High‐temperature gold‐copper extraction with chloride flux in lava tubes of Tolbachik volcano (Kamchatka)

Subvolcanic environments in supra‐subduction zones are renowned for hosting epithermal deposits that often contain electrum and native gold, including bonanza examples. This study examined mineral assemblages and processes occurring in shallow‐crust volcanic settings using recent eruption (2012–2013) of the basaltic Tolbachik volcano in the Kamchatka arc. The Tolbachik eruptive system is characterized by an extensive system of lava tubes. After cessation of magma input, the tubes maintained the flow of hot oxidized gases that episodically interacted with the lava surfaces and sulphate‐chloride precipitates from volcanic gases on these surfaces. The gas‐rock interaction had strong pyrometamorphic effects that resulted in the formation of molten salt, oxidized (tenorite, hematite, Cu‐rich magnesioferrite) and skarn‐like silicate mineral assemblages. By analogy with experimental studies, we propose that a combination of these processes was responsible for extraction of metals from the basaltic wall rocks and deposition of Cu‐, Fe‐ and Cu‐Fe‐oxides and native gold.     

Character of gold mineralization in the late Cenozoic alluvium of the Bauntov area (Vitim highland, Transbaikal region)

Study of gold potential of the Late Cenozoic alluvium in the Bauntov area is based on the Taloi basin and Sivo sector (China River basin). Primary placer-forming gold is mainly represented by endogenous varieties. In contrast to alluvium of streams in the Taloi basin, Middle-Upper Quaternary alluvium of the Sivo sector (China River basin) is enriched in fine and tiny gold (smaller than 0.25 mm). The paper presents data testifying to a low Au content in the silt fraction of slimes from boreholes drilled in the Cenozoic alluvium (alluvium-deluvium) from transverse valleys in the Taloi basin and, hence, to an significant manifestation of the chemogenic concentration of this metal therein. Issue of the existence of specific conditions favorable for the formation of hydrogenic gold in the northern high-latitude zones requires further studies. The results show that lithochemical gold aureoles have an important prospecting significance. They also suggest the practical significance of accumulations of fine and tiny gold in the syn-stratal alluvium and alluvium-deluvium of large ore placer areas.     

Water erosion in the Southern Ural steppes

Ecological-hydrological analysis of erosion processes on the key watersheds of Southern Ural steppe was used to determine the surface runoff as a function of the physico-geographic and anthropogenic conditions, i.e., snow storage and soil moisture reserves before winter, whose contribution reaches 68–81%. The rate of humus losses in chernozems and dark chestnut soils was calculated for different periods in accordance with erosion stress and the extent of the economic development of the territory. Agroecological types of arable lands with different surface runoff characteristics, rates of natural soil formation, and erosionrelated soil losses are identified. Measures aimed to reduce humus losses in soils are proposed. Relationships between the rates of soil formation and erosion losses are proposed to be used as ecological-hydrological criterion (index) of soil stability.     

Unconventional gold placers of the China tectonic depression (Vitim Plateau,East Siberia)

Holocene shallow (0.5–4.5 m, rarely more) and Pliocene–Pleistocene deep (> 25 m) placers occur within the China tectonic depression. The shallow placers are associated with the formation of the present-day drainage valleys of the China River under permafrost conditions, and the deep ones are localized within the preglacial paleovalleys of the river basin. An integrated geological and geochemical study was carried out at ten shallow commercial placers, eight of which are classified as poorly studied and “unconventional.” Placers are considered “unconventional” based on their technological characteristics (commercial gold is small (? 0.25 to + 0.1 mm), thin (? 0.1 mm), and micron-sized or “bound” (invisible)), geomorphologic conditions of formation, confinement to the oxidized zone of active permafrost, significant portion of fine hydrogenic gold, and several other minor features.The formation of shallow “unconventional” placers is controlled by the conditions of active permafrost. Under aerobic conditions, suprapermafrost waters form an oxidized zone, in which iron hydroxides impart a yellowish reddish color to water-bearing rocks. Long-lived geochemical barriers (biogenic, reduction, electrochemical, sorption, and others), including gravitational differentiation, play an important role in the concentration of small and thin gold.Alluvial deposits in Meso-Cenozoic tectonic depressions, such as the China basin, are the most promising in terms of “unconventional” placers. The main factors favoring the formation of these localities and the criteria for their assessment are large feeding sources of gold (mainly carbonaceous and sulfide) mineralization, endogenic and exogenic dispersion aureoles with thin and invisible gold; increased thickness of the suprapermafrost active layer and its temporal and spatial stability, contributing to the formation and functioning of oxidized horizons with the accumulation of ferric hydroxide and hydrogenic gold; specific morphologic varieties of hydrogenic gold, which are the fundamental criterion for primary gold mineralization with migratable metal; fine-clastic clay-rich composition of recent alluvial or alluvial-talus sediments, produced by water reworking of ancient gold-bearing weathering crusts; and development of broad floodplains filled with Holocene sediments and their junction with talus-solifluction erosional slopes.     

Experimental reconstruction of Lomonosov’s discovery of Venus’s atmosphere with antique refractors during the 2012 transit of Venus

In 1761, the Russian polymath Mikhail Vasilievich Lomonosov (1711–1765) discovered the atmosphere of Venus during its transit over the Sun’s disc. In this paper we report on experimental reenactments of Lomonosov’s discovery with antique refractors during the transit of Venus June 5–6, 2012. We conclude that Lomonosov’s telescope was fully adequate to the task of detecting the arc of light around Venus off the Sun’s disc during ingress or egress provided proper experimental techniques as described by Lomonosov in his 1761 report are employed.     

Nanoparticles of noble metals in the supergene zone

Formation of noble metal nanoparticles is related to various geological processes in the supergene zone. Dispersed mineral phases appear during weathering of rocks with active participation of microorganisms, formation of soil, in aqueous medium and atmosphere. Invisible gold and other noble metals are incorporated into oxides, hydroxides, and sulfides, as well as in dispersed organic and inorganic carbonic matter. Sulfide minerals that occur in bedrocks and ores unaltered by exogenic processes and in cementation zone are among the main concentrators of noble metal nanoparticles. The ability of gold particles to disaggregate is well-known and creates problems in technological and analytical practice. When Au and PGE nanoparticles and clusters occur, these problems are augmented because of their unusual reactions and physicochemical properties. The studied gold, magnetite, titanomagnetite and pyrite microspherules from cementation zone and clay minerals of laterites in Republic of Guinea widen the knowledge of their abundance and inferred formation conditions, in particular, in the contemporary supergene zone. Morphology and composition of micrometer-sized Au mineral spherules were studied with SEM and laser microprobe. The newly formed segregations of secondary gold on the surface of its residual grains were also an object of investigation. The character of such overgrowths is the most indicative for nanoparticles. The newly formed Au particles provide evidence for redistribution of ultradispersed gold during weathering. There are serious prerequisites to state that microorganisms substantially control unusual nano-sized microspherical morphology of gold particles in the supergene zone. This is supported by experiments indicating active absorption of gold by microorganisms and direct evidence for participation of Ralstonia metallidurans bacteria in the formation of peculiar corroded bacteriomorphic surface of gold grains. In addition, the areas enriched in carbon and nitrogen have been detected with SEM on the surface of gold spherules from Guinea. Such organic compounds as serine, alanine, and glycine are identified on their surface with Raman spectroscopy. The experiments have been carried out and new data have been obtained indicating the role of micromycetes in concentration and distribution of noble metals in ferromanganese nodules of the World Ocean. Au and Pt were detected in the system with radioisotopes. It has been established that two forms of gold distribution develop within pseudomorphs of fungi colonies: (1) as pseudomorphic concentrates and (2) dispersed form unrelated to the colony structure. Inhomogeneities in distribution of dispersed platinum are manifested in the form of linear anomalies with elevated concentrations at the margins of the colonies.     

Pattern of Shore Use by Spotted Seals in the Sea of Japan

Oceanology - This paper considers the pattern of shore use by seals in relationship with the location of haulout sites, their geomorphological parameters, and the influence of oceanographic...     

Alluvial gold placers directly related to primary sources: An important forecast criterion

Two extreme groups of alluvial gold placers (lost and preserved “live” relation to the primary sources) are distinguished by the character of this relation and mineralogical-geochemical peculiarities. The content of the invisible gold in the first ones is close to the regional background (first mg/t) in contrast to its anomalous (exceeding the local background for several orders of magnitude) amount in placers of the second type. The invisible gold composes the geochemical dispersion flows combined with the placer. The placers of this type are important forecast criterion of the assessment of the nearby areas for the primary gold.     

Allochthonous native gold in piedmont alluvium in the southern West Siberia

The paper presents the results of our investigations carried out to examine the behavior of native gold in the southern West Siberia during the fluvial transport of an auriferous terrigenous material at the mountain-to-plain transition geomorphological zone. The piedmont alluvium accumulates the small- and, to a lesser extent, fine-grained gold transported from the denudation zones by the main mountain-lowland rivers. The background Au content varies from n to 10n mg/m³. High contents (100n mg/m³ to n g/m³) are recorded in some sectors in the upper zones of channel alluvium (spit and shoal facies). Flatness coefficient of particles is an important characteristic of allochthonous native gold in the piedmont alluvium. This property shows direct correlation with the lateral dimension of particles. Composition is an essential typomorphic property of the small- and fine-grained gold in the studied sediments. This statement is primarily valid for the degree of fineness commonly related to the Ag content in gold. In some cases, a significant indicator role can be played by traces of Hg and Cu. For example, Hg is an important indicator for the gold-mercury mineralization, whereas Cu is an essential indicator in the case of gold mineralization associated with rhodingites and high-temperature Cu-Au mineralization. Abundance of the allochthonous native gold in different-age terrigenous sediments testifies to its high stability during the continental sedimentation.