Silver and silver-bearing minerals at the Um Samiuki volcanogenic massive sulphide deposit, Eastern Desert, Egypt

The Um Samiuki Zn–Cu–Pb–Ag mineralisation, south Eastern Desert, Egypt is hosted by felsic volcanic rocks which form part of the 712-Ma-old, east-west-trending Shadli Volcanic Belt. Two major occurrences of massive sulphides are present at the top of rhyolitic breccia in the Western and Eastern mine areas. In each occurrence, a bornite-bearing zone is overlain by a pyrite-chalcopyrite-bearing zone and underlain by a disseminated, Cu-depleted zone. In the massive sulphide ore, sphalerite, chalcopyrite, pyrite, galena, bornite and tetrahedrite–tennantite are major minerals, whereas arsenopyrite, pyrrhotite, molybdenite and magnetite are accessory phases. Covellite and digenite are common secondary minerals. Bornite, tetrahedrite–tennantite and covellite contain high amounts of silver (averages of 1.97, 1.39 and 1.82 wt% respectively). Based on mineralogical balance calculations, bornite and covellite accommodate 80% of silver in the Um Samiuki deposit. Ag was incorporated in the crystal structure of the early-crystallised copper sulphides and sulphosalts and silver minerals. The temperature, sequential precipitation of the fluids and the structure of the crystallising phases control the distribution of silver. Post-depositional deformation and metamorphic processes caused liberation, remobilisation and redeposition of silver within the massive sulphides.Editorial handling: D. Lentz     

准噶尔盆地东南缘绿洲荒漠交错带土壤动物群落特征

为理解准噶尔盆地东南缘绿洲-荒漠交错带土壤动物群落特征,采用国际通用采样方法在2010年4月、7月、9月及11月中旬对该交错带不同生境土壤动物群落进行了调查研究,比较分析了该区土壤动物群落组成、多样性及其季节动态特征。结果表明:①共采集到大、中小型土壤动物9 788只,隶属于4门12纲32目,其中甲螨目、弹尾目、中气门目和前气门目为优势类群,常见类群有垫刃目、鞘翅目幼虫、膜翅目、无气门目、缨翅目和双翅目幼虫,优势类群和常见类群占群落总个体数的96.27%,其他22类群均属于稀有类群,只占总捕获量的3.73%。②在不同生境土壤动物群落组成、个体数量及多样性都表现出了明显的时空变异（P<0.05）,其类群数高低顺序为自然林＞防护林＞牧草地＞灌木林＞耕地＞菜瓜地＞荒草原＞荒漠,而个体数量顺序为菜瓜地＞耕地＞牧草地＞防护林＞自然林＞荒草原＞灌木林＞荒漠。③不同生境土壤动物的垂直分布具有明显的表聚特征,即从地表向下,随着土壤深度的增加土壤动物个体数量逐渐减少。④在不同生境土壤动物个体数量表现出了明显季节变化,其高低顺序为冬季＞秋季＞春季＞夏季。研究结果为进一步开展干旱区绿洲-荒漠生态系统土壤动物生态学的研究奠定了基础。     

Study of the Relationship between Recently Induced Earthquakes and Water Level at the Northwestern Side of Lake Nasser in Aswan Region,Egypt

Geotectonics - Lake Nasser is situated in an area with a very non-recurring earthquake, and revealed the history of Egypt registered 5000 years ago. After seventeen years of filling the Aswan High...     

A two‐step direct method for estimating the seismic response of nonlinear structures equipped with nonlinear viscous dampers

The insertion of fluid viscous dampers in building structures is an innovative technology that can improve significantly the seismic response. These devices could be very useful also in the retrofit of existing buildings. The effect of this typology of damping system is usually identified with an equivalent supplemental damping ratio, which depends on the maximum displacement of the structure, so that iterative procedures are required. In this paper, a simplified direct assessment method for nonlinear structures equipped with nonlinear fluid viscous dampers is proposed. The method proposed in this study is composed by two steps. The first one yields the direct estimate of the supplemental damping ratio provided by nonlinear viscous dampers in presence of a linear elastic structural response. The second step extends the procedure to structures with nonlinear behavior. Both graphical and analytical approaches have been developed. The proposed method has then been verified through several applications and comparisons with nonlinear dynamic analyses. Moreover, an investigation has been performed with regard to the influence of the relations that define the damping reduction factor and the hysteretic damping. Copyright © 2014 John Wiley & Sons, Ltd.     

Path planning in uncertain flow fields using ensemble method

An ensemble-based approach is developed to conduct optimal path planning in unsteady ocean currents under uncertainty. We focus our attention on two-dimensional steady and unsteady uncertain flows, and adopt a sampling methodology that is well suited to operational forecasts, where an ensemble of deterministic predictions is used to model and quantify uncertainty. In an operational setting, much about dynamics, topography, and forcing of the ocean environment is uncertain. To address this uncertainty, the flow field is parametrized using a finite number of independent canonical random variables with known densities, and the ensemble is generated by sampling these variables. For each of the resulting realizations of the uncertain current field, we predict the path that minimizes the travel time by solving a boundary value problem (BVP), based on the Pontryagin maximum principle. A family of backward-in-time trajectories starting at the end position is used to generate suitable initial values for the BVP solver. This allows us to examine and analyze the performance of the sampling strategy and to develop insight into extensions dealing with general circulation ocean models. In particular, the ensemble method enables us to perform a statistical analysis of travel times and consequently develop a path planning approach that accounts for these statistics. The proposed methodology is tested for a number of scenarios. We first validate our algorithms by reproducing simple canonical solutions, and then demonstrate our approach in more complex flow fields, including idealized, steady and unsteady double-gyre flows.     

Investigation of seawater intrusion using stable and radioisotopes at coastal area south of Beirut,the Capital of Lebanon

In this study, field measurements were made and environmental isotopes and radiological properties were determined in six selected wells located in the coastal area south of Beirut, the capital of Lebanon. It is one of the many district areas in Lebanon, threatened by the penetration of seawater into aquifers. Two sampling campaigns were carried out to determine possible seasonal variations. High electrical conductivity was observed, ranging from 1080 to 7900 μS/cm. The total dissolved solids values ranged from 530 to 5600 mg/L. This is attributed to a seawater intrusion confirmed by high chlorine concentrations that ranged from 400 to 3500 mg/L. Isotope data for δ¹⁸O/δ²H showed enrichment that is relatively small at the end of wet season due to recharge by local precipitation and infiltration. Carbon-14 ages and ²³⁴U/²³⁸U ratios confirmed the presence of young water. No radiological hazard was observed as all values lay below the guidance levels of the WHO.     

The El Achour (Algiers,Algeria) landslide delimitation using the H/V ambient vibration method

We present in this work investigations using seismic ambient vibration to delimitate the El Achour landslide (Algiers), upon which independent geotechnical studies were carried out. Acquisition campaign of ambient vibration on the El Achour site on June 2009 and June 2015, over a surface of about 2 ha, consisted of 64 records of ambient noise with a 10 to 20 m grid size. This approach consists of simple, light, and fast H/V acquisitions, in order to determine the extension of the unstable zone, the depth of the sliding surface, and to test the effectiveness of this method. Two peaks were interpreted as one being for the sliding surface and the other for the lithological interface. As results, in the stable area, they are satisfactory. Indeed, the points in this area are not intermediate peaks which could be related to potential sliding surfaces, which led us to think that we could delineate, using this method, the unstable area from the stable area. The HVSR method allows to determine the thickness of the geological formations and to highlight the lateral and vertical facies changes in broad area.     

Relocation of M ≥ 2 events of the 1989 Dôbi seismic sequence in Afar: evidence for earthquake migration

The Ethiopian side of central Afar was struck in August 1989 by the largest seismic sequence (three 6.1 ≤ M _s ≤ 6.3 events, 15 with M _s or m _b ≥ 5.0) since that of Serdo in 1969. Using the Djibouti seismological network, we relocated 297 of the events of that sequence. As most of the large events took place outside the network, we assessed the accuracy and stability of earthquake relocations by using three different velocity models and two relocation codes to try to relate individual shocks to distinct faults and surface breaks. A majority of the events apparently occurred underneath the floor of the Dôbi graben, an area about 45  km long and 15  km wide, rupturing boundary and inner floor faults, in agreement with the surface cracks and scarps that we mapped in the area. The relocation shows that the principal events propagated about 50  km northwestwards along the graben in the first 40  hr. A day and a half after the beginning of the sequence, smaller events ( M ≤ 4) started to propagate more than 55  km eastwards, towards Asal Lake. Using two three-component stations installed near the Ethiopian border, we could determine reliable depths for 21 events. The depths are compatible with a seismogenic crust about 14  km thick in the Dôbi and Hanle graben area. Although the Dôbi sequence ruptured about 50  km of the fault array extending from Serdo to Asal, where the regional stress was released by earthquakes in 1969 and 1978, respectively, a seismic gap about 50  km long still subsists along the northern part of the Gaggade region (Der'êla half-graben).     

A Stress Release Model in Egypt

Geotectonics - The complexity of seismogenesis calls for probabilistic rather than deterministic model. Towards that direction, the stress release models transpose the elastic rebound theory in a...