Iron (Fe) and manganese (Mn) are the two most common redox-active elements in the Earth’s crust and are well known to influence mineral formation and dissolution, trace metal sequestration, and contaminant transformations in soils and sediments. Here, we characterized the reaction of aqueous Fe(II) with pyrolusite (β-MnO2) using electron microscopy, X-ray diffraction, aqueous Fe and Mn analyses, and 57Fe Mössbauer spectroscopy. We reacted pyrolusite solids repeatedly with 3 mM Fe(II) at pH 7.5 to evaluate whether electron transfer occurs and to track the evolving reactivity of the Mn/Fe solids. We used Fe isotopes (56 and 57) in conjunction with 57Fe Mössbauer spectroscopy to isolate oxidation of Fe(II) by Fe(III) precipitates or pyrolusite. Using these complementary techniques, we determined that Fe(II) is initially oxidized by pyrolusite and that lepidocrocite is the dominant Fe oxidation product. Additional Fe(II) exposures result in an increasing proportion of magnetite on the pyrolusite surface. Over a series of nine 3 mM Fe(II) additions, Fe(II) continued to be oxidized by the Mn/Fe particles suggesting that Mn/Fe phases are not fully passivated and remain redox active even after extensive surface coverage by Fe(III) oxides. Interestingly, the initial Fe(III) oxide precipitates became further reduced as Fe(II) was added and additional Mn was released into solution suggesting that both the Fe oxide coating and underlying Mn phase continue to participate in redox reactions when freshly exposed to Fe(II). Our findings indicate that Fe and Mn chemistry is influenced by sustained reactions of Fe(II) with Mn/Fe oxides.
New isotope and mineral data on manganese carbonates of the Mazul deposit (Krasnoyarsk region) in combination with morphology of ore bodies suggest that the ores were formed in several stages with the involvement of meteoric solutions through infiltration and, possibly, exfiltration mechanisms. Based on the geological–geochemical data, manganese carbonates of the Mazul deposit may be ascribed to a new genetic subtype of the catagenesis (epigenesis) zone. 相似文献
Reliable age estimation was obtained originally in this study for gold mineralization of the Malomyr deposit (the eastern part of the Mongolian–Okhotsk foldbelt), which is one of the most well-known deposits in the Russian Far East. The data obtained show that the age of hydrothermal process that resulted in the formation of the Malomyr deposit may be estimated as ～133–132 Ma. Data on magmatism of the same age within the considered region are absent. In the opinion of the authors, mobilization, redistribution of the ore material, and the formation of the Malomyr deposit were mostly controlled by dislocation processes accompanied by hydrothermal activity, which is supported by the results of structural studies. 相似文献
The solubility of gold was measured in dry NaCl salt melt at 860°С in closed systems with SiO2 (silica glass). The reactions do not occur in a closed system without oxidizer. Reaction of SiO2 with salt in the presence of an oxidizer (KClO4) results in the formation of water-soluble sodium silicates (a mixture of meta-, ortho-, and pyrosilicates). Gold mobilization by a salt melt is limited by the diffusion of Na in SiO2. In a closed system with the addition of a strong oxidizer (dry KClO4 salt), the solubility of gold increase with increasing amount of KClO4 and the saturation level is estimated to be ~3 wt % Au. For ampoule configurations used in our experiments, 5.5 g of gold dissolved per 1 g of KClO4. Only cheap, non-toxic reagents were used in our model experiments on gold dissolution in a salt melt, which did not require elevated pressures. The solubility of 30 g Au per 1 kg NaCl will eliminate geochemical problems associated with the compact leaching of gold ores using cyanide. 相似文献
The results of study of the isotopic-lithological compositions of carbonate and terrigenous-carbonate rocks in the Soyana
River section (northern East European Platform, Arkhangel’sk district) are presented. The results make it possible to identify
10 main lithotypes and show a wide variation range of δ13C (from −2.2 to +3.6‰, PDB) and δ18O (from 22.5 to 30.5‰, SMOW). These lithological features and isotopic compositions suggest that the rocks were formed in
a shallow-marine setting characterized by rapidly changing sedimentation conditions in various facies (and/or paleoecological)
zones: inlets, lagoons, supralittoral, littoral, and shoals. Periods of aridization and humidization are recorded. The results
also indicate numerous synsedimentary short-term hiatuses and stages of increased continental runoff—episodic pulsatory input
of clastic material with the continental paleoflows. 相似文献
The paper presents a detailed analysis of 1st April 2015 earthquake, whose epicenter (30.16° N, 79.28° E) was located near Simtoli village of Chamoli district, Uttarakhand. The focal depth is refined to 7 km by the grid search technique using moment tensor inversion. The source parameters of the earthquake as estimated by spectral analysis method suggested the source radius of ~1.0 km, seismic moment as 1.99E+23 dyne-cm with moment magnitude (Mw) of 4.8 and stress drop of 69 bar. The fault plane solution inferred using full waveform inversion indicated two nodal planes, the northeast dipping plane having strike 334° and dip 5° and the southwest dipping plane with dip 86° and strike 118°. The parallelism of the nodal plane striking 334° with dip 5° as indicated in depth cross sections of the tectonic elements suggested the north dipping Main Boundary Thrust (MBT) to be the causative fault for this earthquake. Spatio-temporal distribution of earthquakes during the period 1960-2015 showed seismic quiescence during 2006-2010 and migration of seismicity towards south. 相似文献
Wood fossil charcoal is identified from the upper Lower Cretaceous (Serra do Tucano Formation, Aptian–Albian) of Roraima (North Brazil). The presence of charcoal demonstrates the occurrence of Early Cretaceous palaeo-wildfires for the first time in this region and only the third time for the entirety of South America. A gymnospermous taxonomic affinity can be established for the charred woods and a relationship with conifers is likely, thus providing additional evidence for the taxonomic composition of Early Cretaceous floras in this region. 相似文献
Before starting seismic cycle of Ahar–Varzaghan 2012 event, a partial gap in the form of a pre-seismic calm sequence (seismicity rate, r = 0.46 event/year, b = 1.4) with duration of 303 days spatially has dominated over the entire seismogenic area. From April 17, 2012, to May 31, 2012, r significantly increased to 2.16, indicating strong foreshock sequence, and b value changed to 1.9, remarkably. In the last two months before the mainshock, foreshocks have partially migrated toward the earthquake fault (with a decrease in size, b = 2.0). Significantly, high rate of seismicity and low VP/VS (1.64) in the foreshocks sequence and also very high seismicity rate (17.3) and high VP/VS (1.76) in the aftershocks sequence make substantial differences between the seismic cycle and the background seismicity. Moreover, a significant E–W migration of the microseismicity was confirmed in the study area. 相似文献
The formation of a geological society in Jamaica was dependent upon attaining a sufficient number of interested geologists on the island. Although the earliest study of Jamaican geology dated to the 1820s (De la Beche), few major geologists worked on the island in the 19th (Barrett, Sawkins, Hill) and early 20th centuries (Matley, Trechmann). A ‘critical mass’ of geologists was only attained in the 1950s after foundation of the third Geological Survey of the island, when, for the first time, the island had a resident geological intelligentsia. The director, V.A. Zans (1904–1961), was a Latvian geologist appointed from a camp for displaced persons. His staff included L.J. Chubb (1887–1971), who popularised geology in Jamaica. Chubb and his colleagues devised a three part plan for geological education in Jamaica: high schools were encouraged to introduce geology as an examination subject; introduction of geology as a part of the Natural Sciences curriculum at the University College of the West Indies was supported; and a local geological society for both amateurs and professionals was established. This society, the Jamaica Group of the Geologists’ Association, was established in 1955 and was the only such overseas group ever founded; Chubb was elected President. The first field trip was led by Zans and A.D. Foster in November 1955. The Group was reformed as the independent Geological Society of Jamaica (GSJ) in late 1959, again with Chubb as the first President. The GSJ remembers the name of its first President in the prestigious L.J. Chubb Award. 相似文献
The heat capacity of eskolaite Cr2O3(c) was determined by adiabatic vacuum calorimetry at 11.99–355.83 K and by differential calorimetry at 320–480 K. Experimental
data of the authors and data compiled from the literature were applied to calculate the heat capacity, entropy, and the enthalpy
change of Cr2O3 within the temperature range of 0–1800 K. These functions have the following values at 298.15 K: Cp0 (298.15) = 121.5 ± 0.2 J K−1mol−1, S0(298.15) = 80.95 ± 0.14 J K−1mol−1, and H0(298.15)-H0(0) = 15.30±0.02 kJ mol−1. Data were obtained on the transitions from the antiferromagnetic to paramagnetic states at 228–457 K; it was determined
that this transition has the following parameters: Neel temperature TN = 307 K, ΔtrS = 6.11 ± 0.12 J K−1mol−1 and δtrH = 1.87 ± 0.04 kJ mol−1. 相似文献
Joint burial places of mollusks and Pleuromeia plants allow specification of a period of stratigraphic occurrence of this genus in the west of the Republic of Kazakhstan within the Gorny Mangyshlak. Two places of occurrences of pleuromeias were found in marine Triassic rocks: one in the Karadzhatyk Formation of the northern slope of the Karatauchik Range close to the Dolnapa well, where the fossils of Pleuromeia sternbergii (Münster) Corda plants are associated with ammonoid shells, and the other one in the Karaduan Formation of the southern slope of Mt. Karashek, where this plant was found along with bivalves and gastropods. The mollusk fauna from both occurrences indicates that the Mangyshlak pleuromeias occurred from the late Olenekian Substage to Anisian Stage. 相似文献
The space group and hydrogen positions of -(Al0.84Mg0.07Si0.09)OOH are investigated using a single crystal synthesized using a multi-anvil apparatus under conditions of 1000 °C and 21 GPa. The space group determined by single-crystal X-ray diffraction is to Pnn2, with unit-cell parameters of a=4.6975(8) Å, b= 4.2060(6) Å, c=2.8327(4) Å, and V=55.97(1) Å3. Partial occupancy of the Al site by Mg and Si suggests the possibility of a limited solid solution between -AlOOH, stishovite, and a hypothetical CaCl2-type Mg(OH)2 that is 16% denser than brucite. Difference-Fourier maps reveal two small but significant Fourier peaks attributable to hydrogen atoms. Atomic distances and angles around the first peak indicate a hydrogen bond with O···O distances of 2.511 Å, while those around the second peak are suggestive of a bifurcated hydrogen bond with O···O distances of 2.743 and 2.743 Å. 相似文献
The effect of intergranular water on the conductivity of polycrystalline brucite, Mg(OH)2, was investigated using impedance spectroscopy at 2 GPa, during consecutive heating–cooling cycles in the 298–980 K range.
The grain boundary hydration levels tested here span water activities from around unity (wet conditions) down to 10−4 (dry conditions) depending on temperature. Four orders of magnitude in water activity result in electrical conductivity variations
for about 6–7 orders of magnitude at 2 GPa and room temperature. Wet brucite samples containing, initially, about 18 wt% of
evaporable water (i.e. totally removed at temperatures below 393 K in air), display electrical conductivity values above 10−2–10−3 S/m. A.C. electrical conductivity as a function of temperature follows an Arrhenius behaviour with an activation energy of
0.11 eV. The electrical conductivity of the same polycrystalline brucite material dried beforehand at 393 K (dry conditions)
is lower by about 5–6 orders of magnitude at room temperature and possesses an activation energy of 0.8–0.9 eV which is close
to that of protonic diffusion in (001) brucitic planes. Above ca. 873 K, a non-reversible conductivity jump is observed which
is interpreted as a water transfer from mineral bulk to grain boundaries (i.e. partial dehydration). Cooling of such partially
dehydrated sample shows electrical conductivities much higher than those of the initially dry sample by 4 orders of magnitude
at 500 K. Furthermore, the corresponding activation energy is decreased by a factor of about four (i.e. 0.21 eV). Buffering
of the sample at low water activity has been achieved by adding CaO or MgO, two hygroscopic compounds, to the starting material.
Then, sample conductivities reached the lowest values encountered in this study with the activation energy of 1.1 eV. The
strong dependency of the electrical conductivity with water activity highlights the importance of the latter parameter as
a controlling factor of diffusion rates in natural processes where water availability and activity may vary grandly. Water
exchange between mineral bulk and mineral boundary suggests that grain boundary can be treated as an independent phase in
dehydroxylation reactions. 相似文献
The results of isotope-geochemical studies of carbonates of different mineral types from manganese and host rocks of the Famennian manganiferous formation of Pai-Khoi are reported. Kutnahorite ores are characterized by δ13C values from–6.6 to 1.3‰ and δ18O from 20.0 to 27.4‰. Rhodonite–rhodochrosite rocks of the Silovayakha ore occurrence have δ13C from–5.2 to–2.9 and δ18O from 25.4 to 24.3‰. Mineralogically similar rocks of the Nadeiyakha ore occurrence show the lighter carbon and oxygen isotopic compositions: δ13C from–16.4 to–13.1 and δ18O from 24.8 to 22.5‰. Similar isotopic compositions were also obtained for rhodochrosite–kutnahorite rocks of this ore occurrence: δ13C from–13.0 to–10.4‰ and δ18O from 24.6 to 21.7‰. Siderorodochrosite ores differ in the lighter oxygen and carbon isotopic compositions: δ18O from 18.7 to 17.6‰ and δ13C from–10.2 to–9.3‰, respectively. In terms of the carbon and oxygen isotopic compositions, host rocks in general correspond to marine sedimentary carbonates. Geological-mineralogical and isotope data indicate that the formation of the manganese carbonates was related to the hydrothermal ore-bearing fluids with the light isotopic composition of oxygen and carbon dissolved in CO2. The isotopic features indicate an authigenic formation of manganese carbonates under different isotopegeochemical conditions. 相似文献
The specific heat capacity (Cp) of six variably hydrated (~3.5 wt% H2O) iron-bearing Etna trachybasaltic glasses and liquids has been measured using differential scanning calorimetry from room temperature across the glass transition region. These data are compared to heat capacity measurements on thirteen melt compositions in the iron-free anorthite (An)–diopside (Di) system over a similar range of H2O contents. These data extend considerably the published Cp measurements for hydrous melts and glasses. The results for the Etna trachybasalts show nonlinear variations in, both, the heat capacity of the glass at the onset of the glass transition (i.e., Cpg) and the fully relaxed liquid (i.e., Cpl) with increasing H2O content. Similarly, the “configurational heat capacity” (i.e., Cpc = Cpl ? Cpg) varies nonlinearly with H2O content. The An–Di hydrous compositions investigated show similar trends, with Cp values varying as a function of melt composition and H2O content. The results show that values in hydrous Cpg, Cpl and Cpc in the depolymerized glasses and liquids are substantially different from those observed for more polymerized hydrous albitic, leucogranitic, trachytic and phonolitic multicomponent compositions previously investigated. Polymerized melts have lower Cpl and Cpc and higher Cpg with respect to more depolymerized compositions. The covariation between Cp values and the degree of polymerization in glasses and melts is well described in terms of SMhydrous and NBO/Thydrous. Values of Cpc increase sharply with increasing depolymerization up to SMhydrous ~ 30–35 mol% (NBO/Thydrous ~ 0.5) and then stabilize to an almost constant value. The partial molar heat capacity of H2O for both glasses (\( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{g}} \)) and liquids (\( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \)) appears to be independent of composition and, assuming ideal mixing, we obtain a value for \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \) of 79 J mol?1 K?1. However, we note that a range of values for \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \) (i.e., ~78–87 J mol?1 K?1) proposed by previous workers will reproduce the extended data to within experimental uncertainty. Our analysis suggests that more data are required in order to ascribe a compositional dependence (i.e., nonideal mixing) to \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \). 相似文献
The heat capacity of synthetic pretulite ScPO4(c) was measured by adiabatic calorimetry within a temperature range of 12.13–345.31 K, and the temperature dependence of
the pretulite heat capacity at 0–1600 K was derived from experimental and literature data on H0(T)-H0(298.15 K) for Sc orthophosphate. This dependence was used to calculate the values of the following thermodynamic functions:
entropy, enthalpy change, and reduced Gibbs energy. They have the following values at 298.15 K: Cp0 (298.15 K) = 97.45 ± 0.06 J K−1 mol−1, S0(298.15 K) = 84.82 ± 0.18 J K−1 mol−1, H0(298.15 K)-H0(0) = 14.934 ± 0.016 kJ mol−1, and Φ0(298.15 K) = 34.73 ± 0.19 J K−1mol−1. The enthalpy of formation ΔfH0(ScPO4, 298.15 K) = − 1893.6 ± 8.4 kJ mol−1. 相似文献
The heat capacity of xenotime YPO4(c) was measured by adiabatic calorimetry at 4.78–348.07 K. Our experimental and literature data on H0(T)-H0(298.15 K) of Y orthophosphate were utilized to derive the Cp0(T) function of xenotime at 0–1600 K, which was then used to calculate the values of thermodynamic functions: entropy, enthalpy
change, and reduced Gibbs energy. These functions assume the following values at 298.15 K: Cp0 (298.15 K) = 99.27 ± 0.02 J K−1 mol−1, S0(298.15 K) = 93.86 ± 0.08 J K−1 mol−1, H0(298.15 K) − H0(0) = 15.944 ± 0.005 kJ mol−1, Φ0(298.15 K) = 40.38 ± 0.08 J K−1 mol−1. The value of the free energy of formation ΔfG0(YPO4, 298.15 K) is −1867.9 ± 1.7 kJ mol−1. 相似文献
