Mineralogy, geochemistry, and origin of hydrothermal manganese veins at Wadi Maliek, Southern Eastern Desert, Egypt

The present work deals with the geology, mineralogy, geochemistry, and origin of the metagabbroic-hosted manganese deposits at Wadi Maliek in the southern Eastern Desert of Egypt. The manganese veins are found in the shear zones and channel ways of the fault planes within the metagabbroic rocks pointing to those hydrothermal solutions carrying manganese and iron load penetrating along these fractures. These faults are striking N 80° E?CS 80° W with dipping 65°. These veins vary in thickness from 15?cm up to 125?cm wide; each vein may show difference in thickness from bottom to top. Microscopic examinations, X-ray diffraction, infrared spectral, differential thermal (DTA), thermogravimetric (TGA), and ESEM-EDAX analyses revealed that the manganese minerals consist mainly of pyrolusite, psilomelane, and ramsdellite. Goethite and hematite are the common iron minerals. Petrographically, the manganese deposits can be classified into three ore types based on the predominance of manganese and iron minerals: manganese, manganese?Ciron, and iron ore types. The geochemistry of Maliek deposits indicated that the total averages of some major oxides in manganese, manganese?Ciron, and iron ore types are respectively as follows: SiO₂ (15.64%, 11.52%, and 20.58%), MnO (39.9%, 17.81%, and 0.77%), FeO* (7.13%, 33.31%, and 37.08%), CaO (5.89%, 5.82%, and 5.32%), and Na₂O (1.04%, 1.61%, and 1.53%). With regard to trace elements, the Maliek manganese deposits are rich in Zn, Ba, Pb, Sr, and V. Based on the geological, mineralogical, and geochemical results, the studied manganese deposits are considered to be precipitated from hydrothermal solution.     

A comparative study of hydraulic conductivity estimations using geostatistics

Three approaches for estimating the hydraulic conductivity (K) of the Trifa aquifer, Morocco were investigated: (1) kriging of the K values obtained from pumping tests, (2) cokriging of the pumping test data with electrical resistivity data as a secondary variable, and (3) cokriging of the pumping test data with the slope of the water table. Gauss-transformed values of the variables are used because they provide more robust variograms and transformed values of the primary and secondary variables show correlations higher than the raw values, which is beneficial in cokriging. In cokriging with electrical resistivity, two zones are considered since the geological deposits are different from the north to the south of the aquifer, which is reflected in different correlations between the variables. Comparison of the three approaches is based mainly on the estimation errors, and to a lesser degree on the cross-validations of the corresponding variogram models and general considerations, like the measurements’ reliability and aquifer make-up. The best-estimated K is given by cokriging with the slope of the water table and is therefore preferred for further use in groundwater flow modeling. Thus, electrical resistivity or the slope of the water table can both be used as secondary variables to estimate K, especially in heterogeneous aquifers with lateral variations in lithology, as is the case of the Trifa aquifer.     

The impact of subsurface geological structure on the groundwater occurrence using geophysical techniques in wadi El Kallabiyyah and wadi As Sabil,East Esna,Eastern Desert,Egypt

The present study aims to explain some hydrogeological problems that are related to geological setting in two wadis: El Kallabiyyah and As Sabil East Esna. For this purpose, land magnetic, vertical electrical soundings, and two-dimensional electrical resistivity imaging profiles were measured. The lithological succession comprises Upper Cretaceous to Quaternary deposits that rest on a Precambrian basement rock. The results of the interpretation of the land magnetic measurements in wadi El Kallabiyyah represent the depth to the basement rock which ranges from 260 to 660 m and increases towards the northeast trend, but in wadi As Sabil, there is a large basin at the center of the wadi with the recorded depth to the basement reaching 1,300 m due to the effect of two normal faults (F1 and F2). The results of the interpretation of the vertical electrical sounding and two-dimensional imaging confirmed the presence of these faults in wadi As Sabil. The results of the geoelectrical measurements in wadi El Kallabiyyah represented the water-bearing layer at the third unit that consists of sands, gravels, boulders, and clays. The presence of clay will affect the potentiality of a drilled well. For wadi As Sabil, the results of geoelectrical measurements led to the lower part of the second unit which acts as a water-bearing layer that consists of sands, boulders, gravels, and clays. It can be concluded that the best site for drilling wells in wadi El Kallabiyyah is at vertical electrical sounding no.5 with a total depth of not less than 230 m. In wadi As Sabil, the drilled wells must be concentrated at the center and the downstream.     

Diagenetic origin of Basal Anhydrite in the Cretaceous Maha Sarakham salt: Khorat Plateau, NE Thailand

Development of a diagenetic anhydrite bed at the base of the Cretaceous Maha Sarakham Saline Formation (the `Basal Anhydrite' member) of the Khorat Plateau in north-eastern Thailand took place due to leaching and/or pressure dissolution of salt at the contact between an underlying active sandstone aquifer system and an overlying massive halite-dominated evaporite sequence. Basal evaporites composed of halite with intercalated anhydrite of the latter sequence are undergoing dissolution as a result of subsurface flushing, with anhydrite produced as the insoluble residue. The result is a 1·1 m thick interval of nodular anhydrite displaying unique, basin-wide continuity. Observed textures, petrographic features and chemical data from the anhydrite and associated authigenic minerals support the origin of the Basal Anhydrite Member as an accumulation residue from the dissolution of the Maha Sarakham salts. Petrographically, the anhydrite in this unit is made up of crystals that are blocky and recrystallized, sheared, generally elongated and broken, and is bounded at the bottom by organic-rich stylolite surfaces. Authigenic and euhedral dolomite and calcite crystals are associated with the anhydrite. Traces of pyrite, galena and chalcopyrite are present along the stylolite surfaces suggesting supply of fresh water from the underlying sandstone at highly reducing conditions of burial. The δ<sup>34</sup>S of sulphate in the Basal Anhydrite averages 15 ‰ (CDT) and falls within the isotopic composition of the anhydrite in the Cretaceous Maha Sarakham Formation proper and the Cretaceous values of marine evaporites. Measured δ<sup>18</sup>O in dolomite range from ?4·37 to ?14·26‰ (PDB) suggesting a re-equilibration of dolomite with basinal water depleted in <sup>18</sup>O and possible recrystallization of dolomite under relatively elevated temperatures. The δ<sup>13</sup>C, however, varies from +1·57 to ?2·53‰ (PDB) suggesting a contribution of carbon from oxidation of organic matter. This basal anhydrite bed, similar to basinwide beds found at the bottom of many giant evaporite sequences, has always been considered to be depositional. Here, at the base of the Maha Sarakham Formation, we demonstrate that the anhydrite is diagenetic in origin and was formed by accumulation of original anhydrite by dissolution of interbedded halite from waters circulating though the underlying aquifer: it represents an `upside-down' caprock.     

Exchange of light rare earths for Ca in apatite

Diffusion experiments were carried out on natural apatite crystals that were immersed in molten light rare earth element (REE) chloride salt at temperatures between 900 and 1150 °C for periods up to 35 days. Electron microprobe analysis of the crystals showed that light REEs replaced Ca according to electronic balance, i.e. $\text{2}\text{REE}{}^{\mathrm{3+}}$ for $\text{3}\text{Ca}{}^{\mathrm{2+}}$. These diffusion profiles indicate that a maximum amount of substitution in the structure occurs when two of the ten Ca ions in apatite are replaced by the REE diffusing elements. Anisotropic diffusion is observed between a and c crystallographic directions. Comparison of maximum distance indicates that the larger ions move more easily in the apatite structure. We conclude that the light REEs diffuse within the channel structures of the mineral, and that this diffusion is controlled by the substitution type of elements in the calcium sites. To cite this article: A. Iqdari et al., C. R. Geoscience 335 (2003).     

Potentialité d'utilisation d'argiles marocaines de Jbel Kharrou dans l'industrie céramique

The Ordovician clays of Jbel Kharrou (Rehamna, Morocco) have been studied for their use in ceramic industry. The realised studies were carried out on two samples B1 and B2, the most representative, taken from a clay dominated formation that outcrops 25 km east of the Skhour Rehamna city. The chemical analyses, mineralogical studies and advanced technological tests undertaken on the two samples indicate that these clays can be considered as non-refractory material, so they can be used to the manufacturing of ceramic products: soil and wall tiles, sanitary, pottery, etc. The tested briquettes, cooked at 1040?°C, remain flat, without deformation or defects; they are of cream white dye. These briquettes show a high mechanical resistance to the flexion, the loss in weight remains tolerable with cooking, lightly elevated (12% ); it can be corrected by the addition of a grease-remover. To cite this article: N. El Yakoubi et al., C. R. Geoscience 338 (2006).     

Potential link between exposure to fungicides chlorothalonil and mancozeb and haemic neoplasia development in the soft-shell clam Mya arenaria: A laboratory experiment

The aetiology of haemic neoplasia (HN) is unknown, so far but many causative factors are suggested such as viral, pollution and genetics. The aim of this study was to determine if, under chronic exposure, two major pesticides (chlorothalonil and mancozeb) which are used in potato production could induce HN in soft-shell clams (Mya arenaria). Short-term experiments with acute exposure were also performed. Clams were collected from an epizootic site (North River, PEI) and from a site free of the disease (Magdalen Islands, Quebec). The tetraploid level of haemocytes was assessed by flow cytometry for each clam to determine the HN status. The bioaccumulation of pesticides in tissues was quantified by gas chromatography/mass spectrometry (GC/MS) for chlorothalonil while mancozeb and manganese were quantified by inductively coupled plasma-mass spectrometer (ICP/MS). Long term exposure to fungicide Bravo 500^® did not induce high tetraploid levels on negative calm from North River and the analysis of the digestive gland and the mantle did not reveal any detectable level of chlorothalonil. In the Manzate 200 DF^®, some clams revealed high level of tetraploid cells but no difference were observed between the treatments and the control. The analysis of the digestive gland and the mantle for manganese did not highlight any significant difference in tissue concentration (p = 0.05). For the acute exposure, chlorothalonil analysis showed that the active ingredient is distributed between four chlorinated compounds: 99.5% for chlorothalonil isomers, 0.4% for pentachlorothalonil and 0.1% for trichlorothalonil isomers. For a 72 h experiment, the accumulation was within 4 h; the higher tissue concentration of chlorothalonil was 59.2 μg g⁻¹ in the mantle after 48 h, following by a decrease to an undetectable level at the end. For the manganese, the accumulation was detected after 4 h; the higher tissue concentration was 48.8 μg g⁻¹ in the mantle after 24 h and, over the following 48 h, the accumulation decreased until the end of the trial. Based on the data, the accumulation of these fungicides seems to be transitory. Chlorothalonil and mancozeb are both oxidative-stress promoters and could have induced cell dysfunction while in the tissue. Study on the effect of these fungicides on the p53 protein system is an example of strategy that would provide information on cellular events promoting neoplasia.     

Maximizing the management of groundwater resources in the Paris–Abu Bayan reclaimed area,Western Desert,Egypt

The Paris–Abu Bayan area located along the Darb El Arbaein road is involved in the New Valley Project in the Egyptian Western Desert (EWD) as part of ongoing efforts since the 1960s. In this dryland area, groundwater stored in the Nubian Sandstone Aquifer System (NSAS) serves as the only water resource for a number of different uses. A major concern is the significant groundwater withdrawals from 74 pumped wells since the beginning of agricultural activities in 2000. The recent rapid expansion of agricultural activity and the lack of sufficient groundwater recharge as a result of unplanned groundwater development have led to severe stress on the aquifer. Field measurements have shown a rapid decline in groundwater levels, creating a crisis situation for this sole source of water in the area. In this study, mathematical modeling of the groundwater system (single aquifer layer) of the Paris–Abu Bayan reclaimed area was implemented using MODFLOW to devise a new strategy for the sustainable use of groundwater, by applying a number of scenarios in a finite-difference program. The conceptual model and calibration were developed by generating and studying the hydrogeological records, NSA parameters, production wells, and water level measurements for 2005 and 2012. Three management scenarios were applied on the calibrated model to display the present and future stresses on this aquifer over a 30-year period (2012–2042). The results clearly show a high decline in the heads of the NSA, by about 13.8 m, due to the continuous withdrawal of water (first scenario: present conditions, 102,473 m³/day). In the second scenario, the water level is expected to decrease significantly, by about 16 m, in most of the reclamation area by increasing the pumping rates by about 25% (over-pumping) to meet the continuous need for more cultivation land in the area. To reduce the large decline in water levels, the third plan tests the aquifer after reducing the water withdrawal by approximately 25%, applying modern irrigation systems, and suggesting two new reclaimed areas in the northeastern and northwestern parts (areas 1 and 2), with 20 new wells, at 500 m³/day/well. The results in this case show that groundwater levels are slightly decreased, by about 9.5 m, while many wells (especially the new wells in the northern part) show a slight decrease in groundwater levels (0.8 m). The results comparison shows that the groundwater level in the modeled area is lowered by 0.3 m/year with an increase in the number of wells to 94 and increased cultivation area by about 18% (third scenario), versus 0.45 m/year and 0.60 m/year recorded for the first and second scenarios, respectively. Therefore, based on the results, the third scenario is recommended as a new strategy for improving groundwater resource sustainability in the region.     

Hydrothermal alteration of plagioclase in granitic rocks from Proterozoic basement of SE Sweden

Petrographic examinations and electron microprobe analyses of Proterozoic granitic rocks, SE Sweden aimed to characterize and unravel the mechanisms and conditions of plagioclase alterations. These alterations include saussuritization, albitization and replacement of plagioclase by K‐feldspar. The hydrothermal alterations, which are inferred to have occurred at ca. 250–400°C, resulted in concomitant formation of Al‐rich titanite, epidote, calcite, pumpellyite, prehnite and iron oxides. Replacement of plagioclase by K‐feldspar occurs in red‐stained zones, which have developed close to thin fractures owing to the precipitation of tiny Fe‐oxide pigment particles within the altered plagioclase, whereas saussuritized plagioclase has less systematic spatial relationships to these fractures. Albitization of plagioclase occurred in rocks that are poor in biotite compared to rocks that suffered extensive saussuritization. The chemical and textural characterization of various types of plagioclase alterations allows elucidation of the granitic hydrothermal systems. Features of feldspar alteration in the granitic rocks are similar to those encountered in feldspathic sandstones and should hence be considered in studies on diagenetic changes of siliciclastic successions during basin evolution. Copyright © 2009 John Wiley & Sons, Ltd.