The Gagarka gold deposit in the central Urals, Russia

The Gagarka gold deposit was formed in two stages. The gold-telluride ore of the main early stage was formed ～260 Ma ago synchronously with Permian collision, which was accompanied by retrograde metamorphism with mobilization of Au and Te from geochemically similar massive sulfide lodes in the rift zone. The Au-bearing argillic metasomatic rocks of the late stage presumably Mesozoic in age are distinguished by specific geochemistry and locally superposed on the ore related to the early stage. The upper part of the metasomatic column consists of quartz-kaolinite rock, which is confused in many cases with products of Mesozoic-Cenozoic weathering and because of this is not perceived as a guide for hidden Au-bearing argillic alteration, whose resource potential remains underestimated in the Urals.     

Copper, lead and cadmium concentrations in surface water, sediment and fish, C. Carpio, samples from Lake Naivasha: effect of recent anthropogenic activities

Following recent concerns of chemical pollution around Lake Naivasha, especially originating from recent agricultural activities in the catchment, samples of water, sediments, and fish Common carp (Cyprinus carpio) were collected from the Hippo Point, Kasarani, Mouth of Malewa River, Mouth of Karati River, Crescent Island, Sher Karuturi Discharge outlet and Oserian Bay for analysis of Cu, Cd and Pb by FAAS. The mean heavy metal levels ranged from 5.12?C58.11 (Pb), 1.06?C1.73 (Cd), and <0.03?C2.29 (Cu) mg/kg wet weight in C. carpio muscle, <100?C179.83 (Pb), <10.00?C10.06 (Cd) and <30.00?C32.33 (Cu) ??g/L in surface water, and 17.11?C53.07 (Pb), 1.18?C5.58 (Cd) and 3.00?C8.48 (Cu) mg/kg dry weight in sediment and showed a wide variation within and between samples with relatively high concentrations in sediments and fish muscle tissues. The results indicate that Lake Naivasha, in some parts, is polluted with these heavy metals of which relatively higher concentrations are found at the discharge outlets near Sher Karuturi and Oserian Bay. This indicates possible contribution from surrounding horticultural/floricultural activities and the Mouths of the Rivers Malewa and Karati which flow from it??s upper catchment.     

RECONSTRUCTING THE SOLAR CORONAL MAGNETIC FIELD AS A FORCE-FREE MAGNETIC FIELD

We present some preliminary results on different mathematical problems encountered in attempts to reconstruct the coronal magnetic field, assumed to be in a force-free state, from its values in the photosphere. We discuss the formulations associated with these problems, and some new numerical methods that can be used to get their approximate solutions. Both the linear constant- and the nonlinear cases are considered. We also discuss the possible use of dynamical 3D MHD codes to construct approximate solutions of the equilibrium force-free equations, which are needed for testing numerical extrapolation schemes.     

An Early Investigation Of The Striated Tail Of Comet Hale-Bopp (C/1995 O1)

The Sekanina-Farrell particle fragmentation model for the striated tails of dust comets is successfully applied to two images of comet Hale-Bopp to study the motions of 12 striae in a time span of March 12–15, 1997. There is evidence for recurring outbursts with a periodicity of 11^h21^m, consistent with results based on analysis of dust jets. The ejecta in all the striae appear to have been released from one source on the nucleus between the end of January and the second half of February 1997, some 60 to 40 days before perihelion. The parent particles were subjected to a radiation pressure acceleration of β_p ≃ 0.55 and their fragmentation lifetimes in 11 of the 12 striae were practically constant and equal to 13–15 days, when normalized to 1 AU from the Sun. Brief analysis of Watanabe et al.'s measurements of striae on their images from March 5–9, 1997 shows even shorter fragmentation lifetimes for the parent particles, mostly about 7–11 days at1 AU. This revised version was published online in July 2006 with corrections to the Cover Date.     

Variation of mineral composition,fabric and oxygen fugacity from massive to foliated eclogites during exhumation of subducted ocean crust in the North Qilian suture zone,NW China

Eclogites from the North Qilian suture zone are high‐pressure low‐temperature metamorphic rocks of ocean crust protolith, and occur in both massive and foliated varieties as individual blocks of tens to hundreds of metres in size. The massive type is weakly deformed and shows granoblastic texture characterized by a coarse‐grained peak mineral assemblage of Grt¹ + Omp¹ + Ph + Rt ± Lws (or retrograde Cz). In contrast, the foliated type is strongly deformed and shows a fine‐grained retrograde mineral assemblage of Grt² + Omp² + Cz + Gln + Ph. Both total FeO and aegirine contents in omphacite, as well as X_Fe[=Fe³⁺/(Fe³⁺ + Al^VI)] in clinozoisite/epidote, increase significantly from massive to foliated eclogites. Lattice preferred orientation (LPO) of omphacite, determined by electron back‐scatter diffraction analysis, is characterized by weak and strong SL‐type fabrics for massive and foliated eclogites, respectively. Clinozoisite/epidote also developed SL‐type fabric, but different from the LPOs of omphacite in <010> and <001> axes, owing to their opposite crystallographic long and short axis definitions. The transition of deformation mechanism from dislocation creep to diffusive mass transfer (DMT) creep in omphacite and the concomitant retrograde metamorphism both are efficiently facilitated when the original coarse‐grained Omp¹ + Grt¹ + Lws assemblage is dynamically recrystallized and retrogressed into the fine‐grained Fe³⁺‐rich assemblage of Omp² + Grt² + Cz + Gln. The DMT process with concomitant anisotropic growth assisted by fluids is considered to be an important deformation mechanism for most minerals in the foliated eclogite. P–T estimates yielded 2.3–2.6 GPa and 485?510 °C for the massive eclogite and 1.8–2.2 GPa and 450?480 °C for the foliated eclogite. The significant increase in total Fe and Fe³⁺ contents in omphacite and clinozoisite/epidote from massive to foliated eclogite suggests changes in mineral compositions accompanied by an increase in oxygen fugacity during ductile deformation associated with exhumation. The LPO transition of omphacite, clinozoisite and rutile from weak SL‐type in massive eclogites to strong SL‐type in foliated eclogites is interpreted to represent the increment of shear strain during exhumation along the ‘subduction channel’.     

High-resolution profiles of iron, manganese, cobalt, cadmium, copper and zinc in the pore water of estuarine sediment

The remobilization of iron, manganese, cobalt, cadmium, copper and zinc in the pore water of estuarine sediment cores at Yingkou was assessed using diffusive equilibrium in thin films and diffusive gradients in thin films techniques. A relatively anoxic system (+33.7 to ?224.1 mV) in the sediment cores might cause the reductive release of iron, manganese and cobalt into pore water from the estuarine sediment. High-average concentrations of iron (47.85 μg ml^?1) and manganese (3.81 μg ml^?1) were observed using diffusive equilibrium in thin films on the sediment core, but the concentration of cobalt (18.02 ng ml^?1) was relatively low. A strong correlation between iron and cobalt was observed based on the vertical profiles of the metals. Manganese and iron were more readily released from the solid phase to the solution. The peak cobalt, copper and zinc concentrations were observed in the upper layer (2–4 cm) measured using diffusive gradients in thin films. However, the peak iron, manganese and cobalt concentrations were located in the deeper layer (≥7 cm). In addition, the concentration profiles measured using diffusive gradients in thin films of cobalt, copper and zinc were independent of the iron, manganese and cobalt distribution with respect to depth.     

Influence of Mussel Culture on the Vertical Export of Phytoplankton Carbon in a Coastal Upwelling Embayment (Ría de Vigo,NW Iberia)

The goal of this paper is to find out whether suspended mussel culture affects the vertical fluxes of biogenic particles in the Ría de Vigo on a seasonal scale. With this aim, vertical fluxes of particulate organic carbon (POC) and the magnitude and composition of vertical export of phytoplankton carbon (Cphyto) collected in sediment traps were examined by comparing data obtained inside a mussel farming area (RaS) with those found at a reference station (ReS) not affected by mussels. Our results indicate that mussel farming has a strong impact on sedimentation fluxes under the rafts, not only increasing POC flux but also altering the magnitude and composition of Cphyto fluxes. Average POC flux at RaS (2564?±?1936 mg m^?2 day^?1) was four times higher than at ReS (731?±?276 mg m^?2 day^?1), and much of this increase was due to biodeposit fluxes (Cbiodep) which accounted for large proportion of POC flux (35–60 %). Indeed, because of this high Cbiodep flux, only a small proportion of the POC flux was due to Cphyto flux (3–12 %). At the same time, we observed an increased sedimentation of phytoplankton cells at RaS that could be explained by a combination of mechanisms: less energetic hydrodynamic conditions under mussel rafts, ballast effect by sinking mussel feces, and diatom aggregates. Moreover, mussel farming also altered the quality of the Cphyto flux by removing part of the predatory pressure of zooplankton and thus matching diatom composition in water column and sediment traps.