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101.
102.
103.
Robert L. Brathwaite Hugh J. Cargill Anthony B. Christie Andrew Swain 《Mineralium Deposita》2001,36(1):1-12
Vein distributions in line samples from four epithermal Au–Ag deposits of the Hauraki Goldfield were logged and quantified
by vein spacing, vein density, vein thickness and percentage of vein extension. One deposit is hosted in andesite lavas (Martha
Hill), one in andesite lavas and dacite porphyry, dacitic tuffs and pyroclastic breccias (Golden Cross), and two in rhyolite
lavas and rhyolitic tuffs with minor andesite lavas or andesite dikes (Ohui and Wharekirauponga). The vein systems in these
deposits form fault-controlled arrays of extensional veins. Vein spacing distributions are non-fractal over two to three orders
of magnitude (1 mm to 5 m), and therefore fractal dimension statistics are not applicable. The coefficient of variation (Cv) of vein spacing was used as a measure of the degree of vein clustering. Rock type has a marked influence on vein spacing
distributions, with veining in rhyolite lava having lower average thickness and percentage extension, but a generally higher
degree of vein clustering compared with veining in andesite lava in the same deposit. Vein spacing distributions in well-jointed
lithologies, mainly andesite lava, have Cv values (0.8–1.2) that are indicative of anticlustered to weakly clustered patterns, particularly in the vein stockwork of
the upper part of the Golden Cross deposit. These Cv values are consistent with field observations that joints are a major control on vein spacing. In the poorly jointed dacitic
and rhyolitic rocks, the veins are weakly to strongly clustered as shown by higher Cv values (1.2–2.4), and are commonly associated with normal faults. Overall, andesite lava and dacite porphyry and pyroclastics
host thicker and more persistent veins than rhyolite lava and tuff. These larger veins contain significant volumes of high-grade
gold mineralisation. The higher chemical reactivity to hydrothermal fluids of andesite and dacite compared with rhyolite may
have aided propagation and thickening of the veins in andesite-hosted deposits. Within an individual epithermal deposit, location
close to thick veins, representing major fluid conduits, commonly overrides the effect of different lithologies. Sites that
are deeper and located within or adjacent to major vein structures have higher average vein thickness, percentage extension
and degree of vein clustering. Systematic collection and analysis of vein spacing, thickness and density data can be used
to define trends that are useful in the exploration of gold-bearing epithermal vein deposits.
Received: 25 August 1998 / Accepted: 23 December 1999 相似文献
104.
A maximal spectrum of gravitational radiation from sources outside our galaxy is calculated. The sources are galaxies, quasars and events that occur in the early history of the universe. The major contribution is from galaxies whose effect extends over the frequency region 10–810+4Hz, peaking at 10–110 Hz, with a spectral flux of 10 erg cm–2, s–1. The main processes of gravitational radiation in the galaxies are stellar collapse into a black hole and dying binary systems. In the region 10–4104 Hz the background spectrum is well above the detection levels of currently proposed detectors. FromMinimal considerations of this spectrum it is determined that the density of gravitational radiation is 10–39g cm–3. This background spectrum is sensitive to galactic evolution and especially sensitive to the upper mass limits and mass distribution of stars in galactic models. Therefore, the spectrum could provide information about galactic evolution complementary to that obtained by electromagnetic investigations. 相似文献
105.
Robert J. Glinski Christopher M. Anderson 《Monthly notices of the Royal Astronomical Society》2002,332(2):L17-L22
We have observed the Red Rectangle nebula with the Multi-Object Spectrograph on the WIYN telescope. Moderate-resolution spectra (Δ λ =0.4 Å) in the region of 5800 Å were obtained in 3-arcsec apertures at over 50 positions in the nebula. Accurate and precise wavelength calibrations were obtained against a thorium–argon lamp and the sodium lines in the sky and nebula. The peak position and full width at half-maximum of the 5800-Å Red Rectangle band (RRB) were measured to beyond 15 arcsec from the star. The shortest wavelength of the band is found to be 5799.10±0.15 Å in the rest frame of the nebula. None of the emission bands has intensity coincident with the wavelength of the diffuse interstellar band (DIB) at 5797.11±0.05 Å. The 2-Å offset cannot be explained by an instrumental, spectroscopic or photophysical effect. The hypothesis that the same molecule may be the carrier of the RRB and the DIB is contradicted by these observations. As a further test of the hypothesis, absorption has been sought that would be due to a potential DIB carrier in the nebula. Tentative evidence for absorption is found in the RRB spectra taken within 9 arcsec of the star; but any absorption has a peak position essentially coincident in wavelength with the band maximum of the emission band. 相似文献
106.
107.
A project to deepen shipping and entrance channels in Charleston Harbor was conducted from 1999 to 2002. This generated approximately 22 million cubic yards of sediment for offshore disposal. Assessments of biological and physical conditions in the Charleston Ocean Dredged Material Disposal Site and surrounding areas were conducted prior to deepening (1993-94), and partway through the disposal period (2000). Results from the 2000 survey are presented and compared to the baseline survey. The study area was composed of the disposal zone and surrounding areas and divided into 20 one square mile strata. Within each stratum, benthic grab samples were collected from ten random sites for analysis of sediment composition and contaminants and macrobenthic assemblages. No contaminant levels were above effects range low levels. Results revealed that sediments in the western strata had significantly higher silt/clay content in the 2000 survey when compared to baseline sediments, while sediments east of the disposal zone were similar to baseline. Analyses were performed on a subset of the benthic data that compared baseline to 2000 conditions in western and eastern strata. The benthic communities in western strata were altered following disposal operations. The benthic community east of the disposal area was not different from baseline conditions. These alterations in the benthic community were attributed to changes in bottom habitat characteristics rather than pollution effects. 相似文献
108.
Robert H Wood 《Geochimica et cosmochimica acta》2002,66(24):4365
109.
The northern New England beach wrack community with special reference to the cosmopolitan amphipod crustacean, Orchestia platensis, was examined at estuarine and open coastal habitats. Beach wrack was dominated by the plant genera Ascophyllum, Zostera, Spartina and Chondrus, and was most abundant during spring and late summer. Animal community numbers, biomass and frequency in fresh to moderately decomposed wrack were dominated by O. platensis throughout the year at all habitats; oligochaetes and Collembola were also important. The abundance of O. platensis showed high spatial and temporal variability, with low abundance generally associated with decreased amounts of wrack during colder months. An exception was the winter presence of the species at one estuarine habitat, in patchy aggregations within gravel-cobble refuges. The abundance of O. platensis averaged 1280 (0.04 m2)−1, with a maximum of 7040 (0.04 m2)−1. The life cycle of O. platensis is bivoltine, with summer-hatched young reaching maturity within 1 month. Laboratory studies indicate females with up to 4 broods (30 days)−1, averaging 18 eggs brood−1.Orchestia platensis is omnivorous, eating fresh plant tissue, live oligochaetes, Limulus eggs and diatom ‘fuzz’. The rate of laboratory consumption of algae and Zostera was 0.05 mg plant mg−1 wet body weight day−1. Presumptive predators of O. platensis are juvenile green crab, Carcinus maenus, and the earwig. Anisolabis maritima. The mobility, aggregation and aggressiveness of O. platensis assist the species in establishing and maintaining populations in the rigorous wrack habitat. The general competitive superiority of O. platensis over its congener, O. gammarella, and the co-occurrence of these species on both eastern and western Atlantic shores is discussed. 相似文献
110.
The Current System in the Yellow and East China Seas 总被引:18,自引:1,他引:18
During the 1990s, our knowledge and understanding of the current system in the Yellow and East China Seas have grown significantly
due primarily to new technologies for measuring surface currents and making high-resolution three-dimensional numerical model
calculations. One of the most important new findings in this decade is direct evidence of the northward current west of Kyushu
provided by satellite-tracked surface drifters. In the East China Sea shelf region, these recent studies indicate that in
winter the Tsushima Warm Current has a single source, the Kuroshio Branch Current in the west of Kyushu, which transports
a mixture of Kuroshio Water and Changjiang River Diluted Water northward. In summer the surface Tsushima Warm Current has
multiple sources, i.e., the Taiwan Warm Current, the Kuroshio Branch Current to the north of Taiwan, and the Kuroshio Branch
Current west of Kyushu. The summer surface circulation pattern in the East China Sea shelf region changes year-to-year corresponding
to interannual variations in Changjiang River discharge. Questions concerning the Yellow Sea Warm Current, the Chinese Coastal
Current in the Yellow Sea, the current field southwest of Kyushu, and the deep circulation in the Okinawa Trough remain to
be addressed in the next decade.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献