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31.
The Emarat deposit, with a total proved reserve of 10 Mt ore grading 6% Zn and 2.26% Pb, is one of the largest Zn–Pb deposits in the Malayer–Esfahan belt. The mineralization is stratabound and restricted to Early Cretaceous limestones and dolomites. The ore consists mainly of sphalerite and galena with small amounts of pyrite, chalcopyrite, calcite, quartz, and dolomite. Textural evidence shows that the ore has replaced the host rocks and thus is epigenetic.Sulfur isotopes indicate that the sulfur in sphalerite and galena has been derived from Cretaceous seawater through thermochemical sulfate reduction. Sulfur isotope compositions of four apparently coprecipitated sphalerite–galena pairs suggest their precipitation was under equilibrium conditions. The sulfur isotopic fractionation observed for the sphalerite–galena pairs corresponds to formation temperatures between 77 °C and 168 °C, which agree with homogenization temperatures of fluid inclusions.Lead-isotope studies indicate that the lead in galena has been derived from heterogeneous sources including orogenic and crustal reservoirs with high 238U/204Pb and 232Th/204Pb ratios. Ages derived from the Pb-isotope model give meaningless ages, ranging from Early Carboniferous to future. It is probable that the Pb-isotope model ages that point to an earlier origin than the Early Cretaceous host rocks are derived from older reservoirs in the underlying Carboniferous or Jurassic units, either from the host rocks or from earlier-formed ore deposits within these units.This research and other available data show that the Emarat Zn–Pb deposit has many important features of Mississippi Valley-type (MVT) lead–zinc deposits and thus we argue that it is an MVT-type ore deposit. 相似文献
32.
A survey on the epiphytic microorganisms growing on Posidonia oceanica leaves was conducted along a depth transect along the coast of Eastern Tunisia (Mahdia). Samples were collected by SCUBA diving at depths of 3, 5, 10 and 12 m in July 2008 and January 2009. A total of 58 microepiphyte taxa were identified. Multivariate analyses revealed temporal and spatial variation of the abundance of epiphytic microalgae. Water motion, light availability, temperature and motility of species seem to be responsible of temporal and bathymetric variations of epiphytic microalgae. Unlike diatoms, dinoflagellates were more abundant in deep waters, suggesting that they are more vulnerable to hydrodynamics. The significant correlation between leaf area index and abundance of epiphytic species indicates that the phenological parameters of the host plant influence the abundance of the epiphytic microorganisms. Among the epiphytic dinoflagellates, our data showed a great number of potentially toxic species (Alexandrium minitum, Amphidinium carterae, Karenia selliformis, Coolia monatis, Karlodinium veneficum, Ostreopsis siamensis, Prorocentrum concavum, Prorocentrum minimum, Prorocentrum rathymum and Prorocentrum lima). These species were more abundant in the deep station under more sheltered conditions than found at inshore shallower stations, which are subjected to high water motion. 相似文献
33.
Lazhar Belkhiri Abderrahmane Boudoukha Lotfi Mouni Toufik Baouz 《Journal of African Earth Sciences》2011,59(1):140-148
Water analysis data of 54 groundwater samples from 18 uniformly distributed wells were collected during three campaigns (June, September and December 2004). Q-mode hierarchical cluster analysis (HCA) was employed for partitioning the water samples into hydrochemical facies. Interpretation of analytical data showed that the abundance of major ions was identified as follows: Ca ? Mg > Na > K and HCO3 ? Cl > SO4. Three major water facies are suggested by the HCA analysis. The samples from the area were classified as recharge area waters (Ca–Mg–HCO3 water), transition area waters (Mg–Ca–HCO3–Cl water), and discharge area waters (Mg–Ca–Cl–HCO3 water). Inverse geochemical modeling suggests that relatively few phases are required to derive the water chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area fall into two categories: (1) evaporite weathering reactions and (2) precipitation of carbonate minerals. 相似文献
34.
Spatial scale variability in shoot density and epiphytic leaves of Posidonia oceanica on Kerkennah Island (Tunisia) in relation to current tide effects 
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下载免费PDF全文 Mounir Ben Brahim Lotfi Mabrouk Asma Hamza Mabrouka Mahfoudhi Abderahmen Bouain Lotfi Aleya 《Marine Ecology》2015,36(4):1311-1331
A study was undertaken of the patterns of spatial variability, epiphytic biomass and distribution of epiphytic fauna and flora of Posidonia oceanica. Samples were taken at four stations located approximately 4 km apart, exposed to different current conditions. Stations A and B, situated near the Oued Mimoun tidal channel with its relatively strong bi‐directional flows, were affected by high current tide. The other two stations, North Oued Mimoun (L1) and South Oued Mimoun (L2), were located further from the channel, in low current tide conditions. Sampling was conducted in the Attaya area of Kerkennah Island (Tunisia) in August 2009 at depths between 2 and 3 m, with the results indicating differences among the stations. Shoot density decreased when exposed to high levels of hydrodynamic activity generated by current tides whereas the epiphytic biomass of P. oceanica leaves decreased at sheltered stations located far from the channel. Epiphytic algae such as Heterokontophyta, Rhodophyta and Chlorophyta, and epiphytic fauna represented by Bryozoa, Hydrozoa, Annelida, Porifera and Tunicata, dominated the epiphytic assemblages and were abundant at the station most exposed to high current tide hydrodynamics. Cyanobacteria, however, were dominant in stations exposed to low current tide. 相似文献
35.
Bourhane-Eddine Belabed Xavier Laffray Amel Dhib Mouna Fertouna-Belakhal Souad Turki Lotfi Aleya 《Marine pollution bulletin》2013
This paper presents the results of a seasonal survey of heavy metals accumulated in sediments and in the soft parts of the body of the mussel Perna perna at four stations in the Gulf of Annaba (Algeria). Pooled soft tissues from 10 mussels representing the entire range of sizes were digested in nitric acid. Statistical analysis reveals a significant seasonal effect on all the measured metals, the highest values being recorded in winter. With the exception of Cr, the levels for all metals were significantly higher in the east, at the outlet of the Seybouse River, than at all other monitoring stations. The study also shows that north-western waters are subject to a significantly lower degree of heavy metal pollution than elsewhere in the gulf. Levels were nevertheless within the limits of public health standards. 相似文献
36.
A finite element technique is developed for two-dimensional problems of dynamics of dam–water–foundation systems taking into account all interactions rigorously. Water–foundation interaction, which previous developments have only simulated, is considered by imposing proper conditions at the fluid–solid interface. Furthermore, the technique permits treatment of layered foundations. An application to a concrete gravity dam–water–foundation system is presented and discussed. 相似文献
37.
Lotfi Mabrouk Taher Guarred Asma Hamza Imed Messaoudi Ahmed Noureddine Hellal 《Marine pollution bulletin》2014
Fluctuating asymmetry, a random deviation of bilateral traits, is assessed on grass goby Zosterisessor ophiocephalus Pallas, 1811 living in one disturbed site and in one unpolluted site Gulf of Gabes (Tunisia). Statistical analysis showed that assessed asymmetries are fluctuating. FA of orbital diameter, sub-orbital distance, pectoral fin and post-orbital length are higher in polluted site compared to control. Chemical pollution seems to be responsible for this high FA. 相似文献
38.
H. Borgheipour F. Hosseinzadeh Lotfi Z. Moghaddas 《International Journal of Environmental Science and Technology》2017,14(8):1697-1712
Sugar plants are one of the most energy-consuming industries in Iran; thus, the implementation of measures to improve energy efficiency seems necessary for such industries. This paper investigated sugar plants’ efficiency in different stages for implementation process of energy efficiency measures focusing on determining some relations for benchmarking and reaching efficient status. In doing so, the process of implementation of energy efficiency improvement measures is planned on the basis of experts’ opinions. Also, for deriving the efficiency of each plant in each of the stages of implementation of measures and the aggregate efficiency of them a multi-stage data envelopment analysis model is formulated. The obtained results from average efficiency indicated that the under evaluation population in the first, second, third, and fifth stages have a good performance and in the fourth-stage managers could not perform successfully. Also, the results of determining some relations for benchmarking showed that to what extent each of the outputs of each stage of the implementation process of energy efficiency measures in the sugar plants should be changed in order to achieve efficient conditions. The distance between the current output and the desirable output indicates to what extent manager has been successful in operation, studies of the rate of change of each of the outputs to achieve the efficient conditions are of the utmost importance in developing suitable strategies. 相似文献
39.
Tahar Aloui Lotfi Rhimi Ikram Jabli Arwa Hermassi Fredj Chaabani 《Arabian Journal of Geosciences》2017,10(11):240
The present work focuses on the ability of Late-Barremian sands from Ouaddada Mountain (Central Tunisia), to produce high-quality white cement clinker. Results indicate that these sands are particularly characterized by their fineness of grains (mean grain-size 90–140 μm), high cleanness (sand equivalent 88–98%), extremely low coloring oxides and volatiles levels (less than 0.03 and 1.9% respectively) and high values of whiteness and lightness indices (more than 86 and 90% respectively). Studies based on Bogue calculation, X-ray diffraction (XRD), burnability of raw mixes, Point Counting and Scanning Electron Microscopy (SEM) with Energy-Dispersive X-Ray Spectroscopy (EDS) methods, reveal that the Late-Barremian sands from Ouaddada Mountain can be used in the production of white Portland clinker by mixing with 70.8–75.6% of local limestones and 3.5–24.8% by weight of common Mediterranean kaolins from Guadalajar province (Central Spain), Tamazert (North-East Algeria), ?ile (North-West Turkey), Sebha (South-West Libya), and Abu Zanima area (West-Central Sinai, Egypt). Synthesized clinkers are composed largely of alite (75–76.2%), belite (12.8–16.5%) and aluminate (7.4–8.9%) with subordinate quantities of ferrite (less than 1%), slightly harder to burn and seem to be much whiter than Mediterranean ones with a whiteness index β more than 86%. 相似文献
40.
Formulation and algorithmic treatment of a rate‐dependent plastic–damage model modified to capture large tensile cracking in cyclic‐loaded concrete structures are presented in detail for a three‐dimensional implementation. The plastic–damage model proposed by Lee and Fenves in 1998 was founded based on isotropic damaged elasticity in combination with isotropic multi‐hardening plasticity to simulate cracking and crushing of concrete under cyclic or dynamic loadings. In order that the model can capture large crack opening displacements, which are inevitable in plain concrete structures, the excessive increase in plastic strain causing unrealistic results in cyclic behaviors is prevented when the tensile plastic–damage variable controlling the evolution of tensile damage is larger than a critical value. In such a condition, the crack opening/closing mechanism becomes similar to discrete cracking. The consistent tangent operator required to accelerate convergence rate is also formulated for the large cracking state including viscoplasticity. The validation and performance of the modified algorithm implemented in a special finite element program is exemplified through several single‐element tests as well as three structural applications. The last example examines the model in the seismic fracture analysis of Koyna dam as a benchmark problem and the resulting crack profile is compared with the available experiment. The numerical experimentations well demonstrate that the developed model whose modification is necessary to properly simulate the cyclic behavior of plain concrete subjected to large tensile strains is robust and reasonably accurate. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献