Thermodynamic modeling of REE behavior in oxidized hydrothermal fluids of high sulfate sulfur concentrations

Thermodynamic calculations using the HCh software were made for mineral equilibriums including REEs in the fluoride–sulfide–chloride–carbonate–sulfate–system in the presence of Na, Ca, and P with fluids of various acidities–alkalinities [11]. The obtained thermodynamic characteristics of thenardite allowed us to carry out the calculations for this phase under complicated hydrothermal conditions simulating the presence of oxidized fluids at 500–100°C and 2000–125 bar. Among other solid phases, REEs–fluorite, monazite, and REE–F–apatite were formed as CaF₂–(Ln,Y)F₃, LnPO₄, and Ca₅(PO₄)₃F–(Ln,Y)₃(PO₄)₃ ideal solid solutions, respectively, where Ln is La, Ce, Pr, Nd, Sm, Eu, and Gd. Xenotime, anhydrite, elemental sulfur, and calcite were found as well.     

Introduction of geospatial perspective to the ecology of fish-habitat relationships in Indonesian coral reefs: A remote sensing approach

Coral reef ecosystems worldwide are now being harmed by various stresses accompanying the degradation of fish habitats and thus knowledge of fish-habitat relationships is urgently required. Because conventional research methods were not practical for this purpose due to the lack of a geospatial perspective, we attempted to develop a research method integrating visual fish observation with a seabed habitat map and to expand knowledge to a two-dimensional scale. WorldView-2 satellite imagery of Spermonde Archipelago, Indonesia obtained in September 2012 was analyzed and classified into four typical substrates: live coral, dead coral, seagrass and sand. Overall classification accuracy of this map was 81.3% and considered precise enough for subsequent analyses. Three sub-areas (CC: continuous coral reef, BC: boundary of coral reef and FC: few live coral zone) around reef slopes were extracted from the map. Visual transect surveys for several fish species were conducted within each sub-area in June 2013. As a result, Mean density (Ind. / 300 m²) of Chaetodon octofasciatus, known as an obligate feeder of corals, was significantly higher at BC than at the others (p < 0.05), implying that this species’ density is strongly influenced by spatial configuration of its habitat, like the “edge effect.” This indicates that future conservation procedures for coral reef fishes should consider not only coral cover but also its spatial configuration. The present study also indicates that the introduction of a geospatial perspective derived from remote sensing has great potential to progress conventional ecological studies on coral reef fishes.

     

Results of Photometric Observations of Comet P/2019 LD2 at the Sanglokh Observatory

Solar System Research - The short-period comet P/2019 LD2 (Atlas) was discovered in June 2019. The object was originally classified as a Trojan asteroid, but was later included in the Jupiter...     

On a Magnetic Anomaly in the Umbra of the Following Spot of an NOAA 12192 Active Region

This paper examines the evolution and morphology of a magnetic anomaly: the appearance and disappearance of a longitudinal magnetic flux with opposite polarity at an area of about 10 arc seconds in the umbra of the following sunspot of an NOAA 12192 active region, which was observed from 21 to 26 October 2014 in the SDO/HMI and SOLIS/VSM magnetograms. Information collected by spacecraft and under on-ground observations including data from the Sun Service of the Crimean Astrophysical Observatory of the Russian Academy of Sciences are analyzed. Based on the methods of observation and determination of longitudinal magnetic fields in SDO/HMI in line FeI 6173.34 Å it was revealed, that combinations of contours appearing due to magnetic force lines inclinations relative to the line-of-sight and line-of-sight velocities can cause a significant undervalue of the magnetic field intensity in magnetograms, but polarity does not reverse. The fine spatial structure, evolution features, close correlation with ultraviolet loops system in SDO/AIA images, “moustaches”, and no temporal and spatial correlation with flares point to a connection between the detected anomaly and the new magnetic flux emergence of opposite polarity in a spot’s umbra at an earlier decay stage. We analyze magnetic force lines reconnection and show that annigilation of the magnetic fields of opposite polarities can take place for many hours at small (~30 km) scales and this fact is verified by observation results. There are additional facts in favor of the cluster model of a solar spot by Severny-Parker.

     

Antimony in hydrothermal processes: solubility, conditions of transfer, and metal-bearing capacity of solutions

Based on data on the composition of ore-bearing hydrothermal solutions and parameters of ore-forming processes at various antimony and antimony-bearing deposits, which were obtained in studies of fluid inclusions in ore minerals, we investigated the behavior of Sb(III) in the system Sb–Cl–H₂S–H₂O describing the formation of these deposits.

We also performed thermodynamic modeling of native-antimony and stibnite dissolution in sulfide (m_HS⁻ = 0.0001−0.1) and chloride (m_Cl⁻ = 0.1−5) solutions and the joint dissolution of Sb_(s)⁰ and Sb₂S_3(s) in sulfide-chloride solution (m_HS⁻ = 0.01; m_Cl⁻ = 1) depending on Eh, pH, and temperature. All thermodynamic calculations were carried out using the Chiller computer program. Under the above conditions, stibnite precipitates in acid, weakly acid to neutral, and medium redox solutions, whereas native antimony precipitates before stibnite under more reducing conditions in neutral to alkaline solutions.

The metal-bearing capacity of hydrothermal solutions (200–250 °C) of different compositions and origins has been predicted. We have established that the highest capacity is specific for acid (pH = 2–3) high-chloride solutions poor in sulfide sulfur and alkaline (pH = 7–8) low-chloride low-sulfide solutions.     

A photometric and dynamic study of comet C/2013 A1 (Siding Spring) from observations at a heliocentric distance of ~4.1 AU

An analysis is presented for the photometric data on comet C/2013 A1 (Siding Spring) from observations at a large heliocentric distance (~4.1 AU). Comet C/2013 A1 (Siding Spring) displays intense activity despite the relatively large heliocentric distance. The morphology of the comet’s coma is analyzed. The following parameters are measured: the color indices V-R, the normalized spectral gradient of the reflectivity of the comet’s dust S', and the dust production rate Afρ. A numerical simulation is performed for the evolution of the comet’s orbit after a close encounter with Mars. The most probable values are obtained for the Keplerian orbital elements of the comet over a hundred-year period. The comet’s orbit remains nearly parabolic after passing the orbits of all the Solar System planets.     

The Suzdal gold-sulfide deposit in the black shale of Eastern Kazakhstan

The Suzdal gold-sulfide deposit is situated in the northwestern part of the West Kalba gold belt in Eastern Kazakhstan and belongs to the genetic type of stringer-disseminated mineralized zones hosted in the Lower Carboniferous black-shale volcanic-carbonate-terrigenous sequences. Mineralization is controlled by the NE-trending Suzdal Fault. In the north, the deposit borders on the Early Triassic Semeytau volcanic-plutonic structure. Mineralization is superposed on the Late Paleozoic complex of metadolerite and quartz porphyry dikes. Ore deposition was a long-term process comprising four stages. The first stage was related to deposition of slightly auriferous pyrite syngenetic to host rocks. The second stage is characterized by formation of the first productive (with invisible gold) fine-acicular arsenopyrite mineralization accompanied by sericitization and localized in the tectonic zone. The stockwork ore with pocket-disseminated base-metal mineralization and free microscopic gold of the third stage is hosted in silicified rocks. The ore formation has been completed by quartz-stibnite veins superposed on all preceding types of mineralization. According to Ar/Ar dating of sericite, a chronological gap between the second and the third stages is estimated at 33 Ma. The deposit is an example of polygenetic and multistage mineralization.     

The Asachinskoe epithermal Au-Ag deposit in southern Kamchatka: physicochemical conditions of formation

The Asachinskoe epithermal Au-Ag deposit (southern Kamchatka) is referred to as low-sulfidation in quartz-adularia-sericite in Corbett's classification. Research into fluid inclusions of its minerals gave an insight into the PT-conditions of formation and gas composition of ore-forming fluids as well as the vertical variations in these parameters to a depth of more than 200 m within a 2 km long horizontal site of the deposit ore zone. It is shown that mineral assemblages formed at 320 to <100 °C. Ore-forming hydrothermal solutions were poor in salts (3–9.2 wt.% NaCl equiv.), with NaCl being the main component. Mineral assemblages with high contents of Au crystallized at 250–175 °C. Ore-free quartz-carbonate veins formed at 80–120 °C. High-temperature (300–320 °C) veins also lack ores. Rich gold ores were deposited in the environments where ore-bearing fluids boiled, mixing with meteoric waters.