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

Vadim S. Kamenetsky  Alexander Belousov  Victor V. Sharygin  Liudmila M. Zhitova  Kathy Ehrig  Michael E. Zelenski  Ilya Chaplygin  Marina A. Yudovskaya  Pavel N. Nesterenko  Sergey M. Zakharov 《地学学报》2019,31(6):511-517

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.  相似文献   

Prestack data enhancement with phase corrections in time-frequency domain guided by local multidimensional stacking     

Andrey Bakulin  Dmitri Neklyudov  Ilya Silvestrov 《Geophysical Prospecting》2020,68(6):1811-1818

We present a new approach to enhancing weak prestack reflection signals without sacrificing higher frequencies. As a first step, we employ known multidimensional local stacking to obtain an approximate ‘model of the signal’. Guided by phase spectra from this model, we can detect very weak signals and make them visible and coherent by ‘repairing’ corrupted phase of original data. Both presented approaches – phase substitution and phase sign corrections – show good performance on complex synthetic and field data suffering from severe near-surface scattering where conventional processing methods are rendered ineffective. The methods are mathematically formulated as a special case of time-frequency masking (common in speech processing) combined with the signal model from local stacking. This powerful combination opens the avenue for a completely new family of approaches for multi-channel seismic processing that can address seismic processing of land data with nodes and single sensors in the desert environment.  相似文献   

Origins and evolution of rhyolitic magmas in the central Snake River Plain: insights from coupled high-precision geochronology,oxygen isotope,and hafnium isotope analyses of zircon     

Dylan?P.?ColónEmail author  Ilya?N.?Bindeman  J?rn-Frederik?Wotzlaw  Eric?H.?Christiansen  Richard?A.?Stern 《Contributions to Mineralogy and Petrology》2018,173(2):11

We present new high-precision CA-ID-TIMS and in situ U–Pb ages together with Hf and O isotopic analyses (analyses performed all on the same grains) from four tuffs from the 15?10 Ma Bruneau–Jarbidge center of the Snake River Plain and from three rhyolitic units from the Kimberly borehole in the neighboring 10?6 Ma Twin Falls volcanic center. We find significant intrasample diversity in zircon ages (ranges of up to 3 Myr) and in δ¹⁸O (ranges of up to 6‰) and ε_Hf (ranges of up to 24 ε units) values. Zircon rims are also more homogeneous than the associated cores, and we show that zircon rim growth occurs faster than the resolution of in situ dating techniques. CA-ID-TIMS dating of a subset of zircon grains from the Twin Falls samples reveals complex crystallization histories spanning 10⁴–10⁶ years prior to some eruptions, suggesting that magma genesis was characterized by the cyclic remelting of buried volcanic rocks and intrusions associated with previous magmatic episodes. Age-dependent trends in zircon isotopic compositions show that rhyolite production in the Yellowstone hotspot track is driven by the mixing of mantle-derived melts (normal δ¹⁸O and ε_Hf) and a combination of Precambrian basement rock (normal δ¹⁸O and ε_Hf down to ??60) and shallow Mesozoic and Cenozoic age rocks, some of which are hydrothermally altered (to low δ¹⁸O values) by earlier stages of Snake River Plain magmatism. These crustal melts hybridize with juvenile basalts and rhyolites to produce the erupted rhyolites. We also observe that the Precambrian basement rock is only an important component in the erupted magmas in the first eruption at each caldera center, suggesting that the accumulation of new intrusions quickly builds an upper crustal intrusive body which is isolated from the Precambrian basement and evolves towards more isotopically juvenile and lower-δ¹⁸O compositions over time.  相似文献   

Monocotyledon-like Leaves from the Middle Jurassic of East Siberia (Russia)     

Andrey FROLOV  Ilya ENUSHCHENKO 《《地质学报》英文版》2022,96(6):1884-1896

Leaf fragments of Herbifolia antiqua A. Frolov et Enushchenko gen. et sp. nov. from the Middle Jurassic (Aalenian) of the Irkutsk Coal Basin (Eastern Siberia, Russia) are reported. The following features are characteristic of H. antiqua gen. et sp. nov.: the presence of leaf sheaths, linear smooth-edged leaves with parallel venation, anastomoses between the veins, anomocytic stomata, rhomb-shaped ordinary epidermal cells. Such a combination of characters is widespread in modern monocotyledonous plants and is absent in fossil and modern cryptogam and gymnosperms. Due to the lack of evidence of an enclosed ovule in H. antiqua gen. et sp. nov.we attribute it to a typological angiosperm, based on its unique leaf structure characteristic of monocotyledons. The leaf epidermal structure of Herbifolia gen. nov. is most similar to those of modern Asparagales and Liliales.  相似文献   

An Anisotropic Cosmic-Ray Enhancement Event on 07-June-2015: A Possible Origin     

Agnieszka Gil  Gennady A. Kovaltsov  Vladimir V. Mikhailov  Alexander Mishev  Stepan Poluianov  Ilya G. Usoskin 《Solar physics》2018,293(11):154

A usual event, called anisotropic cosmic-ray enhancement (ACRE), was observed as a small increase (\({\leq}\,5\%\)) in the count rates of polar neutron monitors during 12?–?19 UT on 07 June 2015. The enhancement was highly anisotropic, as detected only by neutron monitors with asymptotic directions in the southwest quadrant in geocentric solar ecliptic (GSE) coordinates. The estimated rigidity of the corresponding particles is \({\leq}\,1\) GV. No associated detectable increase was found in the space-borne data from the Geostationary Operational Environmental Satellite (GOES), the Energetic and Relativistic Nuclei and Electron (ERNE) on board the Solar and Heliospheric Observatory (SOHO), or the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instruments, whose sensitivity was not sufficient to detect the event. No solar energetic particles were present during that time interval. The heliospheric conditions were slightly disturbed, so that the interplanetary magnetic field strength gradually increased during the event, followed by an increase of the solar wind speed after the event. It is proposed that the event was related to a crossing of the boundary layer between two regions with different heliospheric parameters, with a strong gradient of low-rigidity (\({<}\,1\) GV) particles. It was apparently similar to another cosmic-ray enhancement (e.g., on 22 June 2015) that is thought to have been caused by the local anisotropy of Forbush decreases, with the difference that in our case, the interplanetary disturbance was not observed at Earth, but passed by southward for this event.  相似文献   

Influence of background heterogeneity on traveltime shifts for compacting reservoirs     

Rodrigo F. Fuck  Ilya Tsvankin  Andrey Bakulin 《Geophysical Prospecting》2011,59(1):78-89

Compaction induced by pore‐pressure decrease inside a reservoir can be monitored by measuring traveltime shifts of reflection events on time‐lapse seismic data. Recently we introduced a perturbation‐based formalism to describe traveltime shifts caused by the 3D stress‐induced velocity field around a compacting reservoir. Application of this method to homogeneous background models showed that the offset variation of traveltime shifts is controlled primarily by the anisotropic velocity perturbations and can provide valuable information about the shear and deviatoric stresses. Here, we model and analyse traveltime shifts for compacting reservoirs whose elastic properties are different from those of the surrounding medium. For such models, the excess stress is influenced primarily by the contrast in the rigidity modulus μ across the reservoir boundaries. Synthetic examples demonstrate that a significant (25% or more) contrast in μ enhances the isotropic velocity perturbations outside the reservoir. Nevertheless, the influence of background heterogeneity is mostly confined to the reservoir and its immediate vicinity and the anisotropic velocity changes are still largely responsible for the offset dependence of traveltime shifts. If the reservoir is stiffer than the host rock, the background heterogeneity reduces anisotropic velocity perturbations inside the reservoir but increases them in the overburden. As a result, in this case, the magnitude of the offset variation of traveltime shifts is generally higher for reflections from interfaces above the reservoir. We also study compaction‐induced stress/strain and traveltime shifts for a stiff reservoir embedded in a softer layered model based on velocity profiles from the Valhall Field in the North Sea. Despite producing discontinuities in strain across medium interfaces, horizontal layering does not substantially alter the overall behaviour of traveltime shifts. The most pronounced offset variation of traveltime shifts is observed for overburden events recorded at common midpoints close to the reservoir edges. On the whole, prestack analysis of traveltime shifts should help better constrain compaction‐induced velocity perturbations in the presence of realistic background heterogeneity.  相似文献   

Solar modulation in surface atmospheric electricity     

R. Giles Harrison  Ilya Usoskin 《Journal of Atmospheric and Solar》2010,72(2-3):176-182

The solar wind modulates the flux of galactic cosmic rays impinging on Earth inversely with solar activity. Cosmic ray ionisation is the major source of air's electrical conductivity over the oceans and well above the continents. Differential solar modulation of the cosmic ray energy spectrum modifies the cosmic ray ionisation at different latitudes, varying the total atmospheric columnar conductance. This redistributes current flow in the global atmospheric electrical circuit, including the local vertical current density and the related surface potential gradient. Surface vertical current density and potential gradient measurements made independently at Lerwick Observatory, Shetland, from 1978 to 1985 are compared with modelled changes in cosmic ray ionisation arising from solar activity changes. Both the lower troposphere atmospheric electricity quantities are significantly increased at cosmic ray maximum (solar minimum), with a proportional change greater than that of the cosmic ray change.  相似文献   

Inversion of multicomponent seismic time shifts for reservoir pressure and length: a feasibility study          下载免费PDF全文

Steven Shawn Smith  Ilya Tsvankin 《Geophysical Prospecting》2016,64(1):83-101

Pressure drops associated with reservoir production generate excess stress and strain that cause travel‐time shifts of reflected waves. Here, we invert time shifts of P‐, S‐, and PS‐waves measured between baseline and monitor surveys for pressure reduction and reservoir length. The inversion results can be used to estimate compaction‐induced stress and strain changes around the reservoir. We implement a hybrid inversion algorithm that incorporates elements of gradient, global/genetic, and nearest neighbour methods and permits exploration of the parameter space while simultaneously following local misfit gradients. Our synthetic examples indicate that optimal estimates of reservoir pressure from P‐wave data can be obtained using the reflections from the reservoir top. For S‐waves, time shifts from the top of the reservoir can be accurately inverted for pressure if the noise level is low. However, if noise contamination is significant, it is preferable to use S‐wave data (or combined shifts of all three modes) from reflectors beneath the reservoir. Joint wave type inversions demonstrate improvements over any single pure mode. Reservoir length can be estimated using the time shifts of any mode from the reservoir top or deeper reflectors. We also evaluate the differences between the actual strain field and those corresponding to the best‐case inversion results obtained using P‐ and S‐wave data. Another series of tests addresses the inversion of the time shifts for the pressure drops in two‐compartment reservoirs, as well as for the associated strain field. Numerical testing shows that a potentially serious source of error in the inversion is a distortion in the strain‐sensitivity coefficients, which govern the magnitude of stiffness changes. This feasibility study suggests which wave types and reflector locations may provide the most accurate estimates of reservoir parameters from compaction‐induced time shifts.  相似文献   

Initiation of large-volume silicic centers in the Yellowstone hotspot track: insights from H<Subscript>2</Subscript>O- and F-rich quartz-hosted rhyolitic melt inclusions in the Arbon Valley Tuff of the Snake River Plain     

Dana?L.?DrewEmail author  Ilya?N.?Bindeman  Matthew?W.?Loewen  Paul?J.?Wallace 《Contributions to Mineralogy and Petrology》2016,171(1):10

During the onset of caldera cluster volcanism at a new location in the Snake River Plain (SRP), there is an increase in basalt fluxing into the crust and diverse silicic volcanic products are generated. The SRP contains abundant and compositionally diverse hot, dry, and often low-δ¹⁸O silicic volcanic rocks produced through time during the formation of individual caldera clusters, but more H₂O-rich eruptive products are rare. We report analyses of quartz-hosted melt inclusions from pumice clasts from the upper and lower Arbon Valley Tuff (AVT) to gain insight into the initiation of caldera cluster volcanism. The AVT, a voluminous, caldera-forming rhyolite, represents the commencement of volcanism (10.44 Ma) at the Picabo volcanic field of the Yellowstone hotspot track. This is a normal δ¹⁸O rhyolite consisting of early and late erupted members (lower and upper AVT, respectively) with extremely radiogenic Sr isotopes and unradiogenic Nd isotopes, requiring that ~50 % of the mass of these elements is derived from melts of Archean upper crust. Our data reveal distinctive features of the early erupted lower AVT melt including: variable F concentrations up to 1.4 wt%, homogenous and low Cl concentrations (~0.08 wt%), H₂O contents ranging from 2.3 to 6.4 wt%, CO₂ contents ranging from 79 to 410 ppm, and enrichment of incompatible elements compared to the late erupted AVT, subsequent Picabo rhyolites, SRP rhyolites, and melt inclusions from other metaluminous rhyolites (e.g., Bishop Tuff, Mesa Falls Tuff). We couple melt inclusion data with Ti measurements and cathodoluminescence (CL) imaging of the host quartz phenocrysts to elucidate the petrogenetic evolution of the AVT rhyolitic magma. We observe complex and multistage CL zoning patterns, the most critical being multiple truncations indicative of several dissolution–reprecipitation episodes with bright CL cores (higher Ti) and occasional bright CL rims (higher Ti). We interpret the high H₂O, F, F/Cl, and incompatible trace element concentrations in the context of a model involving melting of Archean crust and mixing of the crustal melt with basaltic differentiates, followed by multiple stages of fractional crystallization, remelting, and melt extraction. This multistage process, which we refer to as distillation, is further supported by the complex CL zoning patterns in quartz. We interpret new Δ¹⁸O(Qz-Mt) isotope measurements, demonstrating a 0.4 ‰ or ~180 °C temperature difference, and strong Sr isotopic and chemical differences between the upper and lower AVT to represent two separate eruptions. Similarities between the AVT and the first caldera-forming eruptions of other caldera clusters in the SRP (Yellowstone, Heise and Bruneau Jarbidge) suggest that the more evolved, lower-temperature, more H₂O-rich rhyolites of the SRP are important in the initiation of a caldera cluster during the onset of plume impingement.  相似文献   

3D inversion of gravity data by separation of sources and the method of local corrections: Kolarovo gravity high case study     

Ilya Prutkin  Peter VajdaRobert Tenzer  Miroslav Bielik 《Journal of Applied Geophysics》2011,75(3):472-478

We present a novel methodology for 3D gravity/magnetic data inversion. It combines two algorithms for preliminary separation of sources and an original approach to 3D inverse problem solution. The first algorithm is designed to separate sources in depth and to remove the shallow ones. It is based on subsequent upward and downward data continuation. For separation in the lateral sense, we approximate the given observed data by the field of several 3D line segments. For potential field data inversion we apply a new method of local corrections. The method is efficient and does not require trial-and-error forward modeling. It allows retrieving unknown 3D geometry of anomalous objects in terms of restricted bodies of arbitrary shape and contact surfaces. For restricted objects, we apply new integral equations of gravity and magnetic inverse problems. All steps of our methodology are demonstrated on the Kolarovo gravity anomaly in the Danube Basin of Slovakia.  相似文献