Geochemistry of Triassic Carbonates: Exploration Guide to Pb–Zn Mineralization in North Tunisia

The Triassic carbonate rocks in Northern Tunisia (Nappes, Domes, Jurassic Mountains zones), consist of massive carbonates, clays and gypsum with authigenic minerals. These are associated with several Pb–Zn deposits and occurrences. At Jebel Ichkeul, Bechateur and Oum Edeboua, these Triassic carbonates exhibit enrichment in Pb (0.32 to 228 ppm), Zn (17 to 261 ppm), Cd (5 to 6 ppm) and Co (0.3 to 89.5 ppm), with respect to their average contents in crustal carbonates. The enrichment is more pronounced at Oum Edeboua (near the ore zone). Permeability is one of the most effective factors of dispersion of metallic trace elements, causing the development of geochemical halos. The genetic relationship of the Triassic carbonate rocks with the ore deposits was controlled by diapirism and tectonic movements, which favored mineralization along the Triassic‐cover contact as well as the remobilization of metals from the mineralized rocks. Analysis of metallic trace elements in Triassic rocks provides clues to the presence of possible mineral deposits. These could be effectively used for both geochemical interpretation and mineral exploration. Carbon and O‐isotope data (– 9.3‰ < δ¹³C < +3‰; +21.9 < δ¹⁸O < +31‰) suggest that the Triassic carbonates of all study areas have marine carbonates as their origin; some of them show significantly lower δ¹⁸O values indicating some exchange with hydrothermal fluids. Calcites associated with mineralization at Oum Edeboua have δ¹³C of –6.2‰ to –8.22‰ and δ¹⁸O of +24.88‰ to +25‰. The C‐isotope compositions of these calcites are ¹³C depleted, indicating an organic origin.     

Application of ASTER and Landsat TM Data for Geological Mapping of Esfandagheh Ophiolite Complex,Southern Iran

This research developed an approach to enable the discrimination of lithological units and detection of host rock of chromitite bodies within ophiolitic complexes using the advanced spaceborne thermal emission and reflection radiometer (ASTER) and Landsat thematic mapper (TM) satellite data. Three main ophiolite complexes located in southern Iran were selected for the study. A specialized band ratio (4/1, 4/5, 4/7) of ASTER, minimum noise fraction (MNF) components and spectral angle mapper (SAM) on ASTER and Landsat TM data were used to distinguish ophiolitic rock units. Results show that the specialized band ratio was able to identify different rock units and serpentinized dunite as host rock of chromitites within ophiolitic complexes. Minimum noise fraction components of ASTER and Landsat TM data are suitable for distinguishing ophiolitic rock complexes at a regional scale. The integration of SAM and feature level fusion used in this investigation discriminated the ophiolitic rock units and provided geological map for the study area, including identification of high potential areas (serpentinite dunite) for chromite exploration targets.     

Optimization of Bottom Friction Coefficient Using Inverse Modeling in the Persian Gulf

Ocean Science Journal - A practical method for the calibration of the ocean circulation model is introduced using measured water levels along the Persian Gulf coastlines. Dimensional analysis is...     

Modeling in situ benzene bioremediation in the contaminated Liwa aquifer (UAE) using the slow-release oxygen source technique

Dissolved benzene was detected in the shallow unconfined Liwa aquifer, UAE, which represents the main freshwater source for the nearby residence Bu Hasa camp area. The main source of this contamination is believed to be the rejected water released from Bu Hasa liquid recovery plant. In this paper, a finite element model (METABIOTRANS) is used to simulate the fate and transport of the dissolved benzene plume in Liwa aquifer. Different remediation scenarios were simulated in which the slow-release oxygen source (SOS) technique is utilized to minimize benzene concentrations at the nearest camp supply wells downstream of the contamination zone. Results of the remediation scenarios show that the highest biodegradation rates occur when the oxygen source is placed near the plume center; where higher benzene concentrations exist. The nearest oxygen release source to the contamination zone caused higher stimulation to bacterial growth than further down-gradient oxygen sources. It also exhibited longer resident time of oxygen in the aquifer; and therefore, yielded higher reductions in benzene concentrations. However, using one central SOS proved to be insufficient as contaminant escaped laterally. Additional four transverse oxygen sources were necessary to capture benzene that laterally spread away from the contamination zone. These lateral SOSs were essential to reduce benzene concentrations at the supply wells that are located at the plume fringes. Finally, it was found that increasing oxygen release from one source did not always improve remediation; and that using several SOSs with lower release rates could be a more practical approach to enhance benzene biodegradation in the aquifer.     

New approaches for non‐classically damped system eigenanalysis

This paper presents three new approaches for solving eigenvalue problems of non‐classically damped linear dynamics systems with fewer calculations than the conventional state vector approach. In the latter, the second‐order differential equation of motion is converted into a first‐order system by doubling the size of the matrices. The new approaches simplify the approach and reduce the number of calculations. The mathematical formulations for the proposed approaches are presented and the numerical results compared with the existing method by solving a sample problem with different damping properties. Of the three proposed approaches, the expansion approach was found to be the simplest and fastest to compute. Copyright © 2005 John Wiley & Sons, Ltd.     

Evolution of filamentary molecular clouds in the presence of magnetic fields

The purpose of this paper is to explore the effect of magnetic fields on the dynamics of magnetized filamentary molecular clouds.We suppose there is a filament with cylindrical symmetry and two components of axial and toroidal magnetic fields.In comparison to previous works,the novelty in the present work involves a similarity solution that does not define a function of the magnetic fields or density.We consider the effect of the magnetic field on the collapse of the filament in both axial and toroidal directions and show that the magnetic field has a braking effect,which means that the increasing intensity of the magnetic field reduces the velocity of collapse.This is consistent with other studies.We find that the magnetic field in the central region tends to be aligned with the filament axis.Also,the magnitude and the direction of the magnetic field depend on the magnitude and direction of the initial magnetic field in the outer region.Moreover,we show that more energy dissipation from the filament causes a rise in the infall velocity.     

Sorption of lead on Iranian bentonite and zeolite: kinetics and isotherms

This study deals with the use of the natural, low-cost sorbents bentonite and zeolite for the removal of lead from aqueous solutions. The mineral material is from large deposits of bentonite and zeolite that have been discovered recently in Iran. Experimental and modeling data from our kinetic and equilibrium investigations reveal that (1) the pseudo-second-order kinetic model gave the best fit, and (2) the Koble–Corrigan sorption model describes the interaction between Pb(II) and the two mineral materials better than the Freundlich and Langmuir models. However, the sorption of Pb(II) ions by zeolite and bentonite is complex and probably involves several mechanisms. The experimental data show that natural zeolite and bentonite used in this study exhibited a reasonable sorption capacity for Pb(II), and thus may be useful for the immobilization of Pb(II) from polluted sites.     

Formation of Small-Scale Condensations in the Molecular Clouds via Thermal Instability

A systematic study of the linear thermal instability of a self-gravitating magnetic molecular cloud is carried out for the case when the unperturbed background is subject to local expansion or contraction. We consider the ambipolar diffusion, or ion-neutral friction on the perturbed states. In this way, we obtain a non-dimensional characteristic equation that reduces to the prior characteristic equation in the non-gravitating stationary background. By parametric manipulation of this characteristic equation, we conclude that there are, not only oblate condensation forming solutions, but also prolate solutions according to local expansion or contraction of the background. We obtain the conditions for existence of the Field lengths that thermal instability in the molecular clouds can occur. If these conditions establish, small-scale condensations in the form of spherical, oblate, or prolate shape may be produced via thermal instability.