Relationships between gold concentration and structure in quartz veins from the Hodgkinson Province, northeastern Australia

The Hodgkinson Province is a tract of␣multiply deformed Silurian-Devonian rocks in north␣Queensland, Australia. Gold-bearing quartz veins from the West Normanby Goldfield in the northern Hodgkinson Province were emplaced during the Permian D₄ event, broadly coeval with regional granite emplacement. Taylors Fault, a major structure that formed during D₂, hosts the veins which infill dilatational jogs opened during sinistral-normal reactivation of the fault in D₄. Veins contain graphitic laminations that formed when fault planes segmented wallrocks adjacent to the veins, producing tabular clasts that were tectonically sliced into the reefs. Laminations are the result of progressive shear strain, associated with continued movement on the faults, which caused strain-enhanced dissolution of silicate minerals and residual graphite enrichment in the clasts. This process produced graphite-coated shear planes that delimit zones of grain size reduction in the veins. Laminations commonly contain stylolites, which nucleated on pronounced sinuosities of the shear planes due to progressive shortening during D₄. Gold particles have preferentially nucleated in zones of relatively coarser-grained quartz adjacent to the shear planes, where shortening strain caused microfracturing and allowed fluid access. Gold may have been introduced with the quartz, but was redistributed within the reefs and localized along the laminations by the effects of synchronous, progressive deformation. Regionally, gold deposits show close spatial relationships with granite plutons of the Permian Whypalla Supersuite. Relationships in the West Normanby Gold Field support a regional model of reef emplacement and gold mineralization during the Permian D₄ event. Received: 24 August 1997 / Accepted: 14 October 1997     

A novel continuous magnetic nano-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/perlite fixed bed reactor for catalytic wet peroxide oxidation of dyes: reactor structure

In the present work, a continuous catalytic wet peroxide oxidation fixed bed reactor was employed to treat a simulated wastewater sample with malachite green dye, as a contaminant. Natural perlite particle-supported nano-Fe₃O₄ catalyst was used as a fixed bed inside a reactor, and it was immobilized by a persistent magnetic field. The range of (perlite) particle sizes was from 100 to 1000 nm. The effects of various operating parameters, including temperature of the reactor, pH, initial hydrogen peroxide concentration and initial dye concentration, were investigated on the percentage removal of malachite green dye. Load of catalyst of 2 g and volumetric flow rate of 1 L/h were selected for all the tests. Maximum malachite green degradation was 99.5 ± 0.3%. This removal percentage was attained at temperature of 80 °C, pH = 6, initial dye concentration of 6 mg/L and initial hydrogen peroxide concentration of 100 mg/L. The process was isotherm, and the catalyst showed high catalytic activity in the steady-state condition. The loss of catalyst was less than 0.3%.     

Laboratory Simulations of the Radial Distribution of the Toroidal Magnetic Field in an Axial Jet from a Young Stellar Object

Results from experiments on the radial distribution of the magnetic fields in axial plasma flows formed during the compression of a plasma–current sheath carried out at the KPF-4-PHOENIX plasmafocus installation are presented. The plasma flows were generated in a discharge with stationary filling of the chamber with a working gas of argon or hydrogen, and also with a pulsed injection of argon. Analysis of the radial profiles of the magnetic field distribution and their time variations are used to localize regions of trappedmagnetic field, as well as regions where a return current flows at the periphery of the plasma flow. It is shown that the transverse (radial) size of the plasma flow depends on the density of the ambient medium (background gas) through which it propagates. These experiments were carried out in the framework of a project on laboratory simulations of non-relativistic jets from young stars.

     

Modeling spatial landslide susceptibility in volcanic terrains through continuous neighborhood spatial analysis and multiple logistic regression in La Ciénega watershed,Nevado de Toluca,Mexico

Natural Hazards - Little study has been done on the effect of the pixel neighborhood information when modeling landslide susceptibility using multiple logistic regression (MLR). The present...     

Diverse signatures of deformation, pressure-temperature and anatexis in the Rayagada sector of the Eastern Ghats granulite terrane

The granulites and granitoids around Rayagada in the north central part of the Eastern Ghats belt display structural and petrological differences when compared to similar rocks from Chilka and Jenapore in the northern Eastern Ghats. The impress of F₁ deformation is almost erased while that ofF ₃ is muted. The metapelites have a restricted chemical range and are non-migmatitic. There are two varieties of leptynitic granitoids, one of which is interlayered with yet another S-type granite containing cordierite. The maximum recorded temperature from geothermometers is 780‡C, but the magnitude of pressure is comparatively low, the highest value being 6.3 kbar. Another distinctive feature of the pressuretemperature record is the absence of evidence of decompression in the lower realms of pressure and temperature. Metamorphic reactions that could be identified indicate cooling, a noteworthy reaction being the sillimanite to andalusite transformation. Integration of data from pressure-temperature sensors suggest cooling at two pressures, 6 and 5 kbar. The generation of two types of granitoids from metapelites is interpreted to be due to intersection with solidus curves for pelitic and graywacke-like compositions, constrained by recent experiments, at 6 and 5 kbar. The first melting occurred on a prograde path while the second one was due to increase in temperature during exhumation at tectonic rates. Thus inspite of a broad similarity in the geodynamic scenario across the northern part of the Eastern Ghat belt, differences in exhumation rates and in style of melting were responsible for producing different signatures in the Rayagada granulite terrane.     

Magmatic Evolution of the La Pacana Caldera System, Central Andes, Chile: Compositional Variation of Two Cogenetic, Large-Volume Felsic Ignimbrites

La Pacana is one of the largest known calderas on Earth, andis the source of at least two major ignimbrite eruptions witha combined volume of some 2700 km³. These ignimbrites have stronglycontrasting compositions, raising the question of whether theyare genetically related. The Toconao ignimbrite is crystal poor,and contains rhyolitic (76–77 wt % SiO₂) tube pumices.The overlying Atana ignimbrite is a homogeneous tuff whose pumiceis dacitic (66–70 wt % SiO₂), dense (40–60% vesicularity)and crystal rich (30–40 % crystals). Phase equilibriaindicate that the Atana magma equilibrated at temperatures of770–790°C with melt water contents of 3·1–4·4wt %. The pre-eruptive Toconao magma was cooler (730–750°C)and its melt more water rich (6·3–6·8 wt% H₂O). A pressure of 200 MPa is inferred from mineral barometryfor the Atana magma chamber. Isotope compositions are variablebut overlapping for both units (⁸⁷Sr/⁸⁶Sr_i 0·7094–0·7131;¹⁴³Nd/¹⁴⁴Nd 0·51222–0·51230) and are consistentwith a dominantly crustal origin. Glass analyses from Atanapumices are similar in composition to those in Toconao tubepumices, demonstrating that the Toconao magma could representa differentiated melt of the Atana magma. Fractional crystallizationmodelling suggests that the Toconao magma can be produced by30% crystallization of the observed Atana mineral phases. Toconaomelt characteristics and intensive parameters are consistentwith a volatile oversaturation-driven eruption. However, thelow H₂O content, high viscosity and high crystal content ofthe Atana magma imply an external eruption trigger. KEY WORDS: Central Andes; crystal-rich dacite; eruption trigger; high-silica rhyolite; zoned magma chamber     

Electrokinetic remediation of metal contaminated glacial tills

This paper presents the results of an experimental investigation which studied the feasibility of using the electrokinetic process to remediate contaminated clays of glacial origin, otherwise known as glacial tills. An overview of the electrokinetic phenomena, as well as previously performed laboratory and field investigations, is first presented. The methodology of the electrokinetic experiments which were conducted to investigate the removal of metals from a glacial till is then described. A total of 16 experiments were conducted using glacial till samples obtained from a project site near Chicago. Sodium and calcium were used as the surrogate cationic metallic contaminants. These experiments demonstrated that ion transport during the electrokinetic process occurs due to both electro-osmosis and electromigration, but that due to electromigration is significantly higher than that due to electro-osmosis. Unlike other clays such as kaolinite, the glacial till used for this investigation possessed high buffering capacity because of its high carbonate content which prevented the acid front migration from the anode to the cathode during the electrokinetic process. The ion removal efficiency of the electrokinetic process was found to increase when: (1) the voltage gradient applied to the soil was increased, (2) the initial concentration of the contaminants was increased, and (3) the duration of the treatment process was increased. The ion removal efficiency was also greater for smaller ions which possess less ionic charge and when the ions existed independently in the soil as compared to when they coexisted. This investigation suggests that the electrokinetic process has significant potential for remediating glacial tills contaminated with metals. However, the properties of Na and Ca are not representative of contaminants, such as heavy metals, so further investigations are needed.     

Changes in the water regime of the caspian sea

The article deals with issues of structure and dynamics of the Caspian Sea water balance. On the base of historical, paleogeomorphological and other data the evolution history of the Caspian Sea and its basin has been observed for different time intervals down to 400 thous. years ago. Presented are computerized data on water balance components in the current centenary obtained from instrumental observations, revealed are causes of the sea-level fluctuations within that time interval and anthropogenic factor contribution to this process. Based on the analysis of this material, an attempt has been undertaken to present a scenarion of a possible sea-level position of the Caspian Sea with the expected versions of climatic changes at the end of the XX and beginning of the XXI centuries.     

A 27-Day Period in the Flux of Jovian Electrons at the Earth’s Orbit

Variations in the flux of Jovian electrons near the Earth in two synodic cycles of the Earth–Jupiter system, in 1974–1975 and 2007–2008, are considered. In the 1974–1975 cycle, Jovian electrons were observed by IMP-8 during 13 successive solar rotations; electrons were observed by SOHO during 14 solar rotations during the 2007–2008 cycle. The fluxes of these electrons in each solar revolution experienced variations with a characteristic time scale of ~27 ^d , with the maximum flux near the middle of the rotation. The mean period of the variations does not coincide with the synodic period for the Sun–Earth system, equal to 27.3 ^d . The mean variation periods for the electron fluxes were 26.8 ^d in 1974–1975 and 26.1 ^d in 2007–2008. The detected variations are interpreted as reflecting variations in the structure of the solar wind speed and associated magnetic traps, the confinement time of the electrons in thesemagnetic traps, and the influence of the relative positions of the Earth and Jupiter in space.