煤矿采空区勘探实例

应用瞬变电磁法确定煤矿采空区及积水采空区十分准确,本文介绍了应用该方法确定某煤矿采空区及积水采空区。首先确定煤矿各种围岩阻值,通过钻孔孔旁视电阻率ρτ曲线与钻孔柱状对比,为异常解释建立理论模型,根据瞬变电磁实测数,通过分析,结合煤系地层的物性特征分析,确定煤矿采空区及积水采空区。     

Superficial geochemical dispersion around sulphide deposits: Some examples in France

Examination of geochemical exploration data accumulated in France over a period of almost 20 years has led to detailed consideration of the relationship between anomalies and mineral deposits.Geochemical anomalies associated with sulphide mineralizations seem to follow several general rules i.e. Ag and Pb are almost systematically present, As is very frequent, while Cu and Sb may also be present. The behaviour of Zn seems to be controlled by the lithological character of the host rock with anomalies in carbonate media even for occurrences without economic interest and an absence of anomalies in non-carbonate media, even for Zn deposits of considerable size. Moreover, the contents of this element are greatly amplified by contamination from old workings. The abundance (or scarcity) of supergene minerals in the occurrences directly influences the nature of the anomalies. Lead anomalies frequently correspond to the presence of Pb oxides such as pyromorphite while Zn anomalies derive from Zn oxides which are much more common in carbonate media (smithsonite-hydrozincite) than in schistose host rock. High Cu and As contents are most frequently linked to the presence of “ferruginous fragments” (gossans) derived from sulphides. As a general rule, the various geochemical peculiarities or associations encountered in soils are very much similar to those of the oxidized part of the deposits.We are therefore led to assume that, contrary to the usual conceptions, superficial dispersion is basically mechanical and that the anomalies detected near mineralizations are due to the presence in the soils of supergene minerals, gossan microfragments and more or less mineralised rock debris, etc. Mechanical migration of this kind can be explained by the existence in France during the Pleistocene of cold climates of the tundra type with associated permafrost. The thawing in summer of the superficial part of the frozen overburden resulted in massive downslope solifluction favoring mechanical migration over distances in the order of 100 m and contributing to the surface dispersal of the mineralizations. These phenomena are extremely important for geochemical exploration because they allow and justify the use of large grids (200 m × 200 m or even 400 m × 400 m) during soil surveys at least at the initial stage of prospecting on areas of several square kilometers.These conclusions are valid not only for France but for all regions with the same paleoclimate. These form a belt bounded to the north by glacial formations linked to ancient inland ice and to the south by the maximum extension of Pleistocene permafrost, including, in particular, the north of the United States and Central Europe. This paleo-climate belt characterized by traces of solifluction constitutes a well-defined unit in which geochemical prospecting has proved itself extremely effective.     

Solar shield: forecasting and mitigating space weather effects on high-voltage power transmission systems

In this paper, central elements of the Solar Shield project, launched to design and establish an experimental system capable of forecasting the space weather effects on high-voltage power transmission system, are described. It will be shown how Sun–Earth system data and models hosted at the Community Coordinated Modeling Center (CCMC) are used to generate two-level magnetohydrodynamics-based forecasts providing 1–2 day and 30–60 min lead-times. The Electric Power Research Institute (EPRI) represents the end-user, the power transmission industry, in the project. EPRI integrates the forecast products to an online display tool providing information about space weather conditions to the member power utilities. EPRI also evaluates the economic impacts of severe storms on power transmission systems. The economic analysis will quantify the economic value of the generated forecasting system. The first version of the two-level forecasting system is currently running in real-time at CCMC. An initial analysis of the system’s capabilities has been completed, and further analysis is being carried out to optimize the performance of the system. Although the initial results are encouraging, definite conclusions about system’s performance can be given only after more extensive analysis, and implementation of an automatic evaluation process using forecasted and observed geomagnetically induced currents from different nodes of the North American power transmission system. The final output of the Solar Shield will be a recommendation for an optimal forecasting system that may be transitioned into space weather operations.     

IP法找矿的几个实例

IP法可以直接发现富含金属硫化物的各类矿体,而被广泛应用于矿产普查、详查及勘探等各个找矿阶段.本文介绍了该方法探查机理及野外工作方法,总结了IP法在几个金属矿区的找矿成果.认为充分分析矿区地质物性条件,合理布置野外工作是取得找矿突破的重要前提.     

Quantification of electron microprobe compositional maps of rock thin sections: an optimized method and examples

Quantification of discrete pressure–temperature domains in deformed chlorite + white mica‐bearing metapelites was undertaken on mineral compositions derived by two‐dimensional microprobe compositional mapping of selected areas of rock thin sections. In order to achieve compositional information at sufficient analytical precision, spatial resolution and sample coverage within a typical analysis time of 1 day, an optimization of measurement methods was necessary. The method presented here allows collection of raw counts for eight different element concentrations at an analytical precision of ～1–2 wt%. X‐ray intensity multiplane maps (one map per measured chemical element) are translated into concentration multiplane maps, utilizing selected conventionally measured spot analyses combined with the Castaing approximation for each mineral. As this step requires identification of the different minerals present in the mapped area, a statistical clustering technique to identify different groups of composition was developed, guided by simple petrographic inspection of the thin section, to delineate the important minerals in the mapped area. Finally, the compositions of each pixel are translated into a mineral structural formula thus yielding a new kind of image with a high content of petrological information. The reliability of the mineral composition images was emphasized by carrying out precision tests on the analytical data. The possible use of chemical maps to infer the P–T–deformation history of metamorphic rocks is illustrated with two samples from the Spitzbergen and the Sambagawa blueschist facies belts. In both samples, a strong correlation between structures and chemistry is observed. Qualitative estimates of P–T conditions from the Si‐content of mica and chlorite are in good agreement with their location in microstructures that formed at different times. Therefore, the combination of chemical maps with microstructural observations is a very powerful approach to understand both the evolution of complex metamorphic rocks and the control by deformation of mineral reactivity.     

Total electron content at low latitudes

Radio beacon from ATS-6 at 140 MHz was used to measure the changes in the polarization angle (Faraday rotation) at Bombay, Rajkot, Ahmedabad, Udaipur and Patiala during October 1975 to July 1976. In this paper, results of diurnal, seasonal and latitudinal variations in total electron content (TEC) derived from these measurements are reported. The amplitude of diurnal peak is found to be higher at Rajkot, Ahmedabad and Udaipur as compared to that at Patiala or Bombay, indicating that the peak of Appleton anomaly in the latitudinal variation of TEC was close to the latitude of Ahmedabad. The diurnal maximum of TEC occurs around the same time during summer and winter months. The peak electron content shows a semiannual variation at all the stations with large values in equinoxes as compared to winter and summer. The TEC at Bombay shows a seasonal anamoly with high values in winter as compared to summer. The paper describes the development of latitudinal anomaly with the time of the day for different seasons. This anomaly is maximum during 1000 to 1800 LT and is located between 12° and 14° N (dip latitude) in summer and equinoxes and at about 10°N in winter.     

Some examples of mining in Ireland and its impact on the environment

This article is based on a paper presented at an International workshop in June 1986 on the impact of mining on the environment, held in Tallinn, Estonian SSR as part of the UNEP/UNESCO project entitled Geology and the Environment.     

Some examples of the Middle-Triassic Marine transgression in South-Western Mediterranean Europe

In Southwestern Mediterranean Europe (NE Spain, Sardinia and NW Apennines e. g. Monti Pisani and Punta Bianca) the Middle-Triassic transgression on a margin of an intracratonic basin appears to be controlled by the different morphology and tectonic activity of the margin itself. The analysis of some sequences leads to recognize three different kinds of margins:

1. margin with a narrow shelf sloping toward a very shallow restricted basin (Central and Southwestern Sardinia);
2. margin with a broad shelf gently sloping toward a shallow basin (NE Spain, Monti Pisani, NW Sardinia);
3. margin with a narrow shelf and steep slope marked by tectonic and volcanic activity (Punta Bianca).

     

Influences on the location and behaviour of transnational corporations: Some examples taken from Japanese investment in Australia

This paper reviews previous approaches to studying transnational corporate locational behaviour in host countries. It is argued that an over-preoccupation with corporate bargaining power has obscured influences arising from: (a) the cultural and home country factors which influence transnational corporation (TNC) strategies and motivations; (b) the host country's physical, economic and regulatory environment; and (c) host government intervention in response to TNC activity. Case studies of Japanese post-war investment in Australia are given which indicate that final outcomes have evolved through interactions between corporate motivations and strategies, and local opportunities and constraints.     

Geological, mineralogical and geochemical aspects of Archean Banded Iron-Formation-hosted gold deposits: Some examples from Southern Africa

This paper reports on different styles of gold mineralization observed in Archean gold deposits hosted by Algoma-type Banded Iron-Formations (BIF) in southern Africa. Genetic aspects of various occurrences are discussed in the context of mineralogical as well as geochemical data of BIFs from the greenstone terranes of the Zimbabwe and Kaapvaal cratons. The study revealed that, in spite of their different provenance and age (3.5 to 2.6 Ga), the BIFs are geochemically similar, whereas observed mineralogical differences reflect various degrees of metamorphic overprint. Generally, the BIFs belong to mixed oxide-carbonate-(±sulfide)-facies. REE distribution patterns of the investigated Archean BIF samples exhibit positive Eu-anomalies, which suggest a strongly reducing nature of the solutions which also provided the distinctive element contents now present in the chemical sediments. Irrespective of their formation, gold enrichment in BIF only occurs if the S- and/or As-contents of the BIFs exceed specific threshold values, i.e. gold mineralization is always associated with increased contents of the iron-sulfides pyrite, arsenopyrite and pyrrhotite. The studies indicate that BIF-hosted gold occurrences are not products of a single universal metallogenic process, but may be explained by several different genetic processes such as primary syn-sedimentary formation, diagenetic changes, metamorphic remobilization, and epigenetic hydrothermal emplacement.     

Methodological appraisal: Two examples

Drawing an inference about an empirical situation requires posing a problem or asking a question, collecting relevant data and choosing methods to analyse them. Though ideally under the spell of the muse of objectivity (but unrealistically) one imagines that the inference should be determined by the objective data alone, the former can depend on various aspects of the entire process that precedes it. This is brought out by two examples from earth science literature. They pertain to seismicity classification based on a pattern recognition algorithm and early palaeomagnetic studies. The examples are deliberately chosen from disjoint fields so that it is clear that the objective is not to contribute to any chosen field of earth science, but to make essentially methodological points. These are: (i) no inference is a culmination of a lineal or sequential process, but is a part of it; (ii) Therefore, one can and should return from there to the preceding process and revise it; (iii) All the intermediate and secondary inferences, all the disagreements between what was expected a priori and what happened on way to the inferences, the symptoms of the effects of the format of questions on the inferences should all be critically scrutinized; (iv) The total exercise should be viewed as not only that of drawing inferences about the external world, but also of learning the process of doing so. The latter experience is generally transferable to other problem situations.     

Engineering problems and rock mechanics: some examples

Jaeger, C., 1973. Engineering problems and rock mechanics: some examples. Eng. Geol., 7: 333–358.

The purpose of this paper is to show how rock mechanics interprets geologic information and helps to adapt engineering design to rock conditions. The paper analyses eight case histories of large engineering projects. In five cases the designers took careful account of the conditions prevailing in the rock masses, the rock characteristics, the strength of the rock and the modified stress—strain pattern created by the new structure. The intrinsic curve of the rock mass, the Coulomb condition, the residual stresses and theE-modulus in the families of joints are among the more important characteristics of the rock mass. In two case histories, it is shown how an erroneous estimate of the cleft-water pressures caused disaster.

Rock mechanics is a necessary link between engineering and geology.     

Groundwater and volcanoes: examples from the Azores archipelago

Groundwater at the Azores archipelago is a strategic resource for the freshwater supply. Freshwater, mineral and thermal water discharges occur in the archipelago, and especially at the Fogo and Furnas volcanoes (São Miguel). These discharges provide data for case studies of groundwater chemistry from volcanic monitoring due to the stable composition of the sampled waters. The mineral and thermal discharges are mainly of sodium bicarbonate types and present a large range of temperatures, from cold springs to waters at about 90 °C. Some boiling discharges have a sulfate-dominated composition, suggesting a steam-heating mechanism. Geochemical studies on these mineral and thermal waters began in the 19th century. Data gathered since these earlier studies provide a baseline for pH, temperature, CO₂ and major-element composition. Weekly measurements of pH and temperature also denote a rather stable behavior.     

Regional landslide evaluation: Two Utah examples

Landslide-susceptibility evaluations based on bedrock units, slope inclination, and aspect (slope orientation) incorporate the lithologic, stratigraphic, structural, and topographic passive conditions contributing to landsliding as outlined by Sharpe (1938). Generalized results based on passive condition analyses may define potential for failure over entire states or large parts of states, establishing an approximate landslide susceptibility for specific areas that are still in need of detailed study. This provides a preliminary susceptibility for use in land management and identifies high-priority areas for future detailed investigations. Landslides in the Bear River Range, north-central Utah, and the northern Wasatch Plateau, central Utah, illustrate application of these factors to regional landslide-susceptability evaluation. The greatest landslide potential exists on slopes of between 10 and 40%, with a westerly aspect, underlain by Wasatch or Salt Lake formations in the Bear River Range and on slopes of from 20 to 60% that are underlain by either North Horn or Price River formations in the northern Wasatch Plateau. Results from the two study areas are compared to a statewide landslide evaluation (Schroder 1971) in terms of passive conditions. Lithologic and stratigraphic conditions of the state and of the two study areas are nearly identical. Aspect data detect the presence or absence of structural conditions favoring failure in the two study areas rather than climatic factors as concluded in the statewide analysis. Topographic condition is more precisely stated in quantitative as opposed to qualitative terms to define failure-prone slopes in the two study areas.     

Numerical modeling of moisture transport in sandstone: the influence of pore space, fabric and clay content

In the present study, a numerical modeling of moisture distribution under real climate conditions within sandstone monoliths is accomplished, based on detailed material-specific transport and storage functions. The impact of lithology and pore-radii distributions is modeled with consideration of (1) the single sandstone monolith; (2) the sandstone monolith with clay layers; and (3) the sandstone monolith with clay layers and hydrophobic treatment. The results reveal that the unimodal equal pore-radii distribution of the quartz arenite promotes quickly a (capillary) water uptake during driving rain (liquid stage), but due to its missing smaller capillaries a high drying velocity leads to an almost dry pore space, since moisture can only be absorbed via gaseous stage (e.g. during summer). On the contrary, the sublitharenite with a unimodal unequable pore-radii distribution is characterized by a distinctly higher water content, since in addition smaller pores also allow the absorption of moisture via sorption. Moreover, the high clay content promotes a retarded interaction with the environment, which is also reflected by the high vapor-diffusion resistance. The highest water content shows the feldspathic litharenite with highest clay content and bimodal pore size distribution. Here, over nine magnitudes of water transporting pores is involved at water transport and storage. Results also reveal that moisture accumulations during droughts trace the deterioration shape of rounding. For all sandstones highest annual fluctuations are observable within the rim zone of the monolith, while the center is characterized by more stable moisture content, which mainly depends on rising water content of the bedrock. The presence of clay layers has for each sandstone specific consequences. However, within the whole sandstone the stress index is increased and stress location is displaced to the boundaries of clay layers. Results of modeling the hydrophobic treatment reveal that this conservation strategy is only useful for sandstones where all moisture is absorbed in liquid stage, why then all water absorption is hindered. In case of sandstones with bimodal and unimodal unequal pore size distributions moisture uptake is possible also via sorption. Accordingly, moisture accumulates behind the zone of hydrophobic treatment. This finally will lead to stress transfer to the outer rim during salt- or ice crystallization and will be responsible for flaking.     

Seasonal and solar cycle variations of night-time anomalous enhancements in total electron content

Seasonal and solar cycle variations of the various characteristics of night-time anomalous enhancements in total electron content (TEC) of the ionosphere are presented for a low latitude station, Hawaii by considering TEC data for a full solar cycle. All the characteristics of the TEC enhancements have seasonal and solar cycle dependence. TEC enhancement characteristics such as frequency of occurrence, amplitude and duration are positively correlated with solar activity. The possible source mechanisms for the observed enhancements are also discussed.