Redox problems in the “metallogenic specialization” of magmatic rocks and the genesis of hydrothermal ore mineralization

Considering the history and current state of the problem of the so-called metallogenic specialization of magmatic rocks, the paper places emphasis onto various aspects of the genesis of ore mineralization depending on the redox state of magmas (as a logical continuation of S. Ishihara’s works), fluids, and host rocks. These problems were inadequately poorly explored and discussed by researchers dealing with ore deposits. Various possible variants of ore-forming redox processes for different types of mineral deposits, with ore mineralization affiliated to granites (Ta, Sn, W, Mo, and Be) and mafic magmas (Au, Ag, U, Cu, Zn, Pb, As, Sb, and Hg) and, accordingly, to crustal and mantle origin, are discussed. On the basis of analyzed geological data, including those published over the past three decades, it is shown that the redox state of ore-producing magmas commonly significantly impacted not only the ore potential of magmatic complexes but also the genetic type of the ore mineralization. The redox state of the fluids predetermined the transport and precipitation speciation of metals. Influence mechanisms of hydrocarbons from sedimentary country rocks and gaseous products of their pyrolysis on ore deposition of various metals are considered. Understanding these mechanisms can be helpful for predicting the possible precipitation sites of ore mineralization of noble, radioactive, and chalcophile metals.     

The contrast of faculae near the solar limb

We have measured the contrast of solar faculae near the limb on direct digital video images made with the 65 cm vacuum reflector at the Big Bear Solar Observatory. We used six broad band filters with different wavelengths from red to violet. The range of heliocentric angle covered in our measurements is 0.05 < = cos < 0.4 ( = 87°–66°). About 300 images were measured from observations made during the summers of 1983 and 1985. Over 20000 faculae were measured.By averaging the contrasts of faculae and plotting them vs heliocentric angle, we found that contrast increases monotonically towards the limb for the shorter wavelengths; for longer wavelengths, contrast has a tendency to peak around = 0.15, and then decrease towards the extreme limb. The contrast increases as wavelength decreases.     

Simulation of Hydrophysical Processes in Coastal Regions of the Sea

In the present work, we generalize the results of our investigations in the field of simulation of hydrophysical and ecological processes in coastal regions of various seas and some closed basins. The developed and applied mathematical models and the results of numerical experiments are briefly analyzed.     

Geology and tectonics of the Themis Regio-Lavinia Planitia-Alpha Regio-Lada Terra area,Venus: Results from Arecibo image data

New radar images obtained from the Arecibo Observatory (resolution 1.5–4.0 km) for portions of the southern hemisphere of Venus show that: the upland of Phoebe Regio contains the southern extension of Devana Chasma, a rift zone extending 4200 km south from Theia Mons and interpreted as a zone of extension; Alpha Regio, the only large region of tessera within the imaged area, is similar to tessera mapped elsewhere on the planet and covers a smaller percentage of the surface than that observed in the northern high latitudes; the upland made of Ushas, Innini and Hathor Montes consists of three distinct volcanic constructs; Themis Regio is mapped as an ovoid chain of radar-bright arcuate single and double ring structures, edifices and bright lineaments. This area is interpreted as a region of mantle upwelling and on the basis of apparent split and separated features, a zone of localized faulting and extension. Linear zones of deformation in Lavinia Planitia are characterized by lineament belts that are often locally elevated, are similar to ridge belts mapped in the northern high latitudes and are interpreted to be characterized mainly by compression; radar-bright lava complexes within Lavinia Planitia are unique to this part of the planet and are interpreted to represent areas of eruption of high volumes of extremely fluid lava; the upland of Lada Terra is bound to the north by a linear deformation zone interpreted as extensional, is characterized by large ovoids and coronae, is interpreted to be associated with an area of mantle upwelling, and is in contrast to the northern high latitude highland of Ishtar Terra. Regions of plains in the southern hemisphere cover about 78%; of the mapped area and are interpreted to be volcanic in origin. Located within the area imaged (10–78 S) are 52 craters interpreted to be of impact origin ranging from 8 to 157 km in diameter. On the basis of an overall crater density of 0.94 craters/10⁶ km², it is determined that the age of this part of the Venus surface is similar to the 0.3 to 1.0 billion year age calculated for the equatorial region and northern high latitudes. The geologic characteristics of the portion of the Venus southern hemisphere imaged by Arecibo are generally similar to those mapped elsewhere on the planet. This part of the planet is characterized by widespread volcanic plains, large volcanic edifices, and zones of linear belt deformation. The southern hemisphere of Venus differs from northern high latitudes in that tessera makes up only a small percentage of the surface area and the ovoid chain in Themis Regio is unique to this part of the planet. On the basis of the analysis presented here, the southern hemisphere of Venus is interpreted to be characterized by regions of mantle upwelling on a variety of scales (ovoids, region made up of Ushas, Innini and Hathor Montes), upwelling and extension (Themis Regio) and localized compression (lineament belts in Lavinia Planitia).     

Assessment of Lichen Vitality During a Transplantation Experiment to a Polluted Site

The present work evaluates the stress effects in two epiphytic lichen species with different thallus morphology, the foliose Parmelia caperata and the fruticose Evernia prunastri, as resulting from transplanting from an unpolluted to an air-polluted area. Lichen samples were collected in Portugal in a clean area, during the spring 2003, and transplanted (1) to the same zone nearby and (2) to a polluted area as affected by an industrial complex. Transplant samples were taken periodically during four months in both places. At the same time lichen samples from the clean-air site native (in-situ) populations were also collected. For each sample were measured the chlorophyll content, the chlorophyll degradation and the cell membrane damage, the latter represented by leacheate conductivity. During the experiment the meteorological conditions were registered. The results indicate the absence of stress effects of transplanting as such, and suggest that leachate conductivity may be the more sensitive indicator of general lichen vitality.     

X-ray intensity-hardness correlation and deep IR observations of the anomalous X-ray pulsar 1RXS J170849-400910

We report here on X-ray and IR observations of the Anomalous X-ray Pulsar (AXP) 1RXS J170849-400910. First, we report on new XMM-Newton, Swift-XRT and Chandra observations of this AXP, which confirm the intensity–hardness correlation observed in the long term X-ray monitoring of this source. These new X-ray observations show that the AXP flux is rising again, and the spectrum hardening. If the increase of the source intensity is indeed connected with the glitches and a possible bursting activity, we expect this source to enter in a bursting active phase around 2006–2007. Second, we report on deep IR observations of 1RXS J170849-400910, taken with the VLT-NACO adaptive optics, showing that there are many weak sources consistent with the AXP position. Neither star A or B, as previously proposed by different authors, might yet be conclusively recognised as the IR counterpart of 1RXS J170849-400910. Third, using Monte Carlo simulations, we re-address the calculation of the significance of the absorption line found in a phase-resolved spectrum of this source, and interpreted as a resonant scattering cyclotron feature.     

Oxidative–reductive photodecomposition of perfluorooctanoic acid in water

This article aims to elucidate on usefulness of vacuum ultraviolet (VUV) for photoreductive degradation of perfluorooctanoic acid (PFOA), a representative perfluorinated compound (PFC), in water for the first time. Bench-scale tests were conducted on oxidative and reductive (with aquated electron: e _aq ^? ) mineralization of PFOA using low-pressure UV (LPUV) lamps and potassium iodide. Unlike with 254 nm wavelength (UVC), the reductive mineralization with VUV was very inefficient compared to the corresponding oxidative mineralization. The inefficiency is attributed to low reactivity of e _aq ^? with PFOA and its fluorinated products than that of 185 nm photons. Direct VUV photolysis of PFOA and its products in reductive reaction conditions was not apparent due to a very big difference in reactivity of 185 and 254 nm photons with iodide. The results demonstrated that highly energetic VUV photons are not suitable for photoreductive degradations of PFCs involving e _aq ^? , but they can be best used for oxidative degradations. These findings should serve as an important reference on VUV usage to decompose refractory micropollutants.     

Iron(II) oxide determination in rocks and minerals

The determination of FeO of geologic materials by modern instrumental methods (such as atomic absorption spectroscopy (AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence (XRF), etc.) cannot distinguish between different oxidation states of elements. In many cases, the oxidation state of Fe has to be known in order to perform several chemical calculations (norms, etc.) and discuss the reactions that occur during weathering, hydrothermal alteration and other processes. A modified Wilson method is proposed, giving reproducible results in a much shorter time than the classical method. Back-titration with potassium dichromate and an Fe(II) and ammonia sulphate solution is used, after dissolution of the sample powder in a heated HF/H₃PO₄ mixture and an ammonium vanadate solution. This modified method, tested with several international reference materials, gives reliable results, equivalent to the ones cited in the literature for the reference materials.