Paragenesis of unusual Fe-cordierite (sekaninaite)-bearing paralava and clinker from the Kuznetsk coal basin,Siberia, Russia     

Rodney Grapes  Sophia Korzhova  Ella Sokol  Yurii Seryotkin 《Contributions to Mineralogy and Petrology》2011,162(2):253-273

Sekaninaite (X_Fe > 0.5)-bearing paralava and clinker are the products of ancient combustion metamorphism in the western part of the Kuznetsk coal basin, Siberia. The combustion metamorphic rocks typically occur as clinker beds and breccias consisting of vitrified sandstone–siltstone clinker fragments cemented by paralava, resulting from hanging-wall collapse above burning coal seams and quenching. Sekaninaite–Fe-cordierite (X_Fe = 95–45) is associated with tridymite, fayalite, magnetite, ± clinoferrosilite and ±mullite in paralava and with tridymite and mullite in clinker. Unmelted grains of detrital quartz occur in both rocks (<3 vol% in paralavas and up to 30 vol% in some clinkers). Compositionally variable siliceous, K-rich peraluminous glass is <30% in paralavas and up to 85% in clinkers. The paralavas resulted from extensive fusion of sandstone–siltstone (clinker), and sideritic/Fe-hydroxide material contained within them, with the proportion of clastic sediments ≫ ferruginous component. Calculated dry liquidus temperatures of the paralavas are 1,120–1,050°C and 920–1,050°C for clinkers, with calculated viscosities at liquidus temperatures of 10^1.6–7.0 and 10^7.0–9.8 Pa s, respectively. Dry liquidus temperatures of glass compositions range between 920 and 1,120°C (paralava) and 920–960°C (clinker), and viscosities at these temperatures are 10^9.7–5.5 and 10^8.8–9.7 Pa s, respectively. Compared with worldwide occurrences of cordierite–sekaninaite in pyrometamorphic rocks, sekaninaite occurs in rocks with X_Fe (mol% FeO/(FeO + MgO)) > 0.8; sekaninaite and Fe-cordierite occur in rocks with X_Fe 0.6–0.8, and cordierite (X_Fe < 0.5) is restricted to rocks with X_Fe < 0.6. The crystal-chemical formula of an anhydrous sekaninaite based on the refined structure is | \textK_0.02 |(\textFe_1.54^{2 +} \textMg_0.40 \textMn_0.06 )_{\Upsigma 2.00}^M [(\textAl_1.98 \textFe_0.02^{2 +} \textSi_1.00 )_{\Upsigma 3.00}^T1 (\textSi_3.94 \textAl_2.04 \textFe_0.02^{2 +} )_{\Upsigma 6.00}^T2 \textO₁₈ ]. \left| {{\text{K}}_{0.02} } \right|({\text{Fe}}_{1.54}^{2 + } {\text{Mg}}_{0.40} {\text{Mn}}_{0.06} )_{\Upsigma 2.00}^{M} [({\text{Al}}_{1.98} {\text{Fe}}_{0.02}^{2 + } {\text{Si}}_{1.00} )_{\Upsigma 3.00}^{T1} ({\text{Si}}_{3.94} {\text{Al}}_{2.04} {\text{Fe}}_{0.02}^{2 + } )_{\Upsigma 6.00}^{T2} {\text{O}}_{18} ].  相似文献   

Formation of gold–silver sulfides and native gold in Fe–Ag–Au–S system     

G.A. Pal'yanova  K.A. Kokh  Yu.V. Seryotkin 《Russian Geology and Geophysics》2012,53(4):347-355

We carried out experiments on crystallization of Fe-containing melts FeS₂Ag_0.1–0.1xAu_0.1x (x = 0.05, 0.2, 0.4, and 0.8) with Ag/Au weight ratios from 10 to 0.1. Mixtures prepared from elements in corresponding proportions were heated in evacuated quartz ampoules to 1050 ºC and kept at this temperature for 12 h; then they were cooled to 150 ºC, annealed for 30 days, and cooled to room temperature. The solid-phase products were studied by optical and electron microscopy and X-ray spectroscopy. The crystallization products were mainly from iron sulfides: monoclinic pyrrhotite (Fe_0.47S_0.53 or Fe₇S₈) and pyrite (Fe_0.99S_2.01). Gold–silver sulfides (low-temperature modifications) are present in all synthesized samples. Depending on Ag/Au, the following sulfides are produced: acanthite (Ag/Au = 10), solid solutions Ag_2–xAu_xS (Ag/Au = 10, 2), uytenbogaardtite (Ag/Au = 2, 0.75), and petrovskaite (Ag/Au = 0.75, 0.12). They contain iron impurities (up to 3.3 wt.%). Xenomorphic micro- (<1–5 μm) and macrograins (5–50 μm) of Au–Ag sulfides are localized in pyrite or between the grains of pyrite and pyrrhotite. High-fineness gold was detected in the samples with initial ratio Ag/Au ≤ 2. It is present as fine and large rounded microinclusions or as intergrowths with Au–Ag sulfides in pyrite or, more seldom, at the boundary of pyrite and pyrrhotite grains. This gold contains up to 5.7 wt.% Fe. Based on the sample textures and phase relations, a sequence of their crystallization was determined. At ~1050 ºC, there are probably iron sulfide melt L₁ (Fe,S ? Ag,Au), gold–silver sulfide melt L₂ (Au,Ag,S ? Fe), and liquid sulfur L_S. On cooling, melt L₁ produces pyrrhotite; further cooling leads to the crystallization of high-fineness gold (macrograins from L₁ and micrograins from L₂) and Au–Ag sulfides (micrograins from L₁ and macrograins from L₂). Pyrite crystallizes after gold–silver sulfides by the peritectic reaction FeS + L_S = FeS₂ at ~743 ºC. Elemental sulfur is the last to crystallize. Gold–silver sulfides are stable and dominate over native gold and silver, especially in pyrite-containing ores with high Ag/Au ratios.  相似文献   

Formation of gold and silver sulfides from melts in the Ag-Au-S system: Experimental data     

G. A. Pal’yanova  Yu. V. Seryotkin  K. A. Kokh 《Doklady Earth Sciences》2011,436(1):42-46

  相似文献   

Structural evolution of hemimorphite at high pressure up to 4.2 GPa     

Yurii V. Seryotkin  Vladimir V. Bakakin 《Physics and Chemistry of Minerals》2011,38(9):679-684

The high-pressure structural evolution of hemimorphite, Zn₄Si₂O₇(OH)₂·H₂O, a = 8.3881(13), b = 10.7179(11), c = 5.1311(9) Å, V = 461.30(12) Å³, space group Imm2, Z = 2, was studied by single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions up to 4.2 GPa. In the pressure range of 0.0001–2.44 GPa, the unit-cell parameters change almost linearly. The phase transition (probably of the second order) with symmetry reduction from Imm2 (hemimorphite-I) to Pnn2 (hemimorphite-II) was found near 2.5 GPa. The structure compressibility increases somewhat above the phase transition. Namely, the initial unit-cell volume decreases by 3.6% at 2.44 GPa and by 7.2% at 4.20 GPa. The hemimorphite framework can be described as built up of secondary building units (SBU) Zn₄Si₂O₇(OH)₂. These blocks are combined to form the rods arranged along the c-axis; these rods are multiplied by basic and I-translations of orthorhombic unit cell. The symmetry reduction is caused by the rotation of the rods along their axis. In hemimorphite-I, the compression affects mainly the SBU dimensions, whereas a rectangular section of the channels having mm2 symmetry remains practically unchanged. An appreciable decrease in this section in hemimorphite-II is determined by its oblique distortion with the loss of m planes. It results from opposite rotation of adjacent SBU, which also leads into the loss of I-translation. In hemimorphite-I, the coordination of H₂O molecules is fourfold planar; the hydrogen-bonded hydroxyls and H₂O molecules form infinite ribbons along the c-axis. In hemimorphite-II, an additional short H₂O–O contact appears as a result of asymmetric deformation of the channels. The appearance of this new contact provides the possibility for re-orientation of hydrogen bonds. The planar coordination of H₂O molecules changes to tetrahedral and the ribbons are transformed to islands (OH)₂–H₂O.  相似文献   

Structural transformations in natrolite and edingtonite     

I. A. Belitsky  B. A. Fursenko  S. P. Gabuda  O. V. Kholdeev  Yu. V. Seryotkin 《Physics and Chemistry of Minerals》1992,18(8):497-505

Results of structural transformation studies in the natural fibrous zeolites natrolite and edingtonite are presented. The minerals were studied in situ in a wide range of temperatures, pressures and compositions by differential scanning microcalorimetry, thermogravimetry, dilatometry, X-ray diffractometry, nuclear magnetic resonance (NMR)and Raman-spectroscopy. The high-pressure experiments were done in diamond anvil cell and Be-bronze bomb for NMR using liquids with various dimensions of molecules as pressure-transmitting media. A number of structural transformations in natrolites and edingtonite have been found with constant or changing water content during transformation. Under high water pressures, some additional H₂O molecules entered the framework channels causing a framework deformation and an anisotropic “swelling” of the crystal. Under compression in nonpenetrating liquids no transformations were detected and above 70 kbar amorphization of the minerals was observed. The same displacive-tilt transformations were observed in zeolites at elevated temperatures as a result of the dehydration, e.g. natrolite ? α-metanatrolite at 280° C. Fully reversible phase transitions at constant H₂O content were observed in natrolites and edingtonite at low temperatures (down to -120° C). These are connected with a variation in the mobility and position of exchange cations and water molecules within the framework channels and are followed by significant volume and thermal effects. In dehydrated zeolites, the transformations were found to be similar to the α ? β transition in quartz (α-metanatrolite ? β-metanatrolite). Heating of fibrous zeolites above 500 ÷ 700° C causes their amorphization and formation of porous quasiglass. The principal difference in structural behaviour of microporous crystals under compression in penetrating and nonpenetrating media has essential geochemical implications. Structural transformations of zeolites in P-T-X space demonstrate crystal chemical analogy of these parameters. Some deviations from this analogy depend on complex interactions between channel “filling”, H₂O and cations, and the [(Al,Si)-O_4/2] framework.  相似文献   

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

A.A. Borovikov  A.S. Lapukhov  A.S. Borisenko  Yu.V. Seryotkin 《Russian Geology and Geophysics》2009,50(8):693-702

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.  相似文献   

Visible and “invisible” forms of gold and silver in the crystallization products of melts in the Fe–S–Ag–Au system: experimental data     

G. A. Palyanova  Yu. L. Mikhlin  N. S. Karmanov  K. A. Kokh  Yu. V. Seryotkin 《Doklady Earth Sciences》2017,474(2):636-640

The forms of Au and Ag occurrence in the crystallization products of melts in the Fe–S–Ag–Au system depending on the proportions of Fe/S and Ag/Au have been studied at (Fe + S)/(Ag + Au) = 0.1. It is shown that the S-rich systems with S/Fe = 2 contain Au–Ag sulfides and Au–Ag alloys. The systems depleted in S with S/Fe = 1 contain only Au–Ag alloys. The results of XPS provide evidence for the sulfide and metallic components of Au and Ag among the crystallization products of melts in the system studied at S/Fe = 2 and a metallic component with S/Fe = 1. According to the data of electron microprobe analysis, the content of “invisible” forms of noble metals in pyrite and pyrrhotite is < 0.024 wt % for Au and <0.030 wt % for Ag; the contents of “invisible” Au and Ag in troilites are 0.040 ± 0.013 wt % Au and 0.079 ± 0.016 wt % Ag.  相似文献   

Synthesis and crystal structure of gold–silver sulfoselenides: morphotropy in the Ag3Au(Se,S)2 series     

Yu. V. Seryotkin  G. A. Pal’yanova  V. V. Bakakin  K. A. Kokh 《Physics and Chemistry of Minerals》2013,40(3):229-237

Gold–silver sulfoselenides of Ag₃Au(Se,S)₂ series—Ag₃AuSe_1.5S_0.5, Ag₃AuSeS, and Ag₃AuSe_0.5S_1.5—have been synthesized by fusing the elements in the required stoichiometric amounts in evacuated quartz ampoules. The single crystal X-ray diffraction data indicate the existence of two solid-solution series: petzite-type cubic Ag₃AuSe₂—Ag₃AuSeS (space group I4₁32) and trigonal Ag₃AuSe_0.5S_1.5—Ag₃AuS₂ (space group $ R\overline{3} c $ ). Both crystal structures differ in the distribution of Ag⁺/Au⁺ cations in the same distorted body-centered cubic sublattice of chalcogen anions. The morphotropic transformation results from the shrinkage of anion packing accompanied by the shortening of Ag–Ag distances. The structure of uytenbogaardtite mineral, earlier incorrectly interpreted as a tetragonal or cubic cell, is similar to that of the trigonal Ag₃AuS₂ end-member.  相似文献   

2004年4月1日磁通量传输事件特性的研究——通量管内电流密度、粒子运动与管轴方向的对比分析          下载免费PDF全文

张清和  刘瑞源  黄际英  Dunlop MW  胡红桥  沈超  Bogdanova YV 《极地研究》2007,19(2):121-130

本文利用Cluster四颗卫星上磁通门磁力计(FGM)的同时观测,采用旋度器方法(Curlometer),计算和分析了2004年4月1日12:24到12:54UT期间Cluster卫星观测的多个磁通量传输事件(FTEs)的特性。结果表明:磁通量管内电流密度较大,可达到约10-7A/m2。应用最小方向微分法(MDD),发现这些FTE事件具有准二维结构,即为圆柱形结构,其通量管轴线方向与管内电流方向及粒子运动方向基本平行。  相似文献   

Natural analogue approaches to prediction of long-term behaviour of Ca<Subscript>2</Subscript>UO<Subscript>5</Subscript>∙2-3H<Subscript>2</Subscript>O X-phase: case study from Tulul Al Hammam site,Jordan     

E.V. Sokol  S.N. Kokh  H.N. Khoury  Yu.V. Seryotkin  S.V. Goryainov  S.A. Novikova  I.A. Sokol 《Arabian Journal of Geosciences》2017,10(23):512

The Tulul Al Hammam area in central Jordan is an advantageous natural analogue site to study long-term U(VI) retention in ~?1 Ma old U-bearing combustion metamorphic marbles with clinker-like mineralogy exposed to prolonged supergene alteration for at least ~?100 kyr. The marbles contain abundant grains of high-temperature (ca. 800–850 °C) primary double Ca-U(VI) oxides (mainly Ca₃UO₆ and CaUO₄), which are commonly replaced by hydrated calcium uranates with various impurities (Si, Fe, Al and F). A more hydrous natural analogue of X-phase (Ca₂UO₅·2-3H₂O) occurs as a predominant secondary U compound after primary Ca-U(VI) oxides. The phase was studied by single-crystal XRD, SEM/EDX and electron microprobe (EPMA) analyses and Raman spectroscopy. It is a non-crystalline phase with a specific finger-like microtexture consisting of thin (no wider than 1–2 μm) lamellar particles. Its Raman spectrum shows a single strong band at 706–713 cm^?1, sometimes coexisting with up to three weak diffuse bands (ν ~?390, ~?540 and 1355–1400 cm^?1). The find of the natural X-phase (Ca₂UO₅·2-3H₂O) is evidence of its long-term stability in a natural environment. It proves explicitly that the compound Ca₂UO₅·nH₂O is a solubility-limiting phase in aged cements. The results have implications for geological disposal of radioactive wastes.  相似文献