Recovery of some valuable elements from lamprophyre dykes in the Abu Rusheid area, Southeastern Desert, Egypt

In the Abu Rusheid area, Southeastern Desert of Egypt, polymineralized (HREEs, U, Zn and Pb) lam-prophyre dykes are recently recorded. The lamprophyre dykes cut cataclastic rocks along share zones in NNW-SSE trends. The secondary U-minerals are essentially represented by uranophane, kasolite, torbernite and autunite. Ex-perimental work was carried out on the lamprophyre dykes for the recovery of uranium and other valuable elements (e.g. Zn, Pb and Al) from 50 kg of technological sample. The optimum conditions were: 100 g/L sulfuric acid con-centration, 1:5 S/L (solid/liquid) and soaking for 15 days at room temperature. The leaching efficiencies for the re-covery of uranium and other elements like Al, Zn and Pb were 40, 33.6, 98.8 and 78, respectively.     

Metallogeny of gold in relation to the evolution of the Nubian Shield in Egypt

Gold mineralization in the Eastern Desert of Egypt is confined, almost completely, to the basement rocks of the Nubian Shield that was cratonized during the Panafrican orogeny.Island-arc, orogenic and post-orogenic stages are indicated for the tectonic-magmatic evolution of the Nubian Shield in Late Proterozoic times. Different styles of gold mineralization recognised in the Eastern Desert are inferred to have developed during these stages.In the island-arc stage, which is characterized by volcanic and volcaniclastic rocks in an ensimatic environment, gold mineralization is hosted in stratiform to strata-bound Algoma-type BIF and associated tuffaceous sedimentary rocks. Both types represent exhalative deposits, formed during breaks in sub-marine basaltic and bastalic–andesite volcanic eruptions. The volcanic rocks have a tholeiitic affinity and reflect an immature arc stage. Gold hosted in massive-sulphide deposits within calc-alkaline rhyolites represents another style of gold mineralization connected with mature island arc stage.During the orogenic-stage, ophiolites and island arc volcanic and volcaniclastic rocks were thrust onto the Pre-Panafrican continental margin. Subduction was active beneath the continent while the thrusting was still operative. A phase of calc-alkaline magmatic activity developed during this stage and the compressional deformation event was synchronous with regional metamorphism (greenschist–amphibolite facies). Extensional shear fractures (brittle–ductile shear zones) were broadly contemporaneous with the intense compressional tectonic regime. These fractures opened spaces in which the mineralizing fluids penetrated.Gold mineralization associated with the orogenic-stage is represented by vein-type mineralization that constituted the main target for gold since Pharaonic times. Other styles of gold mineralization during this stage are represented by altered ophiolitic serpentinites (listwaenites), Gold mineralization associated with intrusion related deposits (possibly porphyry copper deposits), as well as, auriferous quartz veins at the contacts of younger gabbros and G-2 granites.The post-orogenic stage is characterized by the dominance of intra-plate magmatism. Small amounts of the element in disseminations, stockworks and quartz veins of Sn–W–Ta–Nb mineralization represent gold mineralization connected with this stage.The link between these tectonic–magmatic stages and gold mineralization can be used as a criterion at any exploration strategy for new targets of gold mineralization in Egypt.     

Structures of quartz (100)- and (101)-water interfaces determined by x-ray reflectivity and atomic force microscopy of natural growth surfaces

The structures of prismatic (100) and pyramidal (101) growth faces of natural quartz crystals, and their modification upon annealing at T ≤ 400°C were investigated ex situ by atomic force microscopy (AFM) and in water by high-resolution X-ray reflectivity. AFM images revealed the presence of ∼ 0.1 to 1 μm-wide flat terraces delimited by steps of one to several unit cells in height. These steps follow approximately directions given by the intersection of growth faces. Modeling of X-ray reflectivity data indicates that surface silica groups on flat terraces have only one free Si-O bond each (presumably hydroxylated), except for some having two free Si-O bonds observed on a single (100) surface. Vertical relaxation of atomic positions (< 0.4 Å for terminal oxygens and < 0.2 Å for silicon and oxygen atoms fully coordinated to structural tetrahedra) is limited to a depth of 14 Å. Electron density profiles for all measured interfaces are consistent with a single layer of adsorbed water, with no evidence for additional organization of water molecules into distinct layers extending into the bulk solution. Similar interfacial structures were observed for natural and annealed surfaces of identical crystallographic orientation, indicating that extensive reconstruction of the silica network at the quartz surface did not occur under the annealing conditions.     

Common evolution of adjacent sunspot groups

The evolution of two adjacent bipolar sunspot groups is studied using Debrecen full-disc, white-light photoheliograms and H filtergrams as well as Meudon magnetograms. The proper motions of the principal preceding spots of both groups show quite similar patterns; the spots move along almost parallel tracks and change the direction of their motion on the same day at almost the same heliographic longitude. Also, three simultaneous emergences of magnetic flux were observed in both groups. These observations support the idea that these adjacent sunspot groups were magnetically linked below the photosphere. Matching the extrapolated magnetic field lines with the chromospheric fibril structure appears to be different in the two groups since they indicate quite different model solutions for each group, i.e., a near-potential magnetic field configuration in the older group (1) and a twisted force-free field configuration in the younger group (2). The latter configuration could be created by a considerable twist of the main bunch of flux tubes in Group 2, which is reflected in the relative sunspot motions. It is also showed how this twist contributed to the formation of a filament between the two groups.     

N2 vibrational distribution in aurorae

The N₂ vibrational distribution is calculated for a specific IBC Class II aurora using as input, data obtained from coordinated rocket and satellite observations and currently accepted excitation and quenching rates. The results of the calculations indicate no significant vibrational enhancements for this specific aurora nor for “upper limit” estimates for more intense aurorae. We conclude from this study that if significantly larger concentrations of vibrationally excited N₂ molecules exist in the aurora, as recent rocket e.u.v. measurements suggest, current concepts of the sources and sinks of N₂ vibrational excitation will require significant revision.     

Carbon content and carbonate 13C abundances in the Early Precambrian Swaziland sediments of South Africa

Carbon content (0.02–0.68% organic), carbonate content (0–69.7%) and carbonate ¹³C abundances (${}^{\mathrm{?}}\text{7.5?+2.3‰}$) were obtained on samples from the Swaziland sediments of South Africa, which are among the oldest known sedimentary rocks on earth (> 3·10⁹ years old). The carbon chemistry of these sediments may serve as evidence for early life and/or for products of chemical evolution. The variation of organic and carbonate carbon concentrations in different sedimentary horizons seems to be controlled by differences in depositional and diagenetic histories. The carbonate δ ¹³C values did not vary significantly from the ordinary range of Phanerozoic limestone values.     

High degree spherical harmonic expansion of gravity data

A spherical harmonic expansion of the gravity field up to degree and order 200 was carried out. Free air anomaly data over Canada (1⁰×1⁰ block averages) with a range of 211.1 mgal were used for testing. A low degree expansion (N=30) produced a map with a range of 63.6 mgal with contour patterns that could hardly be correlated with the original hand contoured map. A high degree expansion (N=200) on the other hand resulted in a map with a range of 199.8 mgal which quite faithfully reproduced the original including its local variations. Test computations verify that by monitoring the RMS values and the range of the expansion it is possible to arrive at an optimum degree of expansion for a given data set. It was also verified by the computations, that, since the computed expansions essentially have a zero value outside the domain of the input, it is possible to combine the results of separate non-overlapping expansions. Contribution of the Earth Physics Branch No. 900. Presented at the 1977 Spring Meeting, AGU, May 30–June 3, Washington, D.C.     

Spatial and vertical trends in sediment-phase contaminants in the upper estuary of the St. Lawrence River

The concentration of selected contaminant trace metals and organic contaminants, namely polycyclic aromatic hydrocarbons (PAHs), normal-alkanes, total polychlorinated biphenyls (PCBs), and other organochlorines, was studied in cores from shallow-water fine-grain sediments from both sides of the maximum turbidity zone (MTZ) in the upper estuary of the St. Lawrence. Average trace metal concentrations in the cores were generally lower in downstream sediments, except for Hg and Pb. Hg levels in the cores were very high, exceeding 0.7 μg g^?1 in core C168 (south shore) and 0.19 μg g^?1 in core LE (north shore). Trace metal concentrations in all the cores were highly variable with depth, but after normalization with reference to iron, the trend was remarkably uniform, thus confirming an important inverse relationship with grain size. A similar lack of a well-defined trend was noted in the profiles of the organic components in the modern sediments. Average PAH values for modern sediments at core sites C168 and LO were 1.05 μg g^?1 and 0.44 μg g^?1, respectively (i.e., less than or equal to those in Lake Ontario and upstream in the river). PCB values far exceeded those in upstream sediments (average: 347 ng g^?1 in core LE and 158 ng g^?1 in C168), but were less than in Lake Ontario. Concentrations of chlordane, heachlorobenzene, and mirex were relatively low and uniform in the modern sections of the cores. The vertical uniformity of both the contaminant profiles and those for Cs-137 (C168) suggests that the sediments are relatively young (i.e., definitely less than 35 yr at C168, and probably even less at LE and LO). Therefore no long-term or historical trend is evident.     

Indications of a biological and biochemical evolutionary trend during the archean and early proterozoic

Micropaleontological observations and organic geochemical analyses imply, but certainly do not prove, that life may not have been present ～3,800 Ma ago in Southwestern Greenland; however, physiologically complex prokaryotes flourished by the Early Proterozoic in other locations. It is, of course, also possible that life may have appeared earlier in locations other than Greenland. Investigations of Precambrian biological and biochemical evolutionary trends require interdisciplinary efforts, up-to-date instrumentation and methodology (such as ultramicrochemical analyses of individual microfossils/microstructures), and caution in the interpretation of experimental results.