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91.
Detailed hydraulic head profiles as essential data for defining hydrogeologic units in layered fractured sedimentary rock 总被引:3,自引:0,他引:3
This paper describes a study in southern Wisconsin where vertical hydraulic head profiles measured in exceptional detail provided the key data for defining hydrogeologic units (HGUs) in a layered sequence of sandstone, siltstone, shale, and dolostone. The most important data were obtained from corehole MP-6 which was cored 131 m into bedrock and instrumented using a Westbay® multilevel system with 36 depth discrete monitoring intervals. The resulting head profile is consistant over time and shows eight distinct inflections in hydraulic head. Several of the inflections occur between adjacent permeable units and are likely due to poor vertical connectivity of fracture sets rather than distinct lower permeability layers or aquitards in the conventional sense. No other type of data was capable of identifying the position of such distinct hydrogeologic features. These zones of abrupt head loss provide the primary dataset for delineation of eleven HGUs at MP-6 and are supported by less detailed head profiles at other locations. Although the detailed head profiles are essential, core logs and geophysical logs from other boreholes are nessessary to fully establish the lateral continuity of the HGUs. 相似文献
92.
M. -S. Krienitz R. B. Trumbull A. Hellmann J. Kolb F. M. Meyer M. Wiedenbeck 《Mineralium Deposita》2008,43(4):421-434
We determined the boron isotope and chemical compositions of tourmaline from the Hira Buddini gold deposit within the Archean
Hutti-Maski greenstone belt in southern India to investigate the evolution of the hydrothermal system and to constrain its
fluid sources. Tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and
metadacite host rocks associated with the hydrothermal gold mineralization. The Hira Buddini tourmaline belongs to the dravite–schorl
series with variations in Al, Fe/(Fe+Mg), Ca, Ti, and Cr contents that can be related to their host lithology. The total range
of δ11B values determined is extreme, from −13.3‰ to +9.0‰, but 95% of the values are between −4 and +9‰. The boron isotope compositions
of metabasalt-hosted tourmaline show a bimodal distribution with peak δ11B values at about −2‰ and +6‰. The wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin
from at least two isotopically distinct fluid sources, which entered the hydrothermal system separately and were subsequently
mixed. The estimated δ11B values of the hydrothermal fluids, based on the peak tourmaline compositions and a mineralization temperature of 550°C,
are around +1 and +10‰. The isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization
reactions from the greenstone lithologies, whereas the 11B-rich fluid is attributed to degassing of I-type granitic magmas that intruded the greenstone sequence, providing heat and
fluids to the hydrothermal system.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
93.
The Lega Dembi deposit is the largest gold producer in Ethiopia. It is situated in late-Precambrian metamorphosed sediments
of the N-S trending, volcano-sedimentary Megado belt, which forms part of the late-Proterozoic Adola granite-greenstone terrane
in southern Ethiopia. The lode-gold mineralization occurs in a N-S trending, steep westerly dipping quartz-vein system that
follows the structural contact between underlying feldspathic gneisses and the volcanosedimentary sequence of the Megado belt.
This contact also marks the northernmost extension of the regional-scale, sinistral strike-slip Lega Dembi-Aflata shear zone.
Mineralization and intense quartz-veining is best developed in graphite-rich sediments within an area not more than 80 m away
from this tectonic contact. Hydrothermal wall-rock alteration includes actinolite/tremolite-biotite-calcite-sericite and chlorite-calcite-epidote
assemblages. Gold occurs preferentially in the sericite alteration zone, where it is closely associated and intergrown with
galena. The variable deformation of the gold-quartz veins suggests a syn-kinematic timing for the gold mineralization during
transcurrent shearing in a dilational segment of the shear zone. In addition to the structural control, lithological control
on gold deposition is indicated by the almost exclusive occurrence of the gold mineralization in graphite-rich metasediments.
This close relationship suggests that gold precipitation was the result of chemical reduction of regional ore-bearing fluids.
Temperature conditions of mineralization are constrained by the actinolite-biotite alteration assemblage and by arsenopyrite
chemistry, which indicate that ore deposition occurred at or close to peak metamorphic conditions at upper-greenschist to
lower-amphibolite metamorphic grades. Rb-Sr dating of sericite indicates an age of about 545 Ma. for hydrothermal alteration
and, thus, for gold mineralization. The style of gold mineralization, structural pattern and lithological assemblages at Lega
Dembi are very similar to lode-gold deposits most commonly reported from Archaean granite-greenstone terranes. These similarities
may open new perspectives for the exploration of lode-gold deposits, which has previously primarily focused on Archaean greenstone
belts rather than Proterozoic or even Phanerozoic meta-volcanosedimentary belts.
Received: 26 July 1996 / Accepted: 8 January 1997 相似文献
94.
Steven Pawson Ulrike Langematz Arnold Meyer Peter Strauch Silke Leder Klaus Rose 《Climate Dynamics》1991,5(3):161-174
Mean fields from a perpetual January simulation of a GCM extending from the surface to 0.01 hPa (near 80 km) are compared to observations. The zonal mean temperature and wind fields correspond quite well with reality; the low stratosphere, especially in the polar night, is too cold, but warmer than in the original version of the model, with an upper boundary at 25 hPa. Mean fields at standard levels show that the major features of the troposphere are represented by the model, but rather over emphasised; the stratospheric winter polar vortex is too strong, too cold, and too barotropic; it resembles an `undisturbed' January rather than the climatology. Differences in the stationary eddy activity between the extended and orginal versions of the model are noted, and used to explain some differences between the two simulations.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute für Meteorology. Guest Editor for these papers is Dr. L. Dümenil 相似文献
95.
Philip D. Meyer 《Ground Water Monitoring & Remediation》1990,10(4):102-109
Wellhead protection programs implemented to this date have not, in general, included a comprehensive ground water monitoring strategy. This is due both to the relatively recent introduction of the wellhead protection concept into the ground water field and also to the complexity of the monitoring problem. A well-planned monitoring program, however, can contribute significantly to the success of a wellhead protection program. The elements of wellhead protection, important from a monitoring perspective, are the management objectives, the types of potential contaminant sources, and the locations of those sources with respect to the wellhead protection area boundary. General monitoring strategies applicable to wellhead protection are derived from the relationships between these elements. 相似文献
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