Corundum-bearing residues produced through the evaporation of natural and synthetic hibonite

Abstract— We have produced corundum-bearing residues through the evaporation of natural and synthetic hibonite samples. The sequence of major element losses as well as volatility related trace element fractionations in these residues are similar to those previously observed in residues from the evaporation of chondritic starting material, which suggests that the processes by which these fractionations occur may be largely independent of the starting material used. However, the mineralogy of the residues does depend on the composition of the starting material and, to some extent, on the conditions under which evaporation took place. Similarly, the degree of isotopic mass fractionation observed in the residues is composition-dependent. This observation means that it may be possible to use isotopic data for several elements to constrain the compositions of precursor materials of Ca-Al-rich inclusions, which have an evaporation origin. Although corundum-bearing inclusions are known, their origins are complex and variable, and the scarcity of such inclusions indicates that melting of hibonite, with or without concomitant evaporation, must have been a rare process in the solar nebula. By evaporating mixtures of synthetic oxides of the rare earth elements, we have reproduced the patterns of Group III inclusions and some of the characteristics of ultrarefractory patterns. However, the extreme conditions required to do so indicate that refractory inclusions with these patterns probably have a condensation rather than evaporation origin.     

Use of genetic algorithm in new approach to modeling of flood routing

The hydrological models and simpli?ed methods of Saint-venant equations are used extensively in hydrological modeling, in particular for the simulation of the ?ood routing. These models require speci?c and extensive data that usually makes the study of ?ood propagation an arduous practice. We present in this work a new model, based on a transfer function, this function is a function of parametric probability density, having a physical meaning with respect to the propagation of a hydrological signal. The inversion of the model is carried out by an optimization technique called Genetic Algorithm. It consists of evolving a population of parameters based primarily on genetic recombination operators and natural selection to?nd the minimum of an objective function that measures the distance between observed and simulated data. The precision of the simulations of the proposed model is compared with the response of the Hayami model and the applicability of the model is tested on a real case, the N'Fis basin river, located in the High Atlas Occidental, which presents elements that appear favorable to the study of the propagation. The results obtained are very satisfactory and the simulation of the proposed model is very close to the response of the Hayami model.     

Three dimensional hydrodynamic modeling over bed forms in open channels

Three dimensional numerical modeling of idealized sand dunes was used to assess the capability of various modeling formulations to capture the flow structure and resistance introduced by bed forms which are similar to those in the Lower Mississippi River. The selected models were: ECOMSED (HydroQual), MIKE 3 [Danish Hydraulic Institute (DHI)] and H3D (Hayco). The study revealed that the hydrostatic versions of models did not capture the flow separation at the crest of the dunes; however, they did respond to the presence of bed forms and gave a total resistance similar to the non-hydrostatic models.     

Trace Elements in Sediments and Mussels – Spatial Distribution,Chemical Partitioning,and Risk Assessment

Sediment samples were collected from 30 different locations in Abu Qir Bay (Mediterranean Sea), East Alexandria, Egypt and analyzed for trace elements. The highest concentrations of most of the elements were observed in the nearshore stations in the vicinity of the major anthropogenic activities as industrial settlements, wastewater discharges, and agricultural drainage. In addition, mussel samples of Mactra corallina and Tapes decussata were collected corresponding to the sediment samples. Concentrations of As, Cd, Cr, Mn, and Zn in the mussel tissues were higher than concentrations in sediments, thus indicating their relatively high bioavailability. Sequential extraction procedure was performed on selected sediment samples. Significant correlations were observed between the concentrations of Cu, Mn, Pb, and Zn in the exchangeable fraction of the sediments and the corresponding tissues of M. corallina. The output of the risk assessment applied on the sediments revealed that adverse ecological effects to benthic species could occur and that a higher level of risk is expected from the exposure to Cd, Cr, Hg, and Zn. No adverse carcinogenic or non‐carcinogenic human health effects are expected from the consumption of the two mussel species from Abu Qir Bay.     

AERIAL RADIOMETRY OF EL ALAMEIN OILFIELD,EGYPT, U.A.R.*

Total gamma airborne radiometric survey of El Alamein area in the Western Desert has been carried out by the Atomic Energy Establishment. The flight lines are directed north-south with 500 m spacing, while the ground clearance is about 50 m. Superimposition of the radioactivity profiles over El Alamein Oilfield shows a general decrease of gamma radiation in the central part of the structure framed by zones of relatively higher values. The aerial radioactivity of El Alamein Oilfield is described and it is correlated with some reported radiometric characteristics of other oil bearing structures. The distribution of aeroradiometric measurements over El Alamein Oilfield and its environment has been found to be lognormal.     

P–T–t evolution of granulite facies metamorphism and partial melting in the Winding Stair Gap,Central Blue Ridge,North Carolina,USA

The Winding Stair Gap in the Central Blue Ridge province exposes granulite facies schists, gneisses, granofelses and migmatites characterized by the mineral assemblages: garnet–biotite–sillimanite–plagioclase–quartz, garnet–hornblende–biotite–plagioclase–quartz ± orthopyroxene ± clinopyroxene and orthopyroxene–biotite–quartz. Multiple textural populations of biotite, kyanite and sillimanite in pelitic schists support a polymetamorphic history characterized by an early clockwise P–T path in which dehydration melting of muscovite took place in the stability field of kyanite. Continued heating led to dehydration melting of biotite until peak conditions of 850 ± 30 °C, 9 ± 1 kbar were reached. After equilibrating at peak temperatures, the rocks underwent a stage of near isobaric cooling during which hydrous melt ± K‐feldspar were replaced by muscovite, and garnet by sillimanite + biotite + plagioclase. Most monazite crystals from a pelitic schist display patchy zoning for Th, Y and U, with some matrix crystals having as many as five compositional zones. A few monazite inclusions in garnet, as well as Y‐rich cores of some monazite matrix crystals, yield the oldest dates of c. 500 Ma, whereas a few homogeneous matrix monazites that grew in the main foliation plane yield dates of 370–330 Ma. Culling and analysis of individual spot dates for eight monazite grains yields three age populations of 509 ± 14 Ma, 438 ± 5 Ma and 360 ± 5 Ma. These data suggest that peak‐temperature metamorphism and partial melting in the central Blue Ridge occurred during the Salinic or Taconic orogeny. Following near isobaric cooling, a second weaker thermal pulse possibly related to intrusion of nearby igneous bodies resulted in growth of monazite c. 360 Ma, coinciding with the Neoacadian orogeny.     

Conservative identification of nodal transmissivities: theory,computational experiments and application to the Rharb coastal aquifer (Morocco)

Abstract

In order to calculate the transmissivity from the inverse problem corresponding to the groundwater flow in an isotropic horizontal aquifer, a numerical conservative approach is tested. The method deals with triangulation of the domain and applies the conservation of mass to elements of the mesh using the harmonic mean for internodal transmissivities. An optimal sweeping algorithm is used to evaluate nodal transmissivities from one element to another with a minimal relative error accumulation. The practical importance of the method is demonstrated through two synthetic examples representing those experienced in the field, then through application to a Moroccan aquifer. The computed hydraulic head is well fitted to the reference one, which confirms the validity of the identified transmissivity model.     

Mineralogy, Geochemistry, and Age Constraints on the Beni Bou Ifrour Skarn Type Magnetite Deposit, Northeastern Morocco

Abstract: The Beni Bou Ifrour deposit of northeastern Morocco is a skarn type magnetite deposit. K-Ar age determination suggests that the mineralization occurred at 7.040.47 Ma. The spatial relationship between skarn and dikes of microgran-odiorite derived from the batholith of Wiksane Granodiorite, and the similarity of age (8.020.22 Ma), confirms that the Wiksane Granodiorite is the igneous rock most probably related to mineralization. The skarn is distributed asymmetrically in the limestone, and magnetite ore was developed just below the calc-silicate skarn as two parallel beds separated by 100 m of barren limestone and schist.
The mineralization can be divided into three stages. The early stage is characterized by the formation of calc-silicate minerals, mainly clinopyroxene (80–70 % diopside) and garnet (early almost pure andradite to the late 60 % andradite). The main stage is characterized by the formation of a large amount of magnetite. Epidote and quartz formed simultaneously with magnetite. Fluid temperatures exceeded 500 C during the early to main stages. Fluid with very high salinity (50–75 wt% NaCl equiv.) was responsible for the formation of the magnetite ore. The oxygen isotope composition, together with the fluid inclusion data, suggests that magmatic fluid was significant for the formation of calc-silicate skarn minerals and magnetite. Low temperature (-230C) and low salinity (-10 % NaCl equiv.) hydrothermal fluids dominated by meteoric water were responsible for the late stage quartz and calcite formation.     

Ore Controls and Metallogenesis of Au-Ag Deposits at Atalla Mine, Central Eastern Desert of Egypt

Gold-silver deposits in the Atalla area occur as hydrothermal quartz veins in NE–SW pre-existing fractures within the Atalla granitic pluton. The orientation of such quartz veins has been attributed to extensional behavior related to the Atalla Shear Zone(ASZ). The Atalla area is covered by a variety of lithologies that are(from oldest to youngest): metasedimentary rocks, metavolcanic rocks, ophiolite assemblage(serpentinites/talc-carbonates), Atalla granite and Dokhan volcanic rocks. Microscopi...