Duration of migmatite formation in the granulite-facies metamorphism zone of Svecofennides of the Ladoga region, southeastern Baltic Shield     

Sh. K. Baltybaev  O. A. Levchenkov  V. A. Glebovitsky  L. K. Levskii  E. V. Kuz&#;mina  A. F. Makeev  S. Z. Yakovleva 《Doklady Earth Sciences》2006,407(2):271-274

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Monte Carlo simulation of mixing in Ca3Fe2Ge3O12–Ca4Ge4O12 garnets and implications for the thermodynamic stability of pyrope–majorite solid solution     

Victor L. Vinograd  Bjoern Winkler  Daniel J. Wilson  Andrew Putnis  Julian D. Gale 《Physics and Chemistry of Minerals》2006,33(8-9):533-544

Static lattice energy calculations, based on empirical pair potentials, were performed for a large set of structures differing in the arrangement of octahedral cations within the garnet 2 × 2 × 2 supercell. The compositions of these structures varied between Ca₃Fe₂Ge₃O₁₂ and Ca₄Ge₄O₁₂. The energies were cluster expanded using pair and quaternary terms. The derived ordering constants were used to constrain Monte Carlo simulations of temperature-dependent mixing properties in the ranges of 1,073–3,673 K and 0–10 GPa. The free energies of mixing were calculated using the method of thermodynamic integration. The calculations predict a wide miscibility gap between Fe-rich (cubic) and Fe-pure (tetragonal) garnets consistent with recent experimental observations of Iezzi et al. (Phys Chem Miner 32:197–207, 2005). It is shown that the miscibility gap arises due to a very strong cation ordering at the Fe-pure composition, driven by the charge difference between Ca²⁺ and Ge⁴⁺ cations. The structural and thermodynamic analogies between Ca–Ge and Mg–Si systems suggest that a similar miscibility gap should exist between pyrope and Mg–Si-majorite.  相似文献   

A Practical Procedure for the Measurement of Fragmentation by Blasting by Image Analysis   总被引：1，自引：0，他引：1  

J. A. Sanchidrián  P. Segarra  L. M. López 《Rock Mechanics and Rock Engineering》2006,39(4):359-382

Summary. The operation of a digital image analysis system in a limestone quarry is described. The calibration of the system, required in order to obtain moderately reliable fragmentation values, is done from muckpile sieving data by tuning the image analysis software settings so that the fragmentation curve obtained matches as close as possible the sieving. The sieving data have also been used to extend the fragment size distribution curves measured to sizes below the system’s optical resolution and to process the results in terms of fragmented rock, discounting the material coming from a loose overburden (natural fines) that is cast together with the fragmented rock. Automatic and manual operation modes of the image analysis are compared. The total fragmentation of a blast is obtained from the analysis of twenty photographs; a criterion for the elimination of outlier photographs has been adopted using a robust statistic. The limitations of the measurement system due to sampling, image processing and fines corrections are discussed and the errors estimated whenever possible. An analysis of consistency of the results based on the known amount of natural fines is made. Blasts with large differences in the amount of fines require a differentiated treatment, as the fine sizes tend to be the more underestimated in the image analysis as they become more abundant; this has been accomplished by means of a variable fines adjustment factor. Despite of the unavoidable errors and the large dispersion always associated with large-scale rock blasting data, the system is sensitive to relative changes in fragmentation.  相似文献   

Metals,arsenic, and sulfur in the Aue and Eibenstock granites,Erzgebirge     

Vikt. L. Barsukov  N. T. Sokolova  O. M. Ivanitskii 《Geochemistry International》2006,44(9):896-911

Average concentrations of Pb, Zn, Cu, and other metals, as well as S and As, were calculated for the Aue granitic cupola, the contact aureole of which hosts the large vein-type uranium deposit of Schlema-Alberoda and the Schneeberg uranium-base metal deposit (Erzgebirge, Germany). The cupola was exposed by mine workings and boreholes, which provided an opportunity to evaluate variations in the abundances of metals in the granites over a vertical interval of more than 2.5 km and estimate their losses in the upper oxidized part of the investigated volume of the cupola (coefficient of iron oxidation, KO _Fe, increases in the granites from bottom to top from 7 to 70%) compared with the lower unaltered and unoxidized part (with a KO _Fe plateau at about 5%). The average concentrations of metals in the upper part of the cupola are lower than those in the lower part by a factor of 2.5 for Pb, 1.56 for Zn, 1.45 for Cu, 1.3 for Co, etc. A similar decrease in the abundances of ore elements along the vertical section associating with the relative epigenetic alteration and oxidation of the granite was previously described by us for U and Th and for the components of high-temperature ores, W, Sn, and Mo. The removal of ore elements from the granite was accompanied by a decrease in the bulk contents of sulfur and arsenic by a factor of 1.35 and 1.65, respectively. The leaching of trace metals from the granites of the upper part of the Aue cupola was followed by their partial redeposition above the cupola in the ore veins of the Schlema and Schneeberg deposits. Original Russian Text ? Vikt. L. Barsukov, N.T. Sokolova, O.M. Ivanitskii, 2006, published in Geokhimiya, 2006, No. 9, pp. 967–982.  相似文献   

The changing role of hydrogeology in semi-arid southern and eastern Africa     

N. S. Robins  J. Davies  J. L. Farr  R. C. Calow 《Hydrogeology Journal》2006,14(8):1483-1492

Much of southern and eastern Africa is semi-arid and heavily groundwater dependent. Borehole drilling commenced over a hundred years ago with magnetic and electrical resistivity surveys for borehole siting being introduced from 1936. Formalised training of hydrogeologists led in the 1970s to an almost standard approach to hydrogeological investigation and a period of stability followed, during which some major investigations were carried out. A period of decentralisation and fragmentation has since taken place in many parts of southern and eastern Africa, and groundwater monitoring and management are inadequate in many countries. All but six of the 14 SADC (Southern African Development Community) member states reportedly have an adequate monitoring network in place. However, groundwater demand is increasing and hydrogeologists need to promote the use of appropriate methodologies as an essential part of tackling the severe issues now facing the water sector in the region.  相似文献   

Metamafic rocks of the Tana Belt, Kola Peninsula: Isotopic age and PT conditions     

L. L. Perchuk  J. D. Kramers  V. O. Yapaskurt  A. V. Krotov 《Doklady Earth Sciences》2006,408(4):623-626

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P-T paths and problems of high-temperature polymetamorphism     

L. L. Perchuk  T. V. Gerya  D. D. van Reenen  C. A. Smit 《Petrology》2006,14(2):117-153

Many Precambrian granulite-facies metamorphic complexes contain so-called straight gneisses, which are massive rocks with a clearly pronounced blastomylonitic texture, lineation, and gneissosity. These rocks occur exclusively in high-temperature ductile shear zones, which can develop either during the primary exhumation of rock complexes or during the overprinting by high-temperature dynamometamorphism. The main criterion for distinguishing between these two types of straight gneisses is the configuration of their P-T trajectories, which are recorded in the mineral assemblages in these rocks and their host gneisses. Ductile shear zones developed in Archean granulite gneisses simultaneously with their exhumation, and, hence, their P-T trajectories are segments of decompression and/or isobaric cooling paths. Straight gneisses in Proterozoic polymetamorphic complexes commonly compose high-temperature ductile shear zones overprinted on Archean granulite complexes, and the P-T paths of these rocks are Z-shaped. This means that, at a constant pressure in the middle part of the continental crust, the T _min of the older P-T trajectory corresponded to T _max of the younger trajectory, and often T _max–T _min > 100°C. Such ductile shear zones commonly have a strike-slip morphology and can be easily seen in aerial photographs and discerned during structural geological surveying. These zones can overprint older gneisses without any notable thermal effect on the latter. Relations of this type were identified in the granulite complexes of Limpopo in South Africa, Sharyzhalgai in the southwestern Baikal area, and Lapland in the Kola Peninsula. The results of our research propose a solution for the well-known problem of the significant discrepancies between the isotopic ages in high-temperature-high-pressure complexes and the partial or complete distortion of radiogenic isotopic systems under the effect of a newly inflowing metamorphic fluid. The application of geochronologic techniques to these situations is senseless, and only P-T trajectories provide insight into the actual age relations between the discrete tectono-metamorphic stages. It is thus expedient to conduct not only structural studies of metamorphic complexes but also their detailed petrological examination and the calculation of their P-T paths before geochronologic dating.  相似文献   

Geodynamic setting of gold ore deposits of the neoproterozoic bodaibo trough     

M. I. Kuz&#;min  V. V. Yarmolyuk  A. I. Spiridonov  V. K. Nemerov  A. I. Ivanov  G. L. Mitrofanov 《Doklady Earth Sciences》2006,407(3):397-400

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Composition of sand storm particles in the Southern Far East   总被引：1，自引：0，他引：1  

L. A. Ganzei  N. G. Razzhigaeva 《Lithology and Mineral Resources》2006,41(3):215-221

Lithostructural composition of the dust storm material (DMS) sampled in the southern Far East in the spring of 2002–2004 has been analyzed. Samples were taken near Vladivostok, where the eolian dust precipitation varied from 0.1 to 6.5 g/m² at that time. Pelitic and fine-silt particles predominate in eolian dust. Grain size, mineral, and chemical compositions of the DSM are compared to data on the DSM in adjacent territories of China, Korea, and Japan, as well as to background data on aerosol precipitation in southern Primorye. Possible mechanisms of the eolian dust transport from inner parts of Asia at different climatic variations in the Pleistocene-Holocene are discussed.  相似文献   

Some aspects of the interrelations between magmatism and ore formation: Evidence from oxygen isotope data on ore-magmatic systems, Armenia     

R. L. Melkonyan  M. S. Akopyan 《Petrology》2006,14(4):413-420

The results of oxygen-isotope study of the Kokhb-Shnokh (J₃) and Vokhci (N₁) intrusive complexes and the related Tekhut and Kadzharan Cu-Mo porphyry deposits of different types, Armenia, were used to discuss the relevant problems of rock and ore genesis and their relationships. It was established that the assimilation of parental mantle basaltic melts by crustal, mainly feldspathic material is a decisive factor in the formation of multiple gabbro-granite complexes. Specifics in the composition and crystallization of the hybrid melt causes the enrichment of the residual melt and hydrothermal fluids in Fe and other elements, in particular, Cu and Mo. The ore-bearing solutions are generated over the solidification time of the melt. They are removed by the hydrothermal system of directionally moving solutions, a process that gives way to a convective-circulation hydrothermal system. A change in the spatial position of the hydrothermal solutions during the formation of the deposit supplies them to different sites, creating a seeming discontinuity in ore deposition, which is observed at many deposits. In fact, the supply of the ore-bearing solutions is continuous process. The ore stage is not a time interval with particular ore-bearing solutions but rather a certain physicochemical state of the solutions attained during their interaction with the environment. This process resulted in the simultaneous precipitation of different mineral assemblages and the asynchronous precipitation of the same assemblages. The formation of deposits of various metals related to a common intrusive complex, as changes in the composition of mineral assemblages, is caused by the influence of various geochemical barriers rather than by compositional variations in the initial hydrothermal solutions.  相似文献