?12?wt.%) that are more primitive than the lavas of the Upper Formations of the Siberian Traps which suggests that the ore-bearing intrusions result from a separate magmatic event. Unusually high concentrations of both HREE (Dy+Yb+Er+Lu) and Y (up to 1.2 and 2.1?ppm, respectively) occur in olivines (Fo79.5 and 0.25% NiO) from picritic and taxitic gabbro-dolerites with disseminated sulfide mineralization. Thus accumulation of HREE, Y and Ni in the melts is correlated with the mineral potential of the intrusions. The TiO2 concentration in pyroxene has a strong negative correlation with the Mg# of both host mineral and Mg# of host rock. Sulfides from the Northern Maslovsky intrusion are predominantly chalcopyrite–pyrrhotite–pentlandite with subordinate and minor amounts of cubanite, bornite and millerite and a diverse assemblage of rare precious metal minerals including native metals (Au, Ag and Pd), Sn–Pd–Pt–Bi–Pb compounds and Fe–Pt alloys. Sulfides from the Southern Maslovsky intrusion have δ 34S?=?5–6‰ up to 10.8‰ in two samples whereas the country rock basalt have δ 34S?=?3–4‰, implying there was no in situ assimilation of surrounding rocks by magmas. 相似文献
27.
Vladislav V. Izmodenov Yury G. Malama Alexandr P. Kalinin Mike Gruntman Rosine Lallement Irina P. Rodionova 《Astrophysics and Space Science》2000,274(1-2):71-76
Williams et al. (1997) have suggested that a population of hot hydrogen atoms is created in the heliosphere through elastic H-H collisions
between energetic `solar' atoms (neutralized solar wind) and interstellar atoms. They used a BGK-like approximation (Bhatnagar
et al., 1954) for the Boltzmann collision term and the collision cross sections suggested by Dalgarno (1960). We show that both
assumptions result in a significant overestimation of the the H-H collision effect. On the basis of calculated momentum transfer
cross-sections for elastic H-H collisions, we argue that elastic H-H and H-p collisions cannot produce hot H atoms in the
heliosphere.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
28.
Tunnels are now an integral part of the infrastructure in major cities around the world. For many reasons, these tunnels have horseshoe-shaped cross-sections with round top and flat bottom. This paper presents some improvements to the use of the Hyperstatic Reaction Method-HRM for analysing tunnels with horseshoe-shaped cross-sections when these tunnels operate under the influence of earthquakes, particularly in cases when the tunnel lining is a continuous lining. The analysis used parameters of a tunnel from the Hanoi metro system, as well as parameters of the strongest earthquake that may occur in the central Hanoi area in the improved HRM and 2 D numerical methods using the ABAQUS software. On the basis of the results obtained, the paper gives conclusions about the HRM methodology when it is used to calculate tunnels that have horseshoe cross-sections operating under the influence of earthquakes. 相似文献
29.
Yuliy A. Dashevsky Semen Petrov Alexandr N. Vasilevskiy Oleg B. Bocharov Gleb V. Dyatlov 《Studia Geophysica et Geodaetica》2017,61(1):69-92
Reliable estimates of the fluid pressure in the pore space of rocks are critical for different aspects of petroleum exploration and production including injection operations and scenarios of water flooding. Numerous approaches are available for formation pore pressure evaluation, however, these measurements become a challenge inside a cased borehole, and a list of possible options is short: either the casing is to be perforated, or the production tubing needs to be disconnected to perform the pressure tests. We present a method for through-casing evaluation of formation pore pressure without shutting down production. We suggest equipping an observation well with a borehole gravimeter and acquiring time variations of the vertical component of the gravity field. Changes in gravity occur during gas production and are related to time variations of formation pore pressure. Gravity changes obtained in the observation well are supposed to be inverted for time-dependent formation pore pressure variations beyond the casing. Our results and recommendations are based on numerical modeling of pore pressure spatial distribution during gas field exploitation and relevant changes in borehole gravity. Benchmark models were elaborated in order to consider a dynamic process of pressure changes in time and space under conditions similar to those in the Medvezhye gas field (Russia). Different modeling scenarios are considered for early and late stages of gas field exploitation. The sensitivity analysis was performed to estimate quantitatively a sensitivity of borehole temporal gravity changes to variations in formation pore pressure behind the casing. Based on resolution analysis we justify the possibility to extract the gravity measurements directly related to changes in pore pressure from the total changes in the gravity field due to reservoir exploitation. The impact of pore pressure on the gravity field measured in boreholes during the water flooding is also evaluated, and obtained results are discussed. 相似文献