На главную К списку выставокАрхив выставок

Всероссийский ежегодный семинар по экспериментальной минералогии, петрологии и геохимии

Журнальные статьи

1. U01624
Barnes C.G., Memeti V., Coint N. Deciphering magmatic processes in calc-alkaline plutons using trace element zoning in hornblende // Am. Miner. 2016. Vol. 101, № 1–2. P. 328–342.

Hornblende in the Kuna Crest lobe (KCL) of the Tuolumne Intrusive Complex (TIC) and the upper zone of the Wooley Creek batholith (WCB) precipitated over a temperature range of 835 to 700 C, and thus has the potential to record magmatic processes. We measured trace element concentrations in hornblende from the WCB, from the KCL of the TIC, and from one sample from an adjacent interior unit of the TIC to compare and contrast magmatic processes in these two mid -crustal intrusions. In both systems the magmatic amphibole is magnesiohornblende in which Ti, Zr, Hf, Nb, Sr, Ba, and rare earth elements (REE) typically decrease from crystal interiors to rims, an indication of compatible behavior of these elements, and the size of the negative Eu anomaly decreases. In the Kuna Crest lobe, hornblende from individual mapped units differs in trace element abundances and zoning trends. Some samples contain at least two distinct hornblende populations, which is particularly evident in the shapes of REE patterns. In contrast, compositions of hornblende from all structural levels of the upper WCB and related dacitic roof -zone dikes form a single broad array and the REE patterns are essentially indistinguishable, regardless of rock type, from quartz diorite to granite. In the WCB, Zr/Hf ratios in hornblende are consistent with crystallization from a melt with chondritic Zr/Hf values. In contrast, most hornblende in the KCL has Zr/Hf values lower than expected from crystallization from a melt with chondritic values, suggesting that zircon fractionation occurred before and during crystallization of the hornblende. Simple fractional crystallization models indicate that REE, high field strength elements, Sr, and Ba were compatible in KCL and WCB magmas as hornblende grew; these trends require removal of hornblende + plagioclase + zircon ilmenite biotite. The uniform variations of trace element concentrations and patterns in the upper WCB and roof zone dikes indicates crystallization from a large magma body that was compositionally uniform; probably stirred by convection caused by influx of mafic magmas at the base of the zone (Coint et al. 2013a, 2013b; cf. Burgisser and Bergantz 2011). In contrast, in the KCL, each analyzed sample displays distinct hornblende compositions and zoning patterns, some of which are bimodal. These features indicate that each analyzed sample represents a distinct magma and that individual magmas were variably modified by fractionation and mixing. Hornblende trace element contents and zoning patterns prove to be powerful tools for identification of magma batches and for assessing magmatic processes, and thereby relating plutonic rocks to hypabyssal and volcanic equivalents.


2. U01624
Cheshire M.C. et al. Bentonite evolution at elevated pressures and temperatures: An experimental study for generic nuclear repository designs // Am. Miner. 2014. Vol. 99, № 8–9. P. 1662–1675.

Geologic disposal of spent nuclear fuel in high-capacity metal canisters may reduce the repository footprint, but it may yield high-thermal loads (up to 300 degrees C). The focus of this experimental work is to expand our understanding of the hydrothermal stability of bentonite clay barriers interacting with metallic phases under different geochemical, mineralogical, and engineering conditions. The hydrothermal experiments were performed using flexible Au/Ti Dickson reaction cells mounted in an externally heated pressure vessel at 150-160 bars and temperatures up to 300 degrees C for five to six weeks. Unprocessed Wyoming bentonite, containing primarily montmorillonite with minor amount of clinoptilolite, was saturated with a K-Ca-Na-Cl-bearing water (similar to 1900 mg/L total dissolved solids) at a 9:1 water:rock mass ratio. The bentonite and solution combination contained either steel plates or Cu-foils and were buffered to low Eh using magnetite and metallic iron. During reactions, pH, K+, and Ca2+ concentrations decreased, whereas SiO2(aq), Na+, and SO42- concentrations increased throughout the experiments. Pyrite decomposition was first observed at similar to 210 degrees C, generating H2S(aq,g) that interacted with metal plates or evolves as a gas. The aqueous concentrations of alkali and alkaline earth cations appear to be buffered via montmorillonite and clinoptilolite exchange reactions. Illite or illite/smectite mixed-layer formation was significantly retarded in the closed system due to a limited K+ supply along with high Na+ and SiO2(aq) concentrations. Precursor clinoptilolite underwent extensive recrystallization during the six weeks, 300 degrees C experiments producing a Si-rich analcime in addition to authigenic silica phases (i.e., opal, cristobalite). Analcime and feldspar formation partially sequester aqueous Al3+, thereby potentially inhibiting illitization. Associated with the zeolite alteration is a similar to 17% volume decrease (quartz formation) that translates into similar to 2% volume loss in the bulk bentonite. These results provide chemical information that can be utilized in extending the bentonite barriers' lifetime and thermal stability. Zeolite alteration mineralogy and illitization retardation under these experimental conditions is important for the evaluation of clay barrier long-term stability in a spent nuclear fuel repository.


3. U10290
Dalou C., Le Losq C., Mysen B.O. In situ study of the fractionation of hydrogen isotopes between aluminosilicate melts and coexisting aqueous fluids at high pressure and high temperature - Implications for the delta D in magmatic processes // Earth Planet. Sci. Lett. 2015. Vol. 426. P. 158–166.

The hydrogen isotopic composition of melt inclusions trapped in phenocrysts during their crystallization and growth in a magma may contribute to a better understanding of the water cycle between the atmosphere, the hydrosphere and the lithosphere. Such understanding relies on the knowledge of the hydrogen isotopic fractionation factors between aqueous fluids, silicate melts, and minerals at temperature and pressure conditions relevant to the Earth's interior. Significant D/H fractionation between silicate melts and aqueous fluids was reported at hundreds of MPa and degrees C by using in situ measurements in hydrothermal diamond anvil cell (HDAC) experiments (Mysen, 2013a, 2013b, Am. Mineral. 98, 376-386 and 1754-1764). However, the available dataset is focused on fluids and melts with D/H ratios close to unity. The relevance of such data for natural processes that involve per mil variations of delta D-values may not always be clear. To address such concerns, the effect of the bulk D/H ratio on hydrogen isotope partitioning between water-saturated silicate melts and coexisting silicate-saturated aqueous fluids has been determined in the Na2O-Al2O3-SiO2-H2O-D2O system. To this end, in situ Raman spectroscopic measurements were performed on fluids and melts with bulk D/H ratios from 0.05 to 2.67 by using an externally-heated diamond anvil cell in the 300-800 degrees C and 200-1500 MPa temperature and pressure range, respectively. In these pressure/temperature ranges, the D/H ratios of fluids in equilibrium with melt barely change with temperature (in average Delta H-fluid = 0.47 +/- 1.15 kJ/mol). In contrast, the D/H ratios of coexisting melts display strong dependence on temperature (average Delta H-melt = 7.18 +/- 1.27 kJ/mop. The temperature-dependence of the D/H fractionation factor between melt and fluid (alpha(fluid-melt) = D/H-fluid/D/H-melt) is comparable in all the experiments and can be written: 1000.ln(alpha(fluid-melt)) = 263 (+/- 26)center dot T-2-126 (+/- 48). Therefore, the alpha(fluid-melt) is independent of the bulk D/H ratio of the melt + fluid system. Experimentally determined alpha(fluid-melt) using D-enriched fluids, therefore, can be applied to natural systems. It follows that for water-saturated magma strong isotopic fractionation of D and H between water dissolved in magmas and deep aqueous fluids may occur. The delta D-values in melt inclusions in phenocrysts in such water-saturated magma will reflect such fluid/melt fractionation effects. A likely result is underestimation of the delta D isotopic composition of slab fluids based on delta D-values in melt inclusions. The temperature-dependent hydrogen isotope fractionation must be taken into account in the modeling of slab fluid-magma interaction in the mantle wedge.


4. S16403
Donmez C. et al. Chromite and PGE geochemistry of the Elekdag Ophiolite (Kastamonu, Northern Turkey): Implications for deep magmatic processes in a supra-subduction zone setting // Ore Geol. Rev. 2014. Vol. 57. P. 216–228.

The geochemistry of chromium spinel and platinum group elements (PGE) provides significant information about conditions in the mantle during the emplacement and genesis of ophiolitic complexes. The Elekdag ophiolite is a greenschist to amphibolite facies ophiolite that was emplaced onto the Sakarya Zone, in the central part of the Pontides of northern Turkey. NW-SE trending Elekdag ophiolite hosts small scale chromitite occurrences in serpentinized harzburgite and dunite, and have maximum resource of several thousands t Cr2O3. The chromitites the Elekdag ophiolite can be divided in to "high-Cr" and "high-Al" types. The calculated melt composition of the high-Cr chromitites is 9.4-13.2 wt.% Al2O3, 0.2-0.4 wt.% TiO2 with FeO/MgO ratios of 0.4-1.9, which are indicative of boninitic compositions. However, the high-Al chromitites have 14.7-173 wt.% Al2O3 and 03-0.8 wt.% TiO2 with FeO/MgO ratios of between 0.3 and 0.8, which are consistent with MORB-like tholeiitic affinities. The total PGE content of the chromitites range between 82 and 1466 ppb, and the average PGE content of the high-Cr and high-Al chromitites are 267 ppb and 195 ppb, respectively. The chromitites are characterized by low Pd/Ir ratios of 0.02-020 that is characteristic of non-fractionated chromitites. The chondrite normalized PGE pattern of the chromitites resemble those of mantle-derived Cr-rich chromitites in ophiolites of the supra-subduction zone (SSZ) elsewhere. Mineral and bulk rock PGE data for the Elekdag chromitites indicate that high-Cr chromitites formed from Cr-rich and, Al- and Ti-poor boninitic melts, most probably in the fore-arc setting in the deeper part of the mantle. This was succeeded by the mineralization of high-Al chromitites from a differentiated boninitic melt at shallow depths close to the Moho Discontinuity.


5. U10290
Fekete S. et al. Contrasting hydrological processes of meteoric water incursion during magmatic-hydrothermal ore deposition: An oxygen isotope study by ion microprobe // Earth Planet. Sci. Lett. 2016. Vol. 451. P. 263–271.

Meteoric water convection has long been recognized as an efficient means to cool magmatic intrusions in the Earth's upper crust. This interplay between magmatic and hydrothermal activity thus exerts a primary control on the structure and evolution of volcanic, geothermal and ore-forming systems. Incursion of meteoric water into magmatic-hydrothermal systems has been linked to tin ore deposition in granitic plutons. In contrast, evidence from porphyry copper ore deposits suggests that crystallizing subvolcanic magma bodies are only affected by meteoric water incursion in peripheral zones and during late post-ore stages. We apply high-resolution secondary ion mass spectrometry (SIMS) to analyze oxygen isotope ratios of individual growth zones in vein quartz crystals, imaged by cathodo-luminescence microscopy (SEM-CL). Existing microthermometric information from fluid inclusions enables calculation of the oxygen isotope composition of the fluid from which the quartz precipitated, constraining the relative timing of meteoric water input into these two different settings. Our results confirm that incursion of meteoric water directly contributes to cooling of shallow granitic plutons and plays a key role in concurrent tin mineralization. By contrast, data from two porphyry copper deposits suggest that downward circulating meteoric water is counteracted by up-flowing hot magmatic fluids. Our data show that porphyry copper ore deposition occurs close to a magmatic-meteoric water interface, rather than in a purely magmatic fluid plume, confirming recent hydrological modeling. On a larger scale, the expulsion of magmatic fluids against the meteoric water interface can shield plutons from rapid convective cooling, which may aid the build-up of large magma chambers required for porphyry copper ore formation.


6. S16403
Kempe U. et al. The genesis of Zr-Nb-REE mineralisation at Khalzan Buregte (Western Mongolia) reconsidered // Ore Geol. Rev. 2015. Vol. 64. P. 602–625.

The sources and formation conditions of unconventional Zr-Nb-REE mineralisation (REE = rare earth elements) presently found in increasing number worldwide are still poorly constrained. One particular problem is the specific role of magmatic and hydrothermal processes active in various geological settings. Investigation of Zr-Nb-REE mineralisation at Khalzan Buregte and Tsakhir, Western Mongolia, enables to evaluate magmatic processes preceding economic mineralisation and, in a second step, to compare similar ore-forming processes developing in host rocks of contrasting rock composition (low- vs. high-silica rocks). The genesis of the Zr-Nb-REE mineralisation is re-assessed using field observations, whole rock analysis (chemical composition, quantitative modal analysis by X-ray diffraction) and by the application of various transmitted light and electron microscopic techniques. Coarse-grained intrusive bodies, dikes and volcanic rocks of alkaline, silica-saturated composition were found to be contemporarily emplaced at subvolcanic to volcanic levels forming four alkaline massifs within the Khalzan Buregte area. The whole rock composition of weakly altered magmatic rocks ranges from syenite to quartz monzonite and alkaline granite (alkali feldspar syenite to alkali feldspar granite according to their modal composition). Magmatic and at least two subsequent hydrothermal processes contributed significantly to the formation of economic concentrations of high field strength elements (HFSE) such as Zr, Hf, Nb, Ta, REE and Y in the Khalzan Buregte deposit and in the nearby Tsakhir prospect. Mixing of magma from at least three sources and the formation of potassium feldspar cumulates resulted in local enrichment of Zr, Nb and light rare earth elements (LREE) in the rocks up to sub-economic levels. There was no significant increase in Y and heavy rare earth elements (HREE) during magmatism. Multistage metasomatic alteration resulted in a pronounced chemical and mineralogical heterogeneity of associated alteration assemblages. The main hosts of Zr and Hf in the ores are zircon and other zirconium silicates (gittinsite, catapleiite-(Ca) and elpidite). The rare metals Nb and Ta are mainly contained in various types of pyrochlore (Khalzan Buregte) and, to a lesser extent, in fergusonite and other minerals (Tsakhir). A large variety of REE- and Y-bearing minerals have been identified, including oxides, fluorocarbonates and silicates. Early hydrothermal alteration by silica- and carbonate-rich fluids yielded extreme concentrations of Zr, Nb and LREE. Later alteration resulted in enrichment of Y and HREE. In the latter case, fluids were very rich in fluorine. Our preliminary genetic model assumes a carbonatite-related fluid system responsible for the early alteration that occurred late during or postdating the intrusion/extrusion of the silica-saturated magmas. A "Li-F granite-type" fluid system was active during the late alteration. The interplay of all these processes resulted in the formation of a complex, economic Zr-Nb-REE mineralisation at Khalzan Buregte.


7. U12629
Mao D., Revil A., Hinton J. Induced polarization response of porous media with metallic particles - Part 4: Detection of metallic and nonmetallic targets in time-domain induced polarization tomography // Geophysics. 2016. Vol. 81, № 4. P. D359–D375.

Time-domain induced polarization (TDIP) is a nonintrusive imaging technique of the subsurface that can be used to localize polarizable bodies including metallic objects and clay-rich materials. We first reviewed recent advances in the interpretation of induced polarization data. Then, we performed laboratory and sandbox experiments to determine the frequency-domain and TDIP signature of (1) a metal bar in sand, (2) dispersed semiconductors (e.g., pyrite) in sand, and (3) bentonite. In the case of the sandbox experiments, the three types of bodies were localized in the center of the sandbox, which was filled with water-saturated sand. We determined that chargeability was the best parameter to characterize metallic bodies (the metallic bar and the dispersed pyrite), whereas normalized chargeability was the best parameter to characterize the cation exchange capacity and therefore the clay content of the subsurface at a given clay mineralogy. For interpretation purposes, it was therefore important to display the right parameters in TDIP depending on the type of target we wanted to image for engineering applications.


8. U09363
Nishimura K. A mathematical model of trace element and isotopic behavior during simultaneous assimilation and imperfect fractional crystallization // Contrib. Mineral. Petrol. 2012. Vol. 164, № 3. P. 427–440.

The process of coupled assimilation and fractional crystallization (AFC) is one of the most popular petrogenetic concepts that explains magmatic differentiation. Conventional geochemical models for this process assume that crystals are removed instantaneously from the magma body as they are produced; however, recent advances in isotopic microanalysis have clarified that the crystals are suspended within the magma body for a certain period, affecting the whole-rock composition in response to the intra-grain isotopic zoning. This study develops a mass balance model for simultaneous assimilation and imperfect fractional crystallization (AIFC) to describe the effects of suspended crystals on the path of magma evolution. The mass balance differential equations for the liquid and suspended crystals are solved simultaneously. The analytical solution of the AIFC equations gives a quantitative account of the evolution paths of trace elements and isotopes within bulk crystals, liquid, and magma (crystals plus liquid). The chemical path of the magma differs markedly from that predicted by the conventional AFC model.


9. U09363
Roberge J., Wallace P.J., Kent A.J.R. Magmatic processes in the Bishop Tuff rhyolitic magma based on trace elements in melt inclusions and pumice matrix glass // Contrib. Mineral. Petrol. 2013. Vol. 165, № 2. P. 237–257.

To investigate the origin of compositional zonation in the Bishop Tuff magma body, we have analyzed trace elements in the matrix glass of pumice clasts and in quartz-hosted melt inclusions. Our results show contrasting patterns for quartz in different parts of the Bishop Tuff. In all samples from the early part of the eruption, trace element compositions of matrix glasses are similar to but slightly more evolved than quartz-hosted melt inclusions. This indicates a cogenetic relationship between quartz crystals and their surrounding matrix glass, consistent with in situ crystallization. The range of incompatible element concentrations in melt inclusions and matrix glass from single pumice clasts requires 16-20 wt% in situ crystallization. This is greater than the actual crystal content of the pumices (< 15 % crystals). In contrast to the pattern for the early pumices, pyroclastic flow samples from the middle part of the eruption show contrasting trends: In some clasts, the matrix is more evolved than the inclusions, whereas in other clasts, the matrix is less evolved. In the late Bishop Tuff, all crystal-rich samples have matrix glasses that are less evolved than the melt inclusions. Trace element abundances indicate that the cores of quartz in the late Bishop Tuff crystallized from more differentiated rhyolitic magma that was similar in many ways, yet distinct from the early-erupted Bishop Tuff. Our results are compatible with a model of secular incremental zoning (Hildreth and Wilson in Compositional zoning of the Bishop Tuff. J Petrol 48(5):951-999, 2007), in which melt batches from underlying crystal mush rise to various levels in a growing magma body according to their buoyancy. Early- and middle-erupted quartz crystallized from highly evolved rhyolitic melt, but then some parts of the middle-erupted magma were invaded by less differentiated rhyolite such that the matrix melt at the time of eruption was less evolved than the melt inclusions. A similar process occurred but to a greater extent in magma that erupted to form the late Bishop Tuff. In addition, there was a final, major magma mixing event in the late magma that formed Ti-rich rims on quartz and Ba-rich rims on sanidine, trapped less evolved rhyolitic melt inclusions, and resulted in dark and swirly crystal-poor pumice that is a rare type throughout much of the Bishop Tuff.


10. U01624
Salje E.K.H. Tweed, twins, and holes // Am. Miner. 2015. Vol. 100, № 2–3. P. 343–351.

Tweed, twin, and porous microstructures are traditionally studied in mineralogy to understand the thermal history of minerals, and to identify their properties such as chemical transport and elastic behavior. Recently, the same research area has blossomed in material sciences 1916 2016 and physics with the aim to design and build devices that are based on the properties of nano-structures. Only the very existence and the properties of tweed, twins, and holes matters in this quest while the crystalline matrix plays only a minor role in the current search for novel device materials. This development has largely bypassed mineralogists while physicists did not profit from the age-long experience of mineralogists in dealing with such materials. In this Invited Centennial article, I will first discuss some key findings and approaches to foster the transfer of ideas in both directions: mineralogists can potentially inspire material scientists while the physics of the fine structure of twin walls and tweed can help mineralogists understand mineral properties in much more detail than hereto possible. Besides the observation that novel physical properties can spring from microstructures, most recent work also includes the dynamics of microstructures under external stress or electric fields. The dynamics is virtually always non-smooth or "jerky." One of the best studied jerk distribution is that of collapsing porous minerals under stress, where the main focus of research is the identification of precursor effects as warning signs for larger events such as the collapse of mines, boreholes, or even regional earthquakes. The underlying physics is the same as in large earthquakes (which can be modeled but not observed in laboratory experiments). The agreement between laboratory experiments of porous collapse and large-scale earthquakes goes well beyond each quake's statistics and includes waiting-time distributions and the Omori law of after-shocks. The same approach is used to characterize high-tech materials in aircraft industry and functional materials such as used in electronic memory devices, ferroelectric sensors and non-volatile memories and ferromagnets.


11. U12629
Sarout J. et al. A robust experimental determination of Thomsen’s delta parameter // Geophysics. 2015. Vol. 80, № 1. P. A19–A24.

A novel inversion method for the laboratory determination of Thomsen's delta anisotropy parameter on cylindrical rock specimens from ultrasonic data has been recently reported in the literature. We further assessed this method through a direct comparison of the results of the traditional method (involving a single off-axis P-wave velocity measurement at 45 degrees) and the new method (involving 65 P-wave velocity measurements at several angles to the symmetry axis). We prepared and characterized two vertical shale specimens from the same preserved vertical core to assess their similarity in terms of structure, mineralogy, porosity, and density. The shale was assumed to be transversely isotropic in view of the observed (horizontal) bedding. We subjected both specimens to the same brine saturation and effective stress state. Using the two methods, we obtained similar results for Thomsen's a (vertical P-wave) and epsilon (P-wave anisotropy) parameters. However, a significant discrepancy was observed for Thomsen's delta parameter: We obtained results of 0.13 using the new method and 0.39 using the traditional method. As a result of the overdetermined nature of the P-wave velocity measurements used in the new method, we believe that the corresponding delta value is more reliable. Also, the value derived with the new testing method seems to match more closely the reported field data.


12. U01624
Su W. et al. Chlorine-hydroxyl diffusion in pargasitic amphibole // Am. Miner. 2015. Vol. 100, № 1. P. 138–147.

Chlorine-hydroxyl diffusion was measured in pargasitic amphibole from Yunnan province, China at 1.0 GPa, 625 to 800 degrees C. Experiments were performed by immersing unoriented crystals in water-bearing NaCl in a piston cylinder for durations from 100 to 454 h. Diffusion profiles were on the order of greater than tens of micrometers in length, and electron microprobe analysis allow us to extract semi-quantitative diffusivities from these experiments. The preliminary diffusion coefficients for chlorine in amphibole in the water-bearing experiments are 2.6 x 10(-16) m(2)/s at 625 degrees C, 4.9 x 10(-16) m(2)/s at 650 degrees C, 7.6 x 10(16) m(2)/s at 700 degrees C, 1.8 x 10(-15) m(2)/s at 750 degrees C, 2.8 x 10(-15) m(2)/s at 800 degrees C. For temperatures between 625 and 800 degrees C, the Arrhenius relation for chlorine-hydroxyl diffusion has an activation energy of 106.6 +/- 7.8 kJ/K mol and a D-0 of 4.53 (+7.3, 2.8) x 10(-10) m(2)/s. Our measurements do not show evidence of anisotropy in the diffusion of Cl-OH into amphibole, but future experiments need to better investigate this possibility.


13. U01624
Witter M. et al. Understanding magmatic processes at Telica volcano, Nicaragua: Crystal size distribution and textural analysis // Am. Miner. 2016. Vol. 101, № 5–6. P. 1052–1060.

Telica volcano in Nicaragua currently exhibits persistent activity with continuous seismicity and degassing, yet it has not produced lava flows since 1529. To provide insight into magma chamber processes including replenishment and crystallization, crystal size distribution (CSD) profiles of plagioclase feldspar phenocrysts were determined for Quaternary Telica basalts and basaltic andesites. Textural analysis of 14 highly crystalline lavas (>20 vol% phenocrysts) indicates that the samples are dominated by sieve-textured plagioclase feldspar phenocrysts whose origin requires thermochemical disequilibrium within the magmatic system. The CSD curves display an inverse relationship between phenocryst length and population density. Concave-up patterns observed for the Telica lava samples can be represented by linear segments that define two crystal populations: a steeply sloping segment for small crystals (<1.5 mm) and a gently sloping segment for crystals >1.5 mm in length. The two crystal populations may be explained by magma replenishment and a mixing model in which a mafic magma is introduced to a stable chamber that is petrologically and geochemically evolving. Residence times calculated using the defined linear segments of the CSD curves suggest these magmatic processes occur over timescales on the order of decades to centuries. The crystal size distribution and textural analysis advocate for the current persistent activity as being consistent throughout Telica's historic and prehistoric eruptive periods and driven by replenishment of mafic magma.


14. U01624
Zhao J. et al. Dissolution-reprecipitation vs. solid-state diffusion: Mechanism of mineral transformations in sylvanite, (AuAg)(2)Te-4, under hydrothermal conditions // Am. Miner. 2013. Vol. 98, № 1. P. 19–32.

Under hydrothermal conditions, diffusion-driven solid-state reactions can compete with fluid-mediated reaction mechanisms. We have obtained an insight into the complex textures resulting from this competition by studying experimentally the transformation of Au-Ag-telluride sylvanite to Au-Ag alloy under hydrothermal conditions, and exploring the effects of temperature (160-220 degrees C), pH (2-10), and redox conditions on the sample textures and the reaction kinetics. Sylvanite transformed to Au-Ag alloy over all hydrothermal conditions investigated, but not under dry conditions. The replacement was pseudomorphic, as the Au-Ag alloy preserved the external dimensions of the sylvanite grains. The resulting Au-Ag alloy was porous, consisting of worm-like aggregates with diameters ranging from 200 nm to 1 mu m. In addition to Au-Ag alloy, a range of other phases were observed as intermediate products, including petzite (Ag3AuTe2), hessite (Ag2Te), and two compositions of calaverite: an Ag-rich-Te-depleted composition, (Au0.78Ag0.22)Te-1.74, and a normal calaverite, (Au0.93Ag0.07)Te-2. The transformation of sylvanite to Au-Ag alloy follows a complex reaction path, with competing reactions proceeding either via interface-coupled dissolution and reprecipitation (ICDR) mechanism or via solid-state exsolution. Initially, sylvanite was replaced by an Au-Ag alloy following an ICDR mechanism, with sylvanite dissolution being the rate-limiting step relative to Au-Ag alloy precipitation. Tellurium was lost to the bulk solution as tellurite or telluride complexes, depending on the redox conditions. Once the concentration of Te in solution reached a critical state, the reaction switched and sylvanite dissolution was coupled to the precipitation of an Ag-rich-Te-depleted calaverite. This Agrich-Te-depleted calaverite decomposes via exsolution to calaverite and phase X (Ag3+xAu1-xTe2 with 0.1 < x <0.55), which in turn breaks down to a mixture of low petzite and low hessite below 120 degrees C via exsolution. As the reaction continues, the calaverite and phase X are all transformed to Au-Ag alloy via ICDR. In the ICDR reactions the Au-Ag alloy precipitated locally near the telluride dissolution site. Such local Au-Ag alloy precipitation is facilitated by fast heterogeneous nucleation onto the sylvanite, calaverite, and petzite surfaces. The dissolution of sylvanite and of the intermediate telluride species, and the overall reaction, are oxidation reactions. The diffusion of oxygen through the porous Au-Ag alloy layer plays an important role in sustaining the reaction. A similar combination of dissolution-reprecipitation and solid-state processes may be responsible for the formation of some of the Au and Au-Ag telluride assemblages observed in Nature. These processes may also play a role in the formation of mineral assemblages in Cu-Fe sulfide systems, where the solid-state mobility of Cu+ ions is relatively high at moderate temperatures. The interplay of different reaction mechanisms results in complex textures, which could easily be misinterpreted in terms of complex geological evolution. At 220 degrees C, solid-state replacement of sylvanite by Au-Ag alloy is slow (months), but under hydrothermal conditions sylvanite grains similar to 100 mu m in size can be fully replaced in as little as 96 h, providing a possible alternative to roasting as a pre-treatment of telluride-rich gold ores.


15. Баренбаум А.А. Возможный механизм нагрева пород литосферы галактическими кометами // Уральский геологический журнал. 2013. № 1 (91). С. 21-38.

Изучается возможный физический механизм нагрева пород литосферы выпадающими на нашу планету галактическими кометами. Согласно этому механизму высокоскоростные галактические кометы в атмосфере Земли полностью разрушаются, преобразуясь в газовую струю из испарившегося кометного вещества и ударно нагретого воздуха. Падая на земную поверхность, струя порождает узконаправленную ударную волну, которая проникает глубоко в литосферу планеты, расходуя энергию кометы на нагрев пород в магматических камерах. Для теоретического изучения механизма такого нагрева использован феноменологический подход, опирающийся на гидродинамические модели, разработанные М.А. Лаврентьевым для исследования взрывных явлений. Изложены существо феноменологического подхода и дано описание теоретических моделей М.А. Лаврентьева, а также обоснована возможность привлечения этих моделей к изучению механизма взаимодействия кометных ударных волн с литосферой Земли. С использованием одной из моделей рассчитаны эффекты от падения на Землю галактических комет разных масс. На основе выполненных расчетов обсуждаются некоторые нерешенные вопросы сравнительной планетологии, геохимии и магматической петрологии.


16. 044066
Бочкарев В.С. Причина появления рудоносных химических элементов на планете Земля. Металлогения и планетология // Горные ведомости. 2015. № 12 (139). С. 6-21.

В статье рассматривается авторская модель геодинамики Земли от двойной звезды к взрывному формированию планет, которая позволила вскрыть и объяснить особенности структуры Солнечной системы. Гипотетическая вторая звезда двойной системы (Елена Прекрасная) после первого взрыва и формирования планет-гигантов в последовательности Нептун, Юпитер, Сатурн и Уран испытала коллапс, обязанный появлению тяжелых элементов от железа до урана. Второй взрыв привел к созданию плотных планет от Марса до Меркурия.


17. 039284
Гусев А.И., Табакаева Е.М. Новые данные по минералогии и геохимии Осокинско-Батунковского рудного поля северного Алтая // Международный журнал прикладных и фундаментальных исследований. 2016. № 5-2. С. 266-270.

В статье приведены новые по минералогии и геохимии руд Осокинско-Батунковского рудного поля Северного Алтая. Впервые выявлены иттрий-торит и торбернит в рудах Осокинского месторождения. Установлены повышенные содержания в рудах и минералах Au, Sc, Y, Dy, Ho, Er, U. В минералах проявлен тетрадный эффект фракционирования (ТЭФ) РЗЭ М- типа при не соблюдении заряд-радиус-контролируемого поведения химических элементов. Максимальные значения ТЭФ РЗЭ М- типа характерны для условий повышенной кислотности среды минералообразования. Генерация оруденения осуществлялась при наложении процессов от верхнего девона до мел-эоценовой тектоно-термальной активизации мантийных процессов.


18. 001200
Добрецов Н.Л., Туркина О.М. Раннедокембрийская история Земли: роль плейт- и плюм-тектоники и космического фактора // Геология и геофизика. 2015. Т. 56. № 7. С. 1250-1274.

Рассмотрены особенности эволюции Земли и геологических процессов в течение хадея и архея на основании имеющейся информации из области космофизики и сравнительной планетологии; изотопной геохронологии, геологии и петрологии пород архейских зеленокаменных поясов (ЗКП) и тоналит-трондьемит-гранодиоритовых (ТТГ) комплексов, а также геодинамических моделей с целью анализа роли плейт- и плюм-тектонических и импактных процессов. Сходство возрастных пиков хадейско-эоархейских цирконов на Земле с событиями поздней тяжелой бомбардировки на Луне, а также судя по изотопному Hf составу, преимущественно мафические источники этих цирконов предполагают существенную роль импактных процессов во временном интервале 4.4-3.8 млрд лет. Появление пород сиалической коры, представленной породами ТТГ комплексов, относится к рубежу 4.2 млрд лет (гнейсы комплекса Акоста), тогда как масштабный ее рециклинг фиксируется в изотопных Hf характеристиках цирконов после 3.75 млрд лет. Анализ породных ассоциаций и их геохимических характеристик показывает, что формирование архейских зеленокаменных поясов было связано с обстановками рифтинга и спрединга, субдукции и мантийно-плюмовыми, в ключевых чертах сходных с современными. Специфика архейского периода проявлена в более широком развитии мантийно-плюмовых (коматиит-базальтовых) ассоциаций, субдукционных производных бонинитовых и адакитовых серий, кратковременности и быстрой смене режимов субдукции, что выражается в перемежаемости типичных известково-щелочных андезит-дацит-риолитовых и адакитовых ассоциаций, которые вызваны более «горячей» мантией, обусловливающей высокотурбулентный режим конвекции и нестационарность субдукции. Это позволяет рассматривать архейский период как переходный, отвечающий тектонике малых плит.


19. 035245
Замятина Д.А., Мурзин В.В. Источники вещества и флюида при формировании золото-сульфидного оруденения Ауэрбаховского вулкано-плутонического пояса на Северном Урале // Литосфера. 2016. № 1. С. 169-177.

Приводятся данные по изотопному составу C, O, Sr и S карбонатов, кварца и сульфидов из Тамуньерского и Воронцовского золоторудных месторождений, локализованных в Ауэрбаховском вулкано-плутоническом поясе. Установлено, что по изотопным характеристикам минералов наиболее близким аналогом оруденения в березитах Тамуньерского месторождения является золото-полиметаллический тип оруденения в джаспероидах Воронцовского месторождения. Расчет изотопного состава С, О и S рудоносного флюида свидетельствует об участии в рудообразовании двух основных резервуаров вещества - породного (морские карбонаты и биогенный пирит вмещающих вулканогенно-осадочных толщ) и флюидного (металлоносные магматогенные, а также метаморфогенные флюиды, связанные внедрением интрузивных масс).


20. Кокин А.В., Трощенко В.В. Зональность эндогенных рудных месторождений как отражение фундаментальных свойств химических элементов // Наука Юга России. 2016. Т. 12. № 2. С. 28-42.

Проанализирована сравнительная распространенность химических элементов в условиях их накопления под влиянием различных физико-химических процессов звездо- и планетообразования, земной коры. Установлено, что последовательность накопления элементов на разном уровне организации вещества (в Солнечной системе, хондритах, земной коре, морской воде, рудах, минералах) находится в зависимости от их фундаментальных свойств: распространенности (кларков), стандартной энтропии, положения элемента в Периодической системе химических элементов Д.И. Менделеева и периодичности нуклеосинтеза в условиях образования звезд разных поколений. Это подтверждается положительной и значимой корреляцией распространенности элементов в Солнечной системе, хондритах, земной коре, морской воде и обратной (значимой отрицательной) связью стандартной энтропии с распространенностью элементов в этих образованиях. Последовательность накопления элементов не нарушается в процессе глубокой дифференциации (фракционирования) вещества под влиянием различных процессов в геохимическом круговороте вещества земной коры, включая рудообразование. Эмпирически рассчитанные общие и частные ряды эндогенной зональности золоторудных, золото-серебряных, золото-редкометалльных, серебро-олово-полиметаллических и марганцевых месторождений отражают фундаментальные свойства распространенности (кларков), стандартной энтропии и Периодического закона. Это может быть использовано не только для оценки уровня эрозионного среза рудных месторождений, конкретных рудных тел, но и для оценки условий рудообразования, которые в рамках этапов и стадий могут формироваться по правилу прогрессивной (прямой) или регрессивной (обратной) зональности, что позволит исключить ошибки в оценке уровня эрозионного среза рудных месторождений.


21. 009132
Колесникова Н.Б., Борисов В.Н., Раков Л.Т. Особенности генезиса сульфидной и вольфрам-молибденовой минерализации на одном из рудопроявлений Приморья // Разведка и охрана недр. 2016. № 4. С. 3-9.

Проведены исследования пород, вмещающих сульфидную и вольфрам-молибденовую минерализацию рудопроявления Александра, позволившие выявить некоторые особенности его генезиса. Результаты проведенных работ дают основание сделать предположение о зависимости состава и характера рудной минерализации от вмещающих пород, о роли последних как одном из возможных источников рудного вещества и значении гидротермального процесса в формировании оруденения.


22. 039284
Курков А.А. Физическая теория описывает эволюцию Земли // Международный журнал прикладных и фундаментальных исследований. 2016. № 5-2. С. 277-282.

На основе наблюдательных данных Солнечной системы вычислены три новые фундаментальные константы и создана физическая теория. Эта теория получила название Эмпирической Теории Вселенной (ЭТВ), так как включает очень важную гипотезу о том, что Вселенная представляет собой частицу. Свойства Вселенной – частицы оказались настолько просты, что позволили найти ряд регрессионных зависимостей свойств планет по наблюдательным данным для Венеры, Земли и Марса. Эти зависимости составили основу теоретической планетологии и позволяют проследить эволюцию основных параметров планет. В данной статье рассмотрена эволюция планеты Земля. Возраст Солнца, всех планет системы и Земли оценивается t = 10,1·109 лет. До возраста t = 4,0·109 лет назад поверхность Земли находилась в расплавленном или пластическом состоянии. Дальнейшая эволюция Земли происходит по мере удаления от Солнца и при расширении самой планеты.


23. Сиротин В.И. Критические замечания к книге В.С. Шкодзинского «Петрология литосферы и кимберлитов (модель горячей гетерогенной аккреции Земли)» // Вестник Воронежского государственного университета. Серия: Геология. 2015. № 2. С. 134-141.

На основе данных сравнительной планетологии характеризуются этапы эволюции доархейской истории Земли в контексте предложенной модели В.С. Шкодзинского о горячей гетерогенной аккреции Земли, которая допускает существование магматического океана вплоть до позднего протерозоя, что противоречит данным сравнительной планетологии и является ошибочной.


24. Судариков С.М., Змиевский М.В. Геохимия рудообразующих гидротермальных флюидов мирового океана // Записки Горного института. 2015. Т. 215. С. 5-15.

Анализируются наиболее полные результаты изучения геохимии гидротермальных рудообразующих растворов в русских и международных экспедициях на глубоководных гидротермальных полях Мирового океана. В зоне разгрузки флюидов формируются растворы как с высокой, так и с пониженной относительно морской воды минерализацией. Положительная корреляция рудных компонентов с хлорид-ионом и отрицательная - с величиной рН может свидетельствовать о переносе компонентов в кислых гидротермальных растворах в форме хлоридных комплексов. Сероводород связан значимой положительной зависимостью с металлами, что говорит о восстановительных условиях, формирующихся в рудоносных гидротермальных растворах. Это подтверждается и тесной связью рудных компонентов с водородом. Перенос металлов преимущественно в форме хлоридных комплексов при высокой температуре раствора подтверждается результатами проведенного нами термодинамического моделирования. Метан характеризуется отрицательной зависимостью от температуры и концентраций рудных компонентов, связан положительной зависимостью с рН и отрицательной - с сероводородом. Каждая из наблюдаемых зависимостей может свидетельствовать против абиогенной теории поступления метана в гидротермальные растворы. Для поисков новых рудных залежей и организации геохимического мониторинга при освоении уже открытых месторождений наиболее перспективны следующие геохимические показатели: Eh, pH, концентрации Cl, Fe, Mn, H 2S, CO 2, H 2 и, возможно, CH 4.


25. 035245
Ширяев П.Б., Вахрушева Н.В. Оливин-хромшпинелевое равновесие в хромититах и ультрамафитах массива Рай-Из, Полярный Урал // Литосфера. 2016. № 2. С. 107-110.

Выполнено сопоставление составов оливина и хромовой шпинели в хромититах и рудовмещающих метаморфизованных ультрамафитах массива Рай-Из. Установлено, что железистость оливина и шпинели прямо пропорциональна и монотонно возрастает от хромититов к ультрамафитам, что свидетельствует о существовании равновесия в системе порода-руда. Составы акцессорных шпинелей из околорудных ультрамафитов соответствуют феррихромиту и хроммагнетиту - высокоокисленным разновидностям шпинелидов, типичным для метаморфических ультрамафитов. Полученные данные позволяют сделать вывод о том, что хромититы и метаморфизованные ультрамафиты являются продуктами одного процесса - метаморфической дифференциации ультрамафитов.


На главную К списку выставокАрхив выставок