埃及东南部沙漠地区汉默斯(Hamash)金矿中金从黄铜矿—黄铁矿中的重新运移

在埃及东南部的汉默斯沙漠地区,黄铁矿、黄铜矿和金有的产于石英脉中和花岗岩中,有的则以星散状、浸染状矿体赋存于高度蚀变的变质火山岩剪切带中。这些矿物的形成部分与磁黄铁矿、蓝辉铜矿、锑黝铜矿、辉铜矿、斑铜矿和铜蓝有关。黄钞矿具有两种晶形:(1)含有原生硫化物包裹体的自形—半自形巨型晶体,(2)细晶集合体。黄铜矿具有三种晶形:(1)自形巨型晶体,(2)细晶含微包裹体,(3)它型残余物。硫化物矿物有三个形成阶段,这三个阶段与热液的连续冷却结晶过程有关。在无序的高温热液阶段金以基质存在于早期硫化矿物中,在温度逐渐降低的后期阶段,含金黄铁矿经过重新运移,产生了自然金,显微镜分析结果证明,金和铜在晚期的黄铁矿中相对富集,分析研究过的表层蚀变矿物有:针铁矿、褐铁矿、金以及铁和铜的碳酸盐矿物和硫化物。     

英国用于找金的水文地球化学方法的初步研究

为了找到一种直接找金的勘探方法,在英国的很多地方对流水中可溶金的富集情况进行了研究。用盐酸和甲基异丁酮(MIBK)进行预富集后,用感应耦合等离子质谱仪对金进行了分析。检出限为0.5ngl~(-1)Au。样品是在以石英为主岩的三个已知金矿区采集的。在北爱尔兰的卡拉菲纳特(Curraghinalt)地区或在苏格兰阿基尔的拉格劳可恩(Lagalochan)地区都没有测列可溶金。在威尔士的道尔格拉(Dolgcllau)地区的金矿中,有十三个样品的金含量为1.5～1.6ng,有三个样品在这个范围之外。在任选的其他三个地区中的两个地区:苏格兰因沃尔内斯—夕尔的罗义桥地区和西康沃尔地区,每一个地区都有一个可测到金的样品,对中威尔士普林里蓑(Plynlimon)地区的样品也作了分析发现其溶解的金含量有重要意义(1～10ngl~(-1)Au)。有几种元素(Fe、Mn、Ni、Cu、Zn、Ca、Co、Pb、U、Li、Rb、CS、Sr、Ba、B、Y和La)可能是找金的指示元素,对它们也做了分析。元素Co、Ni、Li和Ba与已知金矿区的出现有关,Co/Ni的比值特别有用。研究的结果表明:在已知出现金矿化的地区,可溶金富集度的背景值比以前报导过的数值更低。远离已知金异常pH值近中性的几个地区存在可溶金可能与黄铁矿的氧化作用有关。我们认为:浅层地下水中的水文地球化学异常不只是(或可能不是)指示金矿床的存在而且是含金原岩的存在标志。     

An overview of toxicant identification in sediments and dredged materials

The identification of toxicants affecting aquatic benthic systems is critical to sound assessment and management of our nation's waterways. Identification of toxicants can be useful in designing effective sediment remediation plans and reasonable options for sediment disposal. Knowledge of which contaminants affect benthic systems allows managers to link pollution to specific dischargers and prevent further release of toxicant(s). In addition, identification of major causes of toxicity in sediments may guide programs such as those developing environmental sediment guidelines and registering pesticides, while knowledge of the causes of toxicity which drive ecological changes such as shifts in benthic community structure would be useful in performing ecological risk assessments. To this end, the US Environmental Protection Agency has developed tools (toxicity identification and evaluation (TIE) methods) that allow investigators to characterize and identify chemicals causing acute toxicity in sediments and dredged materials. To date, most sediment TIEs have been performed on interstitial waters. Preliminary evidence from the use of interstitial water TIEs reveals certain patterns in causes of sediment toxicity. First, among all sediments tested, there is no one predominant cause of toxicity; metals, organics, and ammonia play approximately equal roles in causing toxicity. Second, within a single sediment there are multiple causes of toxicity detected; not just one chemical class is active. Third, the role of ammonia is very prominent in these interstitial waters. Finally, if sediments are divided into marine or freshwater, TIEs perforMed on interstitial waters from freshwater sediments indicate a variety of toxicants in fairly equal proportions, while TIEs performed on interstitial waters from marine sediments have identified only ammonia and organics as toxicants, with metals playing a minor role. Preliminary evidence from whole sediment TIEs indicates that organic compounds play a major role in the toxicity of marine sediments, with almost no evidence for either metal or ammonia toxicity. However, interpretation of these results may be skewed because only a small number of interstitial water (n = 13) and whole sediment (n = 5) TIEs have been completed. These trends may change as more data are collected.     

Development of a benthic index to assess sediment quality in the Tampa Bay Estuary

The identification, remedial treatment, and monitoring of contaminated sediments are among the priorities for managers of the Tampa Bay Estuary. Tampa Bay, as an urbanized estuary, is subject to the input of watershed sources of chemical contaminants, including metals, pesticides, and organic chemicals. Although the use of biological indicators and their incorporation into multi-metric indices is not new, the refinement and applications of such techniques for determining environmental condition still require further development and exploration. We present a single Tampa Bay Benthic Index (TBBI) that was developed specifically for Tampa Bay. Stepwise discriminant analysis was applied to a comprehensive list of potential benthic metrics. Results from the stepwise procedure identified the metrics that best discriminated between "healthy" and "degraded" conditions, as defined by sediment contaminant effect levels and dissolved oxygen. Discriminant analysis was then applied to the resultant three variables to determine the linear combination for the index.     

The use of meiofauna as an indicator of benthic organic enrichment associated with salmonid aquaculture

Sediment chemistry and meiofaunal samples were collected in the Broughton Archipelago, British Columbia, to examine the relationship between sediment variables and meiofauna diversity across near- and far-field gradients surrounding several finfish aquaculture operations. The sediment variables examined consisted of free sulfide concentrations, redox potential (E(NHE)), organic content, and sediment grain size. A strong trend between sediment texture and organic content was observed across all sampling locations, which reflected a wide range of sediment types (sand-silt) that exist within the Broughton Archipelago. The abundance of certain meiofaunal groups (kinorhynchs, crustaceans, polychaetes) declined in an asymptotic fashion with increasing free sulfide concentrations, an indicator of benthic organic enrichment. Within these relationships, low meiofaunal abundances occurred in fine sediments associated with higher organic contents. Although other groups (nematodes, foraminifera) showed a slight decline in abundance with increasing organic enrichment, a high amount of variability in abundance was observed at high free sulfide concentrations, rendering these groups not suitable as indicators of organic enrichment. This study reports both horizontal and vertical trends in meiofaunal distributions relative to free sulfide concentrations. The abundance of nematode and crustacean taxa decreased with sediment depth as well as increasing sulfide concentration, while polycheate abundance increased with increasing free sulfide concentration. The ratio of nematodes to copepods was also shown to represent the degree of organic loading associated with aquaculture operations and its application as an indicator of benthic impact is discussed.     

Comparison of single-domain and dual-domain subsurface transport models

Subgrid modeling of some type is typically used to account for heterogeneity at scales below the grid scale. The single-domain model (SDM), employing field-scale dispersion, and the dual-domain model (DDM), employing local hydrodynamic dispersion and exchange between domains having large hydraulic conductivity contrasts, are well-known examples. In this paper, the two modeling approaches are applied to tritium migration from the H-area seepage basins to a nearby stream--Fourmile Branch--at the Savannah River Site. This location has been monitored since 1955, so an extensive dataset exists for formulating realistic simulations and comparing the results to data. It is concluded that the main parameters of both models are scale-dependent, and methods are discussed for making initial estimates of the DDM parameters, which include mobile/immobile porosities and the mass exchange coefficient. Both models were calibrated to produce the best fit to recorded tritium data. When various attributes of the dataset were considered, including cumulative tritium activity discharged to Fourmile Branch, plume arrival time, and plume attenuation due to closure of the seepage basins in 1988, the DDM produced results superior to the SDM, while causing no unrealistic upgradient dispersion. A sensitivity analysis showed that only the DDM was able to accurately produce both the instantaneous activity discharge and cumulative activity with a single parameter set. This is thought to be due to the advection-dominated nature of transport in natural porous media and the more realistic treatment of this type of transport in the DDM relative to the SDM.     

The journey from safe yield to sustainability

Safe-yield concepts historically focused attention on the economic and legal aspects of ground water development. Sustainability concerns have brought environmental aspects more to the forefront and have resulted in a more integrated outlook. Water resources sustainability is not a purely scientific concept, but rather a perspective that can frame scientific analysis. The evolving concept of sustainability presents a challenge to hydrologists to translate complex, and sometimes vague, socioeconomic and political questions into technical questions that can be quantified systematically. Hydrologists can contribute to sustainable water resources management by presenting the longer-term implications of ground water development as an integral part of their analyses.