Geologic relationships and mineralization of peralkaline/alkaline granite-syenite of the Zargat Na’am ring complex, Southeastern Desert, Egypt

Tungsten-bearing hydrothermal veins range from tensional veinlets to lodes containing multiple injections of hydrothermal quartz veins. Major composite lodes display greisen alteration envelopes characterized by enrichments in volatiles, K2O, Al2O3, Rb, L…     

Rare metal-bearing pegmatites from the Southeastern Desert of Egypt： Geology, geochemical characteristics, and petrogenesis

The pegmatite province of the Southeastern Desert (SED) is part of a pegmatite district that extends from Egypt (extends to 1200 km2). Rare metal pegmatites are divided into (1) unzoned, Sn-mineralized; (2) zoned Li, Nb, Ta and Be-bearing; and (3) pegmatites and pegmatites containing colored, gem-quality tourmaline. The Rb/Sr data reflect a crustal origin for the rare metal pegmatites and indicate that the original SED magma was generated during the peak of regional metamorphism and predates the intrusion of post-tectonic leucogranites. These bodies developed an early border zone consisting of coarse to very coarse muscovite quartz alkali feldspar, followed by an intermediate zone of dominant quartz feldspar muscovite rock. Garnet, tourmaline, beryl, galena, pyrite, amblygonite, apatite and monazite are rare accessories in both zones. Cassiterite tends to concentrate in replacement zones and along fractures in albite quartz muscovite-rich portions. The highest concentrations of cassiterite occur in irregular greisenized zones which consist dominantly of micaceous aggregates of green Li-rich muscovite, quartz, albite and coarse-grained cassiterite. The different metasomatic post-solidification alterations include sodic and potassic metasomatism, greisenization and tourmalinization. Geochemically, the pegmatite-generating granites have a metaluminous composition, showing a differentiation trend from coarse-grained, unfractionated plagioclase-rich granite towards highly fractionated fine- to medium-grained, local albite-rich rock. Economically important ore minerals introduced by volatile-rich, rare metal-bearing fluids, either primarily or during the breakdown of the primary mineral assemblages, are niobium-tantalum oxides, Sn-oxides (cassiterite), Li-silicates (petalite, spodumene, euctyptite, and pollucite), Li-phosphates (amblygonite, montebrasite and lithopilite) and minor REE-minerals (Hf-zircon, monazite, xenotime, thorian, loparite and yttrio-fluorite). The pollucite is typically associated with spodumene, petalite, amblygonite, quartz and feldspar. The primary pollucite has Si/Al (at) ratios of 2.53-2.65 and CRK of 79.5- 82.2. Thorian loparite is essentially a member of the loparite (NaLREETi2O6)-lueshite (NaNbO3)-ThTi2O6-ThNb4O12 quaternary system with low or negligible contents of other end-member compositions. The mineral compositionally evolved from niobian loparite to niobian thorian and thorian loparite gave rise to ceriobetafite and belyankinite with high ThO2 contents. Thorian loparite is metamict or partly metamict and upon heating regains a structure close to that of synthetic loparite NaLaTi2O6.     

A classification of galactic collisions

The effects of collisions between two galaxies on the test galaxy considered are classified as follows — Type A: the changes in the size and mass of the test galaxy are both negligible; Type B: There is significant increase in the size (at least 10%) or decrease in the mass (at least 1%) of the test galaxy or in both; Type C: The test galaxy becomes a component of a double galaxy by tidal capture; Type D: The test galaxy is disrupted by the tidal forces of the field galaxy.The type of collision is given as a function of the distance and speed at closest approach and also as a function of the initial impact parameter and speed at infinite separation of the two galaxies for two density models of the galaxies. Collisions in which the two galaxies do not penetrate each other are generally of type A while slow interpenetrating collisions are generally of type B. Types C and D occur in head-on or nearly head-on collisions if the relative speed of the two galaxies is sufficiently small; the former is favoured if the two galaxies do not differ appreciably in mass and density distribution. If one of the two galaxies is considerably less massive or less centrally concentrated than the other, it will be disrupted in slow close collisions.     

Changes in sizes and shapes of spherical galaxies in head-on collisions

Head-on collisions of two identical spherical galaxies are studied for two initial velocities (1) nearly equal to and (2) greater than the capture velocity. Orbits of about 500 representative stars are computed taking into account the effects of dynamical friction in the motion of the galaxies. From the computer studies the changes in the structure of the galaxies are deduced. The galaxies contract at closest approach and expand as they recede from each other. When the initial velocity is nearly equal to the capture velocity, the mean radius expands to almost double its size and the galaxies have a prolate structure until the closest approach with the longer axis in the direction of motion. The prolate structure is destroyed as the galaxies recede. For larger collision velocity (V ∼ 1.5 V_cap), the mean radius expands by 50 per cent and the galaxies are prolate until the closest approach and distinctly oblate after the collision. The fractional increase in the binding energy is 0.46 in the first case and 0.30 in the second case.     

Global risks of Bedellia somnulentella (Lepidoptera: Bedelliidae) invasion: a modeling exercise using a mechanistic model,CLIMEX

Theoretical and Applied Climatology - This study aimed to identify the global risk of invasion and establishment of Bedellia somnulentella, a pest of the sweet potato crop, for the present and...     

Modeling and Prediction of Habitat Suitability for Ferula gummosa Medicinal Plant in a Mountainous Area

Natural Resources Research - Habitat suitability modeling and mapping are important aspects of long-term strategies for sustaining plant ecosystems. In this study, seven state-of-the-art machine...