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51.
The focus of this research was to determine if abandoned mines constitute a major environmental hazard in the Black Hills. Many abandoned gold mines in the Black Hills contribute acid and heavy metals to streams. In some areas of sulfide mineralization local impacts are severe, but in most areas the impacts are small because most ore deposits consist of small quartz veins with few sulfides. Pegmatite mines appear to have negligible effects on water due to the insoluble nature of pegmatite minerals. Uranium mines in the southern Black Hills contribute some radioactivity to surface water, but the impact is limited because of the dry climate and lack of runoff in that area. 相似文献
52.
N. F. Gray 《Environmental Geology》1996,27(4):358-361
Both sulfate and conductivity are useful indicators of acid mine drainage (AMD) contamination. Unlike pH, they are both extremely sensitive to AMD even where large dilutions have occurred. The advantage of using sulfate to trace AMD is that unlike other ions it is not removed to any great extent by sorption or precipitation processes, being unaffected by fluctuations in pH. These two parameters are also closely associated as would be expected, as conductivity is especially sensitive to sulfate ions. Therefore, as sulfate analysis is difficult in the field, conductivity can be used to predict sulfate concentration in both AMD and contaminated surface waters using regression analysis. Most accurate predictions are achieved by using equations given for specific conductivity ranges or AMD sources. There is also potential to use conductivity to predict approximate concentrations of key metals when the pH of the water is within their respective solubility ranges. 相似文献
53.
Basins within the African sector of Gondwana contain a Late Palaeozoic to Early Mesozoic Gondwana sequence unconformably
overlying Precambrian basement in the interior and mid-Palaeozoic strata along the palaeo-Pacific margin. Small sea-board
Pacific basins form an exception in having a Carboniferous to Early Permian fill overlying Devonian metasediments and intrusives.
The Late Palaeozoic geographic and tectonic changes in the region followed four well-defined consecutive events which can
also be traced outside the study area. During the Late Devonian to Early Carboniferous period (up to 330 Ma) accretion of
microplates along the Patagonian margin of Gondwana resulted in the evolution of the Pacific basins. Thermal uplift of the
Gondwana crust and extensive erosion causing a break in the stratigraphic record characterised the period between 300 and
330 Ma. At the end of this period the Gondwana Ice Sheet was well established over the uplands. The period 260–300 Ma evidenced
the release of the Gondwana heat and thermal subsidence caused widespread basin formation. Late Carboniferous transpressive
strike-slip basins (e.g. Sierra Australes/Colorado, Karoo-Falklands, Ellsworth-Central Transantarctic Mountains) in which
thick glacial deposits accumulated, formed inboard of the palaeo-Pacific margin. In the continental interior the formation
of Zambesi-type rift and extensional strike-slip basins were controlled by large mega-shear systems, whereas rare intracratonic
thermal subsidence basins formed locally. In the Late Permian the tectonic regime changed to compressional largely due to
northwest-directed subduction along the palaeo-Pacific margin. The orogenic cycle between 240 and 260 Ma resulted in the formation
of the Gondwana fold belt and overall north–south crustal shortening with strike-slip motions and regional uplift within the
interior. The Gondwana fold belt developed along a probable weak crustal zone wedged in between the cratons and an overthickened
marginal crustal belt subject to dextral transpressive motions. Associated with the orogenic cycle was the formation of mega-shear
systems one of which (Falklands-East Africa-Tethys shear) split the supercontinent in the Permo-Triassic into a West and an
East Gondwana. By a slight clockwise rotation of East Gondwana a supradetachment basin formed along the Tethyan margin and
northward displacement of Madagascar, West Falkland and the Gondwana fold belt occurred relative to a southward motion of
Africa.
Received: 2 October 1995 / Accepted: 28 May 1996 相似文献
54.
Heavy metal retention in secondary precipitates from a mine rock dump and underlying soil, Dalarna, Sweden 总被引:7,自引:2,他引:7
This study investigates the retention of heavy metals in secondary precipitates from a sulfidic mine rock dump and underlying
podzolic soils by means of mineralogical and chemical extraction methods. The rock dump, which is at least 50 years old, consists
of a 5–10-cm-thick leached zone and an underlying 110–115-cm-thick accumulation zone. Optical microscopy and electron microprobe
analyses confirm that pyrrhotite weathering has proceeded much further in the leached horizon relative to the accumulation
horizon. The weathering of sulfides in the leached zone has resulted in the migration of most heavy metals to the accumulation
zone or underlying soils, where they are retained in more stable phases such as secondary ferric minerals, including goethite
and jarosite. Some metals are temporarily retained in hydrated ferrous sulfates (e.g., melanterite, rozenite).
Received: 28 October 1996 · Accepted: 24 February 1997 相似文献
55.
Geochemical modeling of coal mine drainage, Summit County, Ohio 总被引:4,自引:1,他引:4
A. Foos 《Environmental Geology》1997,31(3-4):205-210
Geochemical modeling was used to investigate downstream changes in coal mine drainage at Silver Creek Metro-park, Summit
County, Ohio. A simple mixing model identified the components that are undergoing conservative transport (Cl–, PO4
3–, Ca2+, K+, Mg2+ and Na+) and those undergoing reactive transport (DO, HCO3
–, SO4
2–, Fe2+, Mn2+ and Si). Fe2+ is removed by precipitation of amorphous iron-hydroxide. Mn2+ are removed along with Fe2+ by adsorption onto surfaces of iron-hydroxides. DO increases downstream due to absorption from the atmosphere. The HCO3
– concentration increases downstream as a result of oxidation of organic material. The rate of Fe2+ removal from the mine drainage was estimated from the linear relationship between Fe+2 concentration and downstream distance to be 0.126 mg/s. Results of this study can be used to improve the design of aerobic
wetlands used to treat acid mine drainage.
Received: 4 June 1996 · Accepted: 17 September 1996 相似文献
56.
岩浆活动对油气藏形成条件的影响 总被引:13,自引:0,他引:13
结合众多实例,总结了国内外含油地中岩浆活动对油气藏形成的影响。一方面,岩浆活动所携带的高热流可以提高古地温,加速生油岩的演化,亦将使与岩浆岩毗邻的生油岩达到高成熟或过成熟, 相似文献
57.
天山北麓玛纳斯河流域山问洼地位于低山丘陵区山前坳陷带的南部,该区褶皱、断裂、近NS向次级张性断裂与平移构造以及山间洼地的第四系沉积物发育.山区地表水流经该段入渗,加之南部中山区的侧向补给形成山间洼地地下水库.正确认识玛纳斯河流域山间洼地地下水库的形成机理并对其进行合理的开发利用,对解决玛纳斯河流域季节性缺水及枯水年缺水有重要意义.笔应用构造及地表水由山区水站至山口渠首站实测流量损失的研究成果,揭示了玛纳斯河流域山间洼地地下水库的形成及调蓄作用,并概算了补给量,为今后开发利用山间洼地地下水库水资源提供了依据. 相似文献
58.
ChengQiuming ZhangGeorge LuCindy KoConnie 《中国地质大学学报(英文版)》2004,15(3):275-282
Modeling landscape with high-resolution digital elevation model (DEM) in a geographic information system can provide essential morphological and structural information for modeling surface processes such as geomorphologic process and water systems. This paper introduces several DEM-based spatial analysis processes applied to characterize spatial distribution and their interactions of ground and surface water systems in the Greater Toronto Area (GTA), Canada. The stream networks and drainage basin systems were derived from the DEM with 30 m resolution and the regularities of the surface stream and drainage patterns were modeled from a statistical/multifractal point of view. Together with the elevation and slope of topography, other attributes defmed from modeling the stream system, and drainage networks were used to associate geological, hydrological and topographical features to water flow in river systems and the spatial locations of artesian aquifers in the study area. Stream flow data derived from daily flow measurements recorded at river gauging stations for multi-year period were decomposed into “drainage-area dependent“ and “drainage-area independent“ flow components by two-step “frequency“ and “spatial“ analysis processes. The latter component was further demonstrated to relate most likely to the ground water discharge. An independent analysis was conducted to model the distribution of aquifers with information derived from the records of water wells. The focus was given on quantification of the likelihood of ground water discharge to river and ponds through flowing wells, springs and seepages. It has been shown that the Oak Ridges Moraine (ORM) is a unique glacial deposit that serves as a recharge layer and that the aquifers in the ORM underlain by Hilton Tills and later deposits exposed near the steep slope zone of the ridges of ORM provide significant discharge to the surface water systems (river flow and ponds) through flowing wells, springs and seepages. Various statistics (cross- and auto-correlation coefficients, fractal R/S exponent) were used in conjunction with GIS to demonstrate the influence of land types, topography and geometry of drainage basins on short- and long-term persistence of river flows as well as responding time to precipitation events. The current study has provided not only insight in understanding the interaction of water systems in the GTA, but also a base for further establishment of an on-line GIS system for predicting spatial-temporal changes of river flow and groundwater level in the GTA. 相似文献
59.
Proglacial suspended sediment transport was monitored at Haut Glacier d'Arolla, Switzerland, during the 1998 melt season to investigate the mechanisms of basal sediment evacuation by subglacial meltwater. Sub‐seasonal changes in relationships between suspended sediment transport and discharge demonstrate that the structure and hydraulics of the subglacial drainage system critically influenced how basal sediment was accessed and entrained. Under hydraulically inefficient subglacial drainage at the start of the melt season, sediment availability was generally high but sediment transport increased relatively slowly with discharge. Later in the melt season, sediment transport increased more rapidly with discharge as subglacial meltwater became confined to a spatially limited network of channels following removal of the seasonal snowpack from the ablation area. Flow capacity is inferred to have increased more rapidly with discharge within subglacial channels because rapid changes in discharge during highly peaked diurnal runoff cycles are likely to have been accommodated largely by changes in flow velocity. Basal sediment availability declined during channelization but increased throughout the remainder of the monitored period, resulting in very efficient basal sediment evacuation over the peak of the melt season. Increased basal sediment availability during the summer appears to have been linked to high diurnal water pressure variation within subglacial channels inferred from the strong increase in flow velocity with discharge. Basal sediment availability therefore appears likely to have been increased by (1) enhanced local ice‐bed separation leading to extra‐channel flow excursions and[sol ]or (2) the deformation of basal sediment towards low‐pressure channels due to a strong diurnally reversing hydraulic gradient between channels and areas of hydraulically less‐efficient drainage. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
60.
Thorsten Wagener Hoshin V. Gupta 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(6):378-387
Methods for the identification of models for hydrological forecasting have to consider the specific nature of these models
and the uncertainties present in the modeling process. Current approaches fail to fully incorporate these two aspects. In
this paper we review the nature of hydrological models and the consequences of this nature for the task of model identification.
We then continue to discuss the history (“The need for more POWER‘’), the current state (“Learning from other fields”) and
the future (“Towards a general framework”) of model identification. The discussion closes with a list of desirable features
for an identification framework under uncertainty and open research questions in need of answers before such a framework can
be implemented. 相似文献