Geochemical and geochronological characteristics of the Um Rus granite intrusion and associated gold deposit,Eastern Desert,Egypt

The Um Rus tonalite-granodiorite intrusion(~6 km2)occurs at the eastern end of the Neoproterozoic,ENE-trending Wadi Muba rak shear belt in the Central Eastern Desert of Egypt.Gold-bearing quartz veins hosted by the Um Rus intrusion were mined intermittently,and initially by the ancient Egyptians and until the early 1900 s.The relationship between the gold mineralization,host intrusion,and regional structures has always been unclear.We present new geochemical and geochronological data that help to define the tectonic environment and age of the Um Rus intrusion.In addition,field studies are integrated with EPMA and LA-ICP-MS data for gold-associated sulfides to better understand the formation and distribution of gold mineralization.The bulk-rock geochemical data of fresh host rocks indicate a calc-alkaline,metaluminous to mildly peraluminous,I-type granite signature.Their trace element composition reflects a tectonic setting intermediate between subduction-related and within-plate environments,presumably transitional between syn-and post-collisional stages.The crystallization age of the Um Rus intrusion was determined by in situ SHRIMP 206 Pb/238 U and 207Pb/235U measurements on accessory monazite grains.The resultant monazite U-Pb weighted mean age(643±9 Ma;MSWD 1.8)roughly overlaps existing geochronological data for similar granitic intrusions that are confined to major shear systems and are locally associated with gold mineralization in the Central Eastrn Desert(e.g.,Fawakhir and Hangaliya).This age is also consistent with magmatism recognized as concomitant to transpressional tectonics(D2:~650 Ma)during the evolution of the Wadi Mubark belt.Formation of the gold-bearing quartz veins in NNE-SSW and N-S striking fault segments was likely linked to the change from transpressional to transtensional tectonics and terrane exhumation(D3:620-580 Ma).The development of N-S throughgoing fault arrays and dike swarms(~595 Ma)led to heterogeneous deformation and recrystallization of the mineralized quartz veins.Ore minerals in the auriferous quartz veins include ubiquitous pyrite and arsenopyrite,with less abundant pyrrhotite,chalcopyrite,sphalerite,and galena.Uncommon pentlandite,gersdorffite,and cobaltite inclusions hosted in quartz veins with meladiorite slivers are interpreted as pre-ore sulfide phases.The gold-sulfide paragenesis encompasses an early pyrite-arsenopyrite±loellingite assemblage,a transitional pyrite-arsenopyrite assemblage,and a late pyrrhotite-chalcopyrite-sphalerite±galena assemblage.Free-milling gold/electrum grains(10 sμm-long)are scattered in extensively deformed vein quartz and in and adjacent to sulfide grains.Marcasite,malachite,and nodular goethite are authigenic alteration phases after pyrrhotite,chalcopyrite,and pyrite and arsenopyrite,respectively.A combined ore petrography,EPMA,and LA-ICP-MS study distinguishes morphological and compositional differences in the early and transitional pyrites(PyⅠ,PyⅡ)and arsenopyrite(ApyⅠ,ApyⅡ).Py I forms uncommon small euhedral inclusions in later PyⅡand Apy II.PyⅡforms large subhedral crystals with porous inner zones and massive outer zones,separated by narrow As-rich irregular mantles.The Fe and As contents in PyⅡare variable,and the LA-ICP-MS analysis shows erratic concentrations of Au(<1 to 177 ppm)and other trace elements(e.g.,Ag,Te,and Sb)in the porous inner zones,most likely related to discrete sub-microscopic sulfide inclusions.The outer massive zones have a rather homogenous composition,with consistently lower abundances of base metals and Au(mean 1.28 ppm).The early arsenopyrite(Apy I)forms fine-grained euhedral crystals enriched in Au(mean 17.7 ppm)and many other trace elements(i.e.,Ni,Co,Se,Ag,Sb,Te,Hg,and Bi).On the other hand,ApyⅡoccurs as coarsegrained subhedral crystals with lower and less variable concentrations of Au(mean 4 ppm).Elevated concentrations of Au(max.327 ppm)and other trace elements are measured in fragmented and aggregated pyrite and arsenopyrite grains,whereas the undeformed intact zones of the same grains are poor in all trace elements.The occurrence of gold/electrum as secondary inclusions in deformed pyrite and arsenopyrite crystals indicates that gold introduction was relatively late in the paragenesis.The LAICP-MS results are consistent with gold redistribution by the N-S though-going faults/dikes overprinted the earlier NNW-SSE quartz veins in the southeastern part of the intrusion,where the underground mining is concentrated.Formation of the Um Rus intrusion and gold-bearing quartz veins can be related to the evolution of the Wadi Mubarak shear belt,where the granitic intrusion formed during or just subsequent to D2 and provided dilatation spaces for gold-quartz vein deposition when deformed by D3 structures.     

The influence of channel morphology on bedload path lengths: Insights from a survival process model

Tracer studies are a commonly used tool to develop and test Einstein-type stochastic bedload transport models. The movements of these tracers are controlled by many factors including grain characteristics, hydrologic forcing, and channel morphology. Although the influence of these sediment storage zones related to morphological features (e.g., bars, pools, riffles) have long been observed to “trap” bedload particles in transport, this influence has not been adequately quantified. In this paper we explore the influence of channel morphology on particle travel distances through the development of a Bayesian survival process model. This model simulates particle path length distributions using a location-specific “trapping probability” parameter (p_i ), which is estimated using the starting and ending locations of bedload tracers. We test this model using a field tracer study from Halfmoon Creek, Colorado. We find that (1) the model is able to adequately recreate the observed multi-modal path length distributions, (2) particles tend to accumulate in trapping zones, especially during large floods, and (3) particles entrained near a trapping zone will travel a shorter distance than one that is further away. Particle starting positions can affect path lengths by as much as a factor of two, which we confirm by modelling “starting-location-specific” path length probability distributions. This study highlights the importance of considering both tracer locations and channel topography in examinations of field tracer studies. © 2020 John Wiley & Sons, Ltd.     

Spatially-Weighted Factor Analysis for Extraction of Source-Oriented Mineralization Feature in 3D Coordinates of Surface Geochemical Signal

Natural Resources Research - This contribution proposes a spatially weighted factor analysis (SWFA) to recognize effectively the underlying mineralization-related feature(s) in geochemical signals....     

The relationship among environmental variables,jellyfish and non‐gelatinous zooplankton: A case study in the north of the Gulf of Oman

Processes underlying the temporal and spatial variations observed in the distribution of jellyfish and non‐gelatinous zooplankton in the Gulf of Oman are not well understood. This information gap is clearly a major issue in controlling the harmful blooms of jellyfish and non‐gelatinous zooplankton. Samples of jellyfish and non‐gelatinous zooplankton were collected from six stations in Chabahar Bay and three stations in Pozm Bay within four seasons. At each station, environmental variables were also recorded from bottom and surface water. A total of 83 individuals of medusae representing four species of Scyphozoa (i.e., Cyanea nozakii, Chrysaora sp., Pelagia noctiluca, Catostylus tagi) and species of Hydrozoa (i.e., Diphyes sp., Rhacostoma sp., Aequorea spp.) were observed in the study area. A total of 70,727.25 individuals/m^?3 of non‐gelatinous zooplankton dominated by copepods and cladocerans were collected in nine stations within the four seasons. The results of a RELATE analysis yielded no significant association between species composition for jellyfish and non‐gelatinous zooplankton. Among environmental variables, water transparency, nitrite concentration, water depth and temperature were better associated with the total variation in jellyfish species composition than with that of non‐gelatinous zooplankton. Dissolved oxygen, pH, and phosphate concentration were significant environmental variables associated with the variation in the spatial and temporal distribution patterns of non‐gelatinous zooplankton assemblages. Although some jellyfish species (i.e., Rhacostoma sp., Pelagia noctiluca, Catostylus tagi) occur independently of non‐gelatinous zooplankton assemblages, other jellyfish (i.e., Chrysaora sp., Aequorea spp., Cyanea nozakii, Diphyes sp.) are strongly correlated with non‐gelatinous zooplankton assemblages.     

Analysis of symbiotic Symbiodinium in scleractinian corals off Northwestern Kish Island,Persian Gulf

The genus Symbiodinium plays an essential role in the resistance and survival of reef‐building corals during temperature anomalies. Coral colonies inhabiting the Persian Gulf (PG) experience extended periods of different stresses. Kish Island is located in the harsh environment of the Northern PG with previously reported bleaching episodes. Samples of six coral species from Northwestern Kish Island were analysed by internal transcribed spacer 2 of ribosomal DNA to identify in hospite Symbiodinium populations. The results showed that lineage D of Symbiodinium was the most prevalent clade among different coral colonies, while clade C was only detected in symbiosis with a single coral species. However, the detected Symbiodinium subclades belonged to two host generalists. The predominance of the stress tolerant Symbiodinium trenchii and subclade C3 could suggest an acclimatization strategy to cope with the hostile environment of the PG.     

Application of the coral health chart to determine bleaching status of <Emphasis Type="Italic">Acropora downingi</Emphasis> in a subtropical coral reef

The ‘Coral Health Chart’ has become a popular tool for monitoring coral bleaching worldwide. The scleractinian coral Acropora downingi (Wallace 1999) is highly vulnerable to temperature anomalies in the Persian Gulf. Our study tested the reliability of Coral Health Chart scores for the assessment of bleaching-related changes in the mitotic index (MI) and density of zooxanthellae cells in A. downingi in Qeshm Island, the Persian Gulf. The results revealed that, at least under severe conditions, it can be used as an effective proxy for detecting changes in the density of normal, transparent, or degraded zooxanthellae and MI. However, its ability to discern changes in pigment concentration and total zooxanthellae density should be viewed with some caution in the Gulf region, probably because the high levels of environmental variability in this region result in inherent variations in the characteristics of zooxanthellae among “healthy” looking corals.     

Assessing desertification by using soil indices

Desertification generally refers to land degradation in arid, semiarid, and dry semi-humid climatic zones. It involves five principal processes: vegetation degradation, water erosion, wind erosion, salinization and waterlogging, and soil crusting and compaction. The aim of this study is assessing desertification using soil criteria. For this purpose, nine indices including sodium absorption ratio (SAR), soil gypsum percentage, soil texture, the content of HCO₃ ^?, the percentage of the organic matter, electrical conductivity (EC), pH, the content of the soil sodium, and chloride were used. The soil samples were taken in the north of Zayandeh-Rood River in Isfahan province of Iran, using soil data randomly sampled in a depth of 0–20 cm. After assessing the normality of the samples using Kolmogorov-Smirnov test, indices were imported into GIS environment and interpolated with IDW and normal and discrete kriging methods for delineating soil characteristics maps based on MEDALUS model. In this model, the data were firstly changed from 100 to 200. Thus 100 and 200 are estimated as the best and worst quality, respectively. Then the final map of soil criteria has been created by geometric mean of its indicators. The results showed that the maximum area is related to the medium class of desertification and is equal to 44,746 ha. The areas of severe and very severe classes of desertification are equal to 30,949 and 351 ha, respectively. The results also revealed that the indices of the organic matter and soil gypsum percentage are the most influential indices which affect desertification phenomenon.     

Composition,radioactivity, and possible applications of kaolin deposits of Sinai,Egypt

This work discusses the composition, radioactivity, and possible utilization of the kaolin resources in Sinai which are hosted in thick sandstone sequences belonging to the Carboniferous (Wadi Khaboba) and Early Cretaceous (Wadi Iseila and Abansakar) ages. The characterization of kaolin was done by microscopic and SEM examination, supported by XRD and ICP-MS analyses. The studied kaolin resources consist of kaolinite, as the main constituent, associated with subsidiary dickite and halloysite, and minor contribution of smectite and illite. The most dominant non-clay mineral is quartz, besides minor gypsum, dolomite, and hematite. Ferrugination dominates, in most cases, at the upper boundaries of the kaolin lenses, suggesting possible supergene activity. The high Al₂O₃/SiO₂ ratio for the Cretaceous kaolin (0.54, in average) specifies its better grade relative to the Carboniferous kaolin (0.43, in average). The kaolin of the middle part of lens C in Wadi Iseila contains Si/Al molecular ratio of about unity, suggesting high-grade kaolin. The Carboniferous kaolin has enriched the radionuclides: U, Th, and Ra (at disequilibrium state due to leaching of eU relative to Ra) and the REE, relative to that of the Cretaceous age. The Carboniferous kaolin is characterized by a higher contribution of HREE (zircon signature), whereas LREE seems to be more influential for the Early Cretaceous kaolin (monazite signature). In spite of the very high CIA index (93 to 99), none of the analyzed kaolin deposits displays Ce abnormality. The high radioactivity of some Carboniferous kaolin can be a serious impediment for its utilization or its exportation. The kaolin of Sinai does not satisfy the international standards for paperwork industries and refractory manufacturing, but beneficiation may overcome this challenge. However, some lenses have high-grade kaolin with a low percentage of oxides of iron, magnesium, calcium, sodium, and potassium and a low radioactivity, hence nominated for the local refractory industry. The high-grade kaolin of Sinai fulfills the standards required for ceramics manufacturing in the global market. Grade 3 kaolin (< 30%, Al₂O₃) can be used in the manufacturing of white Portland cement and red glaze manufacturing on both local and global markets.     

Development of functionalized carrageenan,chitosan and alginate as polymeric chelating ligands for water softening

Chitosan, carrageenan and alginate are among the most abundant biopolymers in nature. They were prepared in uniform beads shape with a diameter of 2 mm ± 10%, using the encapsulator for removal of calcium, magnesium and iron cations from hard water. Solutions of 100–500 mg/L were prepared from each cation, and the detection of cations was carried out using atomic absorption spectrometer. Carrageenan and chitosan were able to chelate the three cations without further modification. However, alginate beads succeeded to chelate iron and magnesium and failed to chelate any calcium ions; in contrast, it increased the initial calcium concentration! That could be due to the pre-cross-linking of alginate beads using calcium chloride solution, which may be leaked back to the solution. However, grafting the alginate beads with polyethyleneimine and bromoacetic acid rectified this problem and the new functional group, –COOH, has been proved using the FT-IR. Optimization of the results in terms of beads weight (0.25–3.0 g) and cations concentrations (100–500 mg/L) has shown that most biopolymeric beads can chelate 85–100% of the cations in concentrations up to 500 mg/L. According to our finding, we came up with the recommendation to use chitosan for chelation of calcium and iron as it showed 100% chelation efficiency of both cations, whereas carrageenan is highly recommended for chelation of iron and magnesium, as it showed 100 and 98% chelation efficiency, respectively. Further work can be done on the reusability of the beads and scale up for the industrial use.