X荧光分析方法在地球化学勘查中的应用--四川理塘铜、锡、铅、银异常查证

介绍了X荧光技术在四川理塘颇昂佐避地区地球化学普查中的应用。工作现场利用X荧光测量水系沉积物样品的异常区,反映了含矿岩性矿(化)体的大致概况。利用该技术圈定的异常,经探槽揭露证实为矿化异常。实践证明,在四川西部交通、生活极为困难的高寒山区,X荧光技术是一种快速、经济、有效的地球化学普查方法。     

Control of geochemical error through sampling and subsampling diagrams

Sampling and subsampling diagrams provide a means of visualizing and controlling sampling error during analysis of mixtures, especially those in which a minor constituent contributes heavily to assay values. The model employed refers each sampling problem to an idealized mixture of two constituents which has the same sampling or subsampling characteristics as the real mixture to be sampled. A procedure for calculating and constructing such diagrams depends on appropriate use of both Gaussian and Poisson statistics. The argument is simplified by combining the two statistical models.     

井中化探技术在识别烃源岩中的应用

井中化探逐渐成为鉴别油气属性、识别烃源岩特征的重要技术方法。本文以井中化探多指标、多参数方法,对我国东部某盆地探井中的烃源岩进行识别,为油气勘探中选择目的层和储量评估提供了地球化学依据。     

大气传播延迟改正在GAMIT软件中的应用

卫星信号从GPS卫星发射到地面的过程中经过了以充满大气为介质的空间。电磁波在这种变化的介质中传播,其传播的方向、速度、强度都可能随时改变。本文简略地介绍了大气传播延迟的产生及其对GPS测量的影响,并就GAMIT软件对大气传播延迟的控制方法和所采用的改正模型做一简单介绍,并对减弱和消除大气传播延迟的方法和手段进行了讨论。     

元素地球化学在古环境和古生态研究中的应用综述

元素地球化学方法被广泛应用于沉积学研究,保存的古环境、古生态信息可通过多种指标进行释读。本文总结了主量元素、微量元素、稀土元素、同位素和有机地球化学等在沉积学研究中应用相对比较成熟的环境代用指标及其地质意义,认为这些指标在示踪形成构造环境、古气候、古生态、物源区、沉积介质条件等方面具有有效的指示作用;不同指标对剥蚀区和沉积区的古气候指示意义差别较大,需加以甄别;因表生地质环境的复杂性,古环境解释中需注意指标的局限性,应根据研究对象选择多个指标并结合其他沉积学、岩石学特征进行综合验证。     

Interface error analysis for numerical wave propagation

The numerical error associated with finite-difference simulation of wave propagation in discontinuous media consists of two components. The first component is a higher-order error that leads to grid dispersion; it can be controlled by higher-order methods. The second component results from misalignment between numerical grids and material interfaces. We provide an explicit estimate of the interface misalignment error for the second order in time and space staggered finite-difference scheme applied to the acoustic wave equation. Our analysis, confirmed by numerical experiments, demonstrates that the interface error results in a first-order time shift proportional to the distance between the interface and computational grids. A 2D experiment shows that the interface error cannot be suppressed by higher-order methods and indicates that our 1D analysis gives a good prediction about the behavior of the numerical solution in higher dimensions.      

一种新的断裂计算方法

利用单元中嵌合无厚度不连续面的方法 ,模拟断裂面的形成过程。用虚功原理建立包含断裂面影响的有限元平衡方程 ;利用余虚功原理推导了断裂面的矩阵的具体形式 ; 以第一类断裂问题 -开裂问题为例 ,建立了开裂面粘塑性开裂本构关系,进一步得到了以弹粘塑性形式表示的有限元计算格式。 通过简单算例证明了该方法的正确性。     

Uncertainty propagation in geochemical calculations: non-linearity in solubility equilibria

Uncertainty in the results of geochemical equilibrium calculations may be estimated from input uncertainties using either derivative approximations or Monte Carlo simulations. While derivative methods are fast and convenient for many equilibria, inherently non-linear aspects of solubility equilibria may lead to a failure of the linear approximation and thus to asymmetric and/or bimodal uncertainty in calculated concentrations. In these cases, the use of derivative methods and the assumption of Gaussian uncertainty in the calculated concentrations misrepresent the propagated uncertainty. Equilibria with gibbsite, calcite, and the chromate analog of jarosite are examined.     

Error propagation by the Monte Carlo method in geochemical calculations

The Monte Carlo method of error propagation consists of repeated calculation of a quantity, each time varying the input data randomly within their stated limits of precision. The distribution of the calculated quantity then shows the effects of the imprecision of the data. It is an inefficient but very simple method of error propagation. Three examples are given—calculation of the free energy of a compound from phase equilibrium data; calculation of a reaction equilibrium temperature from free energy data; and the calculation of sulfide solubilities. Fifty iterations were generally found to be sufficient in these cases. The method is also useful where precision or accuracy of the data is not known, since the effect of various assumed possible errors is easily calculated.     

地球化学数据的定和化及其在系统误差校正中的应用

地球化学数据间的系统误差,既影响了图幅的拼接,又因破坏了多元总体的相关结构而干扰到地球化学数据的统计分析。针对这一问题,这里分析了地球化学数据的定和特点,探讨了系统误差校正的定和化处理方法。同时,结合实例说明了该方法的实际应用效果,并验证了定和化方法的有效性。     

岩土压力传感器匹配误差的计算

对岩土压力传感器的匹配误差，从解析理论研究出发，提出两次压陷等假定条件，推导出在3种使用场合时的匹配误差计算公式，得出匹配误差计算公式中有关参数的确定方法或具体量值，给出了实用的匹配误差定量计算公式。     

Combining visual and geochemical analyses to source chert on Southern Baffin Island,Arctic Canada

A combined methodological approach using visual and geochemical methods is introduced and preliminary results of a study illustrating its effectiveness to determine chert source provenance are presented. This study focuses on lithic debitage and raw chert samples collected from the interior of southern Baffin Island, Arctic Canada. Chert is abundant throughout this region yet it occurs as small, scattered surface nodules that are highly variable in color. Prior to this study, little was known about the provenance of this local toolstone and whether it derived from local outcrops, glacial till sheets, or both. Given the pronounced variability exhibited by this chert, we use individual attribute analysis and petrography to impose some kind of analytical order upon an otherwise random aggregation of rocks. Thereafter, inductively coupled plasma mass spectrometry and secondary ion mass spectrometry are used to test the validity of these color categories to determine from how many geochemically distinct sources they derive. Using a standard that measures Al to a ratio of Ga/Zr, our results indicate that all of the raw chert samples derive from a single local source, while the debitage derives from four different sources, including the one that is local. We are confident that this combined methodological approach can be applied in other regions where chert variability is pronounced and source provenance is unknown. © 2009 Wiley Periodicals, Inc.     

Applications of grain-pivoting and sliding analyses to selective entrapment of gravel and to flow-competence evaluations

Models of sediment threshold by grain pivoting or sliding over underlying particles are examined in order to explore their application to evaluations of selective entrainment of gravel by flowing water. Of special interest is whether such process-based models provide satisfactory evaluations of flow competence and the movement of large clasts by floods. A detailed derivation is undertaken, focusing first on the fluid flow and forces at the particle level. The resulting threshold equation for the particle-level velocity is then modified to yield the mean entrainment stress for the flow as a whole. This approach is appropriate for considerations of selective entrainment of grains of varying sizes within a deposit, the sorting being due to their relative projection distances above the bed and the dependence of their pivoting angles on grain size and shape. The resulting threshold equations contain a number of coefficients (e.g. drag and lift) whose values are poorly known, but can be constrained by requiring agreement with the Shields curve for the threshold of grains in uniform deposits. If pivoting coefficients based on laboratory measurements with tetrahedral arrangements of particles are used in the models, smaller degrees of selective sorting are predicted than found in the field measurements of gravel entrainment. However, if reasonable modifications of those coefficients are made for expected field conditions, then the models yield good agreement with the data. Sliding models, where sorting is due entirely to projection distances of the grains above the bed, yield somewhat poorer agreement with the field data; however, the sliding models may have support from laboratory experiments on gravel entrainment in that the data and theoretical curves have similar concave trends. The existing measurements lack documentation of the mechanisms of grain movement, so it is not possible to conclusively determine the relative importance of grain pivoting versus sliding. In spite of such uncertainties, the results are encouraging and it is concluded that pivoting and sliding models for grain entrainment do have potential for field computations of selective entrainment and flow competence.     

Statistical evaluation of methods for the calculation of static formation temperatures in geothermal and oil wells using an extension of the error propagation theory

The feasibility of using the more sophisticated weighted least-squares (WLS) model, as opposed to the traditional ordinary least-squares (OLS), in linear regressions of BHT data to estimate the static formation temperatures (SFT) was investigated. The most commonly used analytical methods (line-source; spherical and radial heat flow; and cylindrical heat source) were applied. Error propagation equations were derived to calculate errors in the time function of each method. These errors were combined with the BHT measurement errors to compute weighting factors for applying the WLS. Intercept uncertainties were estimated for all regressions using sets of synthetic and actual borehole logs taken from geothermal and oil applications. SFT computed with the spherical and radial heat flow method were generally greater than those from the other two methods.     

基于数据库的地球化学异常特征参数计算方法

介绍了在地球化学普查中,一种单元素异常特征参数的计算方法。在确定了单元素异常下限,建立了取样点位数据图层,完成了单元素异常图制作的基础上,将单元素异常区图层与点位数据图层做点对区的相交分析,把单元素异常区中异常编号、异常面积字段的空间信息相交分析到异常区内点位数据图层中,将该点图层属性转换成DBF文件,应用FORXPRO软件编写了程序,从而计算单元素异常特征参数。     

Error propagation in equations for geochemical modeling of radiogenic isotopes in two-component mixing

This paper presents error propagation equations for modeling of radiogenic isotopes during mixing of two components or end-members. These equations can be used to estimate errors on an isotopic ratio in the mixture of two components, as a function of the analytical errors or the total errors of geological field sampling and analytical errors. Two typical cases (“Small errors” and “Large errors”) are illustrated for mixing of Sr isotopes. Similar examples can be formulated for the other radiogenic isotopic ratios. Actual isotopic data for sediment and basalt samples from the Cocos plate are also included to further illustrate the use of these equations. The isotopic compositions of the predicted mixtures can be used to constrain the origin of magmas in the central part of the Mexican Volcanic Belt. These examples show the need of high quality experimental data for them to be useful in geochemical modeling of magmatic processes.     

A record of Holocene climate change from lake geochemical analyses in southeastern Arabia

Lacustrine sediments from southeastern Arabia reveal variations in lake level corresponding to changes in the strength and duration of Indian Ocean Monsoon (IOM) summer rainfall and winter cyclonic rainfall. The late glacial/Holocene transition of the region was characterised by the development of mega-linear dunes. These dunes became stabilised and vegetated during the early Holocene and interdunal lakes formed in response to the incursion of the IOM at approximately 8500 cal yr BP with the development of C3 dominated savanna grasslands. The IOM weakened ca. 6000 cal yr BP with the onset of regional aridity, aeolian sedimentation and dune reactivation and accretion. Despite this reduction in precipitation, the lake was maintained by winter dominated rainfall. There was a shift to drier adapted C4 grasslands across the dune field. Lake sediment geochemical analyses record precipitation minima at 8200, 5000 and 4200 cal yr BP that coincide with Bond events in the North Atlantic. A number of these events correspond with changes in cultural periods, suggesting that climate was a key mechanism affecting human occupation and exploitation of this region.     

长江口沉积物碳氮元素地球化学特征及有机质来源分析

根据对长江口水下三角洲上部(CJ16)和口门浅滩(CJ19)柱状样的粒度、总有机碳(TOC)、总氮(TN)和有机碳同位素(δ13C)以及长江口表层样TOC的测定,得出其粒度及碳氮元素特征,利用C/N和δ13C分析有机质来源及不同来源的贡献率。研究结果表明:(1)沉积物中有机碳含量在0.19%～1.17%之间,CJ16柱中有机碳含量比CJ19柱略高;总氮含量均比较少,且变化幅度小;C/N比值在5～17间变化;CJ16柱的δ13C值在24.70‰～22.86‰间变化,CJ19柱为24.88‰～22.37‰,且CJ19柱δ13C值在36 cm以上段较下段明显增大,推测可能与南汇边滩互花米草(C4植物)的引种有关;(2)长江口表层沉积物TOC的含量范围为0.17%～1.16%,平均值为0.52%;(3)粒度特征显示长江口主要以粉砂和粘土为主,砂含量较少,粒度与长江口TN、TOC含量有较好的相关性;(4)C/N和δ13C值的特征均显示该区有机质为陆源和海洋混合,利用C/N比值估算出来自陆源的有机碳比例在CJ16柱约为40%,而在CJ19柱中约为60%;根据δ13C值估算出CJ16柱陆源和海源两种有机质来源几乎是各占一半的比例,CJ19柱来自陆源的有机碳占总有机碳的60%,与用C/N比值法测得的结果较一致。上述结果显示长江口的不同空间位置碳氮元素分布特征不同,沉积记录受到粒度、河口区物源的影响,还受到陆源和海源不同有机质来源输入的影响。     

随钻热解地球化学录井含油饱和度的计算和应用

热解地化录井可以检测储集层含油气总量,推算原油密度值,结合储集层孔隙度值和储层岩石密度,经过换算可得出含油饱和度。热解地化录井含油饱和度是基于热解地化参数而获得,获取的机制是直接检测与合理的理论恢复相结合,能够客观的反映储层中所含油气的数量,评价储集层的性质,经试油结论验证,随钻评价结论与实际情况相符良好。