Genesis of Gold Deposit in Um Trambishi Area, NE Atbara, Sudan.

Um Trambishi area consists of volcano-sedimentary sequence intruded by syntectonic pluton of granitoids composition with marginal fissures injected by aplite, had been subjected to dynamic metamorphism and obliterated by recrystallization forming different rock units varying in composition, forming greenschist terrains. These are an assemblage of recrystalline schists, meta-acid, cataclastic tonalite, granodiorites, meta-andesite, chlorite schists, quartzite, marble, metabanded chert, together with two generations of unmineralized deformed and undeformed white quartz, which are oriented mainly in E-W and N-S direction following faults trend. The area is subjected to four deformational phases of brittle-ductile transition. The metamorphic grade is Green Schist Facies. The alteration around the endo-contact zone is characterized by minerals: albite, chlorite, epidote, sericite, carbonate and kaolin with anomalous Au=0.91ppm, Ag=1.75ppm, As=44.6XRF, Co=15.70XRF, V=65XRF, Ti=4796XRF, Cr=23XRF, Sr=269XRF, and base metals Pb=1.51ppm, Zn=22.02ppm and Cu=13.59ppm. The first phase of hydrothermal solution carrying gold is related to the magmatic high temperature associated with granitoidal intrusions, deposited into the planar fabric S1 and has a characteristic signature of hypothermal processes .The second mode of occurrence is the regeneration of auriferous quartz stringers filling into the tectonic fissures trending 340⁰ and oblique to S1 as a result of D3 (Keraf Shear Zone) and has a characteristic signature of mesothermal processes.

Controls on dolomitization in extensional basins: An example from the Derbyshire Platform, U.K.

ABSTRACT Fault-controlled dolomitization has been documented in Lower Carboniferous (Viséan) platform carbonates at various localities in the Pennine Basin and North Wales. The largest of these dolomite bodies (approx. 60 km2) occurs on the Derbyshire Platform, on the southern margin of the Pennine Basin. This study tests the hypothesis that dolomitization occurred at this locality during deposition, platform drowning, and the earliest stages of burial, coincident with the transition from a late syn-rift to post-rift regime. It also assesses the importance of syn-rift volcanism on dolomitization. Planar, fabric-retentive dolomite with single-phase (i.e., low temperature) fluid inclusions occurs along NW–SE and E–W oriented faults, and in platform margin facies and in proximity to the Masson Hill Volcanic Complex. Oxygen isotope data are consistent with dolomitization from seawater, but slightly depleted δ13C values reflect mixing with magmatic fluids. Volcanic activity is likely to have produced a thermal drive for fluid circulation on the platform margin, and post-depositional alteration of basalts by CO2-rich fluids could have led to alteration of olivine and release of magnesium to convecting seawater. Consequently, the large volume of dolostone on the southern margin of the Derbyshire Platform is attributed to the increased geothermal gradient and a localized increase in the Mg/Ca ratio of dolomitizing fluids at this locality, compared to elsewhere in the Pennine Basin. The results suggest that syn-rift carbonate platforms in volcanically active areas of rift basins have a greater potential for dolomitization from seawater than non-volcanic platforms in the same basin.

Design and Analysis of SMA Woven Fabric

Shape Memory Alloys (SMAs) are often used for robotic, biomedical, and aerospace applications because of their unique ability to undergo large amounts of stress and strain during thermomechanical loading compared to traditional metals. While SMAs such as NiTi have been used in wire, plate, and tubular forms, NiTi as a woven dry fabric has yet to be analyzed for use as protective materials and actuators. Applications of SMA fabric as a “passive” material include shields, seatbelts, watchbands and window screens. Applications as an “active” material include robotic actuators, wearable medical and therapy devices, and self-healing shields and screens. This paper applies a macro-mechanical model from composites analysis to NiTi plain woven fabric to determine the effective elastic constants. The fabric model is based on actual weave geometry, including the presence of open gaps and wire cross-sectional area, and with the same diameter and alloy in the warp and weft. A woven NiTi ribbon has been manufactured (Figure 1) using a narrow weaving machine and has been tested in uniaxial tension. Planar fabric constants were measured at a range of temperatures. The analytically and experimentally derived constants for various weave patterns and cover factor combinations are presented and compared. It was determined that in uniaxial tension the fabric behaves like a collection of unidirectional wires, but has 78% of the rigidity, on average, across all test temperatures. This result is predicted by the fabric model with a 16% error, demonstrating that the proposed analytical model offers a useful tool for design and simulation of SMA fabrics.

Quartz c-axis fabrics in constrictionally strained orthogneisses: implications for the evolution of the Orlica-Śnieżnik Dome, the Sudetes, Poland

ABSTRACT Żelaźniewicz, A., Kromuszczyńska, O. and Biegała, N. 2013. Quartz c-axis fabrics in constrictionally strained orthogneisses: implications for the evolution of the Orlica-Śnieżnik Dome, the Sudetes, Poland. Acta Geologica Polonica, 63(4), 697-722, Warszawa. The Orlica-Śnieżnik Dome (OSD), NE Bohemian Massif, contains in its core several gneiss variants with protoliths dated at ~500 Ma. In the western limb of the OSD, rodding augen gneisses (Spalona gneiss unit) are mainly L>S tectonites with a prominent stretching lineation. The few quartz LPO studies have produced somewhat discrepant results. Reexamination of these rocks revealed that texture formation was a protracted, multistage process that involved strain partitioning with changing strain rate and kinematics in a general shear regime at temperatures of the amphibolite facies (450-600°C). Quartz c-axis microfabrics show complex yet reproducible patterns that developed under the joint control of strain geometry and temperature; thus the LPOs are mixed features represented by pseudogirdle patterns. Domainal differences in quartz microfabrics (ribbons, tails, quartzo-feldspathic aggregate) are common in the Spalona orthogneisses but uncommon in the sheared migmatitic gneisses. In the latter rocks, the constrictional strain was imposed on the originally planar fabric defined by high-temperature migmatitic layering. The constrictional fabric of the Spalona gneisses may have developed in the hinge zones of kilometer-scale folds, where the elongation occurred parallel to the fold axes. Other occurrences of rodding gneisses throughout the Orlica-Śnieżnik Dome are thought to occupy similar structural positions, which would point to the significance of large-scale folds in the tectonic structure of the dome.

The Ainslie Detachment: a regional flat-lying extensional fault in the Carboniferous evaporitic Maritimes Basin of Nova Scotia, Canada

The Ainslie Detachment occurs near the base of the Carboniferous Windsor Group, forming a regional flat-lying extensional fault distributed across 10 000 km2. New mapping has delineated the structure through southwestern Cape Breton Island and into central Nova Scotia. Shearing is concentrated at the top of the basal Macumber limestone along its contact with overlying evaporites and younger allochthonous units. The highly contrasting rheologies of the formations created an anisotropic zone of weakness which acted as an upper crustal stress guide, stratigraphically controlling the trajectory of the detachment through the basin. The detachment is characterized by an approximately 3–10 m thick calc-mylonite zone, with an intense planar fabric featuring alternating very fine grained shear planes and coarser annealed layers. Coarser layers are boudinaged into pinch and swell structures, locally producing segmented augen. Highly strained intraclasts, ooids, and peloids, recrystallized carbonate boudins, and carbonate vein segments are included in the calc-mylonite as semirigid inclusions and rotated porphyroclasts. Thick zones of fault breccia straddle portions of the detachment and overprint the mylonite, demonstrating an evolution to brittle conditions during progressive shear. Listric faults in the hanging wall of the detachment feature a ramp and flat geometry, with an upper detachment occurring along the upper contact of the Windsor Group with the overlying Namurian Mabou Group. Locally up to 2 km of the stratigraphic succession has been removed, with faults cutting downsection in a westerly direction producing rollover in the hanging wall.

Deformation of shale and dolomite in the Lewis thrust fault zone, northwest Montana, U.S.A.

The Lewis thrust fault zone at Marias Pass, northwest Montana, is an example of a fault zone in which hanging-wall dolomite and footwall shale deformed at relatively shallow levels (~7 km). Fabric in the fault zone depends on the rock type. Deformation of dolomite involved coalescence and widening by cataclasis of fractures, formation of anastomosing cataclasite zones that isolate less deformed clasts, and rounding and reduction in size of clasts to produce random-fabric cataclasite. Whereas dolomite deformed by progressive widening of cataclasite zones, shale deformation localized along ultracataclasite zones and slip surfaces that bound shale duplexes. Fault rocks that include both footwall shale and hanging-wall carbonate are characterized by isoclinal, intrafolial folds and a foliation that is defined by alternating shale- and carbonate-rich bands, elongate lenses of carbonate, and preferred orientation of phyllosilicates. Calcitization and subsequent solution of hanging wall rocks incorporated in the shale contributed to the development of this planar fabric. Lenses of hanging-wall carbonate were isolated in footwall shale by the emplacement of shale tongues into the hanging wall along mesoscopic faults. Displacement on the Lewis fault was accommodated by deformation of both dolomite and shale. Grain-size reduction of dolomite, mixing of dolomite and shale, and calcitization of dolomite in the fault zone may have enhanced diffusional processes in the carbonate and thereby weakened the fault zone.