A Note on the Conditions of Formation of Melilite in the Oka Alkaline Carbonatite Complex, Quebec

1972 ◽  
Vol 9 (12) ◽  
pp. 1766-1771
Author(s):  
K. L. Currie ◽  
L. Gelinas
Keyword(s):  
Experimental Data ◽  
Carbonatite Complex ◽  
Alkaline Rocks

The melilite of the Oka complex is chemically equivalent to a mixture of nepheline, wollastonite, and diopsidic pyroxene, a mixture which locally coexists with melilite. The melilite is proposed to result from reaction of this mixture with calcite. Thermodynamic analyses of the possible reactions suggest melilite formed between 800 and 890 °C (1073–1163 °A), and at CO2 pressures less than 2 kbars. Monticellite, a characteristic accompanier of melilite would form from dolomitic carbonate under the same conditions. Experimental data appear to show that all wollastonite-bearing alkaline rocks are emplaced at total pressures less than 3.5 kbars, and all plutonic nephelinitic rocks equilibrated at temperatures of less than 1000 °C (1273 °A).

scholarly journals The Tikiusaaq carbonatite: a new Mesozoic intrusive complex in southern West Greenland

2006 ◽  
Vol 10 ◽  
pp. 41-44 ◽  
Author(s):  
Agnete Steenfelt ◽  
Julie A. Hollis ◽  
Karsten Secher
Keyword(s):  
Lithospheric Mantle ◽  
Chemical Elements ◽  
Country Rock ◽  
Alkaline Rock ◽  
Geological Mapping ◽  
Carbonatite Complex ◽  
West Greenland ◽  
Alkaline Rocks ◽  
Kimberlite Indicator Minerals ◽  
Indicator Minerals

Ultrabasic alkaline magmatic rocks are products of melts generated deep within or at the base of the lithospheric mantle. The magmas may reach the surface to form lavas and pyroclastic deposits; alternatively they crystallise at depth to form dykes or central complexes. The rocks are chemically distinct and may contain high concentrations of economically interesting minerals and chemical elements, such as diamonds, niobium, tantalum, rare earth elements, phosphorus, iron, uranium, thorium, and zirconium. Ultrabasic alkaline rocks are known from several provinces in Greenland, but extrusive facies have only been preserved at a few places; e.g. at Qassiarsuk in South Greenland where pyroclastic rocks occur, and in the Maniitsoq region, where a small volcanic breccia (‘Fossilik’) contains fragments of Palaeozoic limestone. Ultramafic lamprophyre and kimberlite are mainly emplaced as dykes, whereas carbonatite forms large intrusive bodies as well as dykes. The ultrabasic alkaline magmas that have been emplaced at certain times during the geological evolution of Greenland can be related to major episodes of continental break-up (Larsen & Rex 1992). The oldest are Archaean and the youngest dated so far are Palaeogene. Figure 1 shows the distribution of known ultrabasic alkaline rocks in West Greenland. The large and well-exposed bodies of alkaline rocks and carbonatites in the Gardar Province were discovered already in the early 1800s (Ussing 1912), while less conspicuous bodies were discovered much later during geological mapping and mineral exploration. Many alkaline rock bodies, particularly dykes, are difficult to identify in the field because they weather more extensively than the country rock gneisses and form vegetated depressions in the landscape. However, their distinct chemistry and mineralogy render alkaline rocks identifiable in geochemical and geophysical survey data. Thus, the Sarfartôq carbonatite complex was discovered during regional airborne gamma-spectrometric surveying owing to its elevated uranium and thorium contents (Secher 1986). The use of kimberlite indicator minerals has led to the discovery of alkaline rocks such as kimberlites and ultramafic lamprophyres that carry fragments of deep lithospheric mantle. Such rocks may also contain diamonds. Kimberlite indicator minerals are high-pressure varieties of minerals, such as garnet, clinopyroxene, chromite and ilmenite that were formed in the lithospheric mantle. Exploration companies have processed thousands of till samples from southern West Greenland for kimberlite indicator minerals and found many new dykes.

Kimberlites and other ultramafic alkaline rocks in the Sisimiut–Kangerlussuaq region, southern West Greenland

2002 ◽  
pp. 57-66 ◽  
Author(s):  
Sven Monrad Jensen ◽  
Henriette Hansen ◽  
Karsten Secher ◽  
Agnete Steenfelt ◽  
Frands Schjøth ◽  
...  
Keyword(s):  
Great Length ◽  
Carbonatite Complex ◽  
Original Series ◽  
West Greenland ◽  
Alkaline Rocks ◽  
Diamond Exploration ◽  
Rock Types ◽  
Indicator Minerals

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, e.g.: Monrad Jensen, S., Hansen, H., Secher, K., Steenfelt, A., Schjøth, F., & Rasmussen, T. M. (1). Kimberlites and other ultramafic alkaline rocks in the Sisimiut–Kangerlussuaq region, southern West Greenland. Geology of Greenland Survey Bulletin, 191, 57-66. https://doi.org/10.34194/ggub.v191.5129 The alkaline province of southern West Greenland includes swarms of dykes described as kimberlites and lamproites (Larsen 1991), and these rock types are widely distributed in the Sisimiut–Sarfartoq–Kangerlussuaq region (Figs 1, 2). Kimberlites and lamproites are potential carriers of diamond, and since the description of the Sarfartoq carbonatite complex and the kimberlitic dykes related to this complex (Larsen 1980; Secher & Larsen 1980), the Sisimiut–Sarfartoq–Kangerlussuaq region has seen several campaigns of commercial diamond exploration. The latest and most persistent stage of exploration began in the mid-1990s and has continued to date, with varying intensity. Numerous reports of diamond-favourable indicator minerals from till sampling, finds of kimberlitic dykes, and recovery of actual diamonds from kimberlitic rocks have emerged since 1995 (Olsen et al. 1999). A drilling programme in late 2001 confirmed the unusually great length and width of a magnetic kimberlitic dyke (Ferguson 2001).

scholarly journals Minerals assotiations and compositional heterogeneity of zircon from miaskite-carbonatite complex of the Vishnevye mountains, South Urals

2019 ◽  
Vol 5 ◽  
Author(s):  
V.I. Popova ◽  
V.A. Popov ◽  
V.A. Kotlyarov
Keyword(s):  
South Urals ◽  
Compositional Heterogeneity ◽  
Carbonatite Complex ◽  
Alkaline Rocks ◽  
Homogeneous Crystal

In alkaline rocks, pegmatites and carbonatites of the Vishnevye Mountains, zircons co-crystallized with rock-forming silicates (feldspars, nepheline, annite, etc.), as well as with some other minerals (pyrochlore, magnetite, ilmenite, apatite, monazite, calcite, etc.) and cannot be ascribed to metacrystals. The morphology of zircon crystals (their cut and habit) varies from dipyramidal (in miaskites) to short prismatic (in biotite syenites), from dipyramidal to prismatic in alkaline pegmatites, and with a combination of dipyramids in carbonatites, which is explained by variation in alkalinity of mineral-forming conditions from early alkaline (miaskits) to less alkaline (syenites) and alkaline (carbonatites). Zonal and zonal-sectorial zircon crystals with variations in the HfO2 content are dominant and relatively homogeneous crystal rarely occur. In diferent zircon crystals, the HfO2 content of peripheral zones either increases or decreases and unevenly vary. Sectorial composition of zircon is mostly related to distinct HfO2 contents of peripheral zones of prisms {100}, {110} and dipyramid {111} and {221}. The reserves of zircon of are ~75 kt and possible resources are >100 kt.

Microdiffraction Patterns of Small Metallic Particles II; Theoretical Analysis

1982 ◽  
Vol 40 ◽  
pp. 668-669
Author(s):  
A. Gómez ◽  
P. Schabes-Retchkiman ◽  
M. José-Yacamán ◽  
T. Ocaña
Keyword(s):  
Experimental Data ◽  
Electron Diffraction ◽  
Theoretical Analysis ◽  
Size Range ◽  
Dynamical Theory ◽  
Metallic Particles ◽  
Splitting Effect

The splitting effect that is observed in microdiffraction pat-terns of small metallic particles in the size range 50-500 Å can be understood using the dynamical theory of electron diffraction for the case of a crystal containing a finite wedge. For the experimental data we refer to part I of this work in these proceedings.

Evidence for ordered Fe3Ni

1987 ◽  
Vol 45 ◽  
pp. 216-217
Author(s):  
K.B. Reuter ◽  
D.B. Williams ◽  
J.I. Goldstein
Keyword(s):  
Experimental Data ◽  
Martensitic Transformation ◽  
Electron Diffraction ◽  
Room Temperature ◽  
Direct Evidence ◽  
Transformation Product ◽  
Iron Meteorites ◽  
X Ray ◽  
Ni Content ◽  
Temperature Transformation

In the Fe-Ni system, although ordered FeNi and ordered Ni3Fe are experimentally well established, direct evidence for ordered Fe3Ni is unconvincing. Little experimental data for Fe3Ni exists because diffusion is sluggish at temperatures below 400°C and because alloys containing less than 29 wt% Ni undergo a martensitic transformation at room temperature. Fe-Ni phases in iron meteorites were examined in this study because iron meteorites have cooled at slow rates of about 10°C/106 years, allowing phase transformations below 400°C to occur. One low temperature transformation product, called clear taenite 2 (CT2), was of particular interest because it contains less than 30 wtZ Ni and is not martensitic. Because CT2 is only a few microns in size, the structure and Ni content were determined through electron diffraction and x-ray microanalysis. A Philips EM400T operated at 120 kV, equipped with a Tracor Northern 2000 multichannel analyzer, was used.

EELS white line intensities calculated for the 3d and 4d metals

1989 ◽  
Vol 47 ◽  
pp. 388-389
Author(s):  
C. C. Ahn ◽  
D. H. Pearson ◽  
P. Rez ◽  
B. Fultz
Keyword(s):  
Experimental Data ◽  
Line Intensity ◽  
Transition Probabilities ◽  
Initial Increase ◽  
White Line ◽  
Hartree Fock ◽  
Line Intensities ◽  
Integrated Intensity ◽  
X Ray Absorption ◽  
The Continuum

Previous experimental measurements of the total white line intensities from L2,3 energy loss spectra of 3d transition metals reported a linear dependence of the white line intensity on 3d occupancy. These results are inconsistent, however, with behavior inferred from relativistic one electron Dirac-Fock calculations, which show an initial increase followed by a decrease of total white line intensity across the 3d series. This inconsistency with experimental data is especially puzzling in light of work by Thole, et al., which successfully calculates x-ray absorption spectra of the lanthanide M4,5 white lines by employing a less rigorous Hartree-Fock calculation with relativistic corrections based on the work of Cowan. When restricted to transitions allowed by dipole selection rules, the calculated spectra of the lanthanide M4,5 white lines show a decreasing intensity as a function of Z that was consistent with the available experimental data.Here we report the results of Dirac-Fock calculations of the L2,3 white lines of the 3d and 4d elements, and compare the results to the experimental work of Pearson et al. In a previous study, similar calculations helped to account for the non-statistical behavior of L3/L2 ratios of the 3d metals. We assumed that all metals had a single 4s electron. Because these calculations provide absolute transition probabilities, to compare the calculated white line intensities to the experimental data, we normalized the calculated intensities to the intensity of the continuum above the L3 edges. The continuum intensity was obtained by Hartree-Slater calculations, and the normalization factor for the white line intensities was the integrated intensity in an energy window of fixed width and position above the L3 edge of each element.

A fuzzy neural network approach for modeling the growth kinetics of FeB and Fe2B layers during the boronizing process

2018 ◽  
Vol 106 (6) ◽  
pp. 603 ◽  
Author(s):  
Bendaoud Mebarek ◽  
Mourad Keddam
Keyword(s):  
Neural Network ◽  
Experimental Data ◽  
Fuzzy Neural Network ◽  
Treatment Time ◽  
Calculation Model ◽  
Average Error ◽  
Network Approach ◽  
Neural Network Approach ◽  
Fuzzy Neural ◽  
Kinetics Of

In this paper, we develop a boronizing process simulation model based on fuzzy neural network (FNN) approach for estimating the thickness of the FeB and Fe2B layers. The model represents a synthesis of two artificial intelligence techniques; the fuzzy logic and the neural network. Characteristics of the fuzzy neural network approach for the modelling of boronizing process are presented in this study. In order to validate the results of our calculation model, we have used the learning base of experimental data of the powder-pack boronizing of Fe-15Cr alloy in the temperature range from 800 to 1050 °C and for a treatment time ranging from 0.5 to 12 h. The obtained results show that it is possible to estimate the influence of different process parameters. Comparing the results obtained by the artificial neural network to experimental data, the average error generated from the fuzzy neural network was 3% for the FeB layer and 3.5% for the Fe2B layer. The results obtained from the fuzzy neural network approach are in agreement with the experimental data. Finally, the utilization of fuzzy neural network approach is well adapted for the boronizing kinetics of Fe-15Cr alloy.

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