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21.
P. M. Nikolić S. Ðurić D. M. Todorović D. Vasiljević-Radović V. Blagojević P. Mihajlović J. Elazar K. T. Radulović A. I. Bojičić D. Urošević 《Physics and Chemistry of Minerals》2001,28(1):44-51
Electron transport properties of single crystal and polycrystalline natural mineral galena (PbS) samples from the Trep?a mine, Yugoslavia, were determined using the photoacoustic frequency transmission technique. Their thermal diffusivity (D T≈0.16 × 10?5 m2 s?1), the coefficient of diffusion (D between 0.15×10?2 0.16×10?2 m2 s?1) and lifetime of the excess carrier (τ≈35 μs and the front and rear recombination velocity (s g≈65.5 m s?1 and s b≈66.4 m s?1, respectively), were calculated by comparing the experimental results and the theoretical photoacoustic amplitude and phase signals. The lattice parameter obtained by X-ray work was a?=5.936?Å. The free carrier concentration of these single-crystal samples was measured using the Hall method (N?=?3×1018 cm?3). Measurements of the optical reflectivity of the same samples, as a function of wavelength, in the infrared and far infrared ranges, were performed. In the far infrared range a free electron plasma frequency was observed and numerically analyzed, using the least-squares fitting procedure. The values of optical parameters were calculated and the value of the free carrier concentration obtained by the Hall method was confirmed. 相似文献
22.
Methylene blue and rhodamine 6G were used as molecular sensors for the spectrophotometric titrations of the aqueous colloids
of clay minerals (montmorillonite, illite and kaolinite). The dyes adsorbed on colloid particles form molecular aggregates,
which exhibit spectral properties significantly different from those of dye solutions. Spectrophotometric titrations provide
the most sensitive detection of smectites in aqueous colloids (sub-ppm concentrations); and the sensitivity further increases
using second derivative spectroscopy. The endpoint of spectrophotometric titrations can be used for the determination of exchange
capacity of the mineral in colloids and in this way to estimate its amount. The method is selective only to expandable clays,
which was proven by experiments with kaolinite and illite. Spectrophotometric titrations have promising future in the analysis
of clays and can be applied in many fields of geology, mineralogy, chemistry, material sciences or in industry. Its application
may expand to the analysis of other nanomaterials built from charged particles and exhibiting metachromasy in the systems
with organic dyes. 相似文献
23.
Filiz Bilgili Hans-Jürgen Götze Roman Pašteka Sabine Schmidt Ron Hackney 《International Journal of Earth Sciences》2009,98(3):571-583
An unsolved problem of regional importance for both the evolution and structure of the Northwest German Basin is the existence
or non-existence of the so-called Bramsche Massif. Explaining the nature of this massif and the cause of a related strong,
positive Bouguer anomaly (Bramsche Anomaly) is critical. In the study described here, we tested an existing “intrusion model”
against a newer “inversion model” in the southern Northwest German Basin. In the intrusion model, the strongly-positive Bouguer
anomaly represents the gravity effect of an intrusion at depths between 6 and 10 km. More recent interpretations invoke tectonic
inversion rather than intrusion to explain increased burial and the low level of hydrocarbon maturity found in boreholes.
We tested these different interpretations by constructing 3D forward density models to 15 km depth. The intrusion model was
updated and adjusted to incorporate recent data and we also modelled pre-Zechstein structures using different scenarios. The
final model has a very good fit between measured and modelled gravity fields. Based on currently available seismic and structural
models, as well as borehole density measurements, we show that the positive Bouguer anomaly cannot be modeled without a high-density,
intrusive-like body at depth. However, further in-sight into the crustal structures of the Bramsche region requires more detailed
investigations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
24.
Surfaces of phosphorite nodules and pebbles from the “Cambridge Green Sand” (Cenomanian, South England) yielded several discernible types of scratches. These originated before the burial of nodules/pebbles as evidenced by fossil epibiotic oysters cemented to cover the scratches. The individual forms of scratches differ in size and shape; therefore, the set of “scratching instruments” also had to be different. The scratches described differ from scratches generated by glacial processes, namely by the regularity of length and intervals, parallel orientation, existence of recurrent forms and placement along the nodule edges. We interpret the scratches as trace fossils of the ichnogenus Machichnus. Three new species, namely M. normani, M. harlandi and M. jeansi, are erected for them herein. The series of scratches originated probably by teeth on a couple of jaws; the makers possibly scraped bacterial or algal film off the surface of nodules that were covered with the phosphate gel. Both homodont and heterodont animals (probably fish) were involved. 相似文献
25.
Michal Klaučo Bohuslava Gregorová Uglješa Stankov Vladimir Marković Polina Lemenkova 《Central European Journal of Geosciences》2013,5(1):28-42
The Sitno Natura 2000 Site covers an area of 935,56 hectares. The Sitno region is significant due to the number of rare and endangered species of plants, and as a result is considered a location of great importance to the maintenance of floral gene pools. The study area suffers human impacts in the form of tourism. The main purpose of this study is to the measure landscape elements, determine the ecological significance of habitats within the Sitno area, and from this data, organize the study area into conservation zones. The results of this landscape quantification are numerical values that can be used to interpret the quality of ongoing ecological processes within individual landscape types. Interpretation of this quantified data can be used to determine the ecological significance of landscapes in other study areas. This research examines the habitats of Natura 2000 Sites by a set of landscape metrics for habitat area, size, density, and shape, such as Number of patches (NP), Patch density (PD), Mean patch size (MPS), Patch size standard deviation (PSSD) and Mean shape index (MSI). The classification of land cover patches is based on the Annex Code system. 相似文献
26.
Kerstin Drost Richard Wirth Jan Košler Hege Fonneland Jørgensen Theodoros Ntaflos 《Contributions to Mineralogy and Petrology》2013,165(4):737-756
Xenotime overgrowths on detrital zircon in siliciclastic sediments have been reported in numerous studies. However, in natural samples, solid solution of zircon and xenotime is limited to near-end-member compositions. In order to characterize the interface region between both minerals and to draw inferences on the growth mechanisms of authigenic xenotime, we studied xenotime overgrowths on detrital zircon grains from two Phanerozoic sandstone samples with contrasting post-depositional histories. In one sample, the small (≤10 μm), pyramidal xenotime overgrowths are of diagenetic origin and grew without major discontinuity on the detrital zircon grain. The second sample shows up to >50-μm-wide, porous and inclusion-rich, hydrothermal xenotime overgrowths on detrital zircon, whereas the transition zone between both minerals is accompanied by large pore volume. Chemical compositions of the xenotime precipitates from the two samples differ particularly in Y, REE, Th and Sc concentrations, whereas high MREE availability in the diagenetic sample and the presence of Sc in the hydrothermal sample, respectively, appear to have promoted xenotime growth. Transmission electron microscopy on electron-transparent foils cut from the interface region shows that both the diagenetic xenotime and the hydrothermal xenotime are crystalline and grew in optical and crystallographic continuity to their detrital zircon substrata. Only a narrow transition zone (≤90 nm—diagenetic sample, 200–300 nm—hydrothermal sample) between zircon and xenotime is in part made up of nanometre-scale crystalline domains that are slightly distorted and may have formed from dissolution–re-precipitation processes at the zircon rim along with precipitation from the respective fluid. 相似文献
27.
Fleurice Parat François Holtz Miloš René Renat Almeev 《Contributions to Mineralogy and Petrology》2010,159(3):331-347
The equilibrium phase relations of a mafic durbachite (53 wt.% SiO2) from the Třebíč pluton, representative of the Variscan ultrapotassic magmatism of the Bohemian Massif (338–335 Ma), have
been determined as a function of temperature (900–1,100°C), pressure (100–200 MPa), and H2O activity (1.1–6.1 wt.% H2O in the melt). Two oxygen fugacity ranges were investigated: close to the Ni–NiO (NNO) buffer and 2.6 log unit above NNO
buffer (∆NNO + 2.6). At 1,100°C, olivine is the liquidus phase and co-crystallized with phlogopite and augite at 1,000°C for
the whole range of investigated pressure and water content in the melt. At 900°C, the mineral assemblage consists of augite
and phlogopite, whereas olivine is not stable. The stability field of both alkali feldspar and plagioclase is restricted to
low pressure (100 MPa) at nearly water-saturated conditions (<3–4 wt.% H2O) and T < 900°C. A comparison between experimental products and natural minerals indicates that mafic durbachites have a near-liquidus
assemblage of olivine, augite, Ti-rich phlogopite, apatite and zircon, followed by alkali feldspar and plagioclase, similar
to the mineral assemblage of minette magma. Natural amphibole, diopside and orthopyroxene were not reproduced experimentally
and probably result from sub-solidus reactions, whereas biotite re-equilibrated at low temperature. The crystallization sequence
olivine followed by phlogopite and augite reproduces the sequence inferred in many mica-lamprophyre rocks. The similar fractionation
trends observed for durbachites and minettes indicate that mafic durbachites are probably the plutonic equivalents of minettes
and that K- and Mg-rich magmas in the Bohemian Massif may have been generated from partial melting of a phlogopite–clinopyroxene-bearing
metasomatized peridotite. Experimental melt compositions also suggest that felsic durbachites can be generated by simple fractionation
of a more mafic parent and mixing with mantle-derived components at mid crustal pressures. 相似文献
28.
The Mississippi Valley-type (MVT) Pb–Zn ore district at Mežica is hosted by Middle to Upper Triassic platform carbonate rocks
in the Northern Karavanke/Drau Range geotectonic units of the Eastern Alps, northeastern Slovenia. The mineralization at Mežica
covers an area of 64 km2 with more than 350 orebodies and numerous galena and sphalerite occurrences, which formed epigenetically, both conformable
and discordant to bedding. While knowledge on the style of mineralization has grown considerably, the origin of discordant
mineralization is still debated. Sulfur stable isotope analyses of 149 sulfide samples from the different types of orebodies
provide new insights on the genesis of these mineralizations and their relationship. Over the whole mining district, sphalerite
and galena have δ
34
S values in the range of –24.7 to –1.5‰ VCDT (–13.5 ± 5.0‰) and –24.7 to –1.4‰ (–10.7 ± 5.9‰), respectively. These values are
in the range of the main MVT deposits of the Drau Range. All sulfide δ
34
S values are negative within a broad range, with δ
34
S
pyrite <δ
34
S
sphalerite <δ
34
S
galena for both conformable and discordant orebodies, indicating isotopically heterogeneous H2S in the ore-forming fluids and precipitation of the sulfides at thermodynamic disequilibrium. This clearly supports that
the main sulfide sulfur originates from bacterially mediated reduction (BSR) of Middle to Upper Triassic seawater sulfate
or evaporite sulfate. Thermochemical sulfate reduction (TSR) by organic compounds contributed a minor amount of 34S-enriched H2S to the ore fluid. The variations of δ
34
S values of galena and coarse-grained sphalerite at orefield scale are generally larger than the differences observed in single
hand specimens. The progressively more negative δ
34
S values with time along the different sphalerite generations are consistent with mixing of different H2S sources, with a decreasing contribution of H2S from regional TSR, and an increase from a local H2S reservoir produced by BSR (i.e., sedimentary biogenic pyrite, organo-sulfur compounds). Galena in discordant ore (–11.9
to –1.7‰; –7.0 ± 2.7‰, n = 12) tends to be depleted in 34
S compared with conformable ore (–24.7 to –2.8‰, –11.7 ± 6.2‰, n = 39). A similar trend is observed from fine-crystalline sphalerite I to coarse open-space filling sphalerite II. Some variation
of the sulfide δ
34
S values is attributed to the inherent variability of bacterial sulfate reduction, including metabolic recycling in a locally
partially closed system and contribution of H2S from hydrolysis of biogenic pyrite and thermal cracking of organo-sulfur compounds. The results suggest that the conformable
orebodies originated by mixing of hydrothermal saline metal-rich fluid with H2S-rich pore waters during late burial diagenesis, while the discordant orebodies formed by mobilization of the earlier conformable
mineralization. 相似文献
29.
Six samples of non-mineralized black shale from a Kupferschiefer section in the northern part of the Polish Zechstein Basin
(Zdrada IG-8 drill hole: 1026.16–1026.90 m) were studied for Re–Os isotopes and selected major and trace elements. These black
shales, averaging 5.82 wt.% Corg and 1.69 wt.% Stot, display very low base metal values (up to 106 ppb Cu, 792 ppb Pb, and 144 ppb Zn) and have abundances of 64–1376 ppb Re
and 0.37–1.25 ppb Os, with a 187Os/188Os ratio of 6.95–22.5. The regression of all Re–Os data yields an age of 247 ± 20 Ma, which is within the range of uncertainties
of previous Rb–Sr and K–Ar geochronological studies. The scatter in the Re–Os data can be explained in terms of fluctuations
in sedimentary conditions, i.e., restricted basin with terrestrial influence. 相似文献
30.
Daniel Mikeš 《Central European Journal of Geosciences》2010,2(3):420-432
Lack of age dates in the terrigenous Cenozoic sediments of the Duero and the Ebro sedimentary basins has complicated tecto-stratic correlation across the two basins. We tentatively synthesize a range of existing studies and new data to construct a rough general paleogeography throughout Upper Cenozoic times. The more extensive erosion of the Ebro has been previously attributed to the earlier moment of opening. We tentatively analyse lithostratic data to conclude that the lower knick-point and different lithologies have also contributed to the deeper erosion in the Ebro Basin. We conclude from lithostratic data and field evidence that the W half of the Rioja was part of the Duero in earlier times and that the escarpment retreated westward through the Rioja in four subsequent episodes of erosion. The tilt of the NW Duero is a consequence of isostatic rebound to this erosion. 相似文献