Articoli di riviste sul tema "Gravure du chrome massif"

Relevance of the work. The conditions for the formation of chromium ores in alpine-type ultramafites remain a topical subject of research. In recent years, scientific papers have focused on the issue of changing the chemical composition of ore-forming minerals and chromium ores under the influence of deformation and dynamic recrystallization processes accompanying metamorphism. The results of such studies make it possible to formulate a new model of the formation of chromium mineralization taking into account a significant amount of geological data indicating that alpine-type ultramafic rocks are “mantle tectonites”. In our work, we have studied zonal ore-forming spinels from chrome ores of the Polar Urals. The results of the study make it possible to associate the formation of chemical zoning in minerals and ore bodies with recrystallization under the influence of stress tension. Purpose of the work – study of the conditions for the formation of chemical zoning of chromium spinels from alumina and medium chromium ores of the Voikaro-Syninsky massif. Results. Zonal ore-forming spinels from medium-chromium and aluminous chromitites of the Voikaro-Syninsky massif (Polar Urals) have been studied. It was found that replacement rims are developed along the grains of oreforming spinels with an increased content of Cr2 O3 and an oxidation state of iron in relation to the core, as well as a reduced content of Al2 O3 . The oxidation state of iron in the rims of most grains does not exceed the values typical for unaltered ore-forming spinels. T–fO2 parameters of zoning formation in spinels were determined by oxythermobarometry. Comparison with zoned chrome spinels of the Golyamo Kamenyane massif (Bulgaria). Conclusion. Metamorphic transformations of alumina and medium-chromium chromitites of the Voikaro-Syninsky massif, occurring under subcrustal conditions under the action of directional stress at relatively constant T–fO2 parameters, lead to an increase in the chromium content of the ore mineral.

The overall objective was to create a geological and geophysical field test site for chromite mineralization and detailed works in order to determine and test the main search criteria for disseminated mineralization. To create a field test site, an area was selected in the southern part of the Klyuchevsky massif characterized by abundant development of disseminated mineralization in the banded dunite-clinopyroxenite complex and strong processes of superimposed metamorphism. This paper gives a piece of research on the composition of chrome spinel from disseminated ores that underwent metamorphism of different stages. The composition of chrome spinelide, the evolution of its metamorphism and the related changes in its magnetic properties are examined in detail. It was established that all chrome spinels are of a high-chromium type, to one degree or another, they were subject to secondary changes, leading to the appearance of magnetic phases. The degree and nature of the change in chrome spinels in dunites directly depends on the degree of metamorphism of the rocks. The formation of the magnetic phase begins with the formation of nuclei consisting of single magnetic dipoles, groups of 2-3 dipoles or chains of magnetic dipoles, which was first discovered by us in chrome spinel grains. Then there is an increase in the number of such phases, the appearance of optically diagnosed secondary changes in chrome spinelide. A comparison of the degree of variation of chrome spinel and its reflection in the pattern of recorded anomalies of geomagnetic fields allows us to identify some criteria for the search for disseminated chromite ores of this type.

Research subject. The metamorphic ultramafites of the Kalninsky and Ergaksky massifs located in the northeastern part of Western Sayan (Russia) constitute the Kurtushibinsky ophiolite belt. These rocks are considered to be potentially interesting as bearing chromium and noble metals, which fact determines the relevance of this research.Materials and methods. Thin and polished sections of silicate and ore minerals from the ultramafic rocks under study were investigated using a polarizing microscope AxioScop, Carl Zeiss. The chemical composition of minerals was determined by the method of X-ray spectrum microanalysis using a scanning electron microscope Tescan Vega II LMU equipped with an energy-dispersive spectrometer INCA Energy 350 and a wave-dispersive spectrometer INCA Wave 700. The petrochemical composition of the rocks was studied by the methods of XRF analysis using an X-ray fluorescence energy-dispersive spectrometer Oxford ED-2000. A quantitative ICP-MS analysis was carried out using an Agilent 7500 spectrometer.Results. The massifs are found to be composed of dunites and harzburgites, which were formed during an uneven depletion of the mantle. As a result of depyroxenization, the ultramafites were enriched with chromospinelides. Subsequent intense plastic deformations contributed to their segregation into ore bodies. Regenerated olivinites predominate in the northern part of the Ergaksky massif. The microstructural features of ultramafites and the composition of minerals indicate them to have been subjected to inhomogeneous high-temperature plastic deformations, which occurred during their migration in the upper mantle and crust.Conclusions. The petrochemical studies have shown that the ultramafites of the Ergaksky massif are least depleted, frequently featuring clinopyroxene. The most depleted ultramafites of the Kalninsky massif are characterized by a more extensive distribution of dunites, the absence of clinopyroxene and lower contents of REE and rare elements in comparison with the ultramafites of the Ergaksky massif. The obtained geochemical data indicate a fluid-magmatic effect of boninite melts on depleted ultramafites, which apparently occurred under mantle conditions over the subduction zone and consequently led to their enrichment with incompatible LREE (La, Ce) and Sr, Zr and Hf, as well as to the formation of high-chromium chromitites.

The results of investigations of natural iron-chromium spinels of variable composition Fe2+(Cr2-xFex3+)O4 of the chromite-bearing Klyuchevskoi massif (Middle Urals), which are the main carriers of the magnetization of rocks are presented. Substantial changes in the composition and in magnetic structure of accessory chrome-spinels scattered in the host rock are established, unlike the almost unaltered ore-forming chrome-spinels, under the influence of secondary geological processes. To establish the connection between the chrome-spinel changes at the microlevel and features of the geomagnetic field anomalies created by this carrier of magnetization of rocks, it is carried out a complex of investigations of Fe-Cr-spinels (thermomagnetic analysis over the temperature range (4÷1000) K; magnetic resonance (MR) spectroscopy and magnetic force microscopy (MFM) in addition to magnetomineralogical studies). As a result, in the relict areas of grains of the accessory chrome-spinels were first discovered the magnetic clusters (superparamagnetic phases) in the form of single or groups of 2 – 3 magnetic dipoles of tens nanometers in size, or in the form of chain-like structures of magnetic dipoles/single domains.

The composition and age of subalkaline dolerites localized in chromite-bearing ultramafic rocks of the Rai-Iz massif are investigated. Dolerites are traced along tectonic zones inside ultramafic rocks and are not observed beyond their boundaries, spatially tending to deposits and occurrences of chromites.The studied dolerites are characterized by high concentrations of alkalis, TiO2, P2O5, enrichment with large-ion lithophilic elements and Th; the amount of REE varies from 103.3 to 164.2 ppm; (La/Sm)n = 1.3–1.7. The age of subalkaline dolerites was determined by the method 40Ar/39Ar (402.7 ± 3.8 million years). At this time, a deep metamorphic processing of ultramafic rocks of most of the Rai-Iz massif occurred with the formation of high-chromium chrome mineralization and the isolation of a vein series of subalkaline dolerites in the discharge zones.

Research subject. Minerals and mineral assemblages of noble elements in chromitites of the Alapaevsk massif. Aim. A systematic mineralogical study of high-chromium (Cr) and alumina-rich (Al) chromitites with the development of a sequence scheme for mineral formation, including platinum-group minerals (PGMs) and gold alloys. Materials and Methods. Samples of high-Cr and Al chromitites from chromite deposits in various parts of the Alapaevsk massif. Scanning electron microscopy (Tescan VEGAII XMU and JSM-6390LV Jeol with EDX INCA Energy 450 X-Max 80 spectrometers) and electron microprobe analysis (Cameca SX 100 with five wave spectrometers) were used. Results. A diagram showing the sequence of mineral formation in chromitites was designed; primary and secondary mineral assemblages were distinguished, with the latter assemblage being divided into early and late mineral associations. Primary assemblages of high-Cr (Cr2O3 > 50 wt %) and Al (Cr2O3 < 50 wt %) ores are represented by similar minerals, including chromespinel, clinopyroxene, and olivine, with characteristically distinct compositions of these minerals in each type of ores. Minerals of the primary assemblage are synchronous with chrome-spinel and are represented by pentlandite, Cu-bearing pentlandite, chalcopyrite, pyrrhotite, bornite, as well as PGMs (laurite RuS2, erlichmanite OsS2, native osmium) and Cu-rich gold. Minerals of the secondary early association occur in the form of polyphase inclusions within chrome-spinel. Polyphase inclusions are composed of Cr-bearing chlorite, amphibole, garnet, sulfides (millerite, heazlewoodite) and minerals of native elements, including (Ni, Cr)-bearing copper, nickel-bearing copper, (Cu, Fe, Cr)-bearing nickel, awaruite. Noble metal minerals from the secondary early association were found only in Al chromitites and are represented by laurite, Pt- and Pd arsenides and stibnides, Ru-bearing pentlandite, and high-grade native gold. The secondary late mineral association consists of native copper and awaruite, which are intergrown with serpentine in high-Cr ore. The temperature conditions for the formation of secondary assemblages were estimated using a chlorite geothermometer. The formation temperatures of the studied chlorites from chromitites fall within the range of 250–284°C. Conclusions. Noble metal minerals from secondary associations were formed at temperatures below 350°C together with garnet, amphibole, chlorite, and nickel sulfides. Grains of primary Os–Ir–Ru alloys during epigenetic processes underwent sulfurization with the formation of a fine-grained porous mixture of native and sulfide (sometimes with As) phases, and replacement by Ru-pentlandite. The presence of awaruite and native Cu and Ni in both primary and secondary assemblages of chromotites indicates the reducing conditions for the formation of noble metal minerals. The limited occurrence of high-Cr ores, along with the manifested processes of sulfurization for primary grains of Os–Ir–Ru alloys, led to the scarcity of detrital PGM in the area of the Alapaevsk massif.

Research subject. Chromite ores and massive chromitites with alumina (low chromium) chrome spinelide (the Podennoye deposit deposit) and chromite ores with high-chromium chrome spinelide (Kurmanovskoye deposit) of the Alapaevsky hyperbasite massif. Materials and methods. Samples of chromite ores and massive chromitites collected during field research were studied in transparent sections using chemical analysis and electrical methods (electrical conductivity, dielectric losses). Results. The temperature dependences of electrical resistance and dielectric losses in the temperature range of 20‒800°C were obtained. The electrical parameters lgRₒ and Eₒ were determined, and the inverse linear relationship bet-ween them was revealed. The electrical parameters for the three groups of samples were found to differ depending on the degree of metamorphic changes. It was established that an increase in metamorphism leads to an increase in lgRₒ and a decrease in Eₒ. For the studied samples of chromite ore from the Podennoye deposit, Eₒ and lgRₒ vary from 0.61 to 0.96 and from 2.5 to –0.41, respectively. In the Kurmanovskoye field, these parameters vary from 0.81 to 1.35 and from 0.95 to –2.8, respectively. For the studied samples of chromitites from the Podennoye deposit, Eₒ varies from 0.21 to 0.41, while lgRₒ varies from –0.08 to 1.67. In this case, the coefficients a and b are different for each group of samples. For some samples, the chemical composition was determined, and for six samples (two samples from each group), the content of ferrous and trivalent iron oxides in the original sample and a duplicate sample after calcination at temperature of up to 800 °C was determined. Relative change in the ratio of ferrous and trivalent iron oxides in the initial sample (FeO/Fe2O3)* and a duplicate sample (FeO/Fe2O3)** H = [(FeO/Fe2O3)*/(FeO/Fe2O3)**] was compared with the position of the maximum of dielectric losses on the temperature scale. In the coordinates H–T, °C, the studied samples, depending on the metamorphic changes, occupy a certain place. Conclusions. The study indicates the potential of the obtained information to be used as petrogenetic indicators of chromite deposits with a simultaneous assessment of the degree of metamorphic changes.

This paper documents the data on high-Mg porphyrite dykes (PDs) from the mafic to felsic (~2.09 Ma) plutons of Elan complex (EC). The low-thickness (first centimeters) synplutonic dykes are characterized by sharp straight contacts without visible chilling zones, in contrast to the larger (up to 119 m) dykes that have gradual transitions. The dykes are fresh, porphyritic (bronzite, Al-enstatite, labradorite) and has fine-grained mainly quartzo-feldspathic (+biotite, sulfides, accessories, ±hypersthene) matrix. Based on geochemistry data the PDs are intermediate rocks (SiO2 = 58.9–60.3 wt. %) and plot into calc-alkaline series with high magnesian of whole rock (Mg# ~0.7) and felsic (68.9–70.2 wt. %) matrix (Mg# ~0.5). The PDs show differentiated rare-earth element patterns with negligible Eu anomalies. The bronzite phenocrysts varying sizes are characterized by block zoning and contain irregular inclusions of olivine (Mg# ~0.85), clinopyroxene (Mg# ~0.88), phlogopite (Mg# up to 0.94), labradorite, chrome spinel, graphite and sulfides. The Al-enstatite phenocrysts are practically sterile with respect to trace elements and mineral inclusions. The geochemical features as well as diffusion zones, reaction rims, and resorbed faces of the phenocrysts such as orthopyroxene and plagioclase indicate processes of recrystallization and/or partial dissolution of nonequilibrium crystals in the melt and indicate intratelluric nature of the dyke phenocrysts that cores are inherited from the EC derivatives/cumulate. The mineral thermometry estimates are: (1) the parent magma starting temperatures of 1200–1400 °С and (2) the EC crystallization temperatures 1080–1155 °С, (3) the PD emplacement temperatures 910–1070 °С. The petrogenetic model supposes the generation of EC high-temperature magmas similar to boninites from an upper metasomatized mantle. The melt is contaminated with continental crust lithologies. It implies the half-way evolved magma chamber in the crust. The PD melt, as a result of ending of the half-way magma chamber evolution, was emplaced into the still unheated EC plutons.

Introduction. Engineering and geological processes as a result of process operation at deposits often develop at an exponential rate. This problem is specific due to complex and multifactorial nature of the processes which arise when rock mass interacts with mine workings. For this reason engineering and geological information should be obtained step by step beginning with the stage of prospecting and evaluation and proceeding at the stages of construction and operation of mine workings. Research aim is to consider methodological basis to form the databases of geological engineering information about mining facilities at various stages of their life cycle. Research methodology. The types of operations have been described on acquisition and interpretation of engineering-geological information required to detail models of the engineering-geological conditions at every stage. An important factor in creating a reliable and functioning geomechanical model of mineral deposits is survey operations follow-up and gradual transition from regional and provincial engineeringgeological conditions and tectonic structure to engineering-geological conditions of a specific deposits or occurrence. Research results. By the example of chrome field located in the Polar Urals within the Rai-Iz massif, all detail stages of mineral deposits engineering-geological conditions model have been established taking into account the conditioning selected components and factors; possible problems have been described and the results of step-by-step predictive estimates of mine workings stability have been presented. Summary. The research present an example of engineering-geological data detailing by the results of the gamma ray log and caliper logging at the stages of pit slope stability forecast model construction. Obtained in the course of long-term data collecting and processing, the model of Tsentralnoe field has proved its efficiency in the course of mining.

AbstractRotogravure printing cylinders are engraved by electro-mechanical engraving (EME) process in India used for printing purpose. But this process has drawbacks of the emissions of hazardous gases, solid and water pollution. EME cylinders are better in cell size, depth and needed higher copper and chrome plating thickness. By laser engraving (LE) copper and chromium thickness were reduced by 75 µm and 5 µm in a cylinder by laser engraving with also a reduction in power consumption and plating time. The carbon footprints were also reduced by 227 g per cylinder with a cost-effective solution for rotogravure printing process.

Актуальность работы. В тектонической структуре складчато-глыбового сооружения Большого Кавказа серпентиниты связаны преимущественно c зоной Передового хребта, где они ассоциируют с герцинскими тектоническими покровами или крупными разломами, ограничивающими блоки доверхнепалеозойских кристаллических пород. Сведения как об условиях формирования протолита кавказских апогипербазитов (включая их формационную принадлежность и геодинамическую приуроченность), так и об их метаморфических трансформациях в коровых условиях остаются дискуссионными, что в определяющей мере связно с недостаточной изученностью минерального состава. Цель работы – получение данных о минеральном составе серпентинитов Нижнетебердинского массива, анализ особенностей состава зональных хромшпинелидов, получение данных об условиях формирования и преобразования апогипербазитов. Методы исследования. Рентгенофазовый анализ, электронно-зондовый микроанализ и электронная микроскопия, мёссбауэровская спектроскопия. Результаты работы. Нижнетебердинские серпентиниты имеют петельчатую текстуру и хризотил-лизардитовый состав; с серпентинами ассоциируют магнетит, хромшпинелиды, гематит, хлориты, кварц, кальцит, магнезит, доломит, брусит. Хромшпинелиды по строению и составу разделяются на две группы. Одна группа представлена округлыми однородными массивными зернами алюмохромитового состава (Cr# 0,69-0,73, Mg# 0,47-0,51), приуроченными к зонами вязкопластических деформаций породы. Другая – неправильной формы зональными зернами с хромпикотитовыми ядрами (Cr# 0,36-0,43, Mg# 0,66-0,72) и феррихомит – хроммагнетитовыми оторочками. Формирование хризотил-лизардитовой ассоциации происходило в условиях низкотемпературной зоны зеленосланцевой фации в окислительной обстановке под воздействием гидротермальных растворов, насыщенных трехвалентным железом, кремнеземом и марганцем. В этих условиях образовались характерные «атолловые» пористые хромшпинелиды, обогащённые SiO2 и MnO за счет переработки гидротермальными растворами уже зонированных (претерпевших метаморфическую перекристаллизацию) хромшпинелидов. Состав реликтовых ядер хромшпинелидов отвечает офиолитовому тренду. Cоставы нижнетебердинских «смещены» в область, характерную для абиссальных перидотитов. Эта тенденция согласуется с ассоциацией серпентинитов со среднепалеозойскими филлитами и граувакковыми породами Тоханского тектонического покрова, относимыми некоторыми авторами к комплексу преддугового бассейна. Relevance. In the tectonic folded-boulder structure of the Greater Caucasus serpentinites are mainly associated with the zone of the Peredovoy Ridge, where they are associated with Hercynian tectonic sheets or large faults limiting blocks of pre-Paleozoic crystalline rocks. Information on the conditions of formation of the Caucasian apohyperbasites protoliths (including their formational affiliation and geodynamic confinement), as well as their metamorphic transformations in crustal conditions remain debatable, which is largely due to the insufficient study of the mineral composition. The aim of the work is to gain data on the mineral composition of serpentinites of the Nizhnetberdinskiy massif, to analyze specific features of the zonal chromespinelides’ composition, to recieve data on formation conditions and transformation of apohyperbasites. Methods. X-ray phase analysis, electron-probe microanalysis and electron microscopy, Mössbauer spectroscopy. Results. The Nizhneberdinskiy massif’ serpentinites have a loop texture and chrysotile-lysardite composition; magnetite, chrome-spinelides, hematite, chlorites, quartz, calcite, magnesite, dolomite, and brucite are associated with serpentines. Chrome-spinelides by structure and composition are subdivided into two groups. One group consists of rounded homogeneous massive grains of alumochromite composition (Cr# 0.69-0.73, Mg# 0.47-0.51), which are confined to the viscoplastic deformation zones of the rocks. The other is irregularly shaped zoned grains with chromepicotite cores (Cr# 0.36-0.43, Mg# 0.66-0.72) and ferrichomite – chrome-magnetite rims. The formation of the chrysotile-lysardite association occurred in the low-temperature zone of the greenschist facies in an oxidizing environment under the influence of hydrothermal solutions saturated with trivalent iron, silica, and manganese. Under these conditions, characteristic "atoll" porous chromespinelides enriched with SiO2 and MnO were formed due to reprocessing by hydrothermal solutions of already zoned (affected by metamorphic recrystallization) chromespinelides. The composition of relic chromespinelide cores corresponds to the ophiolitic trend. The compositions of the Nizhneteberdinskiy massif are "shifted" to an area of abyssal peridotites. This trend is consistent with the association of serpentinites and Middle Paleozoic phyllites and graywacke rocks of the Tohan tectonic cover, referred to the complex of the pre-arc basin by some authors